Model Engine Maker
Engines => Your Own Design => Topic started by: gbritnell on May 14, 2017, 07:22:19 PM
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Gentlemen,
I have engines in all cylinder configurations from 1 to 8 but I don't have any with 3 cylinders so I thought I would make one. I really like the Fairbanks 3 cylinder engine but I think is would be just a little too complex in this reduced size so I am designing and building my own based on the Holt drawings. It will be 1/2 size so the bore will be .500 and the stroke .625. I plan on the ignition being triggered by a Hall device and the cylinders will have an outer jacket so that if coolant is needed it will be in place.
As my construction technique is machining from solid this will be built that way.
I started with the bottom half of the crankcase. When I made my full sized Holt from scratch I split the crankcase for simplicity and ease of machining. This one is being built the same way.
Picture 1. The block of aluminum squared up and the screw holes drilled. I also have 2 .046 diameter holes in opposite corners for tiny dowel pins to keep the two halves aligned.
Picture 2. The inside of the part was roughed to shape including the oil sump.
Pictures 3&4. Using my Cad program I generated a step-off program to whittle out the inside.
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Picture 1. The lower crankcase was then flipped on the vise and the outer shape was roughed leaving .010 for the finish cutter. (.187 ball mill).
Picture 2. Another step-off chart was created to put the contour onto the crankcase. First half completed.
Picture 3&4. Stepping off completed and a radius was milled around the bottom edge of the oil sump.
The screw holes were counterbored with a .125 endmill going deep enough to put the screw heads below the surface so they won't be seen.
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While the piece was solid I drilled and reamed the cam hole. Trying to do this with the crankcase pockets milled is virtually impossible.
Picture 1. The upper half crankcase was milled to the overall dimensions then the holes were drilled for the mounting screws (1-72) The cylinder holes were drilled then bored to size.
Picture 2. The slots for the bearing caps were milled in the center 2 ribs then the side walls were stepped down. First pocket shown. Being as each side of the crankcase has a different angle I finished one side at a time so I wouldn't have so many numbers to step to.
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The two halves were screwed together and put back into the mill vise.
The side walls of the crankcase are angled so I quickly set it with a protractor then used a DTI to get the angle exact.
Picture 1. Using a flycutter I milled the side wall.
Picture 2. A .025 raised area was created where the cover plate will be mounted and the inspection windows were milled. On the original engine the windows were actually for installing and bolting up the connecting rods as the crankcase was one piece. This was one of the reasons why I went with a 2 piece crankcase.
Picture 3. The windows finished.
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These 3 pictures show the machining finished on the crankcase.
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Great!!! I just love your small projects George and this one will be another beautiful example no doubt! Just please tell me you didn't get all this done in one day :o
Bill
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Now it's time to take all those little ridges off and make a smooth surface.
Picture 1. the surface was painted with an ink marker.
Picture 2. The start of the finishing process. By inking the surface you can see when the high spots are being worked down. On this part a variety of tools was used, riffler files, 1/8 grinding points in my Dremel grinder and emery paper and home-made emery sticks.
Pictures 3&4. About 1-1/2 hours of hand work.
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Not to worry Bill! I have about 3 days in it so far. About 7-8 hours.
gbritnell
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A couple of finish pictures. I'll probably start on the gear cases as that's all I have designed to this point.
Being as it's a 3 cylinder engine I will have to develop a cam and figure out how the intake exhaust configuration will be.
There is nothing unique about the firing order, 1-2-3.
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It looks like you're starting on another master piece George - I'll certainly follow along as usual :praise2:
There is nothing unique about the firing order, 1-2-3.
This still allows for at least two different configurations .... Assuming that you will use a 120 degree crank, it can be 120, 120, 120, coasting 360 or 240, 240, 240 firing interval.
Best wishes
Per
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George,
Its always good to see you start a new engine. I always find it a learning experience. My smart car has a triple in it but that's about all I know about the internal workings.
Art
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As always outstanding !
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George it is always an education following your build threads. I am looking forward to watching the build as it progresses.
-Bob
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Another interesting build to follow along :ThumbsUp: :ThumbsUp: :wine1:
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That is uber impressive of the highest order. :ThumbsUp:
Nick
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Watching along George! Great Start!
Dave
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Another thread to follow. George, thanks for showing the details.
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Gentlemen,
An update to the progress on the mini 3 cylinder.
The gearcase is next. I started with a rectangular block of aluminum the required thickness. I touched it off to get my zeros and then drilled all the mounting and shaft holes. To create the radii in the corners of the screw bosses I drilled them out. The shaft and gear pockets were opened up with end mills prior to boring them.
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The piece was flipped over to mill the rear surface to thickness while leaving metal for a boss that the upper gear train will mount to as well as the crankshaft boss. These were cut with the boring bar inserted backwards and the spindle turning in reverse.
The part was then roughly cut out on the bandsaw and mounted on a fixture plate to cut the outside shapes to size.
The rotary table was set up and indicated. The fixture plate with the gearcase was then centered under the spindle with a tapered brass alignment pin. For shaping parts I find that this will get me within a couple of thousands which is close enough for contours.
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Here's the gear case attached to the front of the engine.
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The next piece is the cover for the gear case. I find that it's often times easier to sacrifice some extra metal to create a part. With small parts like this it's not a lot of metal so this is the direction I took. I figured out how much extra metal I needed to create a picture frame around the part and the stock was cut and milled square. I picked up the crank center which is where all my ordinate dimensions are taken from and as with the gear case put in all the needed holes. I left an island of stock which would become the boss over the end of the camshaft. The cam gear will need to be held in place with a 2-56 screw so I needed a recess on the backside and the boss on the front. The boss was then created using the reverse boring bar method like was used on the gear case. I have a dedicated cutter made from an old end mill that is ground up with a radius on the corner.
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The piece was then flipped over just to put the counterbore in for the cam end. I indicated the crank hole and then moved to the cam location and using an end mill made the pocket.
I then gave myself some rough cut lines so the part could be cut free on the bandsaw. The part then deburred and mounted to the gear case so I could scribe a witness line to file to. Once the part was filed to the line it was put back on the gear case for the final sizing.
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Not being familiar with 3 cylinder engines I did a little searching on the net to see what the cranks and timing looked like. There's not many options with a 3 cylinder engine for timing, 1-2-3 or 3-2-1. I looked into making a 120 degree crank but the firing sequence would leave a big gap from when the third cylinder fired until it got back to the first so I settled on a flat plane crank (180 degree) the end two cylinder up and the center down. This would shorten the space between the last firing and the first. With that settled I drew up the camshaft. It would be an easy job, just a matter of creating a step-off chart to mill too. As with all of my engines I make the cams from W-1 drill rod. I mill the lobe profiles then file and polish. The lifters will be hardened and polished so that there won't be two like surfaced running together.
The cam blank was cut with my small lathe creating the lobes and shaft diameters.
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The plan was to clamp the chuck on the nearest cam lobes (.25 diameter) and work my way out to eliminate any vibration while cutting. The issue would be that when the blank was extended for the next set of lobes I would lose my register so I made up a bushing with a flat milled on it and mounted it on the end of the camshaft. That way every time I advanced the shaft I could re-indicate the bushing to get back to my original starting point.
I set up my H/V rotary table and indicated it true. I set the table to -0-, inserted the blank and indicated the bushing. For added rigidity I supported the end with my home-made tailstock.
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The first set of lobes were cut then the shaft was extended and indicated like the start. The step-off chart starts from the first lobe on the first cylinder as -0- and each successive lobe is cut using the calculated numbers. Each lobe never restarts at -0-.
This thing was a piece of cake compared to doing a V-8 camshaft.
Once the lobes were milled they were filed and polished.
gbritnell
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Amazing work as always George. I always learn someting from your builds.
-Bob
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That is a lot of progress George!! Interesting as to the cylinder timing for three cylinders, but it makes sense once you think about it. Great looking parts as always!!
Bill
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There's not many options with a 3 cylinder engine for timing, 1-2-3 or 3-2-1. I looked into making a 120 degree crank but the firing sequence would leave a big gap from when the third cylinder fired until it got back to the first
Well that is the reason I asked you in an earlier post if you where going to fire 240, 240 and 240 degrees apart or 120, 120, 120 and coast 360 degrees before starting on one again - both schemes are normal for 120 degree crank. Laverda is the only 180 degree crank 3 cylinder engine I know off - see :
http://www.motorcycleclassics.com/classic-italian-motorcycles/180-120-degree-zm0z13mjzbea (http://www.motorcycleclassics.com/classic-italian-motorcycles/180-120-degree-zm0z13mjzbea)
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Thank you for the link. After reading the pros and cons of the two types I decided to go with the 240 degree firing order. With the small displacement of this engine I don't know how well it will run with the gap in firing. That being said I made a new cam today to suit the new firing sequence.
gbritnell
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Gentlemen,
While machining the new camshaft I decided to make a short video of how I do it. I'm not the best movie maker but I think it gets the idea across.
gbritnell
https://www.youtube.com/watch?v=ysuUhHU6MvA
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Thanks for the great video. I viewed it on youtube and left you a comment and subscribed.
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What design criteria do you use in creating the profile, other than the diameter of the camshaft and the lift? I assume the tip needs to be rounded, but is the diameter there critical?
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Probably the most important thing is the valve timing. This will control when the valves open and close relative to the piston position. Next would be the lift but this can be increased with the rocker arm ratio. The combination of these two numbers gives you a starting point for designing the cam. The basic diameter is established by the size of the engine and how much space you have available.
As with all the engines I have designed and built the cams have always had 'mild' cam timing. What that means is the opening and closing numbers, and therefore the duration aren't radical. These little engines are cantankerous enough without throwing a 'wild' cam in them.
gbritnell
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I started on the crankshaft the other day. It's made from 1144 Stressproof steel. The journals on the blank were turned to .375 diameter. The finished size is .281 so this gave enough stock to cut 3 flats that would be used for locating each of the throws when mounted in the fixture blocks. After turning the part was mounted in my dividing head using the tailstock for support. The three indexing flats were cut then each of the throw journals were roughed leaving .03 for cleanup. I have been using this method because the width of the throw journals can be cut to size and there isn't the constant interrupted cut while trying to do it all on the lathe.
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The stroke on the crank is .625 so I made up 2 identical fixture blocks to support the cam for cutting the throws. A reamed through hole (.375 dia.) was put through each block and on one a center drilled hole was also drilled for the tailstock support. The blocks need to be as close as possible to each other so that the can be aligned when cutting in the lathe. On these blocks I used a 1/4-20 setscrew that is ground perfectly flat. This is used to locate on the flats that were milled on the shaft. The other end (tailstock end) just tightens down on the .375 shaft.
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The driving block was mounted in the four jaw chuck and using a dial indicator against a dowel the block was adjusted to give a total reading of .625. After setting the offset it's necessary to indicate the sides of the block to make sure it's centered in the other direction, otherwise the crank pins are off center.
The crank blank was mounted in the head block and the set screw tightened. The tailstock block was slid onto the crank and the set screw brought up until the block was snug but able to rotate by hand. A parallel was then laid across the two blocks and held tightly while the screw was tightened.
Due to the short length of the crank there wasn't any noticeable chatter while cutting the center journal.
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Once the throw journals were finished the crank was clamped in the four jaw chuck and indicated true. The live center was bought up for support and the main journal next to the live center and the first journal in were cut to the finished diameter. The crank was then rotated and the process repeated. The finished crank indicated at .001 total runout between all journals.
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As always, a great tutorial in how to do things the right way!! The crankcase is taking shape nicely.
Bill
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Gentlemen,
I know it's been awhile but with summer in full swing it's hard to spend a lot of time in the shop.
I finished cutting the counterweights on the crank and I made the two inner bearings. On my inline six cylinder engine I adopted a different method for making the crankshaft main bearings. Rather than try to mount bearing caps then try to drill, ream or bore through the whole block and try to get things all in line I machined square pockets into which bronze bearing blocks would be inserted and bolted. This would allow me to machine everything perfectly in line and the bearing inserts could be done in a fixture guaranteeing almost true alignment. For this engine, although much shorter in length I took a similar approach. I drilled and reamed the ends for circular bearings and machined the inner two for rectangular inserts.
There is no planned progression of parts so with the gear case machined I figured I would cut all the required gears. The pitch is 48 and the sizes range from .25 PD to 1.00 PD for the camshaft gear.
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The original design of the Holt model engine has a secondary gear case that has the two smallest gears. The main set of gears has the crank gear turning the cam gear at 2:1 then the cam drives another gear which takes it back to crank speed. From there the secondary gear case goes back to 2:1 to drive the distributor and ignition timing. This in part is to get enough offset for the distributor.
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Next up is the cylinders. These will be jacketed with aluminum shells and have iron liners for the bores. The shells were turned leaving stock on the enlarged area for two eventual bosses, on high on one side and the other lower on the opposite side. These would provide enough metal to thread for a banjo type fitting to supply coolant. The full sized model has triangular flanges held on by bolts but I really don't want to get below 1MM screws on this build so this is what I came up with for the fittings.
After the shells were turned and bored to the finished sizes they were put in the mill and the square base flange was milled and drilled for the mounting screws. (1-72) I then made and adapter bushing that would locate the shells from the square flange and this was set up in my dividing head. The cooling bosses were trimmed to width and the extra material was removed by rotating the shell and cutting with and end mill.
After milling I filed the extra material around the diameter until it matched the original turned diameter.
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All three shells finished and ready to have the tapped holes (3-56) put in for the cooling fittings. I used the same setup in the dividing head to put the holes in.
I turned up the cast iron liners and then with a light press and Loctite inserted them into the shells. On the full sized model the head mounting bolts go through the iron liner and into the aluminum shell but for this tiny version I chose to leave extra material at the top of the liner for the head mounting screws.
I added the quarter and scale as a size reference.
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That's a lot of progress for not much shop time George!! That last picture with the quarter shows well that it is even smaller than I had previously thought. I am loving it though!!!
Bill
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It makes me dizzy to think of the precise detail work done on such a small scale. Beautiful.
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Hi George, I do like it very much to see your progress. Beautifull as always.
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George,
I am glad to see that we both machine our cams in a similar fashion. I use the cam-calc table. I have not yet made a multi cylinder so I like your set up with the flat on the disc to have a uniform flat for the zero. I have as well noticed the summer lack of time in the shop.
Art
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Hi Art,
Normally when I make a cam I use a piece of stock large enough in diameter to mill a flat that won't interfere with the finished cam. The cam blank is then put into a heavy walled busihing with two set screws that are ground flat on the bottom. I only turn four lobe discs at a time ( V8 cam) and then put it back into the bushing in the rotary table for profiling. I find doing it this way keeps the chatter down when milling.
gbritnell
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George-
The quarter really drives it home. I'm always in awe of your work; but, this is really incredible.
-Bob
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The next parts are the cylinder heads. I was going to make them from cast iron but then decided to try 1144 steel. My thinking was that the heads were so small and the 0-80 tapped hole for holding the manifolds in place is short that the iron might not be strong enough.
I turned up 3 pieces allowing enough stock to hold the heads for the next operation. A small boss (.020 long) was turned for a cylinder locator. The parts were then put between a pair of V-blocks in the mill vise and the sides were squared up, three to remove extra stock and one to size for where the manifolds will mount. These heads will have valve guides so a reamed hole (.125 dia.) was put into the head followed by a .187 ball mill to form the port. The spark plug port was also drilled to the proper depth. I was going to reduce the number of head bolt mounting holes from the full sized model but with the port and spark plug configurations I couldn't come up with a reasonable layout so I went with seven.
The head pieces were cut from the parent stock and put in the mill to establish the finished height. (.375)
At this point any further operations would require a fixture so one of my well used aluminum fixture plates was pulled from the fixture storage box and the head bolt mounting holes were drilled and tapped. Two of the holes were just reamed (.062) for a couple of short dowel pins to keep everything square and registered.
The vise was once again removed from the mill and the rotary table installed and indicated. This rotary table is an early Enco 8 inch (very nice) and is getting heavier and heavier to lift. One of the things this old age is bringing is loss of muscle strength but I'll keep lifting as long as possible.
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After spinning the outer diameters the parts were set on the cylinders for a trial fit to see how things look.
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When I put the mounting holes in the fixture plate I didn't think far enough ahead and realized that with the holes near the center of the plate I wouldn't be able to use it for the next operation which is putting the ports and plug holes so I cut off the extra stock and milled the edge square. Oh yeah, the rotary table came off and the vise put back up.
The ports go in at 8 degrees from the face in order to clear two of the head mounting holes so I set up my vernier protractor and 123 blocks to get the plate close. This was followed with my DTI to verify the proper angle.
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The first set of ports were drilled and then the fixture was tilted over and re-indicated to do the other side. Once the ports were finished the fixture plate was squared up to put the 0-80 holes in that would be used for holding the manifolds in place.
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The connecting rods were made from a piece of bearing bronze. I use rods made from the material for my large Holt and my 4 cylinder OHV engine. The material holds up well and with this small size I don't have to make very tiny bearing inserts. When there is any wear a few thousands can be filed from the cap and then the bore refitted to the crank pin.
gbritnell
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Wow - the rods look so much bigger in the first photo, then seeing them with the penny next to them...!
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It's really starting to take shape George. Nice to see this latest progress!!
Bill
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Hi George, these con rods are looking really nice.
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Impressive work George, thanks for sharing.
Dave
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I have the pistons finished and assembled on the rods. I'm going to start with a slip fit, a couple of tenths, and see how that goes. I used the same setup on my Tiny engines and they work fine with a little oil in the fuel. My bores were lapped and came out to within a couple of tenths to each other so the pistons were fitted to each bore and marked.
I also finished the lifter guides, lifters and retaining plates. The lifters were made from W-1 drill rod, hardened then polished.
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As per someone's mention in one of the other threads I went to a printing site called Shapeways. They will print in many different materials, stainless steel, brass, aluminum, gold and a myriad of plastics. I read over their information and realized this was the answer to my manifold creation. I drew the parts up in Solidworks and saved them as .stl files. I went for the stainless steel. The price was only $14.00 plus shipping of $4.00. Trying to fabricate them I would have had at least 4 hours per manifold. I ordered the exhaust to see what it looks like and if I'm pleased I will order the intake. I'll keep you posted.
gbritnell
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Definitely interested in seeing their work on the manifold...
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Yes Definitely!!!! The price seems more than reasonable, especially printing from metal. Hasn't been that long ago that you were looking at a 50-75 dollar minimum just to have a plastic part printed by a third party. Things are changing FAST in the 3D printing world!!! ANd the engine is also looking great George!!!
Bill
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Hi George, the engine is really looking great. Waiting for the result of your 3D printing experience. The price is really very cheap. I could not get it inside our company for that money.
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Yes Definitely!!!! The price seems more than reasonable, especially printing from metal. Hasn't been that long ago that you were looking at a 50-75 dollar minimum just to have a plastic part printed by a third party. Things are changing FAST in the 3D printing world!!! ANd the engine is also looking great George!!!
Bill
From Shapeway's website:
Steel is printed by depositing a liquid binder onto a bed of steel powder one layer at a time. The product is then removed from the printer and infused with bronze. If the clearance between two features or parts is too small, it is difficult to remove residual powder, and bodies can be fused together during the infusion process.
They charge per CC, so small parts are cheap. I've done some sample parts. In plastic the tolerances are excellent, but fall off a bit in metal. For a bolt hole I'd plan to design it smaller and drill out afterwards.
A friend of mine had them print a some large parts for a 2.5 scale loco, and the cost got into the thousands.
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Yes Definitely!!!! The price seems more than reasonable, especially printing from metal. Hasn't been that long ago that you were looking at a 50-75 dollar minimum just to have a plastic part printed by a third party. Things are changing FAST in the 3D printing world!!! ANd the engine is also looking great George!!!
Bill
From Shapeway's website:
Steel is printed by depositing a liquid binder onto a bed of steel powder one layer at a time. The product is then removed from the printer and infused with bronze. If the clearance between two features or parts is too small, it is difficult to remove residual powder, and bodies can be fused together during the infusion process.
They charge per CC, so small parts are cheap. I've done some sample parts. In plastic the tolerances are excellent, but fall off a bit in metal. For a bolt hole I'd plan to design it smaller and drill out afterwards.
A friend of mine had them print a some large parts for a 2.5 scale loco, and the cost got into the thousands.
When I looked at this from Shapeways, they talked about printing the part in wax and then molding from that as lost-wax process. Or was that just for bronze parts?
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Brass and bronze are lost wax, as are the precious metals. Steel is a bit too high melting point I guess.
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Here's the Holiday update.
Valves, retainers and springs are made. The valves are drill rod, .0625 diameter with .215 diameter heads. They are silver soldered together then the heads are turned true to the stems using an ER 11 set true collet chuck. Crankcase inspection covers are also finished. I tossed around a couple of ideas for the outside shape and settled on what you see. I had made a part model for the rocker arm towers with the hope that I could get them cast through Shapeways. Initially they said that they couldn't be made for whatever reason so I started making my own. Halfway through I got an email saying that after a human inspection they passed the criteria for casting and they were being sent to the printer. If I don't like them I always have these pieces.
gbritnell
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I am really enjoying watching this build.
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When I submitted the part model files to Shapeways they told me that the exhaust couldn't be made without making the walls much heavier than I wanted but curiously enough they said that the intake could be made and it has the same wall thickness. That being said I figured I would try to make my own. The manifold is made from 1144 steel. I have kind of gone to this steel as opposed to using 12L14 because it machines nice and it's not prone to rusting like 12L. I machined the elbows first on the lathe turning the .062 x .266 flange and drilling the hole out. I took a spare drill and rounded the tip to create a ball at the bottom of the drilled hole. The main vertical exhaust pipe is .25 O.D. and .187 I.D. The elbows have a spigot that is .213 diameter so the vertical pipe was counterbored to take the center elbow. I first silver soldered the the center elbow and pipe together because I had to chuck the part up to drill for the angular pipes that come from the end outlets. The end outlets were scalloped to match the diameter of the pipes (also .213) The pipes were drilled out leaving material at the end so that after assembly I could radius the corners without breaking through. I made up a fixture to mount all the flanges and then assembled the horizontal pipe pieces into the vertical pipe and cradled into the scallop in the end elbow. Everything was fluxed then silver soldered using 56% silver solder. The penny was added in the last photo to give an idea of the size.
gbritnell
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Wow George the penny sure puts it into perspective!
With work like that who need a 3D printing service? Although I'm still curious to see the printed intake manifold.
The whole project is just amazing and I'm enjoying watching you work too.
Best regards,
Dave
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If the Shapeways version does work, then others interested in building this engine can order them as well.
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Well I'm still waiting on the Shapeways parts. All the website says is they're in production.
I have made plenty of flywheels over the years and it's probably one of the biggest pains in model making. Not the machining part but all the handwork if you want the spokes to have a round profile.
I saw on the Martin Pattern site that they had a 3.00 heavy flywheel. All I needed is 2.78 diameter and with the heavy rim on the casting I could get the finished wheel diameter with room to spare. I ordered 2 of them thinking that I would make the engine somewhat like the Fairbanks with 2 large flywheels but if I didn't like the looks I could always machine up the smaller flywheel like the full sized Holt model has.
I got the castings the other day and the first thing I noticed there was quite a mismatch. Now I'm talking almost .050. Rather than go through the trouble of sending them back I decided to machine them and see how they ended up. The iron is buttery soft and I found no voids or hard spots. I chucked the wheels in the 4 jaw chuck and indicated the rim, both axially and radially. The machining went fine but then I had to spend quite a bit of time trying to blend in the 'off side' using burrs and mounted stones.
I rather like the look of the engine with the 2 wheels so I'll probably go that way as long as they aren't too heavy inertia wise.
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The wheels turned out really nice looking.
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I'm still waiting for the parts from Shapeways so I thought I would proceed with my own. The rocker arms are made from 1144 steel. I turned a piece of stock and drilled it .086 for a 2-56 shaft. The piece was then moved to the dividing head where I roughed it to size and then created the profiles by stepping of the shape with a .125 ball mill. The piece was then moved to the vise and clamped with a V-block to position it vertically. Using a .031 slitting saw I cut the rocker arms from the stock. The arms were then filed and cleaned up prior to the next operation.
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I made up an aluminum fixture plate to hold the arms for the next machining steps. The center hole was drilled and tapped for a 2-56 thread and the top of the hole was counterbored .050 deep to located the fixing screw. I left pads where needed to keep the arm from rotating while machining. Using a .093 end mill with a tiny radius on the corners I stepped off the shape on the side of the rocker arm. Two were done at a time to speed up the operation. Once I had all of one side complete I deburred the parts and flipped them over to do the other side. After machining I used a variety of files and sanding pads to smooth all the cutter marks.
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Those are very impressive parts George. There is allot more going on with them then one realizes at first glance.
-Bob
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The rocker arms needed to be threaded for adjuster screws. The width of the boss at the valve end is only .094 so rather than go with 0-80 threads and leave only .015 around the thread I decided to use 1.2mm threads (.047 diam.) I used the same setup for drilling the adjuster end of the rocker arm as I did for the ball pocket at the pushrod end.
On my full sized Holt the pushrods are adjustable but given that these pushrods are only .062 diameter I didn't want to make the threaded joint so fragile that it might bend or break.
The rocker shaft were turned with a .094 diam. center area and .086 on the ends for the 2-56 retaining nuts.
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Wonderful work, as always George! :ThumbsUp: :ThumbsUp: :ThumbsUp:
Thank you for sharing and inspiring! :cheers:
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Fabulous George. Gosh those rocker arms are teeny (even smaller than tiny). The flywheels look great too, too bad about the mismatch though but still probably easier than making them from bar stock.
Bill
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George,
Looks great as usual.
Art
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What a great engine! Really enjoying watching the progress on this!!
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Well it's down to the last 'big' pieces of the engine, the timer and distributor gear. This engine will have a Hall trigger ignition. Trying to scale it down and still make it workable and pleasing to look at took some doing on the CAD program. The secondary gear case has a hub (.211 dia.) that an adapter plate fits onto. It's held in place with a 1-72 set screw. The plate has a slot that will hold the Hall transistor.
Next on the .093 shaft is the timer disc. This is made of steel and is also held in place with a 1-72 set screw. Mounted to the adapter plate is the distributor base plate. The two plates are bolted together with 0-80 screws. This plate is counterbored to allow the timing disc to turn inside with .010 clearance. This plate also holds the .125 x .062 magnet.
In the first picture you are looking at the timing pieces from the front of the engine. The ear sticking out to the left is part of the adapter plate. It is held to the distributor plate with the 0-80 socket head screw. Sandwiched between you see the timing disc with one of the window cutouts at the top.
The second photo is taken from the rear of the engine and shows the counterbore that the distributor cap will fit into. The larger hole at the 4:00 position is the through hole for the magnet.
The third photo show the timing disc. To the right is the slot for the Hall transistor and to the left of the disc the hole you see is the tapped hole to hold the disc in place.
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The next picture is a front 3/4 view showing the assembly a little better.
The last photo is of the engine with the parts assembled to the secondary gear case.
The distributor cap will be .75 diameter. I could have made it a little smaller but it's size was governed by how tight I could make the timer assembly.
gbritnell
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Looking at the photos it is hard to get a perspective of the actual tiny size. Just beautiful workmanship. :o
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I finished up the components for the distributor. I machined the brackets to give them a little more character. The rotor is complete.
I made the cap and rotor from black Delrin. I have used it in the past with good luck. It machines nice and seems to have good electrical qualities. I turned the cap then mounted it on the end of a fixture rod and set it up in the mill vise, indicating it to achieve true center. The center holes were drilled .062 followed by a .104 dia. drill for the plug wires. I then used my home-made coring tool to cut the terminal posts. The cutter was drilled out to the size of the terminals then bored to add 3 degrees of back draft to allow for clearance while it was cutting. The cutter was then fluted, hardened and the cutting edges honed with a diamond tool. The cap is held in place with 2 0-80 screws.
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Looking fantastic George. I always love your work, you are a fine craftsman.
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Hi George, a very interesting concept your disstributor with the half open running disc.
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HI Achim,
On the full sized model Holt there are a set of points in that location. Not wanting to try to miniaturize the point assembly I went with the Hall setup. The open top is so I can adjust the timing disc without having to disassemble everything. The distributor base is mounted quite securely with three screws.
gbritnell
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Mighty pretty engine, George. The old 3 cylinder industrial engines are among my favorites. As usual, your work is meticulous and admirable. Just curious, do you recall about how long it takes to whittle out something like the interior of the lower crankcase half?
Chuck
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That's a gorgeous little engine :NotWorthy: :NotWorthy: :NotWorthy:
Can't wait to see it running :Lol:
Plani
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Hi Chuck,
To carve out the inside of the lower crankcase probably took about 3 hours. As you know my technique is to make a step-off chart for the shape so it's pretty much a matter of following the numbers. I don't mean to make it sound that simple but as long as you follow the numbers it goes quite fast. I'm guessing the whole lower crankcase took between 10-12 hours. (Machining) Finishing with files and such took another couple of hours.
gbritnell
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Hi Chuck,
To carve out the inside of the lower crankcase probably took about 3 hours. As you know my technique is to make a step-off chart for the shape so it's pretty much a matter of following the numbers. I don't mean to make it sound that simple but as long as you follow the numbers it goes quite fast. I'm guessing the whole lower crankcase took between 10-12 hours. (Machining) Finishing with files and such took another couple of hours.
gbritnell
Yeah, I'm familiar with your technique of whittling stuff out from solid. Kind of blows my mind to see the results you get. I've never mastered the art of working like that, guess I'm too impatient. And, I've only recently begun to appreciate the skill required for using a file. However, I do appreciate the value of good file work. I've also come to appreciate the value of being able to use a jeweler's saw. Very effective, and relatively fast, for cutting out small, intricate parts.
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George--Once again, you have out-done yourself. I love your engine, and I am in awe of your machining skills. I am taking a break from machining for a while, but I still check the forums every day to see what people are doing. Great job.--Brian
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Just catching up on the thread VERY impressive. Those heads are so small and the rockers WOW! You are doing some amazing work George!
:ThumbsUp: :ThumbsUp: :ThumbsUp:
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Thanks Brian, Doc, Chuck, Bill and everyone watching and commenting.
The next project is the carburetor. Having experience with the 'Tiny' hit and miss engines I realized how small the venturi can be made and still have an engine run. With the 'Tiny' hit and miss engines there is the governor mechanism to regulate the speed but having no such mechanism on this engine it's necessary to make a throttling carburetor. I have no idea what it takes as far as venturi size for this engine so kind of basing on the 'Tiny' carb, this engine being a bit larger, I opted for a .093 venturi. This is an air bleed style carb with a rotating barrel for the air control. The inlet and outlet sides are .125 and they taper down to the .093 diameter. I had run out of my small sewing needle supply so I headed to the local fabric store to see what they had. I bought a package of 20 sharps, ranging in size from #3 to #9.
The smallest diameter, the #3 is .028. The next size up has a diameter of .031, just right for using drills of .032 and .032 (#67 and #68)
I machined the body on the end of a piece of aluminum rod. The first one I started I began on the lathe and drilled and reamed the venturi hole. Right after finishing the hole I realize that I would have to put the barrel hole through this hole and it probably wouldn't make for a smooth cut due to no support for the drill. The barrel is .144 diameter and I don't have a reamer that size but I do have a new drill.
I cut this first try off and restarted. This time I put the rod in the dividing head and started cutting the sides, top and bottom. Once I had these sides squared up I put the barrel hole through. I then machined the remaining shapes and drilled and tapped the holes for the barrel retaining screw and throttle stop.
From the dividing head I put the rod in the lathe and put the venturi hole in. To taper the inlet I made a 10 degree D bit.
The body was then stood up vertically in the mill vise to put the 2 mounting holes in. These will be for 1.20mm screws (.047diameter) While standing up I used a slitting saw to part it from the rod.
The thread for the needle valve is 2-64. I have a tap that small but no die. Even if I had a die I wouldn't have been able to get close to the shoulder so I chased it by hand on the lathe.
When I say by hand I set up for cutting the thread, tool, dials etc. and then I have a crank handle that fits into the outboard end of the spindle so I can crank it by hand. (no power). I started using this procedure way back when I built the radial engine and had to get the cylinder thread up against the barrel shoulder.
I made the adjusting barrel first and threaded it. I then hand chased the male thread until the barrel fit nice and smoothly.
The fuel chamber is made from 2 pieces. The inner piece or the piece that goes into the carb body is drilled .026 so the .032 needle can seal into it. The counterbore is .075 and this area allows the fuel to flow in and around the needle. To seal this chamber off and provide support for the needle an outer piece was made and drilled .032. The two pieces were pressed together and the assembly was pressed into the carb body.
To fix the needle into the barrel I first screw the barrel onto the threaded stem until it bottoms. I then back it out about 1 turn. I insert the needle until it seats into the jet hole and mark where to cut it off.
Using a small cutoff wheel in the Dremel I cut it to length then grind a small flat on one side where it fits into the barrel. This allow the solder to flow around the needle and into the flat to secure the needle.
The last piece was a handle. I cut this on the end of a bar of steel and then parted it off with a slitting saw. The edges of the handle were filed and sanded with a nice radius.
These pictures are of the initial machining on the end of the bar.
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The next 3 pictures show the parts before assembly. In the pictures the needle looks huge but consider it's only .032 diameter.
The last picture show the jet which projects through the bottom of the barrel and goes to the center line of the venturi.
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And there you have it, a tiny carburetor. The first picture taken through the venturi shows the jet projecting into the venturi and the tip of the needle sticking out of the jet. The next picture shows the barrel retaining screw and the throttle stop screws, both 1.0x.25 mm.
As an aside these tiny parts are made on my 6 inch Atlas lathe and my 8 x 36 vertical mill.
gbritnell
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"And there you have it....."
Much easier said than done George. You make it look so easy. I am always in awe of your skills. I am really enjoying this build.
-Bob
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Hi George
Is this watch making or engine making? When they say it's engineering in miniature, they are not exaggerating.
Congratulations on this fine piece of work.
:cheers:
Mike
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Wow.
Again. As usual!
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Wow! is right!
And what's even more amazing, is that it's going to work too!
That's amazing George!
Kim
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Thanks Chris and Kim for checking in and commenting.
gbritnell
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Another masterpiece. Impressive. You have big coins there at the other side of the pond.
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Still following with interest :ThumbsUp: :ThumbsUp: :wine1: I do like the way you machined the distributor cap and the carb is magnificent :praise2: :praise2:
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It's been awhile since I posted on the engine. I've had several other projects going at the same time.
I finished the spark plugs. The thread is 6-40 (.138 OD.) I've never made plugs this small before so I don't know how they'll function. I know they should work as Lou Chenot made smaller plugs for his Deusenberg engine and they worked.
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I made the fuel tank and mounting brackets. The tank is .625 O.D. x 1.00 long. The fuel line is 1/16th.
I made up all the fittings for the water manifolds then assembled them on the engine. The intent was to soft solder all the pieces together in place but I didn't know if the electric soldering gun would put out enough heat to do a good sweat job due to the fact that all the other pieces and the aluminum water jackets would be drawing heat away. I fluxed each joint then touched the gun to a piece of 50/50 solder and first applied a dab of solder to the joint itself then held the gun on each fitting. I was pleasantly surprised when the solder wicked all the way around each fitting. A little cleanup with a fine file got rid of the excess solder.
gbritnell
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It's getting close George!! Amazing work, and I thought the "Tiny" had small parts :o
Bill
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Truly amazing such fine work !
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George'
Wanted to let you know I'm still following along. Phenomenal work as usual. I have to say the penny for scale on the carb reflects just how small this thing is.
Art
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George,
I have nothing meaningful to add other than, "Wow!"
I'm always humbled by your work.
Thank you for sharing it,
Kim
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Beyond belief George, your work is amazing.
Thomas
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Still following along :wine1: It looks splendid :praise2: :praise2:
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Just catching up again and WOW! I love that little carb!! That is a beautiful little rendition of a Holt she is just amazing. VERY NICE WORK :praise2: :praise2: :NotWorthy:
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Gentlemen,
An update on the Tiny Holt.
I had an opportunity to take the engine out into the garage for a trial startup a few weeks back. I hooded everything up, put some gas in it and gave it a spin all the while slowly adjusting the carb needle open. I found a spot that it would hit a little but no sustained running. I checked the plugs and they were soaked so I wiped them off and gave it another try. Same thing.
I had some doubts about using plugs that small as I had never done that size before. Not knowing if that was the main problem or not I opted to disassemble the engine and go the next size up with the plugs, 8-36. I have used those in some of my other engines and know they work.
I took the heads apart and set them up to machine for the new plugs. I made a little cutter up as I don't like drilling into a hole that already has threads in it. A drill seems to moves all over the place. The holes were tapped and the engine put back together. While I had it apart to simplify all systems I made another carb up. This one is kind of like the one used on the Tiny Hit and Miss engines. Just a venturi and a needle valve.
New plugs were made and the engine was set up for a second attempt. As I was spinning it over and opening the needle valve the engine started right up, for about 5 seconds, then quit. I checked the spark and it was gone. Crud!! I took the distributor apart and reassembled another Hall transistor which is a real pain. Ok, new Hall assembled and out we go for another try. Exactly the same scenario.
Out of all the distributor combinations I have built over the years I have only had one other that would constantly burn out transistors. I have no idea why. The distance from the Hall to any spark is far enough that that it shouldn't get any feedback and I always use 2 ground wired when running my engines. The Hall in my 302 distributor is 6 years old and still works fine.
Ok, back to the drawing board.
Using my existing dimensions I designed a set of points to replace the Hall setup (photo attached.) The new pieces were installed and once again it was out to the garage for another try.
The engine was fueled up, the ignition hooked up and the engine spun over. As I opened the needle valve the engine started up and ran, this time I got about 12 seconds.
As I looked at the engine I saw that 3 of the pushrods had come loose. Surely the cam couldn't have worn that badly in starting attempts. I tried putting the pushrods back in place but there was way too much clearance. Now as I'm doing this I'm not really looking at anything but the lifters and cylinder heads. Scratching my head I couldn't figure it out. As I took a different vantage point is was then that I noticed the problem. The number 2 and 3 cylinder liners had come loose from the jacket and moved up about .100. (photo attached.)
When I built the engine the liners had a .001 press fit at the top and bottom of the liners and were coated with Loctite. Now I know that Loctite doesn't like aluminum without using an accelerator but I have used this procedure in the past without any problems. Time for another disassembly.
When I built the engine the liners were installed into the water jackets then the assembly was mounted in a fixture for drilling the head bolt holes so the port faces would all line up. Now with the liners needing to be pulled out I had to come up with a way of accurately locating them upon reassembling. I made up a dummy head with a flat milled on one side, this corresponded with a flat milled on the original drilling fixture. The drilling fixture with jacket mounted was clamped onto a solid parallel. The liner was coated with Loctite and with the dummy head mounted was slid into the jacket as far as it would go. The liner and dummy head was lightly clamped to the parallel and the whole thing was set upside down between the jaws of my mill vise. The parallel now resting on the vise jaws with the two parts between the jaws I tightened the jaws and squeezed the two pieces back together.
With the cylinder assemblies back together I mounted them in the original drilling fixture and redrilled all the head bolt holes down into and through the flange of the outer jacket. I then retapped the 0-80 holes deeper. I had to buy some longer screws to assemble everything but there should be no possibility of it coming apart like that again.
Any way that's where I'm at. I have been doing a job for someone so that has taken precedent over running the engine again. I hope to have it running for the Zanesville show in 2 weeks.
gbritnell
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Thank you for sharing your experience. That's some "interesting behaviour" of this little engine.
But I'm sure you will get it all sorted out. I'll keep my fingers crossed while anxiously waiting for the video ;)....
Plani
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Is there any possibility that the cylinders had become flooded with fuel, causing the cylinder liners and heads to be lifted hydraulicaly? It may be worth checking to see if the con-rods are still straight
If the liners were a 0.001 press fit, would there be any Loctite in the joint? Would 0.001 clearance be better?
Just thinking
Mike
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Wow George...! Certainly inspirational. Thanks for sharing the tribulations of trying to get the ignition to work. As always, you never cease to amaze and impress. Paul
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Sorry to hear about the issues George, but you seem to be tracking then down one by one. Will Roy Scholl be in Zanesville. Maybe he has a take on the hall sensor issue.
Bill
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George,
I was just reading getting caught up really. But it sounds like the cylinder sleeve is holding the head onto the cylinder. Isn't the head bolted to the cylinder? and that would keep the cylinder sleeve in place. I must admit having no knowledge of how a Holt is constructed. But if the head isn't bolted to the cylinder doesn't that put a lot of load onto the joint between the cylinder & sleeve?
Art
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Some interesting challenges ::) ::) but you are working through them :ThumbsUp: Hopefully not long until it is running properly :wine1:
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Glad you found it George.....you'll sort it out I'm sure!!!
Dave
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Hi Georg, thanks for the up date. Good luck for the next attempt.
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Now that the engine runs I'm moving on to the radiator. I didn't want to make any more than I had to until I got it running, water pump, brackets, radiator etc.
The radiator is being built by the same construction method as the larger Holt engine rad., fin tube cut from square brass stock, machined tanks and header plates and all soldered together with side plates.
The larger rad has the word HOLT machined onto it. I made up a step-off chart and cut the lettering with a .062 end mill. This one being 1/2 size I had reservations about doing the same job so with some knowledge of modern printing processes I created a model and sent it of to Shapeways to be cast in brass. They said about 2 weeks.
In the mean time I started on the fin tube. I took some .50 brass rod and cut 5 lengths to 2.40 inches long. I then through drilled the pieces to .120 diameter. The pieces were then milled to .312 x .375.
To hold them in the collet I turned up a length of aluminum rod then cut a slot .375 x .154 deep, .002 shy of half the .312 thickness. Two pieces were then cut from the rod and marked with a dot for assembly.
For the first cut the bar was projected out 1.20 and the .04 wide necking tool was touched off to the end. I then turned . 17 diameter for a length of .065. The fins are .018 thick and with the tool .04 wide this gave me progressive steps of .058. I marked all the numbers down on a piece of paper to follow.
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I cut the first set of fins then pulled the bar out to 1.90, picked up the end of the bar, set -0- and then proceeded to cut more of the fins. I did each piece identically with the hope that when the fins were finished the would all match up.
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At this point I marked the rod for registration then turned it around to finish the last .50. Using a magnifying glass I carefully picked up the last cut then stepped out to the end of the bar, cutting the same diameter as the other end. These will fit into the header plates and be soldered.
I lined up all five pieces to show that by doing each one exactly the same way produced very good results.
gbritnell
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Those look great George . Shame about the lead time from Shapeways, but will no doubt be worth it.
Bill
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gbritnell,
I follow and enjoy all your engine builds, but I have to add that the radiators you make are worthy of special mention.
You have got to be the godfather of model radiators.
Thank You for sharing your projects,
ShopShoe
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Hi George,
Your 3 cylinder radiator is another master piece. I would like to inquire why you milled the tube from .5 “ square, as opposed to just using square stock. Just curious about that. Also when you drill the end plates, will you space the holes exactly .375” apart, or will you allow a little more so as not to have any interference between tubes?
Am thinking of making one for my Snow engine. Working up a drawing Fusion.
.
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Actually it was.50 round that I started with. That would let me get the.375 dimension. I didn't have any square stock on hand and I had a lot of the round available. With the price of brass seemingly just shy of gold I really don't want to buy any more than I have to.
I will leave a couple of thousands space between the tube centers just to make sure there is no interference.
gbritnell
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Gentlemen,
I know it's been a long time since I posted anything on the tiny Holt or anything else for that matter. I've been extremely busy working on some engines for a fellow, a couple of Wall engines that are in dire need of refitting, to say the least.
Anyway here's an update on the radiator. I got the top tank back from Shapeways and I'm thoroughly pleased with it. I asked for raw brass (unpolished) but it looks like they went ahead and did some kind of smoothing and polishing. It wasn't the greatest job but it didn't take much to clean it up.
I machined the top and bottom header plates from a solid bar of brass. They are only .060 thick and have a .025 recess so I had reservations about trying to do it from a piece of 1/16th stock. I drilled the holes deep enough for the two plates then cut the recess in the first one. I then cut it free with a slitting saw. Same procedure for the second one.
The side plates had multiple steps so I started with a piece of 1/8th brass strip and and machined everything in one setup. When I unclamped the part it had warped a little but was easy enough to straighten out with a little coaxing.
I didn't know how I was going to hold everything together for soldering so I drilled and tapped one hole in each end of the side plates and headers. These were tapped .80 mm (.032 diameter)
Everything assemble quite nicely and once together I clamped a couple of pieces of flat steel strip across the the side plates to keep everything aligned for soldering.
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I still have to drill the water opening in the top tank and drill and tap for the fill plug. The bottom tank will get a water outlet soldered into it.
gbritnell
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That radiator is stunning!
:popcorn:
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Thanks for the update George. The radiator looks fantastic. Good to hear the shapeways part worked out well too.
Bill
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Gentlemen,
Happy New Year to all. The last time I posted was in the old years hence the greeting.
My last postings were of the radiator. I have has other jobs to do so I haven't really spent much time on the Tiny Holt until now. I kind of knew that the large flywheel in the front of the engine would pose a problem for the coolant line routing so after I started looking closer I decided to make a smaller flywheel for up front much like the larger Holt engine. I had a piece of 2.125 diameter iron so I came up with a design and using the rotary table drilled and carved out the smaller version. The nice thing about using iron is when you're using small burrs to do the shaping you don't get the tiny shards of metal like you do with steel.
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Here's a couple more shots of the radiator prior to the finish drilling and tapping.
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The water pump on the larger Holt is of the centrifugal type but I thought with this smaller size it might not move water properly so I went with a gear type pump. Having made numerous gears over the years I used one of the cutters to cut 2, 10 tooth, 48 pitch gears. The fit was very good, just a little snug at first assembly but with a little spinning with some very fine lapping compound they bedded in nicely. This will provide a tight seal at the tooth mesh for a better seal. The housing is proportionally similar to the larger engine and is mounted about the same, to the fuel tank bracket. The gear shafts and screws are stainless steel because of the water.
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The water will enter at the bottom right corner of the pump and come out the top left. I bent a piece of 1/8th brass tubing and put it in place to see what I needed for the upper connection. The lower connection will be with a piece of neoprene tubing.
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Here's a shot of the finished radiator mounted on the frame. I made the filler cap by turning and threading the filler plug then cross drilling it for the ball ended handle. The trick would be how to ge the handle through the cap and have the balls on each end. I turned the shaft, .047 diameter with a short length of .04x.070 at the end. Before cutting if off I left enough material to form the ball on one end.
I mounted the shaft in a home made reducing sleeve and formed the ball end. The ball for the other end was drilled .04 then shaped as closely as I could get it prior to cutting it off. Once cut off I pressed it onto the shaft then filed the remaining material into the conical shape. Needless to say with the tiny size of the ball I lost couple of them before getting on onto the shaft.
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Stunning, as usual! :praise2:
Maybe in a week the shop elves will bring back those other ball ends...
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The detail of these parts is astounding (and outstanding).
I always like your radiators: This one is even greater with the ball-handled cap and "HOLT" on the tank.
Thanks for inspiring the rest of us.
--ShopShoe
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Haha I can relate to loosing parts trying to get them assembled. Things are really looking good your work continues to impress me :praise2: :NotWorthy: I know I don't post enough but never the less I am following along.
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Excellent as ever :praise2: :praise2: I do think that we need a "Swarf Gnome" emoticon on here as I have also lost several small balls and springs in the last few weeks ::)
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Excellent as ever :praise2: :praise2: I do think that we need a "Swarf Gnome" emoticon on here as I have also lost several small balls and springs in the last few weeks ::)
Need a version with the Monty Python foot coming down on the shop gnome...!
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"Need a version with the Monty Python foot coming down on the shop gnome...!"
Or the 16-Ton Weight or the Giant Hammer.
ShopShoe
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Hi George, again a masterpiece. A fantastic model engine. Thanks for sharing with us.
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The engine is finished. I only have to put the O ring drive belts on the pulleys but Stock Drive Products is out of stock at the moment.
I ordered the 1/8th cast fittings from PM Research and made up a fixture to hold the elbows for machining. These were soldered to the existing piping and then neoprene tubing was cut to join everything together. I made small hose clamps for both the coolant tubing and the fuel lines although they are both different sizes. The ones for the coolant tubing are .187 I.D. and are .012 thick and .070 wide. I made the rings from stainless steel and the threaded pieces from brass. In the past I have used brass for both but after silver soldering the rings get extremely soft and distort. The screws are M1.0x.25.
I made the pulleys and mounted them on the crankshaft and water pump. The other pair of pulleys was mounted to the front of the flywheel and to the fan. The bracket for the fan was milled from one piece of aluminum.
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Stunning George not to mention inspiring!!! Once you get the O-rings and hopefully make a video, please add the finished pictures and video to the showcase section too if you don't mind.
Thanks for taking us along on the ride for this one!! Any other small projects in the works?? :)
Bill
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Another Master Class project from you George - very impressed as always :NotWorthy:
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an incredible beautiful model......Pavel
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George, you've done it again. A beautiful little engine. Congratulations!!
:ThumbsUp: :ThumbsUp: :praise2:
Pete
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Extraordinary.
Regards,
Rudy
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A favorite engine of mine and a fantastic job on it!
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Very nicely done, George!
Chuck
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It really is stunning George. I wish that I could find a way to get to NAMES just to see it in person.
-Bob
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I finished up the components for the distributor. I machined the brackets to give them a little more character. The rotor is complete.
I made the cap and rotor from black Delrin. I have used it in the past with good luck. It machines nice and seems to have good electrical qualities. I turned the cap then mounted it on the end of a fixture rod and set it up in the mill vise, indicating it to achieve true center. The center holes were drilled .062 followed by a .104 dia. drill for the plug wires. I then used my home-made coring tool to cut the terminal posts. The cutter was drilled out to the size of the terminals then bored to add 3 degrees of back draft to allow for clearance while it was cutting. The cutter was then fluted, hardened and the cutting edges honed with a diamond tool. The cap is held in place with 2 0-80 screws.
Hi george,
Very nice bulid. Couldyou say something about how the leads are mounted into the cap? Maybee show a inside photo of the cap?Would like to see the rotor too.
Regards Michael
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Hi Michael,
Here's how I do the wired and cap.
The cap is turned from a piece of Delrin. I counterbore the inside out to the proper depth and cut it off. I make what's know in the wood world as a plug cutter from drill rod.
This is used to form the terminal posts on the top of the cap. The cap is now mounted in a holding device in my mill and centered. I drill through at each of the terminal locations with a 1/6th drill for brass rivets. This is followed with a #38 drill (.101) I also have another #38 drill that I have the tip ground flat to act as a counterbore to flatten the bottom of each hole.
The wire I use comes from S&S Machine Tool. They make the miniature ignition components. The wire is .099-.100 diameter so it's a nice fit in the hole.
I then use my plug cutter to form the outside of the terminals. While I'm doing this I also make a terminal post on a scrap piece of Delrin. (Explanation to follow)
I make up little brass rivets that are drilled through. This allows them to be 'riveted' in place in the cap.
I now take the extra terminal post that I machined and start forming the wire ends that go in the cap. I make up tiny brass discs about .095 diameter with a through hole that the wire will go through. I strip a small amount of wire and pass it through the disc. I then spread the wire out in a fan shape which holds the disc in place. I then touch it with a small soldering iron to solder it in place.
The wire is now inserted into the cap and a piece of shrink tubing is slid over the wire and up against the distributor terminal. This acts as a bushing so that the outer piece of shrink tubing won't have to shrink down as far. I then cut the outer piece of shrink tubing. This is long enough to go over the terminal and over the bushing piece. I then heat shrink it in place. I do this on the spare piece I made because if you try to shrink it on the cap you will start melting the adjacent terminals.
Once the shrink tubing is cool I pull it off the fixture plug and press it into the actual cap. Usually the shrink tubing has formed a nice tight fit so between the fit of the wire in the hole and the outer tubing it holds the wires in place quite securely. If one of them seems a little loose I put a very tiny dab of black silicon sealer on the outside of the terminal and slide the wire assembly down over it. Once the silicone had dried it holds the wire tight but can be pulled off if necessary.
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Words fail me George, absolutely stunning. Work at this level makes me realize how much I yet need to learn.
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George,
many thanks for the detailed description.
Michael