Model Engine Maker
Engines => Your Own Design => Topic started by: tvoght on September 07, 2015, 04:09:52 PM
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The subject of this build is a kind of novelty engine. I don't know of any similar full-scale engine, and I can't think of any reason why one would (or should) have existed.
"Robby" resembles a conventional horizontal mill engine, but instead of a crosshead and guide, he features a straight-line motion to guide the joint where the connecting rod and piston rod meet.
The use of the straight-line motion was the usual practice in the days of beam engines, and in those days the mechanism most commonly used was Watt's linkage (an invention of which James Watt was rightly proud).
The linkage used here is known as the Robert's mechanism, and is chosen because it is different from the usual Watt's mechanism. Thus Robby's name.
I hope to build an engine that will be somewhat entertaining to watch, and might evoke conversation. In other words, an engine tailor-made to show at model engineering expositions.
The following sketchy drawing is a side view of the engine with the crank in 3 different positions to show the general motion of the Roberts mechanism (in blue). Note how the joint at the bottom of the triangular link guides the end of the piston rod in an approximately straight line.
(http://www.voght.com/robby/intro/motion.jpg)
(http://www.voght.com/robby/intro/motion.jpghttp://www.voght.com/robby/intro/motion.jpg--Tim)
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Shold make for an interesting model!
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Tim, that does look like it would have a lot of interest motion! I'll be following along! :popcorn:
Kim
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Good one,Tim. I'll definitely be watching
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You could also call it a "Cheby" engine. That's a form of the Chebyshev linkage used to produce straight line motion.
https://en.wikipedia.org/wiki/Chebyshev_linkage
[Although, I have to admit that "Cheby" just doesn't have the ring that "Robby" does.]
Lots of uniqueness and wow factor. Bound to be a hit at the shows.
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Nice Tim. Looks like it would offer lots of ways to bling it up some too. As Marv said...sure to be well received at shows. Let the chips fly!!
Bill
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An interesting concept Tim. I'll be watching with keen interest as this is the kind of "out of the ordinary" engine I like. I also have a little self interest in that I hope that if your idea works well you could perhaps publish drawings. :P
Jim
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Thanks crueby, Kim, Stan, Marv, Bill, and Jim for checking in. I'm gratified to have some initial interest.
Marv, in fact "Cheby" was a possibility as I explored my options.
My references classify the Roberts and Chebyshev as distinct linkages.
Not only are the radial bars crossed in the Chebyshev, the bar lengths are proportioned differently and the straight line motion is taken from the center of the coupler bar instead of from an extension therefrom. In fact, I eliminated the Chebyshev linkage because the only engine configuration I could come up with resulted in more parts to be made. It would have been even more interesting in appearance, though.
Having not been trained in mechanical engineering, I didn't realize what a fascinating subject linkages could be, although I do remember being intrigued when an ME roommate of mine in school had to build cardstock models of linkages for a class he was taking.
Anyone interested in linkages, and specifically straight-line linkages, might be interested in checking out a little old book which inspired me:
How to Draw a Straight Line by A.B. Kempe (1877)
https://archive.org/details/howtodrawstraigh00kemprich
The book is based on an interesting lecture given to science teachers by the author, and covers the various mechanisms known at the time to approximate the straight line. It finally concentrates on the Peaucellier linkage which can produce a true straight line as opposed to an approximation.
Thanks for watching!
--Tim
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... I hope that if your idea works well you could perhaps publish drawings. ...
Jim
Jim, I'd be more than happy to share what I've got when the whole thing comes together. The only problem is that when I make drawings, I take shortcuts as I don't consider anyone but myself would be using them. They aren't ordinarily dimensioned, for instance (and you wouldn't want them if they were dimensioned by me :-/).
Nevertheless, when they're complete anyone here will be welcome to them such as they are. I'm not inclined to take the time to pretty them up for public consumption. Oh, by the way, they're in 2D DXF format with all parts on one big sheet. To my credit, I do tend to correct them for last minute changes I make in the shop...
--TIm
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The engine frame is fabricated. The sides from hot-rolled angle stock, cross pieces from cold-rolled steel, and bearing blocks from aluminum.
The constituent parts will be epoxied and screwed together. The screw heads will be inset and covered over with epoxy to attempt the appearance of a one-piece frame casting.
First two lengths of angle stock were placed back-to-back in the CNC mill vice, and the angle legs which will form the frame base were faced off. I used bits of sacrificial aluminum to maintain a separation between the work and the vise.
(http://www.voght.com/robby/frame/5.jpg)
The base portions of the two frame sides were profiled by CNC. Here is a preview screen shown by the LinuxCNC control software. Before setting the machine loose to do what it would, caution was in abundance, I studied the screen for a while to verify that the cut paths were what I expected.
(http://www.voght.com/robby/frame/10.jpg)
Roughing of the profile proceeded in several shallow passes, leaving stock for a full-deoth finishing pass.
(http://www.voght.com/robby/frame/15.jpg)
The roughing passes complete.
(http://www.voght.com/robby/frame/20.jpg)
A finishing pass at full depth was done with a smaller endmill.
(http://www.voght.com/robby/frame/25.jpg)
With the finishing pass complete, base mounting holes were drilled. The second photo shows the two frame halves at this point.
(http://www.voght.com/robby/frame/30.jpg)
(http://www.voght.com/robby/frame/35.jpg)
The completely profiled base legs were then clamped back-to-back in the vise, and profiling of the frame sides was commenced.
Roughing first:
(http://www.voght.com/robby/frame/40.jpg)
After a finishing pass, both sides are shown profiled. Note also that holes have been drilled for cross-pieces to join the sides, The photo does not show well that the holes are counter-bored so that the joining cap screw heads can be hidden.
(http://www.voght.com/robby/frame/45.jpg)
Thanks for watching.
--Tim
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Tim, I'm in for the ride. Another beautiful frame made from angle iron. You and Chuck Fellows make them look so nice. This CNC stuff is really starting to stir my old gray matter :thinking:.
Cletus
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Glad to have you Cletus, have a seat on the porch right there next to the washing machine.
It's funny, I didn't realize that Chuck Fellows had been the inspiration for this frame until a couple of days ago when I saw him doing it on his new 2 cylinder. Then I remembered the frame of his Bessemer oil field engine, and that was where he had planted the seed... Thanks Chuck!
--Tim
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Hi Tim
I have pulled up a chair too and will be enjoying your new project. I like the idea of doing the mirror image parts with one tool path.
Dave
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Thanks for the warm invite Tim, don't mind if I do. I bet there is even a matching refrigerator on the other end of the couch 8). Don't worry, I'm well behaved, if my shoes are muddy I'll leave on the back porch by the deep freezer ;). I'm with Dave, the mirroring is sweet.
Cletus
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Hi Tim, no couch and no fridge close by at the moment, but I will following along too.
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Tim I am pulling up a chair so bring it on.
:drinking-41: :popcornsmall:
Don
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Dave, Achim, and Don, thanks for checking in!
Frame fabrication continues.
Three frame cross-pieces were sawn from a chunk of cold-rolled steel and milled to 1/4" thickness. All work to this point was done manually with the Bridgeport. The next shot shows the raw cross pieces roughly in position in relation to the side pieces.
(http://www.voght.com/robby/frame/50.jpg)
(http://www.voght.com/robby/frame/55.jpg)
It often happens that I get "into the zone" and forget completely about the camera. Such was the case when I shaped the front and mid cross pieces with a series of CNC operations. The large hole and the four cylinder mounting holes in the front piece were drilled and bored at the Bridgeport before the outside profile was done by CNC. The inside of the middle cross piece was CNC'd out.
The cross pieces were drilled and tapped for the 0-80 cap screws that will hold the frame together. The rear cross-piece still needs some sawing and shaping.
(http://www.voght.com/robby/frame/60.jpg)
The pivots where the Robert's mechanism mounts to the front and mid cross pieces need to be accurately aligned with respect to each other. To maintain alignment while the frame is assembled, I connected the cross pieces with one long bar. Later, after the frame has been finally glued and screwed together, the pivot holes will drilled, and the middle of the bar will be sawn away.
(http://www.voght.com/robby/frame/65.jpg)
Here's the frame fabrication after epoxy was applied and the screws tightened up. I'm sure JB Weld would have worked fine in this application, but I wanted to try a Loctite product "Epoxy Weld", which seems to work fine.
(http://www.voght.com/robby/frame/70.jpg)
Thanks,
--Tim
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Looks great Tim. Those 0-80's raise my pucker factor when tapping in steel. :popcorn: :DrinkPint: and following along.
Cletus
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Hi Tim,
It looks like it's going to be a very unique engine. I'll definitely be following the progress.
gbritnell
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It's good to have you look in, George!
Cletus, affirmative on the pucker factor of the 0-80 steel tapping.
I need to mention that I have recently been trying out thread-forming taps. I bought #0, #2, and #4 for starters, and I did the tapping here with the the #0 thread-forming tap. Don't get me wrong, the experience in 1018 steel was still hair-raising, but it was done without any mishap. I don't think it would have gone as well or as quickly with the HSS thread-cutting taps I have been using.
I've also used the new taps in aluminum and brass with great results. I'm sold. You just have to be aware that the drill sizes are different (larger) for this type of tap.
--Tim
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Tim, I have been using small form taps for a while now and I use a free smart phone app for my tap chart because the one on the wall has only cutting taps. I use a small tap stand and for tapping and I do not find myself holding my breath waiting for a tiny snapping sound.
I used a 0-80 form tap to thread a stainless steel part from Shapeways, which is something I would not have tried with a cutting tap.
Dan
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Just been looking at my thread flow tap info, they suggest brass, aluminium, stainless steel, and LEADED steel, cast iron does not deform like other metals, and non leaded steel has too much friction.
Used in the right place they are great, and I feel I can tap with more confidence.
Ian S C
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Glad others have found success with these taps. I'm pretty sure Stan S. uses them too.
Yeah Dan, I found the drill sizes somewhere on the web, and penciled in an extra column on my wall chart.
I almost always tap now using a guided tap wrench with the guide either in the mill spindle or the lathe tailstock.
A wrench like this:
http://www.mcmaster.com/#tap-wrenches/=yv3ory
--Tim
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In my DRILL program, I use the following equation to find the tap drill for thread forming taps...
TD = MD - 0.0068*DOT/P
where:
TD = tap drill size
MD = major diameter of thread
DOT = desired depth of thread expressed as percentage
P = pitch of thread expressed as tpi
For example, a 1/4-20 thread with 75% DOT yields:
TD = 0.25 - 0.0068*75/20 = 0.2245"
Closest conventional drill is 5.7 mm but a #2 is close enough.
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For those who always are searching for the calculator in the shop here is a printable tap chart for roll form taps:
http://balax.com/catalog/thredfloer-taps/ansi-thredfloer-hole-size-chart
And the metric version:
http://balax.com/catalog/thredfloer-taps/metric-thredfloer-hole-size-chart
Cheers Dan
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For those who always are searching for the calculator in the shop here is a printable tap chart for roll form taps:...
Who needs a calculator? Do it in your head. :)
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Marv,
If I can not find my phone/calculator I use the simpler rule of thumb found in the MSC catalog, Tap Drill Size = Major Diameter - (Pitch / 2).
The formula you gave is listed just below the one I just wrote.
I have been using the cutting version of the simple fromula for years because it was too far to walk to find a tap chart on most ships.
For cutting taps Tap Drill = Major Diameter - Pitch
Cheers Dan
Edit: I should point out that the formulas I stated use the pitch exprssed as the distance form one part of the thread to the next identical part or for imperial the pitch is 1/TPi. Metric is simple just use the numbers on the tap.
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I'm pulling up another chair for this show.
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Thought I should put up the BA Threadflow chart.
Ian S C
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Dan, Ian, and nevadablue, it's great to see you watching. Also Cletus and Marv, I appreciate your further comments. With so many fine modelers watching, the pressure is on. I trust no one will hesitate to make suggestions or point up any blatantly stupid moves on my part.
The crankshaft will ride in plain aluminum bearings which are part of the fabricated frame. At the Bridgeport, a chunk of aluminum stock was drilled with countersunk holes for mounting to the frame, and also undersized holes for the crankshaft.
(http://www.voght.com/robby/frame/75.jpg)
At the CNC mill, the first bearing block was screwed to a sacrificial plate which had been drilled and tapped to match the frame mount holes. A series of roughing outline passes proceeded, followed by a finishing pass at full depth.
(http://www.voght.com/robby/frame/80.jpg)
(http://www.voght.com/robby/frame/85.jpg)
The second bearing block blank (which was separated from the first by the roughing passes above) was attached to the same tapped tooling plate holes and the identical programs run again.
(http://www.voght.com/robby/frame/90.jpg)
Here are the bearing block pieces ready for mounting, and then glued and screwed to the frame sides.
(http://www.voght.com/robby/frame/95.jpg)
(http://www.voght.com/robby/frame/100.jpg)
Now the bearing caps could be sawed off at the Bridgeport. Here I realized that pre-drilling the crankshaft bores was unnecessary and silly, but not a show stopper. Life goes on.
(http://www.voght.com/robby/frame/105.jpg)
With the bearing caps now screwed on tightly, and the frame mounted on an angle plate, I drilled and reamed the crankshaft bearings.
(http://www.voght.com/robby/frame/110.jpg)
In the same angle plate setup, I drilled the pivot holes for the Roberts linkage and also side-milled the front plate where the cylinder will mount. These crucial elements will now hopefully be square to each other.
The linkage pivots were supposed to be centered on the bar, but you can see they ended up low. The holes are located properly relative to the crankshaft though, so somehow the bar ended up a little high. Not perfect, but again not enough to stop the show.
(http://www.voght.com/robby/frame/115.jpg)
Thanks again for watching,
--Tim
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Tim, just a quick question. After splitting the bearing caps it looks as if the hole is now larger. Are you planning to use a brass or bronze type bushing there for a bearing surface or just the aluminum?
You are making great progress btw and its looking good!!
Bill
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Hi Bill, I reamed the holes to shaft size after splitting the bearings. And yes, the plan is steel shaft in aluminum plain bearings.
--TIm
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The Roberts mechanism has two identical arms which I'll be calling the "radial arms". I decided to make them of aluminum.
After sawing some stock a little oversize, I drilled and reamed 1/8" pivot holes in the stock. This was done on the Bridgeport.
I made three blanks as there was little to lose by making an extra.
I drilled and tapped two holes in a tooling plate on the CNC mill, the holes being spaced to match the holes in the arm blanks. The blanks will be clamped to the plate with shoulder screws which are a slip fit in the reamed holes of the blank.
Here's one of the blanks next to the tapped holes in the sacrificial plate. You'll notice I use the sacrificial plates over and over until there just isn't a good surface left to clamp to. I just make sure to de-burr the edges of any previous cuts so that the parts will clamp down square.
(http://www.voght.com/robby/arm/5.jpg)
A roughing pass was taken at small depth steps to get within 20 thousandths of the final outline.
(http://www.voght.com/robby/arm/10.jpg)
Then a finishing pass at full depth, followed by a pass on the top of the clamped part to provide clearance for the coupler link. The part was then flipped and re-clamped to run the same relief program for a matching clearance cut on the other side.
(http://www.voght.com/robby/arm/15.jpg)
Since I had 3 blanks, I used the same tapped fixture holes and the same CNC programs to produce two more.
Here are the 3 radial arms, two of which have been cleaned up a little. The extra, if it escapes the clutches of the shop gremlin, can be placed on my desk at work.
(http://www.voght.com/robby/arm/20.jpg)
Thanks for watching.
--Tim
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The triangular "coupler link" is perhaps the most visually distinguishing part of the engine. The link consists of two identical parts, one on either side of the radial arms. The two link halves also bracket the joint at the connecting rod and piston rod.
The twin coupler link halves are made of 1/16" thick cold-rolled steel. I sawed two triangular pieces oversize and clamped them stacked on the Bridgeport, where I drilled and reamed three pivot holes through both parts for a perfectly matching pattern.
In a manner similar to that used on the aluminum radial arms, I drilled and tapped holes in a sacrificial tooling plate and screwed down the two stacked pieces with shoulder screws through the reamed holes. All machining could now be done with reference to the large hole.
A CNC profiling operation was run
(http://www.voght.com/robby/coupler/5.jpg)
And then a finishing operation. Here are the stacked parts just after outside and inside profiles had been finish milled.
(http://www.voght.com/robby/coupler/10.jpg)
The parts after quick cleanup.
(http://www.voght.com/robby/coupler/15.jpg)
Thanks again for watching!
--Tim
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Tim,
This is a fascinating idea for an engine. I have to admit to going to Wikipedia to find the difference between Watts and Roberts linkage. Watts was straight forward, Roberts was very formulaic. If I hadn't seen your diagrams of the linkage they would have been speaking Greek. I will continue to follow along.
Art
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Coming along nicely Tim!
Dave
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Hi Tim, I am also watching. An Interesting concept.
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Thank Dave and Achim. Art, it's good to see you watching.
To pin the revolute joints of the Roberts linkage, I made brass pins from 1/8" brass rod.
I have no process photos, but each pin was finished to length in a lathe collet and drilled and internally threaded on each end.
I made the lengths to be very close to the width of the link joint, this required removal from the collet to measure, then replacement and facing. A little error to the short side was acceptable for my purposes.
Here you see 4 pins with example screws and washers that will be used to hold things together. All joints consist of two outside flanges bracketing an inner. The washers effectively fix the pin to the outer flanges, so the inner rotates on the pin.
(http://www.voght.com/robby/joint_pins/5.jpg)
The following photos should give more of the general idea.
(http://www.voght.com/robby/joint_pins/10.jpg)
(http://www.voght.com/robby/joint_pins/15.jpg)
(http://www.voght.com/robby/joint_pins/20.jpg)
(http://www.voght.com/robby/joint_pins/25.jpg)
Thanks!
--Tim
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This looks fascinating, Tim! Following along with interest!
Simon
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Nice progress Tim. If you can, in the next batch of pictures please put something in the picture for size reference. I am trying to figure out what size this little jewel is going to be.
Bill
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Simon, thanks for following!
Bill, this may help a little. I'll remember to throw in some references when I get back to the frame. That'll be more descriptive.
(http://www.voght.com/robby/joint_pins/30.jpg)
--Tim
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Tim
This is getting really fascinating.
Yes, I love form taps, especially for the smaller sizes. The people at Balax were very helpful, even though I'm quite sure my impact on their bottom line is microscopic.
Great work. Looking forward to seeing it at NAMES,
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Thanks Tim....yes that helps a lot.
Bill
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Nice start Tim and thanks for showing the size reference I would of thought it to be bigger looking at it without it. Still following along.
Don
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Stan, Bill, and Don, thanks for your comments.
I made the connecting rod from a piece of 5/16" thick brass, 3/4" wide.
In the vise of the CNC, a quick program was used to profile the big end of the rod, which will have a removable cap.
(http://www.voght.com/robby/rod/5.jpg)
Mounted vertically in the Bridgeport vise, I spot-faced the locations for the cap screws and center drilled.
(http://www.voght.com/robby/rod/10.jpg)
I drilled the depth of the cap plus .040" or so to clear a 4-40 screw, then drilled to a bit more than screw length depth, and tapped with a 4-40 thread-forming tap.
(http://www.voght.com/robby/rod/15.jpg)
(http://www.voght.com/robby/rod/20.jpg)
I'm trying this photo to see if anyone can make sense of it. To align my slitting saw vertically, I laid a steel rule on top of the saw blade and bridged it over to the top of the work. Lit from behind, I could see when there was no light leaking under the rule to determine when the top of the blade was flush with the top of the work. I zeroed my DRO Z axis there.
(http://www.voght.com/robby/rod/25.jpg)
The spindle was lowered and the cap sawn off.
(http://www.voght.com/robby/rod/30.jpg)
Horizontal in the Bridgeport vise, I first found the edge with the cap removed, and then screwed the cap tightly on. I Drilled and reamed. The closed hole on the other end was drilled and reamed as well.
(http://www.voght.com/robby/rod/35.jpg)
This is familiar if you've watched my previous operations. Ready to be clamped to the tooling plate with snug-fitting shoulder screws.
(http://www.voght.com/robby/rod/40.jpg)
(http://www.voght.com/robby/rod/45.jpg)
Roughing passes commenced.
(http://www.voght.com/robby/rod/50.jpg)
Roughing passes done.
(http://www.voght.com/robby/rod/55.jpg)
And after a finishing pass. A side profile (not shown here) is yet to be cut using the same program on both sides.
(http://www.voght.com/robby/rod/60.jpg)
After cutting the side profiles, the small end was notched out for joint with the Roberts mechanism and piston rod.
(http://www.voght.com/robby/rod/65.jpg)
Thanks for watching,
--Tim
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Nice job Tim. I couldn't really tell by the photo, but, the narrative was enough to make me go; "I could have just used that " Great slitting saw tip :ThumbsUp:.
Cletus
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Hi Tim, I am still following along. Nice job with the con-rod.
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Thanks Whiskey and Achim for checking in.
I made a piston rod end of brass. I have no process pictures, but I can tell you that it was made from a length of 3/8" brass rod in a collet (in the lathe, and in a collet block at the Bridgeport).
It's shown here with the connecting rod and the joint pin. It's not clearly visible in the photos, but the piston rod end is threaded for the piston rod.
(http://www.voght.com/robby/mech/5.jpg)
(http://www.voght.com/robby/mech/10.jpg)
Here is the mechanism coming further together.
(http://www.voght.com/robby/mech/15.jpg)
Thanks for looking,
--Tim
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Its really starting to come together Tim. Nice job all around!!
Bill
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Love the connecting rods Tim , they look great. ........... :ThumbsUp:
:popcorn:
Don
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Looking great! Love the design. This should be fun to watch run!!!
:popcorn:
Dave
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Thanks to Bill, Don, and Dave for checking in!
Next on the build list is a built-up crank, starting with two crank disks.
When it comes to my CNC modus operandi, you'll see a lot of similarity here with some of the previous parts. I'm beginning to discover what works for me,
Here two pieces of 1/4" thick steel are stacked and clamped on the Bridgeport for drilling and reaming of the crankpin and crankshaft holes. I glued a paper pattern on the top piece to help me eyeball the position of the center hole with confidence that the outline would lie within the extent of the material.
By placing both holes over the slot, I can clamp directly to the table.
(http://www.voght.com/robby/crank/5.jpg)
Both the shaft and the crankpin holes were drilled. Note that the paper pattern only helped me to eyeball the position of the larger hole and the orientation of the stock. The DRO was used to determine the actual hole spacing.
(http://www.voght.com/robby/crank/10.jpg)
The holes were then reamed.
(http://www.voght.com/robby/crank/15.jpg)
You can see how shoulder screws were again used for clamping to the CNC tooling plate.
(http://www.voght.com/robby/crank/20.jpg)
(http://www.voght.com/robby/crank/25.jpg)
Roughing passes were taken, leaving around .010 inches of meat for the finishing pass.
(http://www.voght.com/robby/crank/30.jpg)
Here are the stacked crank disks after the finishing pass at full depth with a smaller diameter endmill.
(http://www.voght.com/robby/crank/35.jpg)
Thanks for watching!
--Tim
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The main shafts were made from 12L14 leaded steel rod. I cut two lengths and finished the ends in the lathe, then cut keyways in each at the Bridgeport.
(http://www.voght.com/robby/crank/40.jpg)
303 stainless ground rod was used for the crankpin. I used Loctite 609 to bond the crankpin in place while using one of the main shafts for temporary alignment during cure. Spacing in this setup was established by the connecting rod itself.
(http://www.voght.com/robby/crank/45.jpg)
Loctite was applied to the main shafts and the assembly was set up to cure in-situ. I made one regrettable mistake. I didn't pay attention to the orientation of the keyways when I assembled, So the keyways are not oriented in any particular way with regard to the crank or to each other. This is of course only a cosmetic problem. I'm not sure it will be obvious or troublesome to any but the most critical observers.
(http://www.voght.com/robby/crank/50.jpg)
Thanks for watching!
--Tim
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Hi Tim, it seems to be an interesting construction. Waiting for seeing it in motion.
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Really looking nice Tim. You are making some rapid progress too.
Bill
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Coming along nicely Tim!
I'm enjoying seeing all your setups and great progress!
Dave
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Tim...what a great looking design...and a cool little mechanism! I'm going to share this build with my Kinematics students...and I'll be following along until the end!
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Tim,
The whole setup looks good. I like your use of shoulder screws, I wouldn't have thought of that, and I don't have them lying about.
Art
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Tim
This is getting more fascinating with each step.
The work is first rate and I'd love to see it in Rhode Island ( finished or not.)
As for the unaligned key slots; totally unacceptable. I'd toss it and start over. :lolb:
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Achim, BIll, Dave, Chris, Art, and Stan: Thanks for commenting.
I have no recent activity to report, and vacation planning and vacationing may delay things for a while.
Chris, if any of your kinematics students have come to this point, here's a big shout out to them.
Stan, I hadn't really been considering exhibiting any work in Rhode Island, but I can throw this engine in the trunk. I'd like for you to see it.
--Tim
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Tim
If it's not a problem, I'd love to see it
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Tim, I'm really enjoying the build. If anyone should have the governor flyweight balls :lolb: to say anything about the keyways, tell them it was for balancing purposes 8).
Cletus
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Tim, I'm really enjoying the build. If anyone should have the governor flyweight balls :lolb: to say anything about the keyways, tell them it was for balancing purposes 8) .
Cletus
Ahem.. "The unusual placement of the keyways is due to a balancing procedure involving a stochastic algorithm using third-order...bla bla bla..."
Yes, I think I can work that angle if I'm backed into a corner.
--Tim
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Nice work Tim and I wouldn't worry to much about the keyway as it's only for the flywheel anyway. The only reason I would remake is if it bothered me enough.
Don
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It's been awhile since I've reported on this project. Vacationing, working, and various other distractions have
gotten in the way. I'm still not fully engaged, but I have some things to report.
I was showing the engine to my dad, and he thought the engine should have a reverse gear (something
that I had already decided not to bother with). He suggested a slip eccentric, and that started a thought
process.
I found a nice writeup here that arnoldb had done on slip eccentrics, and after reading it over, I got an idea
for an easy build. Here goes.
The eccentric itself is made of 416 stainless. It has an integral flange on one side, and a "driving" flange
on the other. The next photo shows the stock in the lathe with the eccentric diameter and the integral flange
diameter turned to size. The face on the end is quite poor. At this point, I can't explain how it got that way,
but it cleaned up in the end.
(http://www.voght.com/robby/eccentric/5.jpg)
At the mill, the center was carefully found, then two holes located and drilled. In this photo, the
hole to the right is center-drilled for the crankshaft, and the hole to the left will hold the pin by which
the eccentric will be driven by the driving flange.
(http://www.voght.com/robby/eccentric/10.jpg)
The shaft hole was then drilled and reamed for a slip fit on the crankshaft.
(http://www.voght.com/robby/eccentric/15.jpg)
I sawed off the part leaving a nasty looking edge that would be machined away. The part was mounted on
a mandrel and placed back in the lathe.
(http://www.voght.com/robby/eccentric/20.jpg)
I then machined the flange down to thickness, and left a hub.
(http://www.voght.com/robby/eccentric/25.jpg)
Here's the eccentric cleaned up somewhat.
(http://www.voght.com/robby/eccentric/30.jpg)
The washer-like driving flange was then turned up. A hole was drilled and tapped through to the bore. This will
provide for a set screw to adjustably fix the flange to the drive shaft.
(http://www.voght.com/robby/eccentric/35.jpg)
I used the CNC mill to cut the slot where the driving pin will operate. Clamping here was awkward, but I got
the job done.
(http://www.voght.com/robby/eccentric/40.jpg)
(http://www.voght.com/robby/eccentric/45.jpg)
Thanks for watching.
--Tim
-
Hey Tim!
Good to see some progress on your engine; I completely understand about the lack of time and other commitments taking up shop time.
Dave
-
Progress is still progress Tim. I can sure relate to the lack of time lately too. Hopefully that will ease off some soon!
Bill
-
Good to see you moving forward with this engine Tim and we all know how time can be limited.
:popcorn:
Don
-
Hi Tim, good to see you back in business.
-
Thanks Dave, Don, Bill, and Achim for your comments.
Next up is the eccentric strap. Because the driving flange is a separate part, the strap can be made in one
piece, without the necessity of splitting it for a removable cap. Of course this is not very scale-like, but since this
engine is just a stylized version of something that never existed, I can invent any kind of justification for the shortcut.
First, I sided-milled the end of a brass bar, and then bored for a slip fit on the eccentric.
(http://www.voght.com/robby/eccentric/50.jpg)
I sawed off the piece and drilled and tapped the faced end for the rod.
(http://www.voght.com/robby/eccentric/55.jpg)
A flanged bushing was turned to fit the bore for clamping to a tooling plate on the CNC mill.
(http://www.voght.com/robby/eccentric/60.jpg)
I milled a cavity in the tooling plate for the part, leaving an extended portion in the cavity to prevent
rotation around the bushing. You may be able to see a small slip of paper between the aluminum extension
and the brass part. That provides a tight fit. I hope the photo makes this somewhat clear.
(http://www.voght.com/robby/eccentric/65.jpg)
Here's the profiled strap. There is a step in the bore to accommodate a small fillet left where the eccentric
meets the fixed flange. The next shot shows the strap fit to the eccentric.
(http://www.voght.com/robby/eccentric/70.jpg)
(http://www.voght.com/robby/eccentric/75.jpg)
Here's the driving flange added, along with the driving pin in the eccentric.
(http://www.voght.com/robby/eccentric/80.jpg)
And all in place on the drive shaft.
(http://www.voght.com/robby/eccentric/85.jpg)
Finally, a shot showing how I intend to make the flange adjustable on the drive shaft without scarring.
The set screw forces a small brass slug against the shaft.
(http://www.voght.com/robby/eccentric/90.jpg)
Thanks for watching!
--Tim
-
Another interesting thread I've finally caught up to. Cool.
I look forward to seeing more here.
-
Glad you're watching, Zee.
The engine will have a D valve, and the valve stem will be guided in a slide bearing.
All of my attempts at CNC work so far have been of the 2.5D type, tracing outlines at a few specific depths.
This will be my first foray into true 3D work. I designed a valve guide using an open source modeling program called
Wings 3D. While not really intended for mechanical design work, I found it fun and interesting to sculpt the part using
this tool. Here's a rendering of the part. The rendering doesn't show the guide bores or the screw holes for mounting.
These features will be added manually.
(http://www.voght.com/robby/valve_guide/render.png)
My 2.5D CNC efforts have been accomplished without any CAM software except what I create in-house for my own purposes.
3D requires software which I'm unwilling to write myself (lacking the time for a multi-year software development effort).
I settled on MeshCam which is working quite well so far. You can see from the rendering that this part cannot be made
in a single setup. No matter what the orientation, there will be undercuts. The procedure will involve two different
setups and two CNC programs.
I had intended to make the part from 1" square brass, but then I realized that I had 1" square aluminum stock on hand.
I decided to debug the process in cheaper aluminum first before sacrificing any brass. Here's a piece of inch square
aluminum bar. I started by manually drilling the valve stem guide bore clear through the stock.
(http://www.voght.com/robby/valve_guide/5.jpg)
With the stock setup vertically in the CNC vise, the first program was run, consisting of a roughing pass with a .25"
square-end mill...
(http://www.voght.com/robby/valve_guide/10.jpg)
(http://www.voght.com/robby/valve_guide/15.jpg)
Followed by a waterline finishing pass with a .125" ball-end...
(http://www.voght.com/robby/valve_guide/20.jpg)
And then a pencil finishing pass with a .125" square end mill. This cleans out the fillets left by the ball-end mill.
Steps are clearly visible in the finishing pass. I might have chosen a smaller step size at the expense of longer
machining time, but I'm going on a hunch that these will cleanup nicely with a file.
(http://www.voght.com/robby/valve_guide/25.jpg)
(http://www.voght.com/robby/valve_guide/30.jpg)
The workpiece was turned 90 degrees in the vice for the second setup, and roughing and waterline finishing passes made
in that orientation to make undercuts missed in the first setup.
(http://www.voght.com/robby/valve_guide/35.jpg)
(http://www.voght.com/robby/valve_guide/40.jpg)
(http://www.voght.com/robby/valve_guide/45.jpg)
Back in the Bridgeport vise, I touched off on a rod inserted in the guide bore. This way I can drill mounting holes with
respect to the actual location of the rod.
(http://www.voght.com/robby/valve_guide/50.jpg)
I milled counterbores and drilled for frame mounting holes. The plan is to mount it to the frame and putty in over the
screw heads after it has been finally adjusted.
(http://www.voght.com/robby/valve_guide/55.jpg)
(http://www.voght.com/robby/valve_guide/60.jpg)
Initial cleanup with a file went pretty much as expected. The stepped approximation tends to guide the filing.
(http://www.voght.com/robby/valve_guide/65.jpg)
A trial fit up to the frame. I now see no point in making a second part from brass. I think I'm going with this one.
(http://www.voght.com/robby/valve_guide/70.jpg)
Thanks to all watching.
--Tim
-
Quietly following along Tim. :ThumbsUp: :ThumbsUp:
Vince
-
That turned out very well Tim. How did you part it off from the parent stock once all the machining was done?
Bill
-
Just catching up here, and I like your occasional use of CNC!
One comment about that final part; I wonder if it would look better if the bolt holes were in the flat bit, rather than cutting out of the ribs? That way you'd have those nice curves be continuous.
Simon
-
Hey Tim
Looks like you are staring to get the hang of 3d surfacing; isn't is fun watching parts emerge from a solid block of stock?
I'm kind of wondering the same thing as Simon; why not put the mounting holes on the flat? On a full sized engine the bracket would most likely be bolted on and not part of the main casting any way.
Great progress!
Dave
-
Vince, it's good to have you following, quietly or otherwise.
Bill, I won't say the results are good, but approaching good enough. Still lots to learn about 3D machining. Parting was done with a slitting saw after the mounting holes were drilled.
Simon and Dave. Of course you are right. I got caught up in the idea that all the screws holding the frame together were going to be hidden with putty, and I extended that concept to the guide mounting. Dave's comment that in reality the guide would have been a separate casting part turned me around. A slight redesign is in the works.
--Tim
-
I have some progress to report. In the last installment, I had intended to make the valve guide from brass, but then decided to
make a trial one first in aluminum. I had decided to just use the aluminum one on the model, but Dave and Simon suggested I reconsider.
I reconsidered, and then realized I had a chunk of durabar cast iron in about the right size. That seemed like a good material choice.
A few shots will show the results. Here is the part after the first setup and program.
(http://www.voght.com/robby/valve_guide/75.jpg)
And here after the second setup.
(http://www.voght.com/robby/valve_guide/80.jpg)
In the above shot, you see the the arms are squared off at the top. That is from a mistaken setup where I touched off the work incorrectly, and removed a bit too much material at the top. It's going to be alright, and I may still drill small holes in each flat for oiling.
Here's the part after separation from the block with a slitting saw.
(http://www.voght.com/robby/valve_guide/85.jpg)
And here after some cleanup with files and sandpaper.
(http://www.voght.com/robby/valve_guide/90.jpg)
Here's the new guide trial mounted to the frame. Note that all socket head screws currently showing on the engine will eventually
be either covered over or replaced with hex head screws when I'm nearer to completion (studs and nuts are beyond the current scope
of abstraction).
(http://www.voght.com/robby/valve_guide/95.jpg)
Thanks to all watching.
--Tim
-
Tim, as nice as the first part looked, the remake does look better. I like the mounting holes on the flat area too. I am sure the remake was made far easier with the CNC...not a part I would look forward to remaking without it.
Bill
-
Hi Tim, well done. That should push me to do more jobs with my little CNC mill.
-
Bill, I agree this second attempt looks better. And yes, a remake in CNC is not so daunting. It still takes time though, and I seem a bit short on that lately.
Achim, for a model engineer, I think CNC is a valuable addition to the overall toolbox. Like most tools, it's excellent for some tasks and no good at all for others.
Work on the valve gear continues. An end joint for the eccentric rod is needed. A short photo essay follows with minimal words.
A favorite technique is to make small parts from round stock in a 5C collet, switching back and forth from the lathe to a collet block in the mill vise.
360 Brass rod.
(http://www.voght.com/robby/valve_guide/100.jpg)
(http://www.voght.com/robby/valve_guide/105.jpg)
(http://www.voght.com/robby/valve_guide/110.jpg)
(http://www.voght.com/robby/valve_guide/115.jpg)
(http://www.voght.com/robby/valve_guide/120.jpg)
The "arc contour" function of the DRO was used with a ball-end mill in the XZ plane.
(http://www.voght.com/robby/valve_guide/125.jpg)
(http://www.voght.com/robby/valve_guide/130.jpg)
A 303 stainless rod was threaded on each end to finish the eccentric rod assembly.
(http://www.voght.com/robby/valve_guide/135.jpg)
Glad you're watching,
--Tim
-
Happy to be watching. :popcorn:
Came out swell.
-
Hey Tim
The new bracket turned out great; good to see you are continuing to make progress on your engine.
Dave
-
Still watching.
Vince
-
Tim, I've just gone back and re-read this from the start, and have finally
remembered to pop in and say how much I've been enjoying following along.
Looking forward to more...
Cheers, Joe
-
Thanks Zee, Dave, and Vince for your comments. And thanks for checking in, Joe.
The valve linkage work continues. The first shot shows a pivot joint that clamps to the valve rod. I have no build photos for the part, but it's made from 303 stainless rod held in a collet for both lathe and mill operations.
(http://www.voght.com/robby/valve_guide/140.jpg)
Here's the bottom of the pivot joint, showing how it's slit for clamping. No casual observer will ever see the SHCS clamping screw.
(http://www.voght.com/robby/valve_guide/145.jpg)
And here's the eccentric rod connected to the pivot.
(http://www.voght.com/robby/valve_guide/150.jpg)
That's probably it until the weekend. Thanks for watching.
--Tim
-
Progress proceeds at a glacial pace. But progress is progress, right?
I made the D valve. The first photo shows a chunk of 5/8" brass rod in a collet/block. I squared the sides. The dimensions of the valve leave some of the radius of the rod on the corners. This is unplanned, and only a product of my choice of available stock.
(http://www.voght.com/robby/valve/5.jpg)
Crossed slots were milled. The slots are 1/8" wide, and were milled with a 1/16" center-cutting endmill. I cut first through the center in 25 thousandths depth steps, and then side milled each side at full depth.
(http://www.voght.com/robby/valve/10.jpg)
I sloped the sides. Here I'm using my little electronic level for setup. I inked the part up and scribed a target line for the cuts.
(http://www.voght.com/robby/valve/15.jpg)
(http://www.voght.com/robby/valve/20.jpg)
I separated the part from the stock using the bandsaw. The versatile collet block's job is finally done.
(http://www.voght.com/robby/valve/25.jpg)
Back at the mill, the valve bottom is faced, and the cavity pocketed out. I put a 1/8" lathe tool in the previously milled slot to keep the vise from crushing the part. I learned the necessity of this while making the first of three prior failed parts (insert heavy sigh emoticon here).
(http://www.voght.com/robby/valve/30.jpg)
There it is. The "G" written inside the pocket signifies "Good".
(http://www.voght.com/robby/valve/35.jpg)
Sorry I have no meaningful process photos of the 416 stainless steel part shown here. It was made from rod stock in a collet block. Big surprise, no?
(http://www.voght.com/robby/valve/40.jpg)
(http://www.voght.com/robby/valve/45.jpg)
Next, a cast iron cylinder.
Thanks for watching.
--Tim
-
Progress proceeds at a glacial pace. But progress is progress, right?
RIGHT!
I often have to remind people of this on my thread.
(And other people should really slow down. ;D )
Looks good Tim.
Nice fit too.
-
Its still coming along well Tim. That D valve and nut turned out well. Just curious as to why the taper on the edges?
Bill
-
Its still coming along well Tim. That D valve and nut turned out well. Just curious as to why the taper on the edges?
Bill
I've seen the tapers on the d valve top before, was it done to reduce casting volume on full size engines, maybe?
-
Glad you agree Carl.
BIll and Chris: I patterned the valve after one in the book of Ray Hasbrouck's steam engine plans. Ray's was shaped that way, so mine is too! I imagine any reduction of mass in a reciprocating part is desirable, especially in full scale.
--Tim
-
Looking good Tim and just caught up on your thread........ :ThumbsUp:
Don
-
Hi Tim, great progress.
-
Thanks Don and Achim for watching and commenting.
The cylinder was the next item on my list. I started with a 2 inch square chunk of what the supplier calls Class 40 cast iron. I sawed slabs off the sides to get closer to dimension.
(http://www.voght.com/robby/cylinder/5.jpg)
The saw not only saved some endmill life, but I got some quite credible thin cast stock for the pile. You can see how I pasted a drawing on the stock to keep the sawing within boundaries.
(http://www.voght.com/robby/cylinder/10.jpg)
I squared up the sides a bit in the mill and then center drilled the bore location, followed by drilling and reaming for a reference rod.
(http://www.voght.com/robby/cylinder/15.jpg)
It was a toss-up whether I would make the part on the CNC mill or manually on the Bridgeport. The Bridgeport won out. Here I'm centering up the part on the rotary table using the reference rod.
(http://www.voght.com/robby/cylinder/20.jpg)
I used a tailstock for support since I only have the shallow first step of the reversed vise jaws to hold the part at the index end.
(http://www.voght.com/robby/cylinder/25.jpg)
Milling commences.
(http://www.voght.com/robby/cylinder/30.jpg)
(http://www.voght.com/robby/cylinder/35.jpg)
(http://www.voght.com/robby/cylinder/40.jpg)
This is not bad:
(http://www.voght.com/robby/cylinder/45.jpg)
And this is not so good. See the extra divots taken out where the round flange meets the flat. Just a missed step in a long list of operations. I'll have to find some way to cover up the mistake.
(http://www.voght.com/robby/cylinder/50.jpg)
The ends were cleaned up and the mill was centered at the tailstock support center. I drilled 7/8" in one go.
(http://www.voght.com/robby/cylinder/55.jpg)
(http://www.voght.com/robby/cylinder/60.jpg)
It was kind of dicey getting the part both centered and straight in the 4-jaw, but I did my best. I bored to 1 inch in the lathe.
(http://www.voght.com/robby/cylinder/65.jpg)
Then faced off the end in the same setup so that the inboard cylinder end would be normal to the bore.
(http://www.voght.com/robby/cylinder/70.jpg)
Back at the mill, the cylinder was clamped at the correct angle to drill an inlet passage. I spot-faced and center drilled:
(http://www.voght.com/robby/cylinder/75.jpg)
Then peck drilled until I broke out at the valve face. This was repeated for the other end. Not shown is the drilling of the exhaust passage.
(http://www.voght.com/robby/cylinder/80.jpg)
The holey cylinder. The actual valve ports will be machined in a separate plate that will be screwed to the flat face with along with the steam chest. Extra gasketing will be required to seal the port plate, but I wanted to be able to re-cut the ports if necessary without re-making the cylinder. There is still drilling and tapping to do for the heads. Those will be matched drilled from the those parts when they are finished.
(http://www.voght.com/robby/cylinder/85.jpg)
Another shot shows the exhaust pipe nipple trial fitted. You can see clear through the inlet passage to the blue towel behind.
(http://www.voght.com/robby/cylinder/90.jpg)
Thanks for watching.
--Tim
-
looking good there
-
That is some very nice carving there on the cast iron Tim. Bummer about the little divot, but you should be able to recover from that I think. The cast iron is kind of nice to work with isn't it :)
Bill
-
Thanks Bertie! Glad you're watching.
Thanks Bill. The cast iron does machine nicely. A bit dusty, though. I should mention that I will later clean up the faceted edges with a file to make the flanges nicely round.
I won't think twice about using putty to finish up the fabricated frame -that has been the plan all along- but it pains me to think of using putty for this booboo. If I had a surplus of time, I would make another cylinder, but I don't get enough shop time as it is. N.A.M.E.S. is coming up, and I really want to have this engine running by then. Looking at a list of tasks remaining, I see I have to redouble by efforts.
--Tim
-
you could always leave it as a reminder? although that may spoil the look.
-
Looks good to me.
Wow. 7/8" in one go.
Nicely done.
-
Thanks Bertie and Carl. We were last discussing the issue with the nasty endmill gouge on one cylinder flange. I have determined this will be fully hidden by the outboard cylinder cover and the cylinder lagging.
There has actually been a good bit of progress on the engine (I've been spending more discretionary time in the shop, rather than reporting on the progress).
I set to making the cylinder covers. When I bought the square cast iron stock for the cylinder, I added a length of 2 inch round stock to the order. I'm using that for the covers. I cut a piece long enough for both covers and centered it up reasonably well in the 4-jaw.
(http://www.voght.com/robby/cylinder_covers/5.jpg)
The inboard cover -which includes the packing gland- came first.
I turned a 1 inch stub on the end which will fit nicely in the cylinder bore. As luck (and planning) would have it, it also fits nicely in a 1 inch 5C collet...
(http://www.voght.com/robby/cylinder_covers/10.jpg)
(http://www.voght.com/robby/cylinder_covers/15.jpg)
(http://www.voght.com/robby/cylinder_covers/20.jpg)
I cutoff with a cutoff tool as far as possible, then turned to the indispensable bandsaw.
(http://www.voght.com/robby/cylinder_covers/25.jpg)
(http://www.voght.com/robby/cylinder_covers/30.jpg)
A lot of material was turned off, leaving the male part of the packing gland. I drilled clearance for the piston rod and threaded with a die.
(http://www.voght.com/robby/cylinder_covers/35.jpg)
At the mill, I milled the chucking stub down to leave just a short locating boss.
(http://www.voght.com/robby/cylinder_covers/40.jpg)
8 holes were drilled. Every other hole is drilled for a 4-40 through-hole, while every other other hole is tapped through for 4-40.
(http://www.voght.com/robby/cylinder_covers/45.jpg)
Flipped over, the 4-40 through holes are countersunk for 4-40 cap screw threads. These cap screws will be fully hidden.
(http://www.voght.com/robby/cylinder_covers/50.jpg)
There seems no end of holes needing to be made in the cylinder. Here, every other hole is tapped 4-40 to match up with the through holes on the cover. The cover will be attached to the cylinder by the hidden cap screws. The remaining holes are for attachment of the cylinder to the frame. Look how one of the holes intersects the steam passage. A near design disaster. I'll use a short screw there (with a sealing compound to avoid blocking the passage or inviting a leak.
(http://www.voght.com/robby/cylinder_covers/55.jpg)
The other end of the cylinder was drilled and tapped for the outboard cover. The second photo shows a trial fit. I provide no documentation of the making of that cover, which is rather plain looking don't you think?
(http://www.voght.com/robby/cylinder_covers/60.jpg)
(http://www.voght.com/robby/cylinder_covers/65.jpg)
The covers in my traditional blue shop towel pose.
(http://www.voght.com/robby/cylinder_covers/70.jpg)
(http://www.voght.com/robby/cylinder_covers/75.jpg)
More to come when I get the write-ups done.
Thanks to all who watch!
--Tim
-
Nuts were to be made for the packing glands at both the inboard cylinder cover and the steam chest. Both are similar, but of different sizes. The photo grouping here shows the making of the piston rod packing nut.
(http://www.voght.com/robby/packing_nuts/5.jpg)
(http://www.voght.com/robby/packing_nuts/10.jpg)
First drilling for the 5/16-24 tap to be used.
(http://www.voght.com/robby/packing_nuts/15.jpg)
Second drilling through the nut depth for clearance of the piston rod.
(http://www.voght.com/robby/packing_nuts/20.jpg)
Taking a bit of care to chamfer for aesthetics.
(http://www.voght.com/robby/packing_nuts/25.jpg)
(http://www.voght.com/robby/packing_nuts/30.jpg)
In a hexagonal collet block for forming wrench flats. The diameter remaining was made to be distance across hex corners.
(http://www.voght.com/robby/packing_nuts/35.jpg)
Cutoff at the lathe was started...
(http://www.voght.com/robby/packing_nuts/40.jpg)
And part way through, a little chamfering for appearances.
(http://www.voght.com/robby/packing_nuts/45.jpg)
The two nuts.
(http://www.voght.com/robby/packing_nuts/50.jpg)
Thanks.
--Tim
-
Very nice Tim. Those turned out beautifully...Dave Otto has some competition now :)
Bill
-
Nice results Tim, I need to get some good old fashion cast iron stock. I see a lot of members use it..
Don
-
Thanks Bill. Honestly, I don't think Dave Otto has anything to worry about. :)
The cast iron barstock machines like a dream, Don, but as others will tell you, there sure is a lot of tiny chips and black dust to clean up.
--Tim
-
A piston was made from 6061 aluminum. It was drilled to fit a reduced diameter on the end of the piston rod, and a cavity was bored for an inset nut.
(http://www.voght.com/robby/piston/5.jpg)
(http://www.voght.com/robby/piston/10.jpg)
(http://www.voght.com/robby/piston/15.jpg)
After cutting an o-ring groove and parting off, I made a steel nut (which really needs some provision for some kind of tightening spanner). The rod is also shown in this shot.
(http://www.voght.com/robby/piston/20.jpg)
And here's the whole piston and rod assembly.
(http://www.voght.com/robby/piston/25.jpg)
Thanks for checking in.
--Tim
-
That looks good Tim. Maybe just couple of holes in the nut for a pin type spanner. How deep is the o-ring groove?\
Bill
-
That looks good Tim.
Thanks.
Maybe just couple of holes in the nut for a pin type spanner.
Just what I was thinking. And it occurred to me that if I was too lazy to make the spanner, that sticking the tips of a pair of needlenose pliers in the holes just might work as a spanner.
How deep is the o-ring groove?\
Good question. I'll start with what the groove dimensions should be: The o-ring has a cross-sectional diameter of .07. The recommended groove would be .093 wide and .056 deep as measured from the cylinder bore. My attempts to make the groove with a parting tool were less than successful. My groove is slightly deeper and slightly narrower than the recommendation. Still, it seems to seal well in the cylinder without too much friction. If there are problems, I could make another piston (after grinding a proper tool to make the groove).
--Tim
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You may remember that the cylinder passages are terminated in drilled holes in a flat valve face. on the cylinder. I now had to make a port plate for that face to provide the actual ports that the valve will operate against. The part is simple enough, but the placement of the port slots is critical, and the thin (1/32") brass used requires care in clamping. I started by clamping a scrap of tooling plate to the mill bed and milling a recess to locate the plate.
(http://www.voght.com/robby/port_plate/5.jpg)
Note that by running the corner of the recess off the edge of the tooling plate, I eliminated the necessity of milling a square inside corner. The brass plate had been squared up on the sides which meet the sides of the recess. The other 2 sides are cut oversize and will be milled off later in this setup.
(http://www.voght.com/robby/port_plate/10.jpg)
The locator recess allows me to move a single clamp around as needed to access the perimeter of the plate. I used a parallel to spread the clamping force.
(http://www.voght.com/robby/port_plate/15.jpg)
I first drilled for 4-40 threads, then drilled only through the brass for 4-40 screw clearance, then tapped 4-40 into the tooling plate. A clamping screw could then be placed.
(http://www.voght.com/robby/port_plate/20.jpg)
(http://www.voght.com/robby/port_plate/25.jpg)
(http://www.voght.com/robby/port_plate/30.jpg)
By moving the clamp around and repeating the process, I drilled all mounting holes and provided for enough clamping screws to proceed with cutting the port slots.
(http://www.voght.com/robby/port_plate/35.jpg)
Cutting the port slots.
(http://www.voght.com/robby/port_plate/40.jpg)
(http://www.voght.com/robby/port_plate/45.jpg)
Then I milled the two unfinished edges to size.
(http://www.voght.com/robby/port_plate/50.jpg)
The cast iron steam chest is a part which has not been documented here. I made it one day while "in the zone" and in the shop without a camera. I had left the outside edges unfinished. How convenient that I now had this ready fixture with the correct holes tapped for clamping to finish the job.
One thing to notice about the otherwise nice steam chest is that there is an unintended center drill in the upper left corner. Harmless enough, and it will be hidden by the cover, but another mindless and maddening mistake. The steam chest still needs the male portion of the packing gland turned on the right end as pictured. It also needs the steam inlet port drilled and tapped.
(http://www.voght.com/robby/port_plate/55.jpg)
Thanks for watching!
--Tim
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Tim,
wouldn't it have been easier to drill through holes in the steam chest and use one set of bolts, sorry screws, from the cover to the cylinder instead of a two stage attachment?
Just asking,
Steve Fox
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Hi Steve,
That would have been easier to build, but I want to be able to take the cover off without disturbing the placement of the steam chest. I'll want to time the eccentric, for instance, by removing the cover. Since the valve rod goes through a hole in the chest, I want the chest to stay put once I have aligned it, to prevent jamming of the rod. That is at least my reasoning.
A good question, by the way.
--Tim
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Nice to catch up here.
I hadn't seen a 'round' nut before (that I can recall), and I understand the idea of a couple of holes for tightening it.
But why 'round'? Why not just a regular nut? (No implication that it should be something other than what you did...just wondering.)
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Hi Carl,
The idea of making the "nut" round is that it will fill the cavity I bored in the piston. Any space left at the end of the cylinder when the piston is at the end of its stroke is "dead volume" and could be considered a negative aspect of the design. Does it really matter in this little engine? Hardly, if at all. I'm just doin' my thang.
--Tim
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I've seen nuts like this before, but can't recall where. I think it must've been on a camera.
The only use I can recall now is on Leigh woodworking jigs. They use this design to adjust the depth of a tapered bushing to change the clearance.
You can see the design here:
https://www.leighjigs.com/ugs.php
The threads are on the outside. Come to think of it, I think the other ones I remember had the threads on the outside too, not that it makes a difference.
Works for me.
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Does it really matter in this little engine? Hardly, if at all. I'm just doin' my thang.
Works for me.
I thought it interesting and cool.
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Tim,
I got behind, I think I missed your posts, now I'm all caught up. Things are looking good and coming along well. See you at names.
Art
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I've been a lurker here mostly... Signing on to this thread will get me coming back more often.
Cool looking design... Maybe one day I'll be good enough to tackle something like this.
Thanks for taking the time to document the build.
Chris
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Thanks Art, see you at NAMES. Look forward to seeing where you are on the Val project at that time.
Chris, thanks for checking in and glad you're watching.
--Tim
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My write-ups for this project took the back seat to productive shop time as the NAMES show crunch set in. Sadly, not only did I neglect the write-ups, but I forgot to photograph much of what was going on.
I'll do what I can to catch you up.
I showed where I was on the steam chest back when I showed the port plate. Here's a quick review of the chest as I showed it then:
(http://www.voght.com/robby/port_plate/55.jpg)
I managed to make the steam chest cover from scrap cast iron I sawed off to make the cylinder. Here you see one side of the scrap plate milled flat and drilled for screws. I outlined the outside dimensions of the cover with a 1/8 inch endmill.
I then sawed near the milled lines leaving some for cleanup. Finally, back at the mill I cleaned up the other side, and cleaned up the saw lines at each edge using the previously milled outline as witness.
(http://www.voght.com/robby/steam_chest/5.jpg)
I mounted the chest on the cylinder with the brass port plate, and with the cylinder mounted on the frame, I could then use a drill bit through the valve rod guide to mark the exact location for the valve rod hole in the chest.
(http://www.voght.com/robby/steam_chest/10.jpg)
With the rod location marked, I centered the mill's DRO on the mark and drilled the rod clearance hole. I then cut away excess material around the packing gland boss.
(http://www.voght.com/robby/steam_chest/15.jpg)
I used an inward-facing tool in the boring head to cut the boss round concentric with the drilled hole. The boss was threaded for the packing nut using a die holder in the same setup.
(http://www.voght.com/robby/steam_chest/20.jpg)
(http://www.voght.com/robby/steam_chest/25.jpg)
Thanks for watching.
--Tim
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Nice to see an update Tim. The steam chest looks great.
Bill
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Beautiful work Tim and glad to see progress........ :ThumbsUp:
8) Don