Pottymill horizontal engine build

[tinglett]

The Connecting Rod

The connecting rod is formed by a main part that includes the rod with a nice decorative angle, a bearing brass on both ends...one of which is split in two parts for assembly, and a little end plate that bolts it together.



I started on the main part since the other parts must be made to fit it.  I didn't happen to have any bar stock quite this size, so I went to my home center and got some hot rolled steel that would hopefully have a good enough finish.   I machined the ends, but decided to leave the long edges unmachined to maximize the material.  Later on I'd regret this, though it didn't foul anything up.

I'm going to turn this bar between centers to form this as a single part.  No soldering or threads to put it together.   I drilled both ends for centers, but found it hanging pretty far out in mid-air.



This is a general problem I have with my lathe.  There isn't much room, and yet the headstock center (an MT3) sticks way out.  I need a driving pin longer than 2 inches.  I'd really like to find a center that isn't so long.  Rather than invent a solution now, I decided to go with plan B, and that was the setup Stew showed for his Dad's and Lad's engine which is a nearly identical arrangement.  This involves turning a little center that can slide into the chuck and the chuck jaws can drive the work.  It worked really well, and I'll remember this trick for the smaller parts.

I first turned a bit of 0.5 inch rod.  With my big AXA tool post, I found it more natural to turn this on the back side with the work spinning in reverse.


But there was trouble.  I was thinking a 0.5 inch rod would be plenty wide for centering a part that is only 0.25 inch thick...but it wasn't due to the way my chuck jaws are formed.  You can see how the jaws are going to drive the work, but it wasn't a rigid enough setup.  I tried working with it this way for a bit, but eventually decided to fix the situation.


So I found some 0.75 inch rod and decided to turn down a stub for the center so it wouldn't get too deep in the chuck (the 0.5 inch center was deep enough).   I used my parting tool and guessed at the depth.  I was pretty close, but should have gone just a tad deeper.


Then I turned away.  I worked in reverse on the back side as before.  Here I'm zoomed back so you can see the tool post better.  Both the 4-jaw chuck and the tool post are very large for this 7x12 lathe.


I mounted the part between centers using this tiny center and it worked fine.  I wasn't terribly happy with the finish I was getting on this hot rolled steel, but it was turning ok at least.


I used the parting tool to clean up the shoulders.  It worked fine.


I thought about how to turn the angled part.  The plan showed an 8 degree angle overall.  I thought about adjusting my tailstock out of line so it would cut a taper, but it took so much work to get it aligned so I really didn't want to do that (until I add an adjustment screw to the tailstock).  I started moving the headstock end of the part until I realized that, duh, that wasn't going to work.  All I'd do is remove material from one side of the part.  Not exactly a taper.  So I finally decided to go with the compound.  I'm not sure why this wasn't the first thing to come to my head -- maybe because the angle was so small.  So I set it to 4 degrees from center.

You can also see I messed up my layout lines on the part.  If I recall I used the diameter as the radius.  I decided to actually scratch the circle, which turned out to be a good idea because it caught the mistake.  Note that I painted on layout dye to the diameter I am about to turn.  I thought it would make it easier for me to track what material I am removing.


Here I am turning it, using the compound to move the tool.  For each pass, I would back the cutter back beyond where the previous pass started, I'd crank in 5 thousandths on the cross slide, then I'd use the compound for another pass.  It worked fine.  Later on, I looked back at Stew's Dad & Lad's and found he did the same, except he used a 3 degree angle.  My 4 degree angle was ok, but if I were to do again I think I'd go with 3.  It feels a little bit flimsy on the ends.   Still not too happy with the finish.


I flipped it around to do the other side, and then used my parting tool to clean up the ends.  I thought the little round bit looked nice, so I left it much like this.


Once it was cleaned up a bit, I pulled it from the lathe, trimmed the excess off the end with the bandsaw, and then off to the mill to flatten the edges properly.  This is where I was wishing I had done this up front.



Next it was time to drill and tap holes for the brass bearing on the one end.  I had a scrap of steel that was fairly well matched to the part, so I used it to balance out the vice.  This gave me the idea to leverage it for clamping for a little added stability.



I went with #2-56 threads so I tapped by hand.  I know it sounds odd not to guide it, but I don't have a special tapping guide and the mill is much too clumsy for this tap.  It worked fine, and in fact was quite easier than aluminum as I didn't have to worry so much about tearing out the fine threads.


Next I drilled out the circular end.  This is partly why I needed to mill the edges flat.  I probably could have gotten away without doing that.


I made a couple filing buttons for the end out of 3/4 inch steel rod.  These were fairly big so I didn't need to tap them.  I experimented a little to allow them to rotate.  In later pictures you'll see I started using a longer bolt with two nuts jammed (I didn't have nylon this size).  I also used lock washers to let them be a little loose yet still stay nicely aligned.



Filing took a bit longer than previous work because there was a lot of steel to remove.  I used a rough file across and started by making flat areas as if I was making a hex shape.


When I got real close I started using black sharpie marker to color it, then I'd file, and then I'd add more marker as needed.  This let me see when I was nicking into the buttons.  Much of the diameter was easy because I could file with the rotating buttons, but near the conrod side I couldn't do this.



Well, that's it for this post.  Next are the other little bits that form the connecting rod, and then a little overall cleanup.

Todd

[Stilldrillin]

Nicely done. Nicely shown, Todd! 

David D

[tinglett]

Completing the Connecting Rod

In the last post I finished making the main part of the connecting rod.  I continued to sand and tune it up.  I'd "paint" it with a black marker, and then sand away until it was finally getting to a nice match with the buttons.  I fine tuned it while watching the first two Hobbit movies, then took my kids to the last one at the theater.  (I'm having a lot of fun machining, but I'm not so crazy to bring it with me to the theater, though!  I've seen knitters go around that bend before ).

Here's the main part for reference.  I need to create a bearing for the flat end, and insert a bearing in the round end.  I'll do them in that order.


I first needed to make a little steel "holding" part to go on the end.  Bolts will start through this end, go through the split brass bearing I am about to make, and thread into the main part at the flat end.  I drilled clearance holes for my 2-56 "bolts" in the end of some of the same bar from which the main part was turned.  This part will be only 3mm thick, so I drilled 3mm deep.


I chopped it off slightly long (~4mm) in my bandsaw.  I was VERY happy my new bandsaw could slice this accurately.  Here I have it flipped over and will mill it down to thickness.


I made light passes of 5 thousandths of an inch until the holes appeared.  The thickness of this part isn't so important, but it ended up at 3.07mm anyway.  Not bad for not measuring.  Note that I didn't clean up the other dimensions.  The top side was already milled flat, and I didn't really care about the other four sides because I plan to flatten them all together when they are bolted as an assembly.


And the bolt holes line up.  Always a good sign.


Next, it was time to make a split bearing out of brass.  The trouble was that I didn't have brass close to the size I needed (3/4" wide by 1/4" thick).  I need to add that to my wish list.  But I did have 2" wide brass, so I sliced off a bit.  The bearing is to be split, so I figure I'll make the two side by side.  The bearing is to be 12.7mm in total, so I cut this about 7mm to have a little extra to flatten it out.


I roughed them to length on the lathe by parting off lengths that were close (not shown).  Here I am trimming it a little closer in size.  In the end, I will flatten them when bolted together so it's ok to be long.


Next, I drilled for the bolt clearance holes.


I found they weren't quite the right thickness so I had to skim them again.  Not the best time to do it, but it worked out ok.


Here they are bolted up.  I carefully measured from end end of each brass part when I drilled the holes, so the two brass parts line up pretty good on one side.  I needed this as a "better than nothing" reference for skimming the sides flat.  Which I did.  I'm never quite sure when to insert paper in the vise, but this part wasn't perfectly even so it seemed it could use it.  It was bolted together so maybe this didn't matter so much.  And maybe I should have used it on both sides (I didn't).




I decided not to skim the large flat areas.  They are very close and I thought sandpaper on a flat surface will go better.  The steel on the ends will act as filing buttons.


Sanding worked pretty good.  This only took a couple minutes.


Next, I used the round end to locate a useful position on the part (using a button made this even easier), and used that to locate the hole for the brass 60mm over.  I decided to drill and ream this hole to 0.251 inches.  I'll make the crankshaft from 0.250 inch rod.





Looking good.  Now it needs a bearing for the other end.




The Cross Slide Bearing

The trouble I expected to have with the cross slide bearing was to get a nice tight fit into the connecting rod, so I cooked up a scheme to get there.  I don't have a means to measure a hole precisely, but I can take the time to make test fits.  So I turned down some 1/2" brass rod to a close fit, and then turned down the tip to what I think will fit.  I used my parting tool for all this work.  You can see at the tip that it's turned down in two steps.  The step closest to the edge went too far.  I knew the hole was drilled 5/16" (0.312) so I went for 0.322 for my first attempt and found I went too far.  Go figure that it would be that far off!  So I moved inland and tested one thousandth by one thousandth until it just slipped on.  Each time it didn't fit, I would double check (of course!) and if it really was still too big, I would skim over the rest.  Once the part slipped on to this little bit on the end, I knew the rest of the brass was 1 thousandth over.  That's just what I wanted.


Next I drilled it out by stepping a few bit sizes until I got to a D bit which fits the pin this bearing rides on.  I debated if I should drill it now or later, but opted to do it now while the part was perfectly centered.  Centering isn't critical, but since the bearing is so thin I thought it would be easy to see if it's off center.  In hindsight it didn't matter because you can't see the bearing anyway.  Sad really.


I tested the fit for the pin.  It's good as far as I can stick it in, anyway.


Finally I trimmed a bit from the end, but left just a little of the undersize brass as a guide for pressing it.  Then I parted it off to just a hair over length.


I had to file off the bit that remained from parting. This was easy enough, but I did it by hand.  I didn't want to risk bending it out of round in a vise.  A twist of a chamfering bit took off the last bit of it.


Now it was time for pressing it in.  I don't have an arbor press, but I thought the vise would work fine.  It did.  It resisted a little -- but not much.



I need to sand it flush, and also found the inside hole changed diameter ever so slightly.  I was expecting that. The metal has to go somewhere.


But this was easy to fix.  I twisted in the D bit with my fingers and gave it a spin.  That's all it took to fix it up.  Must've been only a thousandth or so.  Dunno...remember I don't have a way to measure it.


I ended up with a very close fit.  I wasn't thinking about this when I was machining the the cross head.  But it ended up well by luck.


And now the parts are fitting together nicely!


I'm not positive where I'll go next.  I think it will be the cross head slide bar assembly.  Then I can also make the block that supports the engine and the base plate.

Todd

[vcutajar]

Quietly following your progress Todd.  Keep it up.

Vince

[Jo]

Nice Todd. Like you I put some sort of marker on the rod before I cut a taper so I can see what is happening .

A second thing worth doing is take to tool to the small end and then back it out to the start of the cut. If you slip a feeler gauge behind the tool you can measure half of what you are about to turn off so you can check if the angle will cause the rod to become a bit thin before cutting metal and adjust accordingly .

Jo

[Roger B]

Nice work    Still following along   

[b.lindsey]

That turned out great Todd. Still following along here as well. 

Bill

[tinglett]

I finally got back into the shop to make the four slide bar pillars.  Not much, but they took a while for me to make.

Slide Bar Pillar

There are four slide bar pillars that look like the following.  Since I'm building in imperial measurements, I decided to leave the larger radius as-is (16mm) and the smaller radius as 1/4 inch, which will match the slide bars.  I'll use 2-56 threads for the top, and 4-40 threads for the bottom.  Height gets adjusted later, but I wanted them to look as identical as I could get to the eye without spending gobs of time measuring.  So I was thinking about how I might automate this a bit since I was making a few of these.



I turned and faced some 3/4 inch bass rod.  I didn't have 5/16 inch rod which would have been nearly correct as-is.  In hindsight, I could have used 1/2" rod and the bases of these pillars would have been a bit smaller, but would have looked fine.  I had enough rod extending to make two at a time.


I don't yet have a carriage stop, but after doing this job making one has drifted very high on my to-do list.  The smaller diameter of this pillar is 1/2 inch tall, so in this picture I have the carriage positioned without moving after the facing operation.  I clamped a bit of brass as my stop, and I spaced it with a bit of scrap 1/2 inch diameter rod.  It was a quick way to set the stop.  I wasn't too keen on placing a C clamp here, but it worked out ok.


I turned it down to 1/4 inch diameter using the stop for my starting point and letting it feed to the right.  This was backwards for my cutter, but it actually made nice chips and a nice finish.  I had to be careful with that C clamp handle which was pushed back a way for the picture.  Don't get that in the chuck jaws!


Next I drilled and tapped the top with 2-56 threads.  I used the chuck jaws as a guide for the tap and it worked pretty good.  I spin these little taps by hand with my fingers.  If it gets stiff, I back it out, clean it up, and run it in again.  It looks like the tap is in the chuck, but it's only pressing up against it for guidance.




I rounded over the edge next.  I decided to try to make a cutter for it, and it turned out pretty good.  I took a 1/4 inch hss blank, ground it on the corner edge of the grinder to get the internal radius, gave it a fairly generous clearance angle on the front edge (can't see in the picture), and gave it a clearance angle on the right that wasn't really needed.  I ran it in at the angle shown here, and then did a little fine adjustment pushing in with the cross slide.


I came up with this arrangement for positioning the parting tool by using some outside calipers which were pre-set.  That's a parallel that's squeezed between the tailstock and the part.



I flipped them around and faced them off.  I switched back to my little 3-jaw chuck for this.  Note that this particular part has already been drilled at the bottom.  On my first part I decided to drill all the way through for the 2-56 threads.  What I found was that the drill was slightly off by the time it came out the other end.  That meant the next part had a little dimple off-center as a starter for the next part. Not good.  It wasn't off much, but enough.  After this "education" I decided to drill partway, and then later drill in from the bottom.  I'll get to that below.  Right now I faced this one and then left the cutter in this position and ran it over the others so the bases would be the same thickness.


Here's how they looked after the first pass.  They were pretty close to a common thickness.


I gave them all another pass to clean them up just a bit more.


Finally, I drilled for 4-40 threads into the bottom of each.



I tapped by hand the same as with the 2-56 threads.  For larger than 4-40 I've been chucking the tap in the tailstock and rotating the lathe chuck to do the work.  That seems a bit clumsy for these little ones and I was worried about stripping out the new threads.


Here they are holding up a parallel.  The one on the left was the first I made as I figured out how I was going to set the stop.  It came out a 12 thousandths shorter than the middle ones.  The two in the middle are identical height, and the last one I made on the right was 4 thousandths shorter than the middle ones.  Not too bad for almost no measuring.


I'm not sure how I'll finally level them.  I could skim them with the mill after screwing them down, but I'll probably just end up doing a little filing where I need it.  Tolerances are probably a little loose.  I doubt the cross slide will care too much about a few thousandths, but I'll probably clean them up a little anyway.

That's it for now.  Thanks for looking!

Todd

[arnoldb]

Good progress Todd 

Kind regards, Arnold

[tinglett]

I've been working a little off and on making some bits.  It's time for a report.

The Cross Head Slide Bar Assembly

There are two sets of slide bars, each of which is a pair of bars separated by a spacer.  These sit on top of the pillars that where shown in my last post.  The net is that I need to make four bars (two per side) and four spacers.  One of the spacers is special in that it is also a guide for the valve rod.  My thinking was similar as with the pillars -- what can I do for repeated cuts?  I do have a vise stop so it will get used here.

The bars and spacers are all 6.3mm (1/4") in size.  I started with the spacers and decided to make four, even though I only need three.  I drilled deep enough for two at a time.


I tried various means to precisely measure the length of the rod for parting it off.  Here I show a DI setup that worked ok, but not great.  I also tried dialing since I had the compound parallel to the lathe axis, but I found the dial markings are fairly meaningless.  They may be metric and I suppose I ought to figure that out.  The cross slide is very close to thousandths, so this surprised me.  If I had a carriage stop, I could have set it to match the face and then used a spacer to move it toward the headstock for each operation.  That's another vote for making a stop.  This is also another vote for a DRO...but that's going to have to wait.


In the end, I used the DI to get them close, and then I tidied them up one by one as shown here.  I got pretty close...one was off by 2 thousandths, but the others were exactly matching.  And I only needed three so this worked out.



Next, I needed to make a fourth spacer that is also a valve rod guide.  I decided to make it from the same 1/4" stock I'll use for the slide bars, but this will be a problem as the spacers need to be slightly larger (0.2mm or 8 thousandths).  I thought I'd try to mill a little spacer.  I was curious if this was possible, or if the mill would send it across the room.  I took some light passes on shim stock and was surprised it worked out ok.  I had it resting on a parallel and used a bit of rod to clamp it tight.



I tried a failed experiment to loctite it to the guide bar.  The idea was to have enough strength to drill the hole through this shim and the guide.  But I found loctite doesn't work that way.  It fell right off...only good for threads.  I thought about epoxy, but decided to drill it directly.  To my surprise, that worked!  I thought I took a pic of that, but I guess not.  I do show drilling the valve rod guide bar.



Then I drilled the main cross slide guide bars.  These were cut slightly over length and I was able to use the stop I had set for the previous small guide bar.  I drilled one end only as the length wasn't correct yet.  I did this for all four bars.


Next I used my X dial to position 62mm down the bar.  The vise stop stayed put.  I drilled all four bars like this.


And finally, I repositioned the stop to get a perfect 64mm length on the bars.  I did this in two passes.  The first pass matched the length of the shortest bar.  It was close enough that I could mill off the end in a single pass.  Then I milled one bar to 64mm using the dial.  The other three were done in a single pass at that dial position.  I took off maybe 5 or 6 thousandths to get here.  It was already very close.  In fact, it was pointless to "fix" the length as it isn't important, but I thought it was good practice for future projects.  I'm sure this is "machining 101" stuff.


Here's a family shot of the guide bars.


Next I had to drill the valve rod guide for the rod.  This guide turned out too short, but I kept going anyway.  I decided to drill and over-ream this since I had a 0.126 reamer (the valve rod I used is 0.125 inch).


Finally, here are the parts semi-assembled.  I need to make slides and thrust washers for the cross head, and I still need to make the supporting block for the cylinder.  It's resting on scrap bits right now.


Next up, I'll make the slides, cylinder support block, and a base.

Todd

[Perry]

Very nice 

[b.lindsey]

That is starting to come together very nicely Todd...

Bill

[tinglett]

Thanks all for watching   Here's a minor update from earlier.

I needed to make the slides for the cross slide.  It also looked like I needed to remake the little valve rod guide from the previous writeup, so I set about doing that here.  I observed that all three of these are identically sized.  I hadn't noticed that earlier, so I embarked on making three parts this time.

Since I was making a few, I could balance out the vise as I trimmed up the rough cut steel.  This is 1/4" square bar that I'm milling to 16mm length.  It's interesting I'm mixing measuring systems like that


It was time to extend my vise stop for little parts like this.  I happened to have the correct threaded rod and it worked nice to trim the three parts to identical length.  Really, the length isn't critical, but at least I wanted the two slide bars to match.


The cross head has 10-32 threads, so here I'm drilling for 10-32.  When I was done I noticed two things.  First, that hole is mighty big for the 1/4" slide.  Using 8-32 threads on the cross slide may have been a better choice.  I was thinking bigger is better, but I was pushing it here.   Second, that hole looks off center.  Dang.  But hey, I have a spare.  So much for remaking my valve rod guide, though.


Now I had paranoia going on, so I bothered to hit the next one with layout dye just to check my work.  This time it was dead on.  I'm not sure how I screwed up the previous, but I'm using the dials so maybe I got off by one turn.  The messed-up one on the left is really obvious in this photo.  Note that I threaded it anyway.  I checked it out on the cross head looking for any other trouble.


Here I finished up drilling and threading the second slide.


Now we have a family shot, so to speak, that's semi-assembled for show.  The slides are installed on the cross head and move about in that space just fine.  Before trying to tune anything up, though, I really need to make the base to lock everything down.  Then I'll see where things need adjustment.  In order for that to happen, I need a real base for the cylinder.


The cylinder base is 16mm square aluminum.  I used 5/8" which is 5 thousandths short.  If the cylinder isn't high enough, I'll either need to shim it up, or I'll need to trim the pillars.  In a way this is good, because I can use a feeler gauge to measure the adjustment.  How's that for positive thinking?  Here I'm drilling the holes for attaching it.  I'll use 8-32 screws for this.


And now I recalled that I never did get around to drilling and tapping the attachment holes in the bottom of the cylinder.  I had to pull the cylinder assembly all to pieces and do it now.  One side of the cylinder is flat and the other round.  I placed the rounded side against the back (fixed) jaw of the vise and measured to the center from there.  The cylinder is 1.25 inch diameter so this was easy.


Now I have quite a "kit" of parts.  I told you I had to pull it apart!


I needed a base, so I painted and marked up some 1/4" x 2" aluminum with layout dye and set some parts on for a sanity check.  Looks ok.


Time to drill.  Dang, that hole looked mighty big.  I realized I drilled for a 10-32 screw and I was using 8-32.  Doh!  I went ahead and drilled the other, and I also checked with the screws I was going to use.  It doesn't matter...the screw won't slip through so it's ok.  In fact, I guess the one larger hole will give me a lot of wiggle room for adjustment, even though I'm sure I won't need it.  Just being positive again .



A test fit for sanity.  The block won't attach this way, but the screws are lined up which is what I wanted to know.


Next I drilled for the slide bar assemblies.  I had the aluminum hanging out of the vise so I didn't need to move it.  As it turns out, I decided to reset the dials for this anyway.  It was most important for the slide bars to be parallel to the base, so I did the two holes with a fixed Y setting, and then reset and did the other two holes.  The layout dye was a nice blood-pressure reducing addition.  They were landing perfectly.   This involved A LOT of spins of the dials!



Here it is all assembled and screwed down.  The cylinder height is good, partly because there is quite a bit of clearance between the slide bars.



And here's a close up.


Next I need to make thrust washers that sit between the cross head and cross head slide bars that I just made.  These will keep the head from wiggling side to side.  I also need to remake that valve guide that is front and center in the last picture.  Its position is good, but it's too tight, and there simply isn't enough material to drill it out further.

Oh, and I think the layout dye's got to go.  It just doesn't fit with the style of this engine

Todd

[sbwhart]

Looking very good Todd

 

Stew

[Roger B]

Looking good