Well, the holidays certainly interfered with progress on the engine as did a few other things, but I did manage to do a bit of work, most of it yesterday so i thought I'd better catch up on my posting regarding the progress on this engine.
The major part that I had been putting off until last was the connecting rod. I'd thought a lot about how I was going to do this part. I'd contemplated silver soldering 3 parts together but couldn't figure out how I'd keep everything aligned well enough. I'd thought about threading 3 parts and then silver soldering them, but that seemed like a lot of work without a sure ending. So in the end, i decided to make it more or less like Stew Hart and others had done, that is turning it from a piece of solid stock. But I still very carefully thought thru the order of operations to give myself the best chance of success. So here's the tale!
i had some stock that was 3/4" x 5/16". I didn't show the operation, but I took that piece of stock down to 3/4" x 1/4" as called out on the drawing. In this pix, I drilled a small center hole in one of the ends of the stock and 2 small holes .089" (#43) fairly deep. These holes will become the bolt holes for the bearings eventually. I drilled these something like .40" deep and you'll see why in a bit. I've found that I can drill small deep holes fairly easily by turning the spindle pretty fast and using the Unist coolant/air blast to keep the drill cleaned and lubed. I withdraw the drill quite often and this seems to work. I don't show a pix of it but I turned the stock over and drilled a center hole in the other end also, just as a contingency as I wasn't sure if my conceptual technique would work or not.
I also didn't show the operation of drilling the hole for the bearing/bushing as that's pretty straightforward. I simply did the edge finding and then left 3/8" extra stock on the each end beyond what I needed. I'm showing the part on the print with a layout line marked showing where the round portion of the con rod is to start. Notice the extra stock top and bottom.
Shown is how I ended up mounting the stock in the lathe. I used the 4J chuck and carefully centered it in the jaws using a dial indicator. This process is a bit tedious as you can't simply hand-rotate the chuck without first backing out the dial indicator. After I got that end centered in the jaws, I installed a live center and rechecked the centering. Everything remained true. The technique I used to remove most of the stock was to plunge in with a 2mm carbide grove/turning insert until I got close to the required OD and then I took a light pass to take out the resulting grooves. I really don't like interrupted cuts but this process worked ok.
Next i switched over to a 3mm carbide radius insert and brought the ends to dimension and started forming the radius that makes the transition from the round section to each end.
Next, I moved the compound to 3 degrees so as to cut a taper toward the headstock. I also slewed the tool around so that it could get into the root of the joint and not rub when approaching the headstock end. I also marked the center of the con rod to give a reference as to when I'd completed the taper.
Then I set the compound 3 degrees the other way and cut toward the tailstock. This was the part that had me worried and the reason I put center holes in each end in case I had to turn the part around in the lathe. I wasn't sure that I'd have enough clearance to cut a taper in this direction but it ended up working fine. The radius tool I used was long enough to work well for this op.
Some work with emery cloth and Scotch Brite got the part to a pretty good finish on the round portion. The marks from the 4J will be taken care of in future ops. Hopefully this pix shows why I left extra material on each end for the lathe work.
A closeup pix of the crank end of the con rod showing the bolt holes magically appearing! Doing the drilling earlier was easier as i was working in a solid piece which meant I wasn't worried about alignment or flexing.
Then back to the mill to take the crankshaft end of the con rod down to 1/8" thick as called out on the drawing. Since the part still has the 3/4" width available, alignment in the mill is easy.
A pix on the print showing the crankshaft end done.
Then I needed to make the con rod bearing retaining plate. I had some of the 3/4" x 1/4" stock that I'd earlier prepared and after edge finding, drilled the 2 required .089" hole in the end just deeper than 1/8". This is clearance size for the 2-56 bolts to be used.
Then I used a .035" thick slitting saw to cut off the retaining plate at 1/8" thick. I used the Unist running air and lube to keep the chips clear and the cut lubricated. I'm always amazed how well slitting saws work. This blade is 2.5" OD and I turned it at about 100 rpm. The part was on dimension and required almost no deburring.
The bearing retainer cap and con rod shown on the print. They even fit together properly! Another minor miracle!
Then on to the con rod bearings. I had a piece of Al bronze flat bar and milled down a small bit of it to 3/4" x 1/4". I didn't show that process as it's pretty straightforward. Then I drilled thru the solid piece in 2 locs with a #43 drill for the clearance holes for the 2-56 bolts.
Then I used the slitting saw to cut the stock into 2 more or less even pieces. The Al Bronze cut very easily. Same setup as earlier.
Next I put the 2 halves on a parallel in the mill mise and took them both down to exactly .25" thickness as the drawing calls for. The holes will match since they were drilled thru the solid prior to cutting them apart.
The completed bearing bronze's on the print.
Next was to drill the bearing bronzes for the crankshaft in exactly the correct spot. Since I still have sufficient flat stock, mounting it as shown in the mill vise was easy. I then located the center of the existing hole with a DTI and then moved down using the DRO to the exact distance required. This pix shows the centering operation.
I didn't show the spot drilling, thru drilling a bit undersize and then reaming to .001" over 1/4" but i do show a small piece of the crank material fitting thru the hole. This felt about right to me at .001" over. It rotates freely without any slop.
Now, since I'm pretty well done with needing to hold for alignment, I started bringing the round end of the con rod to size. Here I'm milling down the end to get fairly close to the required OD of the round end.
Next I made a simple 'filing button' that's a 1/2" OD with a stub of 5/16" that fits within the con rod end ID. I also blued and marked the to be round end. And you'll note that the part is laying on the belt sander. I used the belt sander to get the part very close to round and to the final OD.
Here's a pix of the con rod in an intermediate state. More finishing work is required!
One of the issues that I'd been having is workholding for small parts. I had some aluminum caps for my bench vise that were held on my magnets. These work ok, but only if the work can be held to the center of the jaws. When attempting to hold small parts near the top or ends, the caps would flip and slide around. So I took some time and copied the Wilton vise jaws but in AL and added 2 shallow grooves to hold round work as required. Grooves are only on one jaw, the other is completely plain. The grooves are dimensioned to be able to hold work as small as 3/32" round stock.
Now I can finally hold small parts as I need to! A very worthwhile upgrade!
To get to the final radius around the circular end, I used needle files and then to smooth out the finish I used this setup. That's a piece of 2" round grey Scotch Brite that uses the 3M Roloc fastening system. I chucked that up in my drill motor and gently applied it to improve the finish in that root area.
A pix of the con rod with the work so far.
I made the bushing for the con rod out of a piece of SAE 660 bearing bronze. Shown is after the OD was turned and the con rod is a slip fit onto it.
Drilling thru the to-be bushing using a 15/64" drill. (1/64" under 1/4")
Reaming .001" under .25"
Parting off just a bit over .25" using a 2mm carbide insert tool.
Completed bearing/bushing shown on the print.
And the final pix for today. This is the bearing/bushing pressed into the con rod using some Loctite 603 to retain it.
I still need to do a bit more work on the con rod with some abrasive paper on a flat surface to clean up the flat sides of the con rod. I'll hopefully get this done today.
Then the only remaining bits I have are the piston valve rod, and the eccentric rod plus 2 little fittings to join the 2. That should all go pretty quickly! Famous last words I'm sure. Then I'll start to assemble the engine to start setting up the various parts and to check for final fit. Hopefully that means I'll try to run it on air pretty quickly now!
All for now.
Enjoy!
Mike.
