Well, I'm glad it worked out, Ryan.
I took several pictures of the process, and have included them here for those interested in how we did it. This was a first time for me, so chime in if you have any suggestions.
NOTE: I referred to the bolt size as 8x1.25mm. It is actually 10x1.25mm and uses a 8MM Allen wrench.
A friend of mine has a company that re-furbishes medical lasers. The guy is super smart, and has made many modifications and improvements to legacy systems to help them function better, as well as produce parts that are no longer available from the manufacturers. He does prototyping and builds the parts in a his little machine shop with a Haas CNC turret lathe, a Haas vertical mill, a Bridgeport knee mill, an engine lathe, and other assorted tools. He has allowed me to use his manual machines in the past, and offered to machine this on the CNC lathe to save time and get the best accuracy.
Anyway, we needed to machine the shaft diameter on the coupler down to a usable diameter for the JD400 drive shaft--1.000" if I remember correctly. We first tried the Haas CNC lathe, but couldn't find a pre-programmed routine that would move the cutting tool around the flange on the end.
We finally chucked the part in the engine lathe. I machined a step in the flange of the adapter that was about .008" smaller than the counterbore on the pulley--I wanted to keep it closer to .005" but I turned the crossfeed dial a little too much at the end.
I then turned the shaft down to about .005" under nominal diameter and 2" long. We got a bit of taper bBecause we had to chuck the part by the end of the shaft, and couldn't use a center in the other end. I don't think it will cause a problem as Ryan will probably have to trim some more off the shaft once he get's his U-joint or whatever coupler he decides to use.
I used my abrasive cut-off saw to remove the end of the shaft that was chucked in the lathe, then put a slight bevel on the end with my grinder.
We had already elongated one existing hole as shown previously. I now had to locate the other 2 holes as precisely as possible. The method I came up with was to put a bolt through the existing hole into the pulley (8mm x 1.25mm pitch) to locate the shaft adapter, then use transfer punches to mark the location.
My transfer punches are English sizes, and the closest punch was a little sloppy in the hole. Transfer punches are typically about .025" undersized anyway, and you need some means to position it more accurately in the hole. I took electrical tape, and wrapped two layers around the punch. That made it too tight, so I unwrapped one layer. Then, to eliminate the tape overlap, I used my knife to cut the end right at the starting edge of the tape. This gave a 100% wrap of consistent thickness.
To help eliminate any other variability, I used a small square to line up the punch before I hit it. I could only line up one side, using the machined surface of the pulley. I used my calibrated eye balls to made sure that the punch was straight from side to side by looking across the narrow edge of the square--similar to centering the front sight of a gun on a target. Then a light tap with a hammer and repeated on the second hole.
Before drilling the holes, I lined up my drill press spindle to the table, using a length of steel rod and a square. Since the marks were on the side opposite the flange, I used a new vice jaw with a vertical "V" groove in my machinist vice to hold the adapter.
I drilled a pilot hole using a 3/16" drill, then drilled to size--I found a letter drill that was .005" larger than the bolt diameter-the "Y" drill if I remember correctly. I did this two weeks ago, and I've slept since then so my memory has failed me--guess I should have written it down.
I dug out some 8X1.25mm bolts from my stash and installed them in the holes. I had to make judicious use of a round file as the holes were a little tight and one of the bolts wouldn't start, but I soon had all three bolts screwed in.
The next challenge was that the heads of the hex-headed bolts were too large for the hole location--they hit the side of the tapered side of the adapter, and wouldn't screw in all the way. I didn't want to turn much more from the side as the adapter is a casting with a hollow center on the flange side and I may have ended up weakening the metal.
The obvious solution was to use socket-headed screws. A quick search of Mc Master-Carr turned up a package of 8x1.25mm screws approximately 1 1/4" long. Regular split washers were larger in diameter than the heads of the screws, so I used an external star washer.
As it turned out, the screw heads were still too large.
I resolved this by setting my drill press to the highest speed, and chucking up a 3/4" diameter abrasive stone. I placed the flange on the table and brought the stone down to where it just touched the edge of the flange. I then ground against the tapered side of the casting by pushing the adapter laterally against the spinning stone. The bottom of the stone kept rounding off, so I trued it several times by holding the stone against the side of the grinding wheel on my Baldor grinder and spinning the stone in my hand as I trued it up.
This process ended up grinding a shallow arc into the tapered side that permitted the screws to be fastened all the way down.
After I'd trued the stone a few times, I found that the drill chuck kept me from going in as far as needed. So, I put the shaft of the stone in the flange hole, then chucked it up and ground from the top side of the stone to finish off the cutouts. All in all it worked pretty good.
After I fastened the adapter to the pulley, I chucked the shaft in my little HF 7x10 lathe. I wanted to run a dial indicator over the pulley and the adapter shaft to ensure they were concentric. I found about .003" variance, so that was good to go.
I also wanted to see if the assembly was balanced as there is a pocket machined out of part of the pulley. The lathe has infinitely variable control, and goes up to 2500 rpm. I had tweaked the pots in the controller so it turned at about 20 rpm at it's lowest setting--this allowed me to start out slow and build up speed gradually.
I found that there was quite a bit of vibration above 1,500 rpm--however, I could only chuck about 1" of the shaft in the lathe, and all the mass was hanging at the other end--which would be closest to the crankshaft when installed so I figured it wouldn't be a problem when on the engine.
I told Ryan to check the shaft after he installed it on the engine and see if there was excessive runout, etc. From his comments above, I take it that everything worked fine.
Anyway, there you have it. Feel free to ask questions or make suggestions--I'm by no means an expert at this.
Edited by Utah Smitty, April 22, 2014 - 07:00 AM.