First, thanks to all that are watching this build. I really appreciate and would love any feedback or suggestions for improvement for my methods.
So, I finished up the crankshaft over the last couple of days and I'll show the process in this post.
Here's the start. I sawed off and cleaned up the ends of a piece of 5/16" drill rod and had a small chuck of 1215 material left over from an earlier project.
I turned down the OD of the stock to 1.82" and drilled and reamed the center hole 5/16", the diameter of the drill rod. This will become the crank throw and I'm not following the original print at this point, but instead 'borrowed' Brian Rupnow's throw configuration that add a bit of counterweight to the part.
After parting the to-be throw off in the lathe, I moved over to the mill and cleaned up the surface that had been parted and drilled and reamed the crank pin hole. Again I deviated from the original print and made this 5/16". It's drilled .625" from the center hole as per the original print. I did this by offsetting in X via the DRO.
Here's the throw blank on the print, showing the 2 drilled and reamed holes and I also scratched a centerline on the throw just for reference. I wasn't sure I'd use it but it ended up being a handy reference for the steps to come.
I also quickly made a .031" thick washer from bearing bronze as the throw is flat as I didn't turn the 1/2" diameter feature on the throw. I''m parting off the washer here, after turning the OD and drilling the ID.
The bronze washer shown against the to-be throw, just checking it for size.
I struggled for some time on exactly how to create the angular feature to make the Brian Rupnow style throw but finally wrapped my head around a method and made a drawing with the required dimensions. My hang up seemed to be the offset required from the center hole when the part is rotated. Suddenly I got the necessary inspiration and figure out that what I needed was simply the distance from the center of the center hole to each side of the angle. And I needed to rotate about the center hole. So first I made an alignment pin for my rotary table, that fit the RT and was 5/16" above the table which then centered the throw on the RT. Shown in the alignment pin installed in the Vertex RT.
I put some waste stock under the throw and after carefully centering the RT under the spindle and setting the RT to zero degrees rotation, and zeroing the DRO, I moved in Y exactly .625" and using a piece of 5/16" brass rod, I rotated the throw until the brass rod slipped thru the hole. This should align the center hole and the pin hole exactly in the Y axis. Then I secured the clamps and locked the X mill table axis and returned the mill to 0/0.
Then I rotated the RT 20 degrees and moved in X .499" and locked the X axis and the RT. Then I started taking passes to cut the throw as indicated using only Y.
I repeated the same operation for the other side, except rotating the RT 20 degrees the opposite way and reclamping the part to avoid colliding with the clamps. Shown is just after both sides of the throw were finished.
The part shown against the print where you can see the critical .499" dimension that's the key to setting up the RT and mill to get the cut done as called out on the print.
I next made the crank pin. I didn't show any of those operations, just the completed part. This was mostly straightforward, although drilling the small oil hole made me pucker up a bit. I used a collet block to hold the part in the mill vise, found the center and edge and gently drilled the hole. You can see it, but it but the part is drilled and tapped 8-32 for the grease cup.
I"m going to borrow another of Brian Rupnow's suggestions, which is to add a starter hub to the end of the crankshaft. To that end, I milled a 1/8" keyway, 1" in length in the end of the shaft. Depth was .062" and I took it quite easy with the small EM, taking only about .015" depth per pass. I used a 2 flute HSS EM spinning fast.
And the shaft completed laid on top of the print.
Well, there was nothing left but to get to the part of the operation that I was dreading, silver brazing everything together. The reason I was nervous was that I wasn't super confident that the pin and shaft would be parallel with each other and perpendicular to the throw due to the short amount of engagement. I do know how to silver braze so I wasn't worried about that, just the process to get everything in the correct place. This is the silver braze and flux that I use. It's commonly available at the local welding supply houses here in Wichita, KS.
So, the process I decided on was to braze the shaft in place first. I ended up using a center punch to put 4 tiny dimples around the shaft where it fits in the throw. I did this since I wanted it to have some resistance to coming out of place while I was handling it. I generously applied flux to the shaft and hole in the throw and pressed the parts together using my bench vise. I applied heat with an oxy/acetylene rig setup with a small brazing tip. This pix show the part after brazing and I did manage to apply a bit too my braze material as is my usual and terrible habit!
This is the backside of the part showing that the braze material wicked thru the shaft/throw interface very well, so the joint should be good, IMO.
I put the assembly in the lathe with a collet setup and lightly skimmed the face of the throw, both to clean up the excess brazing material but also make sure that the face of the throw as perpendicular to the shaft. My theory being that when I press the pin in, it wil be in the correct alignment with the shaft and the throw, strong emphasis on 'theory'.
I didn't show the brazing operation, but I pressed the pin into place after applying flux and then heating and applying the silver braze as I did on the shaft. Shown in the pix is cleaning up the backside of the throw after brazing the pin into place.
A closeup of the backside of the throw, shaft, nad pin.
And of the front side of the crankshaft assembly.
Since I was terrified that everything wouldn't be aligned well enough to rotate, I quickly assembled the parts I've made to date on the frame and base and by some miracle, they all went together and they actually rotate!!
So, I'm calling the crankshaft a success!
Next I'll move to the flywheel to get it finished off so that i can fit it and the cam drive gear to the overall assembly.
Again I appreciate everyone that's watching this project and sincerely do appreciate comments and suggestions for improvements!
Enjoy!
