Weekly Update on the 1 by 1 - Part 12

As I mentioned yesterday, I've completed the crankshaft for the 1 by 1.  A little "pose for pictures" time.

Those counterweights, the first pieces I made, are just sitting where they'll be mounted.  I don't have any #5-40 hardware to mount them, but I do have a tap that I bought while building my Duclos flame eater engine so I tapped the holes as designed.  A smaller #4-40 screw goes into the hole, showing they line up.

Before this, I had to turn both sides to the proper diameter (rough turning here), cut to length and trim the rectangular sections of the crank to proper size (0.500 by 1.000).  I've come to call those rectangular pieces the crankshaft cheeks although they say the word can be webs, cheeks or arms.  Cutting to diameter and length were fiddly operations done slowly and gingerly, and then it was time to try to cut the major remaining feature, a keyway exactly on the top of the long side (left in the above shot).  

The tricky part was how to support the work and hold it so that it would take the cutting forces, while being perfectly parallel to the mill's table.  I first thought of just putting mill parallels (something like this) under the shaft while putting the base of the left crankshaft cheek on the reference surface of the vise.

That was a dopey idea.  The parallels don't hold position well enough and there's nothing resisting movement to the side from cutting forces.  After some thought, I decided to make a fixture that uses the exact dimensions of the cheek that would hold the shaft the same distance off the vise base as the one highlighted here.  This was an hour or so of work on a piece of scrap aluminum I had.  

The tool is on the left, and I made it so that the shaft either slides in from the end or snaps into place.  The setup was to put the new fixture on the left base of the vise and the left cheek on the right base.  Then I verify X, Y and Z are zeroed properly, and cut left to right.  I used a 1/16" wide end mill spinning as fast as my mill can spin it (~2200 RPM), but still only cutting at 1 Inch Per Minute (IPM) in three .018" deep passes. The keyway, though, needs to be 3/32 wide, which is 1/32 wider than 1/16, or 1/64 (.0156") on each side of the keyway.  So I moved the mill table 1/64 on both sides and cut two full vertical depth, .0156 off-the-side passes.  That didn't quite fit a 3/32 drill bit that I tried, so I moved both edges out another .0005" (.001" total width change) and that fit fine. 

The keyway is more visible in this view than the top picture. 

Once that was cut, it was pretty routine to tap the two #5-40 holes you can see, and it's done.  Actually, it's not quite done.  There's still some epoxy on the bearing surface that the piston rides on, from when I epoxied a piece into the gap opposite the journal bearing, between the crankshaft cheeks.  That's to keep the pressure from the lathe centering points from bending the shaft.  I think I can soak that in acetone for a while and then peel it off.

The crankshaft is bound for the finished parts box.  Lots of new things learned, one damaged (but recovering well) finger, and surprisingly little (zero) scrap.  There are 47 pdf files in the document package and it seems that that I've completed four of them.  By ordering a raw flywheel casting made of cast iron, I've eliminated at least one drawing but added things I'll need to either figure out separately, resurrect out of that eliminated drawing, or something.  

First, though, I need to give my big lathe a tuneup.  A few times while working this part, it seemed like it wasn't quite right at a few things.

Speaking of the damaged finger, I saw the surgeon today for a followup and she discharged me.  No followup needed - it's coming along as best as could be hoped for.  She said something like, "if you want, drop by in about a year and show us how it ended up."