Saturday, October 16, 2021

This Week's Update on the 1 by 1 - Part 10

I concluded the last report by saying I was going to sand the journal to get it down to the final size, using the plastic sticks I had made to hold the sandpaper.  It had been filed down to a bit oversized and I used the plastic sticks with 220, 400 and 1000 grit to finish.  The final size of the journal varied from 0.3751 to 0.3752", or within 1/10,000 of an inch over its length.  Since I make the other side of that matching pair, the piston, that should end up being easy to live with.  

I didn't get as far as I wanted to because I continued to dump hours into troubleshooting the odd printer problems I spent days on last week, but I was able to make progress on the crankshaft. 

Once I had let it sit for a day, and measured it another few times, the next task is to take off the extra metal around that journal and prepare it for turning the rest of the bar down to its final size (also 0.375").  I did that on my bandsaw and didn't take any pictures until it was done and put back on the lathe.  Which is when I realized I had problems with the tooling.  

The problem?  Look at the top left of the picture where you'll see a kludge of a bolt, a wingnut, two washers (to increase diameter) and a hex nut.  That was because the system I bought from Little Machine Shop offered a bolt for that radial slot in the plate, but the bolt was at least 1/4 inch above the end of the rod it needed to be pushing.  I replaced that M8 (metric) bolt with a 5/16-18 bolt from my stash, going through a couple of lengths before I found one that work for the job.

While that worked, and I skinned back the side of the "cheek" holding the journal, I thought it felt flimsy enough that it was worth making a replacement tool.  My first thought was an L-shaped bar that would replace the hex nut and stick down far enough to push on that steel bar (the lathe dog's tail?) and be more secure.  

I had two rectangular (steel) bars that used to be the other half of that crankshaft blank, and cut down one to make the reinforcing piece in the middle of the shaft (visible just above the rounded journal above).  I tried to think of how that leftover piece could work and couldn't see a way.  So I took an inch off the end of a 3/4 x 1" wide steel bar I had and made the tool from that.  (The reinforcing block is there to keep the pressure on the ends of the crankshaft bar from bending it around the journal - it's epoxied in place while I work.)

There's not much adjustment range, you can see the adjustment slot just above the nut and washer, but it's about 1/2 or 5/8" long.  It feels more secure than the stacked washers.

So with that in place, it was time to start turning down the rectangular steel bar and making it round.  It's far from done, but I took this picture at a convenient stopping point yesterday. 

The top side of the bar here is flat from the saw cut.  I think the numbers tell me that it ends up circular before it reaches final size, but I have to admit I'm sweating it a little.  

Both ends are too long and will be cut to final size.  Both sides should have had enough extra material coming off the (manual) cut on the bandsaw.

Operations left to do:

  1. Turn this side, the long side, to final size and shape.  That will reduce the width of the rectangular block and put a raised ring on the left end of the bar ( .025" tall by 0.440" diameter).
  2. Cut length to final size
  3. Flip the shaft end for end and turn the other side to final diameter with the same detail ring on it.
  4. Cut other side to length. 
  5. Move to the mill and cut a 3/32 wide keyway on the short side. 
  6. Reduce the thickness and length of the rectangular side blocks to final sizes (currently .025" over)
  7. Drill and tap a 5-40 hole in the centers of both side blocks.


  1. The drive pin in the dog might be threaded in metric. If so then you could replace it with a longer bolt.

  2. After the first cut to length, and the crank is flipped end for end,will it go back to the chuck to hold it?
    I guess I don't see the reason to move the part- it is already between centers, usually the reason for center work is to ensure realignment if the part has to be removed then replaced for some other operation- but if the center is cut off one end of the part, that advantage is lost.

    Why not just turn it all in one go, both left and right sides?

    1. I was out of town all day yesterday, but I wanted to tell you that I'd been thinking of losing the center when I flip the part and I think I need to do it as you say. Turn both sides to the proper diameter and then go to the next steps.

      A practical issue is that I did this side first because I could easily use the tools I have and use the power feed on the lathe to cut this side to diameter. I may not have a cutter on hand to do the left side (in these views). Shouldn't be more than a few days delay, though.

  3. This is a wonderful blog. There is a ton of pictures of space craft and other interesting objects you show. Very nice to come and browse the older posts.
    Thanks a lot for all the work you put into this blog.
    Have a Merry Halloween this month.