Thursday, October 24, 2019

Let's Get Small

I have been trying to make a 1/4"-20, 3/8" square bushing for the telescope rebuild.  The first attempt failed because getting the 3/8" part square enough to get a reasonably square hole was very hard.  Threading just went off the edge.

The Sherline mill vise has always been the most disappointing part of their mill.  The clamp is a socket head screw into a ball that engages a progressive set of notches.  The theory is that clamping force is more down than in.  In practice, it is not very effective at clamping.  Worse, it is 2" of workspace capacity.

So, I pulled out Frankenvise, a drill press vise that I squared up several years ago.  It has plenty of clamping force and can take a 4" workpiece.  But I have never found parallels usable on either.  They fall down on thee Sherline before I can get the workpiece in place, and because it is aluminum, the magnetic strips one of you sent won't stick.  They stick to Frankenvise's jaws, but there is a gap at the bottom of the vise that prevents the parallels from working.  I will mill that space between the jaws flat to solve that problem.  In the meantime, trying to get the right combination of square blocks 3/8" wide or less tall enough to expose the right amount of acetal is very hard.  The last attempt sliced through one side of the threaded hole. Still waiting on fuses, so I have a one axis CNC mill right now, on which I am learning a lot about mill rates.

Perhaps irrelevant.  The spider maker can make the right size bushing for $19.  Sold!

Soon it will be dark enough for astrophotography.

In retrospect, I should have used a 3/8" diameter rod, drilled through on the lathe.  I would have likely needed to turn it down anyway to fit so I could have still gotten a press fit.

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