A little bit of lathe, a little bit of mill, some drilling, some tapping... next thing you know you got a... thing.

December 21.

Spent way more time than I intended building a revised micrometer focusser for the refractor. Lathe and millwork is not fast, not for me anyway, and probably deserves a teamsisyphus page all its own.

I cut down a length of thick-walled aluminum tube, turned it on the lathe to get rid of some corrosion and just generally clean it up, finished the ends, milled a slot along one side, drilled and tapped a hole to cinch it down on the focus knob, and attached the micrometer holder using a hex nut trapped in a 3/8-inch hole.

The device still has its problems -- it needs more reach, for one thing -- but it will work as it is and it's clearly a nice refinement. Unlike in the JBWelded version, all the bits of this focus attachment are replaceable, so I can find ways to get more range, less reduction, different spacing, and so on.

This was the first use of the milling attachment on the Barnes lathe. It worked very smoothly with no excitement, no special pleading. Surprise!

The micrometer focuser has some awkfward aspects, but the 1/4-inch thumbscrew to clamp it to a 2-inch focusser knob should make it easy to set up in the dark. Whatever faults it may have, it does provide repeatable movement of the CCD across 25 thousands of an inch (measured directly at the drawtube with a caliper micrometer). More range can be got out of it in a couple of ways and I'll eventually pick one. There is some binding on outward motion that I don't fully understand. It's so dirt simple, how can there be any mysteries? It's a meta-mystery.

Wait! I know what the next version will look like! Stay tuned! Take it apart, snip, drill, bingo!

 

 

 

 

Doesn't it look a little like that symbol
by which the artist once again known
as Prince was once known?

 

 

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Text & Photos by David Cortner
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