Saturday, October 28, 2023

Repairing Annoying Broken Parts

 The Losmandy Polar Scope is used to align the mount pretty precisely on the North Celestial Pole, which is not quite Polaris.  (Close enough if you are lost and navigating at night.)  There is an illuminstor that screws into the scope; why this is optional eludes me; you could not make any practical use of the reticle for doing the alignment without it.

So a week ago, I removed the illuminator because I feared the battery might have gone bad.  This is unlikely, because it shuts off after two minutes of blinking the LED.  It came time to reinstall it, and I cross-threaded in its hole.

At first, I thought it was in too tight.  There is no good gripping surface so I used a vise grip.  Results predictable :

The illuminator screw shaft broke and was stuck in the hole.  When I tried removing the short piece still in the hole, I realized it was not tight, but cross-threaded.  Aluminum turning into aluminum makes this too easy.  Use of the vise grip also meant removing the anodized finish (which I will make presentable with flat black paint).

The 1-24 threaded part had a .130" hole for the light to reach the reticle.  I bought a screw extractor that was intended for .140" extraction, and slowly ran the power screwdriver, until it backed it out.  I was concerned the threads in the scope were damaged but a 10-24 tap went in smoothly for the first few threads.  (Too far and I wouild have hit the edge of the reticle.)

Every threaded hole is supposed to be countersunk to make it easier to get the screw started and avoid cross-threading.  The hole in the polar scope seemed to have a countersink a bit less than it needed, so I added a bit more countersink.

The illuminator costs $85; the scope $300.

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