Ad Astra Observatory

I have a new brass worm gear on the way. I hope that it will make my life better. In anticipation of its arrival, I decided to do some work on the mount.

I swapped the gearboxes between RA and Dec. The RA one has a stripped screw hole on one of the 2 motor mount holes, so I decided that the Dec one would work better.

In order to get the gearbox off, I bought a pair of Delrin-tipped pliers (not available at Home Depot, but I found one at the local esoteric tool store, Dale Hardware). They work good and don’t mar the threaded tube (why oh why did Scott Losmandy not use hex tube for the gearbox mounts?!)

As I started really paying attention to the coupling between the gearbox and the worm (which is in the form of a Oldham coupler), I noticed that the coupling is not straight– there is both a horizontal and vertical component to the deflection between the two objects (the gearbox output shaft and the worm gear).

The horizontal part of the deflection can be solved by the same process that meshes the worm gear and the worm wheel; just rotate (or shift) the worm across the worm plate.

The vertical part of the deflection is a little trickier — this involves changing the relative heights of the worm block and the gearbox. I attacked this problem in 2 ways.

First (and against my better judgement), I widened the mounting holes on the gearbox so that they are now oval instead of round. I did this with a hobby-size rattail file and mesured with calipers. This did not give anywhere near the necessary deflection (which is on the order of a couple of millimeters), so I also shimmed the worm bearing block using postage stamps. I am pretty close to the right height now, and there is something like 8 layers of postage stamps between the bearing block and the worm plate. Only the motor-side bearing block is shimmed — I need to measure the outer bearing block, and I began to run out of light. I assume that I’ll need about the same amount of shim on the outside, too.

I might need another layer of stamps as well; I’m not sure that I’m totally shimmed to the height I need. I will probably end up using the height adjustment in the gearbox to do the final adjustment (ie shim “too far” and then roll back a little).

The good news is that it would seem that my efforts paid off a little. At full speed, the ammeter now hardly twitches. At idle, it still wavers, but instead of wavering over ~0.04A (40mA), it’s now wavering over ~0.02A (20mA), and I’m not done yet! Nice.

So more shimming tomorrow, and hopefully the brass worm will be here tomorrow as well.

At the moment, it’s a 3-day moon, so we’re into the “maintenance” part of the month. That’s a good thing — at the moment, my mount has no Dec axis, and there are pieces and parts strewn everywhere. If I get this really working this week, then I’ll start tweaking the Dec axis next week. It needs cleaning and relubing.

TODO: I need to add some photos to the past few posts.