Tag Archives: worm gear

New RA gear: looking good

The new RA worm block is installed, and I had time for a brief test.  Testing was cut short because of a sudden cloud-over, but looked pretty good.  Next clear night I have a bit more testing to do.

Recall that I was unable, with all previous adjustments, to get uncorrected Periodic Error consistently below about 7.5 arcseconds peak-peak.  For example:

With the new worm block in place, here is a first uncorrected PE data collection:

This is incredible – 1.5 arcseconds peak-peak, with no correction being applied.  More in a moment on why the curve is so jagged, but this is certainly great performance.

Then I loaded the above as a correction curve, and did another data collection with PEC turned on:

1 arcsecond, peak-to-peak.  The wild fluctuation that is just visible on the right edge of the graph is when the guide star was lost when the clouds suddenly moved in.  I deleted those data points to get this graph – but I guess I missed one.

Both of these – uncorrected and corrected – are, in fact, error smaller than the seeing fluctuation I have on a typical night.  I think that’s why the curves are jagged – that’s seeing bouncing around.

I was going to test this theory, when it suddenly clouded over.  So next clear night, I’ll do another set of runs (uncorrected and corrected) but with guiding exposures of 3 or 4 seconds.  The long exposures should “smear” seeing jitters out and, if I’m right about the effect of seeing, should produce smoother curves.  I’m looking forward to testing this.

I’d also like to do another data run just to convince myself that this isn’t “too good to be true”.  Did I do something wrong that resulted in this excellent performance?   I don’t think so, but I’d like to replicate.  Adding guiding to a PE of 1 arcsecond should produce a very stable image.  In fact, I’m interested in seeing how long an exposure I can use unguided – that would certainly be convenient.

Standby for another clear night.  Looking out the window, that’s not tonight.

Cleaned and Re-Greased DEC worm block

Following the instructions in Bisque’s video, I removed the Declination worm block, cleaned all the grease out of the drive gear and the worm gear, and re-greased.  Because of our winters, I used MolyKote 33, which is rated for much lower temperatures than the standard Lubriplate 103 that Bisque normally uses.

Some photos of the cleaning process, but I forgot to take photos of the re-greasing:

I then reassembled the Dec worm block into the mount and reset the cam stop and spring plungers to factor spec, and ran the Dec motor through 10 end-to-end exercise runs.  I ended up backing the spring plungers off 1/8-turn more than the lower end to eliminate a slight binding noise I could hear in the exercise.  (The manual specifies 2.5 to 3.5 turns back from bottom.  I ended up using 2-5/8 back from bottom.)

Next I’ll do the same procedure with the RA block.