Tag Archives: plungers

Tune-up journal 2: 1st worm adjustments

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Evening of July 15, it’s moderately clear.

Before dark, I finished re-connecting all the cables to the mount and related gear without doing any through-mount cabling.  Ran the mount and the rotator through their full ranges of motion several times to ensure nothing snags on anything.

Adjust worm tension plungers

My plan said to start with a new, small, TPoint run to verify polar alignment.  However, I decided to change that and do an initial check if the worm tension plungers are in-spec.  I thought that, if they aren’t, I should discontinue running the mount around with out-of-spec gears as soon as possible.  So, I checked the cam stop and worm spring plunger settings of both gear boxes.

Declination gearbox

I adjusted the cam stop to spec (1/8 turn out from bottomed-out).  It was already in more-or-less that position, so I don’t think it was out of spec.

Then I adjusted the 2 spring plungers.  The spec for these is “3 to 3.5 turns out from bottomed-out”.  They were a bit loose so, wanting them tighter, I set them to 3 – the tight end of the spec range.

Both of these adjustments can be done without removing the gearbox cover, so I haven’t yet inspected other components for tightness and tension – that will come later.

Right Ascension gearbox

Again, cam stop seemed OK but I re-adjusted it to spec just to be sure.

Spring tension plungers were quite a bit too tight.  They were about 1.5 turns out from bottom, so I readjusted them to 3, per the spec.

Quick re-check of periodic error

Continuing to deviate from my carefully thought-out plan, I couldn’t resist doing a new Periodic Error data gathering run to see if those adjustments had any effect.

Guiding reference plate solveSo, I carefully checked all the various settings that I have got wrong so many times:

  • Camera rotation close to zero (used a plate-solved image to confirm this);
  • PEC, TPoint, and ProTrack all off;
  • Autoguider set to do no corrections;
  • Pointed to a star near zero Declination, and just West of the Meridian.

PE data capture in-progressI gathered 1/2 hour of tracking data, which is about 8 worm rotations.  I used the main camera, binned 1×1.  During this data gathering, I noted that the guide star was showing up as 100% saturated.  This might be a problem – if it is over-saturating it may be difficult to calculate the FWHM radius.  This goes into the list of things to check next time.

7.7 arc-seconds error peak-to-peak, uncorrectedA quick analysis of the results shows it has certainly improved things.  Uncorrected periodic error is now at 7.7 arc-seconds peak-to-peak, down from 12.  That’s almost within spec (which is 7-7).

After I get back on-plan by checking polar alignment, I’ll do another test with a couple of minor additional changes:

  • Shorten exposure or use a dimmer guide star to get saturation below 100%; and
  • Loosen those RA plungers another 1/2 turn, to the loose end of the specified range.  If “looser” improved things, maybe “more looser” will improve them more.