How To ~

Buck's Gears

By John Bartucci 
March 8, 2006


Buck's Gears at
http://www.petersonengineering.com/sky/index.htm

After reading the myriad of Internet posts discussing the shortcomings of the Meade LX200 gear trains, I posted a query with the Yahoo Groups LX-200 group about the Buck's Gears and proceeded to ignite a firestorm.  A few of the replies were wildly enthusiastic, most were cautiously positive, one in particular was extremely negative - the usual kinds of responses you get off the Internet.  I hesitated for several months, not wanting to actually take a working telescope apart.  But I did notice a few things which I thought needed attention:
 

  • The RA axis seemed to whine rather loudly when slewing - not abnormally, just annoying. 
  • The DEC clutch had to be locked very tightly or a load of cameras on the OTA would cause it to slip. 
  • The DEC knob only has about three threads grabbing the inner clutch - this looked ominous - I bought an aftermarket knob and found it had exactly the same length screw - so it was no help - it was better because it was knurled and easier to turn but it provided no more assurance that the threads wouldn't be stripped than the OEM knob.
The scope pointing accuracy had greatly improved with Rev 4.0l of the Autostar firmware, so pointing accuracy has always been good.  I want to do some PEC training so I decided I might as well go ahead and upgrade the gears and clutch before I go to the trouble of training.

I bought the gears and EZ-Clutch kit directly from Peterson Engineering - Pete's a nice guy to talk to and seems to know his business.  I had asked him for a copy of the installation instructions ahead of time so I could see what I was getting into (he provides all the tools you need, one of which was a drill bit - I wondered what I might be drilling - turned out to be nothing), but he told me he considered the actual adjustment procedure proprietary information - he did say he had a money-back guarantee (which I'm happy to report, I didn't have to take advantage of - no grammatical corrections, please).

It was obvious I would have to do the DEC gear installation and EZ-clutch installation at the same time, so I started with the DEC gears.  The instructions are reasonably clear - the photos could be better - and I highly recommend taking close-up photos of the mechanism prior to disassembly, just in case.  Pete warns about extremely fine wires and to be careful, etc...so I looked for some extremely fine wires.  Finding none, I presume he meant the 24 or 26 ga wires attached to the sensor on the worm mechanism (I was looking for maybe 40 ga wires...).  Anyway, removal of the motor, spur gears and worm was easy.  The new gears were easy to replace and getting 100% mesh turned out to be a snap.  They are a bit smaller in diameter - not too much and I didn't actually bother to measure them - but they do necessitate an adjustment to the worm.

Since the worm gear was also out, now was the time to clean it up and install the clutch material.  Cleaning the gears was, at best, messy.  Took me more time to clean the gears than to install the gears.  Once the gears were cleaned up and re-lubed, re-installation wasn't too bad - the spring which is used to position the motor and worm assembly is a pain to get into it's retaining cup - but once that's done, it's just a matter of tightening the two screws holding the motor to the fork.  My OEM adjustments were all decent so  I didn't have to do anything extra - like adding spacers, etc.

Pete recommends doing the installations in separate sessions - I concur.  The effort detailed above took about two and half hours.  The RA axis is easier but I decided to wait to tackle it since I had to dismount the scope, remove the finder, balance weights, etc.

It was warm in the garage last night, and cloudy, so I decided to install the Buck's Gears on the RA axis.  The instructions say to be very careful standing the OTA on end (to get at the underside of the base) so I measured the position of the secondary with respect to the end of the tube.  Turns out my secondary sticks OUT from the end of the tube (the instructions implied it was INSIDE and to be careful that the dust cover didn't bend inward and push on the secondary).  Naturally, mine was different - can't say why but it is what it is.

I also checked out Bob's Knobs and they imply "later" model LX200's have 6 screws on the secondary cover - three to hold it (I'm guessing) and three to collimate.  Mine has the "older" 3 screw version - which leads me to ask why Astronomics sold me an "old" model in November 2004.  And since the secondary sticks out so far anyway, ole Bob is not on my list of essential items...but I digress.

So, I proceed to follow the Next Best Approach described in Pete's instruction sheet, which is to just lay the scope on a soft surface and prop up the base (which means I'm on hands and knees trying to get at these immeasurably tiny screws).  I decided not to actually take the motor and worm assembly off the base (you can use a dental mirror to check gear mesh).  OEM gears didn't look bad - had all their teeth and gear mesh looked pretty good.  I did notice some axial play on the motor shaft, supposedly no big deal.  No axial play on the worm - another good thing.

Getting the OEM gears off was a challenge.  The VERY tiny setscrews were hard to get to - would have been easier if the base were in the right position or I had taken the drive assembly out - but after a little work, I managed to get them off.

The motor spur gear goes on first and it was straightforward.  The worm spur was a little more awkward due to the position of the base and the fact that it is behind the motor gear.  I found that, like the DEC axis, the steel gears were a bit smaller than the nylon (were talking mils here).  So I had to adjust the worm housing - not a big deal, again just awkward due to not having the assembly off the base.  A few tries at adjusting and voila! we had 100% mesh.  Greased the gears, buttoned it back up, put it  back on the tripod and powered it up. 

I talked to Pete about the gear dimensions and he said the tolerance on the nylon gears is 2.5 mils while for the stainless steel gears, the tolerance is 0.5mils, about what I observed.

First impressions: 

  • RA axis is definitely quieter with the steel gears 
  • DEC axis seems about the same as the before 
  • The EZ-Clutch seems to be a good investment - just a very light touch on the DEC knob and we're locked down. 
 Second impressions:

Finally got the scope out.  After a good Easy Alignment (using Sirius and Dubhe - not very far apart in RA), I found that I probably need to retrain the drives.  GoTos were still reasonably good - maybe 5 arc-minutes or so, but I think it was a bit better before.  Drive training should take care of it.  (As an aside, in a 9mm eyepiece, M31 and M42 were dead-on, Saturn and Mars were about 5 minutes off).  The drives do seem to run quieter and smoother, especially the RA drive.

So, for an 8" LX200, the gears are probably overkill but still a good investment.
 

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