Last updated: 18 April 2010
Subject:	Delrin drive gear for ETX
Sent:	Friday, May 9, 2008 06:29:38
From:	Glenn Craig (
I emailed you a while ago trying to find a tiny Delrin (or Acetal, same
thing, different name) drive gear for an ETX90EC. In fact, I emailed
quite a few people, but nobody had a clue as to where to get these
gears. Since Meade won't help with an older model like the EC, but just
wanted me to "upgrade", I was stuck for a few frantic days, until I
found a site called that stocks these tiny metric gears.
They airmailed me 5 of them from Hong Kong and the replacement was
almost the same thing as the original. Diameter, pitch and number of
teeth in a somewhat sturdier version. The new gear had to be trimmed a
bit to fit (about 2mm too long) and opened up about .5mm to spin on the
shaft like the original, but I managed to get this telescope running
again, better than new. This time, though, I have adjusted the worm gear
tension so that it works much more freely without putting pressure on
the drive train.

Figured you might like to know where this impossible to find item might
be found.

-Glenn Criag

Subject:	re: replacement gears for ETX
Sent:	Monday, May 12, 2008 15:44:50
From:	Richard Seymour (
Your note to Mike about the  source of gears
was very interesting...
but to save thousands of readers a LOT of work,
-which- gear product number was the magic cookie?

(i realize that some gear trains may use other gears, 
but your discovery will be a good starting point).



Hi Richard-

I figured that this was more of a general gears info thing, but the one
that I replaced was the small single gear (called a spur gear, since it
rotates freely on its tiny shaft) that is the last one in the drive
train on the ETX90EC before the step up to the big gear that in turn
drives the worm in the Horizontal axis.

The Gizmoszone stock number for this gear is: GSO .5 -24-29

.5 is the metric size, 24 teeth (they are a standard pitch, I believe it
is 20 degrees), and 29 for 2.9mm, the hole in the gear.  2.9mm is a
press-fit for the Meade shaft, and you want a slip-fit, so you have to
ream it a bit so that it rotates easily on the shaft. I used a very
small phillips screwdriver that was the same size as the shaft until the
Delrin wore enough to slide easily onto the shaft. This gear is the
right diameter and pitch and tooth # for a direct replacement, but it is
a bit too long by a couple of millimeters. Both the original gear and
the replacement have a central boss that acts as a spacer to correctly
locate the gear, and the extra length of the boss on the replacement
gear is what gets trimmed.

(X-acto makes a very nice little plastic saw that does serious work and
can save you a lot of trouble in case you don't have a vast collection
of saws for every material.)

This little Acetal or Delrin gear only cost $2.10 but they have a
minimum order of $10- still cheap as dirt if it will save your

I wasn't looking for any compound gears, which is what most of the other
ones are in the drivetrain. If they don't have them, it might be
possible to splice one together from 2 separate gears, but that's a
problem I'm glad I didn't have to deal with.

The failed gear was in the stress-position, and its almost as if
somebody actually designed it to be easily replaceable.

Imagine that!

Glenn Craig


Thanks for the info... i hope the raw numbers will help folks
looking for compound gears, too.

Also, it's an excellent lesson in "how to -think- about specifying a gear"

have fun

Subject:	more replacement gear info
Sent:	Wednesday, May 14, 2008 20:18:18
From:	richard seymour (
I posted a link to your page in the Yahoo Roboscope group,
and one of their members (George Cushing) did some digging through
the gizmogear catalog seeking a good replacement for the typical
"compound" gears used in the various small Meade scopes.

His posting is at:
but, in short, theorizes that Gizmo's GCO.5-12/24-20
would probably be the closest fit.  You'd have to drill out
the center hole from its current 2.0mm to about 3.0mm...
for which a 1/8th inch drill (3.175mm) would be close enough.
(since it wants to spin freely on Meade's 2.8mm shaft).

The width of the gear teeth themselves is greater than Meade's,
but that should only help reduce breakage.

This is only a theoretical analysis done by comparing Meade's
gear (in hand) with the measured drawings at the site.

have fun

P.S. The comparison can be seen at:

(group membership may be required)

Subject:	Replacement Gear For #1247 focuser? [NEW!]
Sent:	Friday, April 16, 2010 17:18:39
From:	Mark Gatman (
Thanks for all your help Mike.  I found a replacement for the broken
gear, but not from a telescope shop.  The replacement for the small
pinion gear came from a radio control hobby shop.  If anyone else ever
has that problem, the pinion gear for the #1247 focuser is an 11 tooth,
48 pitch, 2 mm shaft, pinion for a micro motor.
Mark G

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