ETX TECHNICAL TIPS Last updated: 31 March 1999

ETX Base Modification

From: james chambers (ucjttjc@ucl.ac.uk)

Hallo ETX owners.

I purchased my scope recently, but was disappointed with the rotating fork turntable. I had 2mm vertical slack and the 3 pads were scuffed after a little use. I put a Quick cam on the 20mm eyepiece and looked at the motion of a brick wall some way off. Very erratic. So took the base and the selftapping screw out and had a look.

So this is what I've done, the 3 pads are NOT Fluon (PTFE) as I thought, but were a nylon or similar plastic, this gives a high co-efficient of friction. So with a new scalpel and a 1.5mm wide watchmakers screwdriver sharpened like a chisel I proceeded to dig a neat trench, about 16mm long and 2mm wide by 2mm deep.

I cut 3 tiny blocks from a small piece of scrap ptfe and made them a push fit in the trench, leaving 1 mm protruding. Re-assemble the turntable with a smear of light silicone grease on the touching parts, and tighten up the screw to just remove the vertical play.

It now rotated as if on ice, a tap on the lens barrel sends it round a quarter turn, and it now rotates with the RA motor just fine without jerks, even with a Pentax camera on top!

As an instrument maker the idea of the fork and turntable hanging by a self tapper to the base is a bit of a scare. Come on Meade, lets have a bit more quality control!

I could have taken the ETX back, but what the hell, I'd get another one just the same. In the final analysis fine optics- crap mechanics.

By the way if you can't find any Fluon, get an RF plug with Fluon inserts. This pure white stuff cold flows fine. Just put it between smooth jaws of a vice and flatten til you get the right thickness, then cut with sharp craft knife.

Jim Chambers. Haringey Astronomy Society. North London. England.

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