Re: Vixen Great Polaris periodic error and slow tracking #backlash


Mike Ahner
 
Edited

On Wed, Jul 15, 2020 at 08:31 PM, <biggs@...> wrote:
Regarding belts, are there ever issues with using GT2 belts with MXL gears?  I think my DEC axis is an MXL 60T gear.
Difficult finding the 60T GT2 gear with 6mm bore, and may have bought an MXL not noticing the difference.

On the RA the belt seems to bulge a little going over the 60T gear in 1 spot. 

Hi Biggs, I don't think you can mix gear & belt types successfully. The pitch is wrong so the belt won't fit correctly into the teeth and the bending radius will likely differ. I think that's what you're seeing with the bulge. Or perhaps the set screw isn't flush or below the teeth.

First, it's possible to buy a pulley with a 5mm bore and then bore it out on lathe or even a drill press. (although that's not as precise as a metal lathe). You can do this easily if you can go to a machine shop, or if you know a friend with a lathe, or you can go to a local maker shop or college metal shop.
Here is a 60T 5mm bore on Amazon, if you're in the US it can be delivered next day.

Second thought: I have a Vixen GP2 and I use a 3:1 ratio with 16T x 48T pulleys. It works very well and I can get slew speeds of about 2 or 3 d/s with a Vixen VMC200L mounted on it. 48T pulleys are possibly easier to find in 6 mm bore and I believe you'll not have any issues with 3:1. I don't remember where I bought my 48T pulleys, possibly from China but now so much is very slow shipping out there.

Another source but more expensive is from Stock Drive Products. Here's a 60T with 6 mm bore. It's flangeless which makes the outer diameter somewhat smaller and might allow it tuck in closer to the mount.

-Mike

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