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Modify Ebony Star?

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#1 briansalomon1

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Posted 06 July 2022 - 12:50 PM

I've been trying out some different ways to improve my telescope's motion and I've settled on just a tiny amount of mineral oil on the friction surfaces. It feels as good as bar soap to me and I think it's close to perfect except I can feel that some of the bumps in the ebony star are larger than others and the movement sort of "sticks" when it reaches them.

 

I think I recall someone mentioning putting a bevel on the edge of my teflon pads and I'll try that first.

 

It would be easy to make a sanding block the same radius as my rocker and use some #600 sand paper to make the ebony star bumps all about the same height, then buff the ebony star back to a glossy finish so it won't score the teflon.

 

I'd be interested to hear if anyone has tried this.



#2 kfiscus

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Posted 06 July 2022 - 12:59 PM

I always bevel my Teflon blocks with 45-degree edges.


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#3 Jon Isaacs

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Posted 06 July 2022 - 01:04 PM

I always bevel my Teflon blocks with 45-degree edges.

 

:waytogo:

 

I would not sand or modify the Ebony Star.  If the Teflon pads are large enough, there shouldn't be an issue. The Obsession UCs are somewhat different that standard classic designs in terms of the altitude bearings.  Which axis is giving you the problems?

 

Jon



#4 briansalomon1

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Posted 06 July 2022 - 01:35 PM

The vertical. It's noticeable tracking Saturn at 325X.

 

*edited* I just took a close look at all the teflon edges. They were definitely not bevelled. I put a nice 45 degree edge on everything and it will be interesting to see how the motion responds at high magnification.


Edited by briansalomon1, 06 July 2022 - 07:12 PM.


#5 Binojunky

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Posted 08 July 2022 - 11:14 AM

On all the Dobs I have owned a small amount of Turtle wax car polish (the liquid cream) put on the bottom board then buffed off when dry worked for me and lasted all season,Dave.


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#6 Starman1

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Posted 14 July 2022 - 09:40 AM

Careful: most lubes reduce the friction to too small a level and then the scope becomes super-sensitive to imbalance.

Soap might not be ideal (it picks up dirt a bit), but it only reduces friction a tad and eliminates the stiction that induces jerkiness in motion.

I tried wax, but it reduced friction WAY too much--I had to clean it off.

Azimuth motion is a bit different.  It can be a trace lighter touch than the altitude without any issues but be careful there, too.

If friction is too low, the scope will 'weather-vane' in the wind.

Ideally, you want both axes to have identical stiction and kinetic friction so that the scope can easily be moved in two axes with one hand on the UTA.

But not too little friction, either.

 

As for bumps in the formica, my own dob has FRP as the azimuth bearing material (larger bumps than Ebony Star formica), and, when moving the scope very slowly in azimuth, I can sometimes notice a particular bump in the material

takes a stronger-than-normal push to get over, and that is with beveled edge teflon pads.  Ebony Star has a better feel than FRP on a scope the size of my 12.5".  In a 30" scope, I doubt the bump size would be noticeable.

It's too bad Ebony Star was discontinued by Wilsonart.  I suppose there are similar or identical formicas that will work as well--there are some threads about that right here on CN.




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