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Mistakes I Have Made

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#1 Claytoncramer

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Posted 29 September 2022 - 08:22 AM

I rebuilt a 17.5" f/4.5 Dob into a Newtonian on a Celestron CI-700.  Listen carefully.  You can hear it screaming.  Yes, that is a semi-fiberglass tube.  Sonotube wrapped in layers of fiberglass cloth and epoxy, inside and out.

 

And this is the mirror cell I made.

 

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Edited by Claytoncramer, 29 September 2022 - 08:25 AM.

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#2 NinePlanets

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Posted 29 September 2022 - 08:34 AM

I can hear it!  smile.gif

 

My mistakes tend in the other direction. They groan horribly...

 

 

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Edited by NinePlanets, 29 September 2022 - 08:39 AM.

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#3 rhaskins

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Posted 29 September 2022 - 06:12 PM

Mr. Nine: how many moving parts on that monster?

Rick

#4 NinePlanets

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Posted 29 September 2022 - 06:41 PM

I wouldn't know where to start counting (do balls in the bearing races count?). The beast is currently in dozens of pieces in a corner of the basement floor. Not sure if I'll resurrect it this time or not.

 

What is the price per pound of scrap steel these days?

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Edited by NinePlanets, 29 September 2022 - 06:49 PM.


#5 luxo II

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Posted 30 September 2022 - 11:34 PM

Nice, but it would have been better with helical gears...



#6 NinePlanets

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Posted 01 October 2022 - 10:37 AM

Well, yeah, it has some gears... This project actually started as a requirement in a machine trades course to make a spur gear. Rather than make a useless aluminum spur gear I got permission to make a steel anti-backlash gear for grading.

 

An anti-backlash gear is actually two identical gears, one riding on the same hub as the other, fitted with a spring (or in this case, 3 springs) to squeeze the gear's teeth together on the pinion gear that drives it. This eliminates any backlash in the mesh.

 

So, the heart of the R.A. drive is this ~11-inch diameter, 144-tooth anti-backlash gear, which is fitted with three strong springs to put the bite on two separate pinions, mounted on opposite sides of the polar shaft.

 

Each of the two pinions are driven by 120-tooth worm gears, which in turn are driven by right-angle gear sets, which in turn are driven by reduction gears affixed to a pair of synchronous AC motors.

 

So in effect, backlash is eliminated and periodic error is split between two separate drive trains. The beast was permanently mounted outdoors and served faithfully for many years, solid as a rock with any scope you cared to put on it, but it is the very antithesis of portability or efficient use of materials.

 

A huge mistake, but a great learning experience.

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Edited by NinePlanets, 01 October 2022 - 10:44 AM.

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#7 NinePlanets

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Posted 01 October 2022 - 10:45 AM

I suppose this should be moved to the ATM forum?



#8 NinePlanets

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Posted 01 October 2022 - 10:50 AM

BTW, the Dec axis is driven by a 440-tooth worm wheel. So yeah, there are gears.

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Edited by NinePlanets, 01 October 2022 - 10:50 AM.



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