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# How to make a barn door tangent error “corrector”?

5 replies to this topic

### #1 whopperlover17

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Posted 20 January 2020 - 10:39 AM

I’ve read everywhere about this but can’t seem to find the way to make a physical corrector. I know I could do it in code but I’d rather have a physical solution.

Here’s what I’ve got so far: https://imgur.com/a/i8l9yE2

I know I can print that paper out to make the corrector, but I’d like to know the mathematical equation of the slope so I can 3D print it. Does anyone have experience or knowledge with this?

### #2 Couder

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Posted 20 January 2020 - 11:49 AM

I made one of these years ago. It uses a threaded rod, (without going out and looking) maybe 3/8-24. I made a stepper drive circuit and a used small stepper motor. Put a small gunscope on the hinge to point to the north pole. It does pretty good. If you want I can take pictures.

### #3 Stephen S.

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Posted 20 January 2020 - 12:51 PM

You can use a bent threaded rod to reduce tangent error

cheers,

Stephen

Edited by Stephen S., 20 January 2020 - 12:52 PM.

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### #4 whopperlover17

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Posted 20 January 2020 - 03:25 PM

I made one of these years ago. It uses a threaded rod, (without going out and looking) maybe 3/8-24. I made a stepper drive circuit and a used small stepper motor. Put a small gunscope on the hinge to point to the north pole. It does pretty good. If you want I can take pictures.

Thank you! I’ve also made one but my question is specifically about the tangent error and the correction piece. There’s not too much information on that.

### #5 StarmanDan

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Posted 20 January 2020 - 06:59 PM

Look up "double arm barn door mount" often called a Scotch mount too. The double arm design greatly reduces tangent error. But the curved bolt design pretty much eliminates it.

### #6 S.Boerner

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Posted 20 January 2020 - 07:06 PM

I remember the page and did build one.  Apparently it is now gone.

This may work for you...Wayback Machine...

https://web.archive....n-corrigee.html

and maybe

https://web.archive....lanche-fab.html

Edited by S.Boerner, 20 January 2020 - 07:19 PM.

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