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Mr Magoo
Carpal Tunnel
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Reged: 11/05/05

Loc: Franklin, Indiana
Mirror Cell
      #5616962 - 01/11/13 10:13 AM

I was wondering if someone out there has the PLOP numbers for a 13.1", f/4.5, 6 point mirror cell. Secondary size is a 3.1". For one reason or another I've had the worst time trying to use PLOP and was hoping for a bailout by some kind soul.

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Arjan
super member


Reged: 01/21/09

Loc: Netherlands
Re: Mirror Cell new [Re: Mr Magoo]
      #5616980 - 01/11/13 10:27 AM

Supports are at about 60% radius for 6 points. In case of 3 points this is about 40%.
Thickness doesn't matter too much, but if it is 1.5" or so you might get away with only 3 point cell.


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Pinbout
Postmaster
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Reged: 02/22/10

Loc: nj
Re: Mirror Cell new [Re: Mr Magoo]
      #5617024 - 01/11/13 10:53 AM

you didn't state how thick your mirror is.

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Mr Magoo
Carpal Tunnel
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Reged: 11/05/05

Loc: Franklin, Indiana
Re: Mirror Cell new [Re: Pinbout]
      #5617037 - 01/11/13 11:01 AM

Mirror is 1.1" thick.

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Pinbout
Postmaster
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Reged: 02/22/10

Loc: nj
Re: Mirror Cell new [Re: Mr Magoo]
      #5617070 - 01/11/13 11:17 AM Attachment (33 downloads)

here's what I get. also attached is a pdf that you can print at kinkos for full size.



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Mr Magoo
Carpal Tunnel
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Reged: 11/05/05

Loc: Franklin, Indiana
Re: Mirror Cell new [Re: Pinbout]
      #5617225 - 01/11/13 12:48 PM

Thanks Danny! Well, I guess I didn't have PLOP too messed up, because this is close to what I got on one of my tries. I need to keep messing with it.

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Starman1
Vendor (EyepiecesEtc.com)
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Reged: 06/24/03

Loc: Los Angeles
Re: Mirror Cell new [Re: Mr Magoo]
      #5617759 - 01/11/13 06:40 PM

At 1.1" thick, I would recommend an 18-point cell. A 9-point cell would be OK. Smaller numbers of support points result in a lot of deformation of the mirror surface.
My 12.5" is 1.25" thick and I use 18 points.


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Pinbout
Postmaster
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Reged: 02/22/10

Loc: nj
Re: Mirror Cell new [Re: Starman1]
      #5617797 - 01/11/13 07:00 PM Attachment (18 downloads)

here's a 9 vs 6...

which one is which?

but 18 did really get better than either of these.


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piaras
professor emeritus


Reged: 01/26/09

Loc: Niagara Region
Re: Mirror Cell new [Re: Pinbout]
      #5617981 - 01/11/13 08:42 PM

I was not the OP but I did a comparison for 6, 9, and 18 point cells using Plop for my Coulter Odyssey 1 (5/8" thick) vs a ZOC that is near completion. See the topic here. Another Plop question

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Mr Magoo
Carpal Tunnel
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Reged: 11/05/05

Loc: Franklin, Indiana
Re: Mirror Cell new [Re: Pinbout]
      #5618127 - 01/11/13 10:25 PM

I am certainly open to suggestions or outright help. Like I said, PLOP is not my thing. I'm a sheet metal worker/welder. I can build anything given the plans, but this engineering is stumping me a bit. It was my understanding from other posts I had read in the past that a 6 point was better for this size than a 9 or an 18. I know that Dennis at DobStuff suggests a 9 point for the old Coulter mirror scopes like mine. Is the 9 the one on the left? Seems like it because the right one has 6 clearly defined spots. I'm assuming that the big red donut hole in the center of the right one is not good. I'm building this as an experiment to replace the old tailgate on my blue tube Coulter. If it works out well like I plan, I'm making another for a friend.

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Pinbout
Postmaster
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Reged: 02/22/10

Loc: nj
Re: Mirror Cell new [Re: Mr Magoo]
      #5618194 - 01/11/13 11:05 PM Attachment (16 downloads)

Quote:

Is the 9 the one on the left? Seems like it because the right one has 6 clearly defined spots.




yes, the 18 is so much better but the 6 is still to the -6exp. where the 9 is to the -5exp.


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StarDusty
sage


Reged: 10/02/07

Loc: Parsippany, NJ
Re: Mirror Cell new [Re: Pinbout]
      #5618241 - 01/11/13 11:51 PM

PLOP is a great program. I used it for both 13" and 16" home made cells. I used 6 points on both. As I recall the 13" mirror was the same thickness as yours is.

You can see these at:

13" Dob:

http://www.clearskyobserver.com/index.php/20-telescopemaking/14-13-truss-tele...

and

16" Dob:

http://www.clearskyobserver.com/index.php/20-telescopemaking/7-16dob


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Mr Magoo
Carpal Tunnel
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Reged: 11/05/05

Loc: Franklin, Indiana
Re: Mirror Cell new [Re: Pinbout]
      #5618255 - 01/11/13 11:59 PM

Yes, that looks excellent even to my uneducated eye. I will have to try and see if I can run the numbers for an 18 point in PLOP and get it correct. Thank you so much for everyones help so far.

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Pinbout
Postmaster
*****

Reged: 02/22/10

Loc: nj
Re: Mirror Cell new [Re: Mr Magoo]
      #5618278 - 01/12/13 12:17 AM Attachment (27 downloads)

see if this will do ya...

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mark cowan
Vendor (Veritas Optics)
*****

Reged: 06/03/05

Loc: salem, OR
Re: Mirror Cell new [Re: Pinbout]
      #5618403 - 01/12/13 02:56 AM

Quote:

here's a 9 vs 6...

which one is which?

but 18 did really get better than either of these.




The 6-point is quite adequate at 2nm RMS surface.

Best,
Mark


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starman345
Wait, I'm Thinking
*****

Reged: 07/06/10

Loc: New Brunswick, Canada
Re: Mirror Cell new [Re: mark cowan]
      #5618586 - 01/12/13 08:23 AM

Ken, take a look here

It helped me a lot to understand what the numbers mean.


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Arjan
super member


Reged: 01/21/09

Loc: Netherlands
Re: Mirror Cell new [Re: starman345]
      #5618729 - 01/12/13 10:14 AM

For this mirror 6 points is really sufficient.

You can theoretically get a better one with 9 points as long as you put the supports in one ring. However, the 9 and 18 points cells are harder to make and require lower tolerance. It is hard to screw-up a 6 point cell on the other hand.


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Mr Magoo
Carpal Tunnel
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Reged: 11/05/05

Loc: Franklin, Indiana
Re: Mirror Cell new [Re: starman345]
      #5618797 - 01/12/13 10:54 AM

Thanks Brian. That is one of several PLOP threads I have toggled.

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Mr Magoo
Carpal Tunnel
*****

Reged: 11/05/05

Loc: Franklin, Indiana
Re: Mirror Cell new [Re: Pinbout]
      #5618802 - 01/12/13 10:57 AM

That is really great Danny. I can't thank you enough for doing that. I'm looking at what I want to do. This will be a temporary home for these optics until I can find the time someday to build a more portable, user friendly truss design scope around them. I will probably try the 18 for the trusser and may still now. I have a laser to cut my parts, so I can be very precise.

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Pinbout
Postmaster
*****

Reged: 02/22/10

Loc: nj
Re: Mirror Cell new [Re: Mr Magoo]
      #5618879 - 01/12/13 11:35 AM Attachment (22 downloads)

I guess I'm avoiding doing the dishes so I had some avoidance time... all parts from mcmaster's



if you got a laser you can download this txt file [right click attachments and save target as] and relable the .txt extension to .dwg and have the autocad file for the laser.

Edited by Pinbout (01/12/13 11:36 AM)


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