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Simple CNC Carbon Cell Design

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#1 rdeason

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Posted 04 March 2024 - 02:12 PM

I'm looking for feedback on a cell design. For context I am new to ATM and have an engineering background.

 

I have access to a CNC that can cut carbon fiber sheets and I want to make a cell for a 10in x 1in mirror. The attached cut plan fits on a 260mm x 4mm square CF sheet. Support arms were located from PLOP output. I will have the CNC cut a 1mm groove across the plate/support arms shown in red, then set a 1.5 or 2 mm rod in the groove to serve as a fulcrum and secure support arm to rod to plate with silicone. The 3 tabs/ears on the main plate will house a 5/16in or 8mm bolt that will provide a mounting point for hold-down clip, and whiffle tree edge support. I think I can fit some whiffle tree arms into the cut waste. They will be set on a bearing that is held on the bolts with some nuts. Bolts will extent to angle brackets fixed to the tube and threaded through a compression spring for collimation adjustment. Hold-down clip head and wiffletree bearing bushings will be 3rd printed CF. Center hole is for cooling fan.

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#2 TOMDEY

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Posted 04 March 2024 - 02:23 PM

4mm sounds very thin --- expect it would be "springy", changing alignment with elevation and subject to vibration.    Tom



#3 rdeason

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Posted 04 March 2024 - 03:34 PM

I calculated ~0.02mm displacement for by 6.2 lb mirror when at azimuth. Not sure if that is going to mess up alignment. Could cut two of these and sandwich in some filler for more stiffness I suppose. 



#4 Bob4BVM

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Posted 04 March 2024 - 03:53 PM

I calculated ~0.02mm displacement for by 6.2 lb mirror when at azimuth. Not sure if that is going to mess up alignment. Could cut two of these and sandwich in some filler for more stiffness I suppose. 

Two of them sandwiched over a 3/4" pink insul. foam core would be very stiff.

1/8"or 3/16" plywood over the same core would probably be indistinguishable in stiffness from CF, without the electrolysis issues of mounting hardware on the CF.

 

The added thickness would allow you to flush-mount your fan in a pocket hole  for no protrusions; that would also make it easy to add an air filter over the fan intake, something overlooked by most builders.

Speaking of fans, consider integrating Ed's CVS system in your build, it covers all facets of air handling on a newt, far beyond just the cooling aspect:

 

https://www.cloudyni...or-a-fast-newt/

 

Good luck with your build !

Bob


Edited by Bob4BVM, 04 March 2024 - 04:00 PM.

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#5 designbydave

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Posted 04 March 2024 - 04:02 PM

I build something somewhat similar to this except I used 1.6mm carbon fiber sheet, bonded to a 3D Printed backbone. The backbone add stiffness as well as mounting locations for various hardware. Pictures about half way down the page here - https://www.cloudyni...bearings/page-3

 


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#6 CrazyPanda

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Posted 04 March 2024 - 05:21 PM

I build something somewhat similar to this except I used 1.6mm carbon fiber sheet, bonded to a 3D Printed backbone. The backbone add stiffness as well as mounting locations for various hardware. Pictures about half way down the page here - https://www.cloudyni...bearings/page-3

Yeah was going to say - a simple triangular "beam" that runs from collimation bolt to collimation bolt and roughly under the rockers, would stiffen this up without adding much weight.

 

Roughly like this, but with clearances for the bolts and rocker bars:

 

cell-beam.jpg

 

Each beam could be about 6mm thick and maybe 12mm wide. Epoxy them to the underside of the CF plate and it will be very stiff and light.


Edited by CrazyPanda, 04 March 2024 - 05:25 PM.



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