6 replies to this topic

[epee]

I have an Orion XX12g and have recently modified the primary cell. I replaced the collimation springs with Belleville washers (thanks Starman1!), and while I had the mirror cell out, I replaced the cork pads with Nylon screwheads (I drilled and tapped the support points and threaded in 1/4" Nylon screws with 1/2" heads).

 

The new pads (screwheads) hold the mirror a little higher than the cork pads did, so now the mirror only rests on the nine supporting points in the middle 50% of the mirror's rear surface. Should I add support points farther out along the bottom edge, and if so, how many and in what locations?

 

The mirror is also supported/held along its circumference by three factory-supplied, Nylon-tipped, centering screws.

[Bob4BVM]

Sound like a new support geometry, so who knows.

Also a 9-point support is the worst for mirror distortion according to PLOP.

Are the 9 points fixed or are they floating ? If fixed, i doubt they are all touching the mirror back (3 points determine a plane)

A pic of the cell would sure help, we are just guess without seeing it.

Check out PLOP, it is a good tool for these questions.

[epee]

 

Points are floating in sets of 3 and are indicated by the red dots. The red arrows indicate the position of the centering/edge support screws. The yellow dots indicate the back of the mirror parimeter ring which also encompesses the back portion of the mirror's edge. It is the where the yellow dots are that is currently unsupported.

Edited by epee, 10 January 2025 - 06:00 PM.

[Dan Watt]

The red dots are all you want for support points. Whether they are in the optimal position/configuration is another question but if it star tests well like this then I'd sleep fine at night.

[TOMDEY]

The 9-point Whiffles appear to be nominal; the three radial screws that touch the side are deficient... but you can probably get away with that for such a small mirror if it is "full thickness". If the scope is pointing substantially upward, the side screws don't matter all that much. A sling would provide more gentle (less stressful) side support, but incorporating that might be more effort than it's worth.   Tom

[Pinbout]

Your picture looks fine 

 

so now the mirror only rests on the nine supporting points in the middle 50% of the mirror's rear surface

this is incorrectly stated and misleading, glad you posted the picture 

 

You’re good 

[Dale Eason]

It will have the same support points the original cell had so if it was good enough then this is too.