Re: RE ATM: I had good luck making corrector cell out'a Delrin

[Ed Taychert <elt@irony.com>]

Thomas A Simmons wrote:

> [...]
>
>  1) Is the meniscus cored to support the diagonal? (If not,
> I have LOTS of follow on questions.)

Cored. There's a picture of the optics set at
http://www.irony.com/Ed/astro/6inMN/Mirror1.JPG


> 2) How are you supporting the meniscus in the Delrin? It appears as
> though you used (screwed?) clips, but don't want to assume this. Did
> you size the ID of the ring to avoid pinching?

Sizing is one thing; cutting it is another! I think it's easy to se up the
jig to 1/64 inch accuracy ... since a 1/4 inch bolt has a bit of play in a
1/4 inch bushing, you can fine tune the cut based on whether you
push the work towards the cutter or pull it away from it as you work.
This cell came out a little loose; it's shimmed with a few pieces of
black vinyl tape... this isn't precision machining, but it doesn't need to
be.

The meniscus is held down by UV-protected black nylon washers.
The cell is about 1/32 shallow so that that lens sticks out. The washers
are #8 washers and I use a #6 screw ... this allows the washer to be
offset and at an angle, one side on the cell and once side on the lens.
The screws are tightened until you see the nylon washer flex, then
backed off until the flex just disappears.

I put some Loctite in the screw hole to hold the screws. The Loctite
label says not to use it on plastic. I know know if Delrin is "plastic"
for purposes of their warning; nothing seems to have eaten through
anything yet ...

> 3) It appears that you are going the sealed tube route. True? comments?

You mean regarding tube currents and thermal equilibrium and stuff
like that? I have made provisions for mounting a small fan but that
doesn't go on until I see that I need it ... otherwise, sealed tubes help
keep the optics clean and that's a plus. (Sorry, no real wisdom to
share here ...)

> 4) I can't tell if you masked the outside of the following picture, or
> somehow blacked white Delrin. Could you fill me in?

Black was certainly first choice but the plastic place didn't have the
black Delrin I ordered ... so they _gave_ a 15 pound piece of white.
Thank you very much. Encouraged that it blackened with a Sharpie, I
masked and sprayed the inside parts of the cell with Krylon Ultra
Black. I'm surprised that the Delrin took the paint as well as it did ... I
don't think it's all that durable but it's only in no-wear areas.

Thanks for your feedback!

- Ed.