Re: [ATM] Plop Flop

["Jan van Gastel" <jhm.vangastel@wanadoo.nl>]

Why should you use a 27 point cell? A 18 points cell, or even a 12 point
cell is good enough for a 20 inch, one inch thickness mirror and much easier
to make.

Jan
http://home.wanadoo.nl/jhm.vangastel/Astronomy/
----- Original Message ----- 
From: "Jay Kirkland" <jaykirk2@compusmart.ab.ca>
To: <atm@atmlist.net>
Sent: Wednesday, June 30, 2004 8:42 PM
Subject: [ATM] Plop Flop


> Over the last 2 months, I think I've broken just about every drafting
> template/too/pencil/etc I have as I've grown more and more frustrated with
> trying to design a new mirror cell for my scope. The reason for my
> frustration: yes, I'm a non-mathematician trying to use Plop. You'd think
> that something with a GUI would give you a result that would be easy to
> translate. Ha! I have no idea what any of this stuff means. So I thought
> I'd take the easy way out and just plot the graphic full size and use
that.
> Which I did today. The graphic has the right angles, but the radii are all
> way off. So when I draft up the right radii on paper, the angles make
sense
> but then the parts dimensions that Plop gave me don't match a single
> measurable thing on the paper. Not even close. And where does part 4
> balance anyway? Is it the COG of the part? And if it isn't, does the COG
of
> the part matter at all?  The Plop user manual is of no use. If anything,
it
> adds to the confusion.
> Is there anyone out there who has actually successfully used Plop (man,
> you have my greatest admiration and respect) who wouldn't mind taking a
> crack at my cell design? I know it's asking a lot, but I'm absolutely
> stymied. Or alternatively, if you've designed a 27 point cell for a 20" of
> any thickness/focal length, my machining won't be to the millimeter
> tolerances required by Plop anyway so I think any non-Kriege/Berry cell
for
> a 20" of any fl would work just fine. But in case, my specs are 508mm
> diameter, 54mm thickness, 2895.6mm fl (yes, f5.7), and a 79mm obstruction.
> I've been trying for a 27 point support, and have used Monte Carlo and not
> (same results either way). All I need is simple Kriege/Berry-type #'s for
> the triangles: base/altitude or outside/short side/third side, balance
> point from vertex, and radius to balance point for the 3 (4) triangles. I
> mean, all this stuff that Plop spews out, why can't it also  give results
> in those terms for the rest of us??? AAAURGH!!!
> Huge thanks to anyone who can help!
>
> Had a full head of hair two months ago,
> Jay
>
>
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>

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