[ATM] Best locations for 4-Pt. Wiffletree edge support PLS

[polaraligned <polaraligned@optonline.net>]

I am with you Bob.  If you get an answer please let me know.
I have to mount a 32" f/3.6, 2.25" edge thickness mirror in an
eq mount.  "Center the support bars at 45 degrees off the vertical
axis" is the only answer I have been able to get in the past, aside from
"see what the pros do".  I already have designed my edge support and
I am comfortable with it.  I used 3 bars each with universally pivoting
Teflon pads on each end.  The pivot for each bar is spaced 120 degrees
around the mirror.  If you can read AutoCad drawings I would be glad
to send you my drawing.
John Hudek told me the key is to make the pads fit the curve of the
mirror edge as closely as possible.  He did not provide specific
geometry other than saying put bars at "about 1/3 points"
I believe I got the 3 bar edge support idea from a picture of a
commercial scope I saw online somewhere, even though there
was no specifics as to pad locations.  You just may have to try
this out and make the adjustment if you have a problem.
You are right that the list is very knowledgeable, but then again
they can argue day and night how best to support using a sling.
There may be no right answer unless you can find someone who
is using this type of edge support with success.  The guy who
told me the "key" is to separate the supports by 45 degrees was
using similar edge support successfully on his mirror at Stellefane.
It certainly does not mean you will not find success with a different
geometry.
BTW, interested in what type of mount you are using?
What is the focal ratio?  Will this scope be used visually or
imaging or both?


Best luck,
Scott



> From: "Bob Drew" <gofast3@hotmail.com>
> Subject: [ATM] Best locations for 4-Pt. Wiffletree edge support PLS.
> To: atm@atmlist.net
> Message-ID: <BAY120-F33A5B50C922BFB28EFC360F4E90@phx.gbl>
> Content-Type: text/plain; format=flowed
>
> So what ARE the best specs for a 4-point wiffletree mirror lower edge 
> mount?
>   Ie. Two pivoting arms, each holding 2 edge support points.  What's the
> current,  very  latest  conclusion for this design?  (27 point [plop]
> triangles already done.)
>
> The F4 primary is 32" diameter, 3" thick, 200 lbs,  modulus 6760. 
> Although
> that shouldn't affect the geometry.
>
> This is my first post to what is a very talented, knowledgeable List.
> Returning to atm after a few years. This scope is my dream project and 
> I'll
> be seeking your latest, up to date views in a number of areas. I had
> designed and built a West-epoxied wood and aluminum break down 18" f4.3
> scope for a club, and then my personal portable aluminum Serrurier truss 
> 20"
> F4.
>
> 1. At what angle from center/vertical should the 2 inner and 2 outer
> support points be?
>
> 2. Should the pivot point of the support arms be centered between
> these 2 points, to self-locate, or could there be a reason to design
> it to be asymetrical?
>
> 3. Is there some definitive authoritative source setting out where
> the 4 points should be? (not anecdotal stuff.) Since I am
> trigonometry-challenged - am just looking for the final angles.
>
> The saw is ready to hit the metal, but want to avoid costly re-dos. So any
> advice or references now would be really appreciated!
>
> Bob
> 

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