RE: [ATM] Use of bearings in (static) mirror cells

[Ken Hunter <atm_ken_hunter@yahoo.com>]

I imagine a Plop or otherwise designed cell glued with
RTV as is normal but with additional support installed
as follows.

Perforate the mirror and add a counterweight that
applies side (locating) pressure to the mirror at the
COG by virtue of a gimballed pivot in front of the
cell face with the counterweight hanging behind. The
lateral force (referenced to the glass) would be
applied through a rubber O'Ring at the COG and
"INSIDE" the mirror itself to eliminate the distorting
forces from the point contacts being offset from the
COG.

If anyone has access to a "higher quality" audio
turntable" (PRE-CD ERA) you can get an idea of the
design where the GYMBALS and counterweight are
adjustable for fine tuning the effect on the glass.
Imagine the GYMBALS as part of the cell and the tone
arm the link to the mirror.

The worst aspect of this is the weight needed to
counterbalance the mirror. This could easily approach
the weight of the glass or require a long lever arm to
gain the mechanical advantage needed for lighter
counterweights. I don't build portable scopes so I
don't see a problem with this. You portable scope guys
might.

I can whip up a drawing and post it on the ATM_FREE
Group if interested.

Ken Hunter

--- Jerry <wa4guu@verizon.net> wrote:
> Hello Arjan
> 
> Yep. I agree. I just can't support not using edge
> supports. I can see
> counterbalancing but I'm not even sure that is not
> just a marginal "illusion
> solution".
> 
> Personally I have never thought of gluing in lieu of
> lateral edge supports
> as being reasonable except in small thick mirror
> maybe 6" or smaller. But
> now I'm sure that is an even worse idea than I had
> previously thought. 
> 
> I think with edge support gluing would be plausible
> and maybe with the
> stictionless flex-bearing very good. But if just for
> keeping the mirror from
> falling out of the cell gluing a few tethers would
> work just as well and not
> have to alter the mechanics of the cell.
> 
> This has been a good thought exercise for me. I
> think I have a good cell
> design for a 16"X1" blank I have.
> 
> Arjan... The 6 point cell optimized by plop.....  I
> can't help but notice
> that if this is the optimum it is quite interesting
> that the fulcrums for
> the cantilevers are located virtually perfectly at
> 50% radius.
> 
> 
> Jerry
> 
> 
>    
> 
> -----Original Message-----
> From: Arjan te Marvelde 
> Jerry,
> 
> Of course you can compensate the torque with
> counterweights, but does
> anybody actually do this? Side support is probably
> easier to build, and
> requires less space/weight.
> 
> AtM
> 
> ----- Original Message ----- 
> From: "Jerry" <wa4guu@verizon.net>
> To: "'Arjan te Marvelde'"
> <arjan.te.marvelde@hetnet.nl>; <atm@atmlist.net>
> Sent: Saturday, 23 April, 2005 4:52
> Subject: RE: [ATM] Use of bearings in (static)
> mirror cells
> 
> 
> Hello Arjan,
> 
> 
> Referring to
>
http://home.hetnet.nl/~artm/atm/articles/deformation.html
> 
> This raises several questions in my mind. I will ask
> the first as the others
> dependent on my understanding of the answer.
> 
> 
> Why assume that the cantilever as viewed in the
> vertical position (as in
> Fig. 1B) is asymmetric in mass to the left and right
> of the fulcrum? Can't
> we balance that so that it imparts no force to the
> glass that is a result of
> its attitude from vertical all the way to
> horizontal?
> Instead of shaping it like  ]  shape it like  I  .
> If Balanced I do not see how it imparts any
> deformation to the mirror as a
> result of tilt and the fulcrum being some distance
> from the glass.
> 
> 
> Jerry
> 
> 
> 
> -----Original Message-----
> From: Arjan te Marvelde
> 
> Hello Jerry,
> 
> 
> These numbers can be compared with an analysis of
> deformation of a mirror
> glued to its cell:
>
http://home.hetnet.nl/~artm/atm/articles/deformation.html
> As you will see, the force couple caused by glueing
> the mirror to the cell
> is way more than this 3.6 gr caused by stiction:
> 120gr when pointing at horizon,
> 60gr when pointing at 60deg elevation,
> 0gr when pointing at zenith.
> 
> 
> 
> 
> 
> 
> _______________________________________________
> ATM mailing list http://www.atmlist.net/
> 

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