Re: [ATM] Mirror cell ramblings re: thin plate glass 3/4-inchx24-inch

["Bob May" <rmay@nethere.com>]

Discrete support points are located at well known and stable
points of the surface.  They do poke the surface up a bit but
that is the reason why there is the error answer in the program.
Put enough points in and you get a decently good surface.
With a continous support, you don't really know where the actual
support really is.  You're dealing with nanoinches (0.000000001")
and your machining efforts are only in the thenths of a
thhousandth of an inch (0.0001") which is a long distance away.
As a result, you get by placing the glass on the aluminum
actually only 3 points that are rigid that are really holding the
glass up.  Compare that against the seperate point support with
compliant points that will all press approximately (within the
abilities of the joints to equalize) the same amount on the
glass.  54 properly located points are a lot better than 3 random
points!
Now, why am I saying 3 random points?  This is because the only
stable support on a surface is 3 points.  4 rigid points will
have 3 points on the ground and the 4th point up from there
somewhere.  One of the standard jokes I've seen on TV and movies
is the guy trying to make a table not rock on a floor.  Next
thing you know, the table is 5" high and it still rocks!
Bob May

rmay at nethere.com
http: slash /nav.to slash bobmay
http: slash /bobmay dot astronomy.net

----- Original Message -----
From: Ted Cohen <tcohen@blakeglobal.com>
To: <atm@atmlist.net>
Sent: Monday, May 26, 2008 7:19 PM
Subject: Re: [ATM] Mirror cell ramblings re: thin plate glass
3/4-inchx24-inch


> I apologize if it seems that I don't appreciate the excellent
advice on this
> list, since I really do appreciate the feedback I've received.
>
> For those who feel strongly about using PLOP, I'd be interested
to know from
> a design perspective, why discrete support points are superior
to a
> continuous support system?
>
> _______________________________________________
> ATM mailing list http://www.atmlist.net/
>

_______________________________________________
ATM mailing list http://www.atmlist.net/