Re: ATM reducing the weight

["A. Suykerbuyk" <asuyker@wxs.nl>]

Jan,

You can reduce the weight of the rockerbox.
The bottom has four sides, but it rests on the three teflon bearings.
The bearings push back against the bottom with a force equal to
the weight of the telescope. The same forces are pushing
downwards on the side panels.
As a result the bottom wants to twist, it is subjected to torsion.
I think it is not wise to cut material out of the bottom, you will
lose stiffness.
A closed box structure resists torsion very well.
You could construct the bottom out of two layers of thin plywood
(e.g. 8 mm). Between the two layers you could glue small strips
of wood, thickness 30 mm for instance. These wooden strips are
needed at the sides and on the circle, described by the teflon
bearings. This way the bottom wil be a closed box, the layers
are attached to each other by the wooden strips.
For the side panels 18 mm must be thick enough, even 12 mm will do.
You could glue small blocks of wood on the outside of the panels,
where you plan the support points for the teflon bearings.
This will give you more "surface" for the teflon.
As you wrote, you could cut out a part of the midsector too.

Adrie Suijkerbuijk.
-----Oorspronkelijk bericht-----
Van: Jan van Gastel <jhm.van.gastel@mdw.vu.nl>
Aan: ATM <atm@shore.net>
Datum: zaterdag 19 augustus 2000 12:18
Onderwerp: ATM reducing the weight


>
>The total weight of the scope I am building is 90 kilo: 198 lbs. Thats
>heavy. Heavier then the 150 lbs Kriege and Berry mention in their book. I
>followed their directions, so I don't know why mine is so much heavier. I
>have allready lowered the mirrorbox from 20.5 to 19.3 inches and the
>rockerbox from 12.2 to 11 inches, but this was only a 3 kilo (6.5 lbs)
>reduction. I can't lower the mirrorbox further without creating balance
>problems (which means adding weight). The weight of the mirror, mirrorbox,
>cell and tailgate together is 41.6 kilo (91.7 lbs), the sec. cage all in
>weights 4.9 kilo (10.1 lbs) and the trusses 6 (13.2 lbs).
>The only two things I can change a bit to reduce the weight are the
>trunnions (19.4 lbs) and the rockerbox (47.8 lbs).
>
>The trunnions are massive 1.4 inch thickness semi circles.
>I am thinkingof  cutting some wood out the semi circles, leaving the edges
>about 2 inches wide and two "bars" or "rays" running from the center of the
>flat topside to the circular side, also 2 inches wide. So I will cut out
>three parts of about equal size.
>
>As for the rockerbox I want to cut some wood out of the two (1.4 inch
thick)
>side panels. The support points for the bearings are about 70 degrees
apart,
>so I think I could cut out a substantial part from the midsector of the
side
>panels. The weight of the telescoop will be mostly directed to the ends of
>the sidepanels, because of the 70 degrees angle (I think).
>I am also thinking of cutting wood out of the (1.4 inch thick) bottom of
the
>rockerbox. I think I can cut away about 25% of the wood, leaving 3 inches
on
>the four sides and two "bars" in between from one side to the other, about
2
>inch wide, at equal distances from the front and back side and from each
>other.
>
>Does this make sense or will this weaken the construction to much. Or could
>I maybe cut more wood from the trunnions and the rocker?
>
>
>
>Jan van Gastel
>http://www.geocities.com/janvangastel/
>
>