These are all of the old posts from the first two years of the forum. They are locked.
Updated: 2005-03-28 by HoloM (the god)
Colin Kaminski

The other thread was overflowing so I though I would start a new one. John, What is the height variance in the cans you are finding?

John Klayer

I've been gone a few day and haven't done anything with the cans. I hope to measure a big bunch of them tonight and find the average and deviations. I'll be able then to join the ones with positive and negative deviations of the same magnitude.

John Klayer

I've been using sheets of 1/4 inch glass as platens to press the sheet metal skins flat while the epoxy sets. Is there any reason I couldn't just use the glass plates as the skins? I can buy the glass with the surface frosted so the epoxy will bond better and I could glue a sheet of steel to the top for my magnetic mounts. The equation that Colin posted shows that the deflection is inversely proportional to the skin thickness. 1/4 inch glass is 4 times thicker than the 16 GA sheet steel I am using now.

Colin Kaminski

"The equation that Colin posted shows that the deflection is inversely proportional to the skin thickness. 1/4 inch glass is 4 times thicker than the 16 GA sheet steel I am using now."

I don't have that equation handy and I am running out the door, but I am sure there is a paramater for youngs modulus of the skins and glass will not be as stiff as steel by a long shot. I'll look it up in a day or two if someone does not beat me to it.

John Klayer

Yep, Young's and thickness are both factors in the denominator of the first term. What I gain with the thicker material I lose due to the smaller Young's, unless I make the glass thicker.

Greg G

If you're not having enough fun with table manufacture, try fiberglass laminated to the steel..It's pretty stiff per pound and bonds well with epoxy.

For deeper pockets, Tap Plastic sells carbon fiber sheet which can be used for the same purpose but is a lot stiffer per pound.

John Klayer

I'm still working on the cans. I didn't expect the large variation in height that I'm measuring.

I found at least 2 honeycomb manufacturer's web pages that say that a doubling of the core thickness multiplies the stiffness of the panel by a factor of 7. This gives me more reason to continue on the 2 can heigh breadboard experiments.

John Klayer

I remember a "Saturday Night" skit that finished with Eddie Murphy saying somthing about George Washington Carver trying to play a record with a peanut.
Here I am trying to make holograms on top of a beer can.
I've been experimenting with ways to glue cans together- (sounds simple, try it). For the last few weeks I've been trying to add dampening. I tried varius foams with lousy results and decided on trying a comercial damping product-Dynamat. I'm putting small pieces at the top, bottom and sides of the cans.

Tony

I've been following this thread with interest, as I'm interested in making a 2x2' can table. I've collected the cans, now looking for sheet steel.

John- If you're results aren't what you expect, is it because the table is not stiff enough, or because it is vibrating? I suspect that because it is so much lighter than other table materials (concrete, stone) that even when placed on a spring like an inner tube, it still has a fairly high natural resonant frequency of vibration. This would allow vibrations from the floor to couple into the optical mounts, which could then be vibrating themselves.

see my post at:

http://www.network54.com/Forum/message? ... 1075343246

Part of the deal with these tables is to get the natural frequency down below the frequency of either the source vibrations, or the optical mounts.

I wonder if maybe the cans should be filled with sand?

Maybe you could try increasing the mass of the sprung part of the table, by adding a layer of patio blocks between the inner tube (or whatever) and the table, to see if this improves the stability.