bonding steel to slate?

I obtained a free piece of slate, about 2.75' x 4.5' x 1" thick from my local pool table dealer (the slates come in matched sets of 3, precision
ground to .001, and sometimes one breaks leaving the other two as garbage). I had the idea of using it has a cheap optical table for some random laser experiments I do. I would like to fasten a piece of magnetic stainless steel to the slate so I can use the cheap magnetic bases like you get at MSC with my optical fixtures.
What thickness of stainless steel plate should I use and how should I fastenen it to the slate? I was toying with the idea of using liquid nails or something and a boatload of concrete bags on top of the plate as the glue sets, but perhaps using screws would be better? I had the impression that if I used screws at say every 6 inches square I would get localized warpage in the steel plate.
Suggestions?
Thanks,
Rick
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Rick wrote:

Wouldn't the glue and the cheap base negate the precision?
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Rick wrote: I would like to fasten a piece of magnetic stainless steel to the slate so I can use the cheap magnetic bases like you get at MSC with my optical fixtures.(clip) ^^^^^^^^^^^ Your idea might work, but it doesn't sound easy, and if it doesn't, you will be way behind where you are now. How about using a vacuum pump to hold down some cup-shaped bases? One pump will work on any number of bases. Each one could be connected through a three-way valve, so they can be individually moved. I use a vaccuum chuck on my wood lathe, and it doesn't take much of a vacuum to provide firm support
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Leo Lichtman wrote:

That sounds like a much better plan.
I've done a lot of gluing in my time and the idea of getting a glue film of constant thickness (within a few tenths) over an area that large scares me. I wouldn't even consider doing it with anything but a very low viscosity epoxy with no filler.
Also, 300 series stainless steels are basically non-magnetic and a sheet of 400 series that size (if available) would cost a fortune.
Ted
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Ted Edwards wrote:

The idea of bonding SS (or any other material) to slate is an invitation to madness (G). Here is a little tale to amuse. When I built the maintenance shop for our local golf course I put sheet aluminum on top of wooden work benches. Fastened with nails (low budget). Should work, I thought. After all was complete I turned on the heat..................... Ken.
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Turn down the edge of a flat bolt-like object so that you've got a central portion which touches the baseplate, and a ring which you apply the glue to the outside.
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Rick writes:

Something thin.
Consider contact cement like you would use with Formica. Can be applied in a very thin, even layer. Can be gotten off again if need be.
Consider improvising a vacuum bag for clamping.
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Why do you need magnetic bases? When I did holography at the university physics lab we used a stone table and the optics was simply placed where they were needed. They did not move around on their own. At least not as far as we could mesure. And we could measure me bending that 4 inch granite slab with hand pressure. If your bases are flat bottomed I would use them as is Henning
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Dont forget that a lot of stainless is not magnetic Henning
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nails
I believe most 400-series stainless steels are magnetic, although not as corrosion resistant as 300-series.
Good question about fastening a sheet to your stone base. Perhaps you could drill a bunch of holes in the stone and epoxy some kind of magnetic material into the holes. Since you're going to have the adjustable magnetic bases anyway, you'd probably be able to get everything where it needs to be. Besides, the professionally vibration isolation tables have bolt patterns on them anyway.
The thing about a sheet is that if it's not entirely supported, you could get vibration from air currents or something. I suppose gluing the entire thing down would work. I wonder if the adhesive would inhibit or encourage vibration.
Have you checked the price of stainless? Unless you have a surplus source, you should be sitting down when you're quoted....
HTH.
Regards,
Robin
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I think you have been given a lot to consider here, first that if the stainless is thin, your base will not clamp to it well, and if thick, you will not be able to bond it flat to the slate.
Further, slate and stainless have different thermal expansion constants, so any temperature change is likely to induce a bit of a potato chip effect.
And if you are trying to achieve 0.001 inch flatness, then you will need to have an adhesive layer that is constant to that degree.
I think the real question you should ask is, do companies like Oriel or Thorlabs produce slate/stainless composite optical tables, and if not, then, why not?
I think your best bet would be to a) abandon the mag base idea, and just use heavy steel bases, as has been mentioned. Better yet would be b), try to find small, proper, optical breadboard that will accept the bases. These come drilled and tapped in an array for 1/4-20 screws and are exactly what you are looking for. Ebay, maybe?
Jim
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