Table testing Hades

For what seems like forever now, I’ve been working on developing a DCG process for myself that I could use when making white-light copies of my silver masters.

After some inconsistent results I stripped the table top of all components and set up an interferometer to see how stable the table was.

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I found that there was significant ringing in the plate holder when I tapped it, on the order of several seconds and there was a fair amount of drift as well.

After several rounds of testing I remembered someone at a PCG meeting recommending leaning metal rods on various components to damped ringing. I used blue-tak on the ends to "mate" them with the table and tried this on the plate holder which damped the ringing to the point where it settled out within a second of the holder being tapped. I followed up by putting metal rods on all the mounts which also damped the ringing in those.

After that I started experimenting with different pressures in the inner tubes, attempting to find the optimum level and finally determined that overall I saw better stability with no inner tubes at all.

Ironically enough, that same day I listened to an interview of Ken Dunkley by Frank DeFreitas and Ken mentioned that he found that during his extensive table testing many years ago inner tubes made his table less stable as well.

I proceeded to strip my table to the ground and re-build it. I put down two sheets of plywood topped with the steel sheets I use for my first two tables in this house.

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Set up three sand-filled legs and put the first layer of the table on that for testing.

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I set up an interferometer and began a long series of tests.

After a week of on and off testing (work’s kept me busy) I found that a combination of bubble-wrap and carpet is the best damping material for my environment.

I now have about 10" of a carpet/bubble-wrap layer on top of each leg and I can stand still next to the table (off the joists it sits on) and not see any motion. I still won’t be able to walk around normally upstairs while an exposure is going on but at least there’s no more drift due to pressure changes in the house.

I’ll have to do more testing to see what high winds outside do to the table but it’s been quiet the last several days.

Author: Michael Harrison

Husband, Programmer, Irish dancer, tinkerer, astronomer, layabout (as much as possible)

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