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Stefan Rostyne
scholastic sledgehammer
Reged: 10/19/04
Posts: 940
Loc: Assenede, Belgium
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Yeah! We also should need a decent metal stand. Now it's a waste plywood thing with a hinge and some *BLEEP*. Was good enough for our 8" mirrors, but 18" is a bit over it's capacity...
Overload 
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Stefan Van de Rostijne
4.5" F4.5 newt 5°widefield/finderscope
8" f/5.6 travel dob
old 12.5" F5 dob (used to look better...)
30 cm f/30 Classic Cassegrain (polishing primary)
23" f/4 dob project
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PrestonE
scholastic sledgehammer
Reged: 04/29/05
Posts: 818
Loc: Houston,Texas
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Stefen, I personally would stay away from metal stands...I too thought that a nice metal stand would be better than the wooden one that we originally used...
Trouble with the nice metal stand, it transmits floor and other vibrations and made testing impossible...the wooden stands dampen vibrations very quickly...Note Mark C's wooden test stand 
Regards,
Preston
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A few I enjoy,
and a few more in the works ;<)
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Mark Harry
Carpal Tunnel
Reged: 09/05/05
Posts: 2492
Loc: Northeast
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This last picture looks quite a bit better! Still a tad rough, but you can catch that near the end and smooth it off.
M.
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Scopes in the works-
Too many for putting down here! Favorites- 8" F/6, 8" F/4.72, 4.5" F/5.4, 14" F/4.455, all completed.
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rwiederrich
Goldfinger
Reged: 11/17/05
Posts: 6024
Loc: Bremerton Washington
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Quote:
Stefen, I personally would stay away from metal stands...I too thought that a nice metal stand would be better than the wooden one that we originally used...
Trouble with the nice metal stand, it transmits floor and other vibrations and made testing impossible...the wooden stands dampen vibrations very quickly...Note Mark C's wooden test stand
Regards,
Preston
Preston...I supose that depends on your design and application.
I build an optical bench (from wood) that included two rail systems. One for the tester and one for the stand. They do not connect to avoid vibration.
The cement floor is very stable and as you said the wood bech obsobes any vibrations.
The metal stand is built so it can slide up and down the rail system for varied focal lengths. It also can tilt giving me optical axis control when I am testing. (If need be).
The face of the stand is like that of Mark C's and can accomodate mirrors from 4"-24".
The tester rails are designed to allow the tester to move freely and to permit a Ross Null lens to be incorporated. it to can freely move along the rails.
I can also elevate the tester to aim at any mirror that needs to be tilted. I personally haven't experienced any unacceptible vibrations.
This image was taken just after the bench was built and does not reflect current tester mods or the temperature/current curten that can be drawn the length of the OB.
Rob
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www.goldmtobservingcenter.com
Providing a great place for amateur astronomers, and ATM's to come and enjoy their hobby.
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PrestonE
scholastic sledgehammer
Reged: 04/29/05
Posts: 818
Loc: Houston,Texas
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Rob, I said a metal stand. Your metal is on a wooden bench.
I meant that I had made a metal stand that sat on the floor and had our tester on a linear rail that allowed it to be moved about 36" to be adjustable. The testing setup sat on a heavy wooden bench.
With the metal to concrete interface, we got vibrations going from trucks and cars driving 500 meters away. We spent quite a bit of time trying to get the metal stand to be workable, but were not successful. Rubber pads under the 3 legs, hanging chain, lead shot filled tubes, ect... 
Anyway, I like your testing setup. 
Regards,
Preston
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A few I enjoy,
and a few more in the works ;<)
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mark cowan
Vendor (Obsidian Optics)
Reged: 06/03/05
Posts: 1370
Loc: salem, OR
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Inner tubes are said to work well for isolation. I'll be trying a few things to separate the interferometer bench from vibrations in the concrete floor, I'm sure. 
Best,
Mark
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rwiederrich
Goldfinger
Reged: 11/17/05
Posts: 6024
Loc: Bremerton Washington
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Quote:
Rob, I said a metal stand. Your metal is on a wooden bench.
I meant that I had made a metal stand that sat on the floor and had our tester on a linear rail that allowed it to be moved about 36" to be adjustable. The testing setup sat on a heavy wooden bench.
With the metal to concrete interface, we got vibrations going from trucks and cars driving 500 meters away. We spent quite a bit of time trying to get the metal stand to be workable, but were not successful. Rubber pads under the 3 legs, hanging chain, lead shot filled tubes, ect...
Anyway, I like your testing setup.
Regards,
Preston
I assumed your definition of metal stand was that of just a stand that was placed on a bench....not the whole cantraption... bench and stand together. setting on a cement floor..
I agree that that would act like a harmonic fork.
I see what you actually meant now. From what I gathered you were talking about just a stand to rest mirrors in on a table of some kind. I got ya...
Yes...my optical test bench was designed to test long focus mirrors. My tester can be set 21" from the mirror if need be. It is also cantilevered so nothing can *bump* a leg by accident.
Rob
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www.goldmtobservingcenter.com
Providing a great place for amateur astronomers, and ATM's to come and enjoy their hobby.
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PrestonE
scholastic sledgehammer
Reged: 04/29/05
Posts: 818
Loc: Houston,Texas
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Mark, I remember somewhere someone talking about using a dual intertube arrangment, but cannot remember just where 
Seem to recall the layer on the floor being made up of 3 tubes in a triangle and then a second one somehow placed up above the 3 ???
This was a cheap fix for some testing back on the east coast in a facility that could not send the optics out for testing.
Do you recall something like this being mentioned in the past 3-5 years?
Retards,
Preston
ps, sorry for getting a bit off topic
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A few I enjoy,
and a few more in the works ;<)
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mark cowan
Vendor (Obsidian Optics)
Reged: 06/03/05
Posts: 1370
Loc: salem, OR
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Yeah...now I'll have to try to remember it, and I'm already short on sleep.  It was some clever arrangement...?
Best,
Mark
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Owen
sage
Reged: 06/21/07
Posts: 353
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nothing clever needed... The innertube needs :
1/ high mass on top
2/ to be minimally inflated.
That puts the resonant frequency at a very, very low frequency.... Use cinderblocks 'glued' with silicon for the base. The bottom can be a simple concrete slab (home-cast, reinforced is good).
3 points of contact will allow you to 'level' the top.
To take out the high frequency vibration, place a sand box on top, and rest a solid, flat, slab in the sand (not touching the sides).
This DIY rig has been used in the past for home-brew electron-microscopy, and will be complete overkill here - the results should be spectacular.
Owen
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Mark Harry
Carpal Tunnel
Reged: 09/05/05
Posts: 2492
Loc: Northeast
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We had a solid granite block, about a foot thick in a metal frame. the whole thing was supported/isolated by an appropriate number of tennis balls underneath the monolithic block, though I can't recall how many. Just that there were quite a few. Worked beautifully.
M.
--------------------
Scopes in the works-
Too many for putting down here! Favorites- 8" F/6, 8" F/4.72, 4.5" F/5.4, 14" F/4.455, all completed.
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Stefan Rostyne
scholastic sledgehammer
Reged: 10/19/04
Posts: 940
Loc: Assenede, Belgium
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Quote:
This last picture looks quite a bit better! Still a tad rough, but you can catch that near the end and smooth it off.
In excess of about 30 minutes of 'try and find' work, there hasn't been any further polishing since when I took the first pic. I guess the mirror still needs about 8 or 10 hours of work before being fully polished out.
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Stefan Van de Rostijne
4.5" F4.5 newt 5°widefield/finderscope
8" f/5.6 travel dob
old 12.5" F5 dob (used to look better...)
30 cm f/30 Classic Cassegrain (polishing primary)
23" f/4 dob project
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mark cowan
Vendor (Obsidian Optics)
Reged: 06/03/05
Posts: 1370
Loc: salem, OR
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Quote:
nothing clever needed... The innertube needs :
1/ high mass on top
2/ to be minimally inflated.
That puts the resonant frequency at a very, very low frequency.... Use cinderblocks 'glued' with silicon for the base. The bottom can be a simple concrete slab (home-cast, reinforced is good).
3 points of contact will allow you to 'level' the top.
To take out the high frequency vibration, place a sand box on top, and rest a solid, flat, slab in the sand (not touching the sides).
This sounds excellent (and cheap!) and I'm saving it to try, but it's not the same method that Preston is referring to, SFAIK. That one involved little more than 4 inner tubes but I'm *BLEEP* if I can recall the details.
We have trains regularly within a mile or so of my location and I think that's going to be a problem.
Best,
Mark
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mark cowan
Vendor (Obsidian Optics)
Reged: 06/03/05
Posts: 1370
Loc: salem, OR
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Quote:
We had a solid granite block, about a foot thick in a metal frame. the whole thing was supported/isolated by an appropriate number of tennis balls underneath the monolithic block, though I can't recall how many. Just that there were quite a few. Worked beautifully.
That's a good one too, and used tennis balls are nearly free as well as already pre-deadened. There are quite a few granite suppliers around and I bet they have the occasional "oops" piece that would work well. You'd want the frame to go down almost to the floor to keep the balls corralled, I take it.
Thanks!
Mark
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Mark Harry
Carpal Tunnel
Reged: 09/05/05
Posts: 2492
Loc: Northeast
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Yeah something like that. There was a stand on the floor, and a track or pockets near the top, underneath the slab. That particular slab is 8-10 feet long, and 4 feet wide. It'll cost something just to transport something of that light weight! And I distinctly remember it being pink, or red granite, FWIW.
M.
--------------------
Scopes in the works-
Too many for putting down here! Favorites- 8" F/6, 8" F/4.72, 4.5" F/5.4, 14" F/4.455, all completed.
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