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Here is a plan for a Vacuum Bridge Clamp I made. The bottom needs to be sealed with a good vacuum gasket tape. I used two rows of the 3/8" x 1/8" size from http://www.veneersupplies.com/default.php?cPath=60_46. The rest of the drawing should be self explanatory.

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Steve Smith
"Music is what feelings sound like"

Here's a few photos:
You can see I left the membrane a little loose so it could get down around the bridge as good as possible.


Here is a photo from when I did the initial testing. Since then I have used it with hot hide glue to put a bridge on my walnut/sitka OM and it worked great.


Closeup

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Steve Smith
"Music is what feelings sound like"

Hey Steve,

Great Stuff !

Thanks - Luc

Chris, cost depends on how much and what you buy, most of this I had laying around. The callouts on the drawing will show the part#/sources used except for delrin which is available at McMaster Carr and other industrial suppliers.

Thanks Luc!

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Steve Smith
"Music is what feelings sound like"

Thanks for making the effort to share Steven.

Cheers

Kim

Great tute Steve. I've been putting off making one, but you've pushed me over the edge. How long do you leave it on with HHG? Do you take it off momentarily to clean glue squeeze out during the process?

Thanks

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I didn't mean to say it, but I meant what I said.
http://www.brackettinstruments.com/

Woody, I've only used it on the one, so far. I left it on for 10-15 minutes, cleaned up the squeeze-out then put it back on for 30 minutes. Probably overkill but so far it seems to have worked well.

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Steve Smith
"Music is what feelings sound like"

Hi Steve,
Isn't there a foam gasket that would be attached to the bottom delrin ring? I don't see it on the plan and it seems to me that similar rigs I've seen have some sort of gasket. It appears that your plan would have the hard plastic contact the top, am I wrong?

Rene

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Bob Garrish
Former Canonized Purveyor of Fine CNC Luthier Services

Thanks for the drawing, Steve. Even gave us the screw numbers from McMaster!

1 Question: I have some UHMW kicking around that's plenty big. Does anyone know if UHMW is suitable for vacuum fixtures?

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-Clint Beacock

Oops! Sorry, I don't know how I missed that. Thanks Bob!

Rene

Yes, given that you can deal with:

1-It doesn't glue to anything with anything, really. The contact adhesive on your sealant tape will hold the tape in place well enough to work, but it'll slide around if you put a side-load on it.

2-It doesn't hold screws very well when tapped, so you'll need to use more and deeper tapped holes to hold the top plate down and you'll have to be very careful about stripping the threads.

Those two are annoying, but not insurmountable. If you have the option, I'd go with something like Delrin or Acrylic that'll hold a screw once it's tapped.

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Bob Garrish
Former Canonized Purveyor of Fine CNC Luthier Services

Thanks Bob. I think I'll pass on the UHMW. Plenty of other good uses for the stuff. I don't really have trouble coming across delrin. It passes through our shop now and then (I'm a machinist too).

We have tons of aluminum lying around - just up for grabs. Would that be better or worse than delrin for vaccuum fixtures? My assumption is that the adhesion of the sealant tape would again be an issue.

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-Clint Beacock

It'll stick to the aluminum, PSA works on it alright. Just make sure to clean it off with acetone or whatever to get any coolant off of it. Aluminum works as well or better than Delrin, and it holds threads best.

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Bob Garrish
Former Canonized Purveyor of Fine CNC Luthier Services

Thanks again, Bob. I'll go with the aluminum. Cheers.

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-Clint Beacock

Guess I need to check in here more often. Thanks Bob for lending your experience!

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Steve Smith
"Music is what feelings sound like"