Official Luthiers Forum!

I have a nice vacuum pump that I got when a previous employer went belly up and I would would like to use it to glue my bridge. The LMI vacuum bridge clamp looks real nice but is a bit expensive.

Has anyone put together one in the shop and , if so, would you be willing to describe it or show some photos? I have some ideas but would like to hear the voices of experience before I dive in.

_________________
Steve Smith
"Music is what feelings sound like"

This one was made by St. Luthery for 1/2 the price of the LMI one. Its outside dimensions are 5" x 9 3/4". It is made of 1/2" lexan with rubber membrane and neoprene gasket. Looks like not that hard to build. Hope this helps.

_________________
A higher purpose for wood.
Rich Smith
Issaquah, WA

I've made many vacuum clamp fixtures, but not a bridge clamp, yet, but these things are real easy to make. I coped out and bought one (was rushed for time). If you want some close-up photos of it, let me know and I'll post some.

All you need to make one yourself is:
- Some gas-impervious frame material (like metal, acrylic or nylon, or even hardwood/plywood!) to make a simple two-part frame
- Some neoprene/rubber gasket material (which you can buy at a lot of places fairly inexpensively, e.g. RubberSheetRoll )
- Some wide weather-strip seal (Home Depot/Lowes/ACE/etc. or specialists like Vaculok or Grizzly)
- A plastic vac-pipe fitting (Home Depot etc.)
- Fixings to clamp the two halves of the frame together
- Drill bits and possibly a tap for the vac-pipe fitting

Cut out the center of the frame pieces and drill them to accept fixings.
Drill a hole through the side of the bottom part of the frame to accept the vac-pipe fitting. You may have to tap the hole depending on the fitting type.
Clamp the gasket material betwee the two halves of the frame using appropriate fixings that mount flush or below the surface of the frame.
Stick weather-strip around the bottom edge of the frame, and voila, your're in business.

The only warning I would give is to make sure the finish on the guitar is completely cured before you vacuum clamp the bridge on, otherwise the clamp outline will be visible in your nice new guitar! (DAMHIKT)

HTH,
Dave F.

_________________
Cambrian Guitars

"There goes Mister Tic-Tac out the back with some bric-brac from the knick-knack rack"

Thanks for the information and encouragement, sounds like something I can do fairly easily. I have some 1/2" Delrin that should work for the frame.

It would be nice to have some kind of clear flexible membrane to use. Anyone have any idea if the Dura-Max Elite Polyurethane vacuum bag material from Joe Woodworker would work for this application? Here's a link: http://www.veneersupplies.com/product_info.php?products_id=2808

_________________
Steve Smith
"Music is what feelings sound like"

Edit - The poly stuff might not be stretchy enough for a bridge clamp....
Maybe you already have some? If so, try it and see!

Delrin would be great for the frame halves. Edit - You want to make the bottom half of the frame just a little bit taller than the top of your highest bridge, so that the neoprene sheet sits just above or just touching it, prior to starting up the vacuum. If your vac-pipe fitting is too large to fit in the side of the frame, then you might consider mounting it on the top of the frame, and drilling an airway down and then inwards to the vacuum space in the bottom of the frame. If you do this, you'll have to make sure there's a good seal between the top and bottom frame halves where the airway passes through.

Post some pictures of it when you are done, we love to see stuff like this!

Cheers,
Dave F.

_________________
Cambrian Guitars

"There goes Mister Tic-Tac out the back with some bric-brac from the knick-knack rack"

The bridge clamps I was making were acrylic (Plexiglass, Lucite), not polycarbonate (Lexan), but any nonporous material will work fine. The membranes on those were actually put on with CA, but you need to be careful putting it on to make sure you got a full glued seal to the membrane. Clear material helps, as you can look through it! To replace the gasket, you can slice the previous one off with a razor or chisel, then glue on a new one. I chose that way because acrylic is problematic to tap, and there's no worry about leaks due to screws not pushing the top frame onto the bottom frame strongly enough. On the few metal ones I made, I used a screwed-on top plate.

The frame material only needs to be thick enough to get your fitting into it; there's no advantage (and some disadvantage with respect to gasket life) in making it taller/thicker. If I'd been sharper back when I designed mine, I'd have put the fitting into the top face of the 'ring' and drilled a hole in the interior for air access (ie: the fitting would stick straight up when in use) to thin down the frame thickness.

Dave gave a good list of all you need. All I've got to add to that is doubling up on some things. #1 is to use something nonporous, you're just shooting yourself in the foot at the get-go if you decide to make it from wood and mess around with trying to get things airtight with sealers, etc, instead of using a $5 piece of plastic. To get a good seal with your bottom gasket, when using adhesive-backed neoprene foam strip, make sure that your butt joints are under some pressure where they butt together so that the neoprene is sealing well against the next piece.

_________________
Bob Garrish
Former Canonized Purveyor of Fine CNC Luthier Services

Great suggestions and information. Thanks!

I'm going to try and track down a more flexible, clear membrane material only because I would prefer to be able to see the bridge while I clamp in case something goes wrong (am I overthinking again?). Any ideas?

I'll make the frame out of Delrin because I've got it and it's easy to machine and it threads easy. I'll clamp the membrane between 2 pieces because most glues don't stick that well to Delrin.

_________________
Steve Smith
"Music is what feelings sound like"

One of my buddies thought that some of that heavy, clear shower curtain material would work for the membrane. Anyone tried it?

And any reason why silicon wouldn't work to seal everything?

Good timing for this. I'm at the point of making one myself. I'm still kinda sitting on the fence with regards to vacuum or hand clamp.

Cheers,
Danny

I think its possible that the clear shower curtain material might work for some vacuum clamp applications but I don't think it would be flexible enough for a bridge clamp.

I'm going to try the Dura-Max Elite Polyurethane from Veener Supplies.

Looking through the McMaster Carr catalog I found several products that would probably work but none of them is transluscent or clear:
1) Ultra-Elastic natural latex rubber with a tensile strength of 3760 psi and a stretch limit of 810% -- I've used this before for another application; it's great stuff and I think it would work well but the color is red,
2) There are many different neoprenes but a typical, stretchy variety has a tensile strength of 1500 psi and a stretch limit of 500%. None are clear.

The Dura-Max Elite Polyurethane from Veener Supplies reads: "advanced thermoplastic polyurethane that can withstand pressures exceeding 3,750+ psi and stretch more than 6 times its width and length". More stretch than neoprene and as strong as the natural latex. Plus the price is reasonable.

_________________
Steve Smith
"Music is what feelings sound like"

I've got the clamp done. I built it to the size suggested by Ricardo. I left the membrane a bit loose when I assembled it and I put the vacuum fitting on top as suggested by Bob Garrish.

Delrin is too slippery to glue to very well so mine is designed to clamp the membrane between two 1/2" thick Delrin rings (I already had the Delrin on hand). The membrane is Dura-Max Elite Polyurethane from Veener Supplies, and the foam seal is also from Veener Supplies.

The guitar is not ready so I tested it on my bench. It pulled about 25mm Hg so it seems to seal well. If anybody wants, I have a drawing and some other how-to photos I could post in the tutorial section.

Thanks all for the suggestions, this one seemed to work out real good.

_________________
Steve Smith
"Music is what feelings sound like"

Steve, would you mind showing pictures of the rest of your setup? I have a Gast pump and the bridge clamp, but don't know where to go from there.

_________________
My Facebook Guitar Page

"There's really no wrong way, as long as the results are what's desired." Charles Fox

"We have to constantly remind ourselves what we're doing....No Luthier is putting a man on the moon!" Harry Fleishman

"Generosity is always different in the eye of the person who didn't receive anything, but who wanted some." Waddy Thomson

Rod. I'll be happy to. I play on Wed nights so it'll be after work tomorrow before I get to the shop to take more photos then I'll post them.

_________________
Steve Smith
"Music is what feelings sound like"

Very nice, Steve! That's pretty similar to my current design (short clamp, vertical air fitting).

_________________
Bob Garrish
Former Canonized Purveyor of Fine CNC Luthier Services

Bob, thanks for the kind words.

Rod, here's a picture of my pump. If I had bought the pump new I would only have put the muffler and filter on it, as shown. The muffler, gauge and ball valve were left over from a previous life testing seal integrity on subsea housings so I just left them on there. The inlet and exhaust fittings on my pump are 1/4" NPT size.



My pump is rated for continuous duty so it doesn't need a reservoir. If yours is not continuous duty then you would need to set it up differently.

Not counting the ball valve and gauge, here are the parts, in order, that I've used. I ordered my parts from VeenerSupplies.com so I've used their nomenclature. If you go to their website they have nice pictures of all the parts:

1. Brass pipe - 1.5 inch (to connect the pump intake to the filter).
2. High-Flow Vacuum Pump Filter 5 Micron (to keep junk out of the pump)
3. Brass Barb Fitting 1/4" NPT Male to 3/8" Barb (connect filter to 3/8" ID hose)
4. Vacuum Tube - heavy Duty Braided 3/8" ID
5. Brass Barb Fitting 1/4" NPT Male to 3/8" Barb (connect 3/8" ID hose to the Brass Tee)
6. Forged Brass Tee 3-Way Splitter - 1/4" NPT Female (Allows connecting the vacuum gauge in-line)
7. Vacuum Gauge - HD Glycerine Filled (Connects to the Brass Tee)
8. Brass Close Nipple 1/4" NPT (connect the Brass Tee to the Lock-On Vacuum Connector)
9. Lock-On Vacuum Connector (Quick Disconnect so you can hook the pump to different accessories)
10. Brass Tube adapter for Vacuum Clamping Jigs (Allows you to quick connect/disconnect the Lock-On Vacuum Connector to a 1/4" hose)
11. Vacuum Tube (Black Hi-Flex) 1/4" ID (I like this stuff, it's real flexible but he sells them in 1 foot lengths and I would prefer a 2 foot length of something so I can keep the metal fittings away from the guitar)
Brass Barb Fitting 1/8" NPT Male to 1/4" Barb (this is the fitting that connects to my vacuum clamp)

Not listed are two worm drive hose clamps I used on the 3/8" ID braided vacuum tube. I didn't see any need for clamps on the 1/4" tubing.



When assembling the tubing on the hose barbs a little spit in the end of the tubing will help things go together much easier.

All of the threaded fittings have 3 wraps of teflon tape on them.

I hope this is what you were looking for, if not or you have other questions just let me know.

_________________
Steve Smith
"Music is what feelings sound like"