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Vacuum Bridge Clamp
http://www-.luthiersforum.com/forum/viewtopic.php?f=10102&t=5706		 Page 1 of 1
Author:  RussellR [ Fri Mar 17, 2006 9:46 pm ]
Post subject: 
I am considering making the move over to vacuum to clamp my bridges, I have found someone to supply silicone sheeting, I'm still searching for a suitable pump.

Looking at the pictures of bridge clamps I have seen, I had a couple of questions.

How is the silicone joined to the clamp ?

is the silicone pulled tight or left slack so it pulls downwards when vacuum is applied.
Author:  Dave Rector [ Sat Mar 18, 2006 1:29 am ]
Post subject: 
Russell, I just bought one of these from LMI.

The silicon in mine is sandwiched between two mating halves of the clamp itself. It is nice and flat but not streched tight, if that makes any sense.

If you have any more questions, feel free to ask. Also, you can check it out on LMI's website. For vacuum pumps give eBay a try. They usually have quite a few up for auction.
Author:  RussellR [ Sat Mar 18, 2006 2:57 am ]
Post subject: 
Dave thanks Very Much

I couldn't quite tell from the pics on LMI's site, I have my eye on Ebay for a pump, we don't get quite so many come up over here, and I think it would be too heavy to ship from the states.
Author:  A Peebels [ Sat Mar 18, 2006 3:00 am ]
Post subject: 
I use a refrigeration pump. They can be obtained from appliance repir shops cheap to free. They work good, and are quiet.

Al
Author:  russ [ Sat Mar 18, 2006 3:55 am ]
Post subject: 
I use a fridge pump for this too.

I made the clamping fixture itself from birch ply, then coated it in resin to avoid leaks. I also slightly domed the bottom of the fixture to match the dome of my soundboards.

The rubber sheeting should be taught (no wrinkles), but not pulled overly tight. Over the sheeting, I added some thin plexiglass to protect the rubber (don't forget the air hole(s) in this piece!)secured with screws and washers. Some vacuum tape or weatherstripping makes the seal.

If you can get hold of the old LMI catalogue (binder version), there is a very good article about making this fixture. I use the manifold that LMI sells between the pump and the fixture and it works great.
Author:  Grant Goltz [ Sat Mar 18, 2006 4:09 am ]
Post subject: 
I use vacuum bridge clamping, but I did not pay the $80-some for the LMI unit. A foot and a half of sealing mastic strip (reuseable), a small scrap of nylon vacuum bagging film (we use both of these vacuum bagging wood/epoxy kayak hulls) and a $4 plastic fitting to attach the hose to the film, and that's it. Very simple and works great.



Of course, we already have a couple of vacuum pumps, but for something this small a used refrigeration pump is probably adequate.

Save your money and buy wood

Grant
Author:  Daniel M [ Sat Mar 18, 2006 5:12 am ]
Post subject: 
If you are buying a vacuum pump on Ebay, it's a good idea to ask if it was used in medical equipment in its former life. Aparently, some hospital vacuum pumps are a potential bio-hazard.
A fridge compressor works great for the bridge clamp, but most won't operate a larger press for bracing tops & backs.
Two compressors T'd together work fine on my large press.
I used Lexan for the frame of my bridge clamp, but MDF works fine too if you seal it well with paint or varnish.
Author:  Daniel M [ Sat Mar 18, 2006 5:30 am ]
Post subject: 
Here's a pic of my clamp. I didn't bother with the protective plexi top. The connector is a short piece of 1/4" OD copper tubing epoxied into a hole drilled in the frame. The vinyl tubing is a tight fit, but if you warm it up with a lighter or boiling water, it'll slip over a bigger tube easily. When it cools it tightens up & no clamps are needed.


Author:  peterm [ Sat Mar 18, 2006 7:53 am ]
Post subject: 
I think vacuum is the way to go... maybe i should start planning on making one too.
How do you make sure the bridge doesn't move when you place the vacuum clamp over is and start the pump? is there a way to it?
Author:  RussellR [ Sat Mar 18, 2006 7:59 am ]
Post subject: 
Hi Peter you Drill the two outer peg holes and then put little pegs in them to hold everything in place.

Something like these

Bridge Pegs

Of course you can't do that if you bridge is pinless so I am not sure how you handle a pinless bridge.RussellR38794.6676157407
Author:  Daniel M [ Sat Mar 18, 2006 8:00 am ]
Post subject: 
When I have the bridge placed in the correct position, I drill two 1/16" holes through the bottom of the saddle slot   & install 1/16" pins to maintain the alignment. Just have to make sure the pins don't stick up above the slot or they'll puncture the diaphragm.
Depending on your vacuum pump capacity, you might want a vacuum resevoir & have the system fully charged before you start clamping. You will certainly need a resevoir if you use a fridge compressor. They don't have a high capacity.
(A 20 Lb propane tank works great & old ones are free at the propane dealer)Daniel M38794.6715509259
Author:  peterm [ Sat Mar 18, 2006 8:10 am ]
Post subject: 
Russel, you are right....I use a pinless bridge
Author:  RussellR [ Sat Mar 18, 2006 8:47 am ]
Post subject: 
Hi Peter

well I guess you would have to use something like daniels method for a pineless bridge.
Author:  L. Presnall [ Sat Mar 18, 2006 12:13 pm ]
Post subject: 
How 'bout a drawing (MichaelP) or quick plan of one of these with the particulars? I had the LMI one (pricey) but sold it to go back to the "old ways"...I never sold the vac pump tho and I'm thinking of giving it another try....
Author:  crazymanmichael [ Sun Mar 19, 2006 4:57 am ]
Post subject: 
russell

i had been using a vacuum pump for about 8 or nine years for a variety of vacuum clapming tasks, bridges being one of them but also for routing, etc.

but last year i went to joe woodworkers site and bought his venturi kit to use my compressor to generate vacuum and built a reservoir type vacuun setup. it is far superior to using a vac pump in terms of convenience, speed, noise, etc. it is simple to build, and is light weight for shipping purposes, and relatively inexpensive.

before you make any decisions i would encourage you to have a look at his site. it is extremely informative and his prices are very attractive. and as i recall he also sells the switches which will work on uk current.
Author:  RussellR [ Sun Mar 19, 2006 7:31 am ]
Post subject: 
Thanks everyone for all of the advise, I appreciatte the help.

Michael

I will check out the Venturi Kit.

By the way France won the Six Nations, and Ireland the Triple Crown.
Author:  crowduck [ Sun Mar 19, 2006 8:46 am ]
Post subject: 
I have a Gast Vac Pump Model 1531, 20" Hg, 1.5 CFM Open Flow, 10 PSI Max Vacuum.

Is this enough vacuum to work with just a bridge clamp? I'm not interested in vacuum clamping anything else at this time.

CrowDuck
Author:  John Mayes [ Sun Mar 19, 2006 12:26 pm ]
Post subject: 
[QUOTE=crazymanmichael] russell

i had been using a vacuum pump for about 8 or nine years for a variety of
vacuum clapming tasks, bridges being one of them but also for routing,
etc.

but last year i went to joe woodworkers site and bought his venturi kit to
use my compressor to generate vacuum and built a reservoir type vacuun
setup. it is far superior to using a vac pump in terms of convenience,
speed, noise, etc. it is simple to build, and is light weight for shipping
purposes, and relatively inexpensive.

before you make any decisions i would encourage you to have a look at
his site. it is extremely informative and his prices are very attractive. and
as i recall he also sells the switches which will work on uk current.[/
QUOTE]

I've found just the opposite. I have a venturi kit and it is only as quite as
the air compressor, and unless you have a big two stage one it is most
likely loud. My small vac pump pulls 26hg easily, and is very quite.
Author:  Daniel M [ Sun Mar 19, 2006 9:43 pm ]
Post subject: 
Chris;
I think 20" is marginal for vacuum clamping. Most systems advertise a minimum of 25". My little fridge compressor rig pulls 28 1/2".
Author:  Robbie O'Brien [ Mon Mar 20, 2006 3:03 am ]
Post subject: 
Grant,

Where can I get some of that nmastic strip from?
Author:  Robbie O'Brien [ Mon Mar 20, 2006 3:05 am ]
Post subject: 
now that we are on the subject of vacuum clamping bridges...does anyone have a secret for holding a classical bridge in place while clamping with a vacuum? A steel string bridge can be held in place by screws or bridge pins but not a classical. Would a piece of masking tape on the wings do the job? If so, what affect will the vacuum have on the tape? Will I be able to remove the tape afterwards?
Author:  crazymanmichael [ Mon Mar 20, 2006 4:16 am ]
Post subject: 
if you are using a reasonable sized compressor(mine is a true 2hp, 12a running on 220v with a 25 or 30 gal, 150 psi tank), and your vacuum setup has a resonable reservoir, i use a five gal air tank, with a vacuum pressure switch, and your clamp has good seals, the noise is negligable.

joe woodworker sells the seal tape as well.
Author:  Pwoolson [ Mon Mar 20, 2006 4:38 am ]
Post subject: 
Robbie, tape works just fine. I use it on my braces to keep me from knocking them out of position as I'm getting the set-up in my vacuum press. The vacuum often breaks the tape but at that point, it doesn't matter because the membrane is tight against the rest of the object being clamped.
Author:  Keith M [ Mon Mar 20, 2006 11:29 am ]
Post subject: 
Robbie, I drill a couple of widely spaced 1mm dia holes in the under side of the bridge then epoxy in cut off brad points so they stick up about 1.5mm. Dry fit to the proper location and press down to pierce them into the top. It's easy to locate them after the glue is applied and the bridge will stay where you put it.
Author:  Robbie O'Brien [ Mon Mar 20, 2006 3:58 pm ]
Post subject: 
Thanks Paul and Keith. I am getting ready to glue on two bridges and thought I would try the vacuum system this time around.
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