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I'm looking for a vacuum rig to glue bridges. The LMI offering seems expensive, any suggestions? I'd prefer to use my compressor with a vacuum valve instead of a pump, any caveat? Lastly, except LMI, anybody else selling that stuff, pre-made or in kit form?

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Laurent Brondel
West Paris, Maine - USA
http://www.laurentbrondel.com/

Laurent, by "vacuum valve" do you mean "venturi"? I'm sure you know the caveat that the compressor and valve are loud. And the venturi will need to be running during the entire clamping process.

New vacuum pumps are very expensive, close to $300 plus shipping, but you can easily find a used or surplus vacuum pump on Ebay for around $50 or $60. Even with $30 in shipping, that still lands one on your dooorstep for one third the price of new. Just google the part number and read the specs, and make sure the pump pulls at least 21 or 22 inches of mercury (may be listed like: 21"Hg)

Check this topic (viewtopic.php?f=10101&t=24180) and look at what John Cross made.

Also, check with our friends Down Under, at the ANZLF forum, and search for vacuum or just look in their Jigs & Fixtures section for vacuum stuff. One discussion there will lead you back to the Joe Woodworker site, and the vacuum reservoir concept. I had not bothered with that whole rig, but now I do plan to build the whole rig (similar to the EVS rig on the Joe Woodworker site.) There are also plans for a venturi system if you elect to go that way. http://www.joewoodworker.com/veneering/ ... amping.htm

Hope this helps,

Dennis

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Dennis Leahy
Duluth, MN, USA
7th Sense Multimedia

I got mine from Bob Garrish several years ago. Still goes every day. My brace rig is based off his, just a little bigger and heavier. If he isn't doing them now, I can send you some pic's as easy to make one. If make one, don't buy the rubber, I have some big enough for a bridge rig I will send you.

If you are just vacuum curious and don't want to spend a lot of time and money then simply find an old small compressor that you can hook a hose up to the intake side of the pump. Voila! Instant vacuum rig. Garage sale cheapies are great for this sort of thing. You don't need that large a unit to accomplish the effect. I even understand that an old compressor out of an air conditioner or even a household refrigerator will do. They can be had for free or next to nothing from your local appliance repair shop. Just make sure the freon has been properly removed first.

If you want to get a little more sophisticated there is lots of good info at http://www.joewoodworker.com/veneering/welcome.htm.

Laurent:
How much "suck" do you actually require? The maximum vacuum posible is 30" Hg. Most shop-vacs can give you most of that. Figure out just what you require first and then look for the equipment required to do the job, you may already have it.

Cheap is my middle name.

Bob

I had an old fridge compressor which worked really well. Consistently sucked down to 28" Hg.
I used a (free at the dump) dead 20 LB. propane tank for a reservoir & a few fittings from joewoodworker.com.
One caveat... The fridge compressor needs a little bit of oil in it & a small amount of oil vapour was expelled while it was running. (You have to drain most of the oil out, or it will spew the oil everywhere when you run the thing.) I eventually ran my vent line outside, but it was a concern for me. Also, it got pretty hot when it was running. I was never completely confident it wasn't going to seize up. I ran it many hours & it worked great...
Making a bridge clamp is no big deal. Take a look at the LMI pics & you'll be able to cobble one together pretty easily.

That's just outright false. The most I've seen from a shop-vac is less 3" Hg, though maybe a really special one could get to 5" or so.

I only make the clamps in orders of 5 or more now (and they're all aluminum with a different design now), so feel free to use the old design or any elements of it.

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Bob Garrish
Former Canonized Purveyor of Fine CNC Luthier Services

Trust me......use a venturi vacuum source that is capable of about 25hg using the least cfm. A shop vac won't make near the vacuum you need for this and a vacuum pump that is made to suck 25hg and have constant operation is pricey. I assume you'll want to hold vacuum for a long time so a venturi is a quiet and feasible solution. 25hg or higher is MORE than adequate to provide about 32 psi clamping pressure when gluing on bridges. Venturis use far less compressed air than you might think although sometimes they sound like they are blowing like crazy due to the exhaust.

Go to McMaster-Carr - http://www.mcmaster.com/#vacuum-pumps/=63shw3 - And find #41605K13......That's what you need right there.

I've made 100's of vacuum fixtures for cnc production.

You could make a simple vacuum frame from maple as depicted. Use a scroll saw to cut the shapes.

The orange color is maple (pore free so vacuum holds). The purple color is .01" clear silicone sheeting - source McMaster-Carr. The gray color is cheap close cell foam weatherstripping - Home Depot. The gray tube is 1/4" aluminum tubing glued into a hole drilled into the frame (you just slip pvc tubing over it) - Ace Hardware or McMaster. On the bottom you can run another strip of weather stripping to create the seal between the guitar and the fixture. Then small wood screws to hold it all together.

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I read Emerson on the can. A foolish consistency is the hobgoblin of little minds...true...but a consistent reading of Emerson has its uses nevertheless.

StuMusic

Also not true. We've got 14.696PSI of atmospheric pressure at sea level which is about 29.92"Hg. It's close enough to a 2:1 ratio that you can equate 2"Hg to 1PSI, so you'd be getting 12.5psi at 25"Hg

Where are people getting these numbers? First a shop vac pulling a lab-grade vacuum and then a vacuum clamp pulling over two atmospheres of pressure

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Bob Garrish
Former Canonized Purveyor of Fine CNC Luthier Services

Here's a plan for a bridge vacuum clamp I posted in the tutorial section - similar to Bob's though probably not as nice although it works very well.
http://www.luthiersforum.com/forum/viewtopic.php?f=10117&t=23895

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Steve Smith
"Music is what feelings sound like"

Correct....I was conflating barometric pressure and hg. The point is that using a 25hg venturi is going to provide more than adequate pressure to hold down a bridge.....no need to stress about getting a vacuum pump that produces 29.92hg.

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I read Emerson on the can. A foolish consistency is the hobgoblin of little minds...true...but a consistent reading of Emerson has its uses nevertheless.

StuMusic

As Dennis said, vacuum pumps are not all that expensive. Do a search for 'JB vacuum pump' on eBay.
I bought a used JB 'Eliminator' pump (locally) and it works fine - on a few occasions I've (deliberately) left it running overnight with no obvious damage.
A proper pump is a lot quieter, and more economical to run than a venturi attached to your compressor. Anyway, my compressor is in the garage and I usually vacuum bag 'stuff' in my inside shop, so it makes sense for me.


Cheers
John

I have wondered about reservoirs & what can be used for storing vacuum. I built the Joe Woodworker DIY plan with my 1\3 hp gast & it's OK. But I wonder if there is an advantage to having a bigger reserve? What else besides propane tanks can be used ? Does there need to be a safety on it like compressore tanks. Is ther any danger if a tank 'implodes' Anyway I have more problems with a proper bag seal when there is a big "side mold" inside & you have to reallly scrunch things up.
Mike McNerney
[quote="Daniel MI used a (free at the dump) dead 20 LB. propane tank for a reservoir & a few fittings from joewoodworker.com.

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Mike McNerney

Since a propane tank is rated to well over 100 PSI pressure inside, I don't think there is any danger of "implosion" at around 14 PSI negative pressure. I have had zero deformation in my tank after many hours of use. joewoodworker has plans for a sewer pipe reservoir using 2 lengths of plastic pipe with caps glued on the ends. Seems to me a propane tank would be at least as strong. And WAY easier to adapt to your system. All you need is a 3/4" TPT brass barb fitting from any hardware store.
The only thing I didn't like about the propane tank was it smelled really bad for the first month or so. That stuff they put in propane to make it stink really works! If I do it again, I'll wash the tank out with lacquer thinners before I hook it into the vacuum system.

You don't need a vacuum tank to do this. This application doesn't require any cfm at all so a high cfm pump will only serve to apply full vacuum sooner. Even the lowest cfm will take mere seconds to evacuate a bridge fixture. Once full vacuum is applied there is no flow at all (one hopes). A vacuum tank only serves the purpose of storing vacuum when there is an even cfm flow required under vacuum, or there is a highly cyclical application, or just a large number of static applications attached to the same vacuum source.

A venturi pump is the cheapest way to do this assuming you already have a compressor. When I use a venturi pump to hold parts into fixtures the compressor kicks on every 30 - 40 minutes.

Or....to put it another way...buy a $60 venturi and see if you ever need another vacuum setup.

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I read Emerson on the can. A foolish consistency is the hobgoblin of little minds...true...but a consistent reading of Emerson has its uses nevertheless.

StuMusic

For only about $30 more, (including shipping), you can find a used or surplus vacuum pump. If the venturi was just $5, I'd defer to your suggestion to try it, but I have on too many occasions bought a wimpy tool or a not-quite-what-I-really-needed tool, and when I finally break down and get what I really should have bought in the first place, I now have way too much invested. Sort of the 'penny-wise; pound foolish' thinking. In fairness, I've never heard a venturi, so maybe they are not as bad as what I'm imagining. What I'm imagining is like the sound when a female air fitting breaks and allows air to escape. That I have heard, and it is nasty. I figure hearing, acute hearing, is one of the treasured senses for a luthier.

Widening to the 'big picture', there may be quite a few uses for vacuum in the luthier shop besides bridges. There may also be times when you may want a vacuum in a "burst" mode, like turning on a light switch and having light immediately. The reservoir provides that "instant on", and keeps the pump from running as much. I don't have a reservoir yet, but only recently recognized (thanks to my friends at the ANZLF) both the advantages of instant vacuum and that the uses for vacuum in the shop are kinda only limited by ones imagination.

Dennis

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Dennis Leahy
Duluth, MN, USA
7th Sense Multimedia

Thanks much for all the answers. I do have a compressor and would rather not purchase another machine, space is tight. My question was if there is any caveat using LMI vacuum valve or similar, or a venturi pump. For instance how long does it take before it is at full clamping force?

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Laurent Brondel
West Paris, Maine - USA
http://www.laurentbrondel.com/

"Better" is relative to your situation. I have used both systems and currently prefer the small pumps for my limited runs. When I was working in a shop that had a large tank/big pump compressor the little vacuum valves were great. They didn't use a whole lot of air compared to what was available. When I tried them in my home shop though my compressor had less storage capacity and cycled frequently. Glue ups intended to dry overnight quickly became a problem as the noise of the compressor disturbed peoples sleep. If my compressor were quieter perhaps I would still be using the valves.

My little vacuum pump is very quiet and can run all night if asked. Gets a little hot though so I hooked her up to a Joe Woodworker style system. The tank allows the pump to cycle just like a compressor would and keeps the pump cool. If I have a good seal it may cycle once or twice the whole night. If I don't (like when I am re-setting a bridge and I have done the best I can to seal off the existing bridge pin holes) it might cycle every 5 minutes.

The tank also gives you a reserve of vacuum so that you can evacuate the bag instantly by opening the valve.

Someone mentioned using lacquer thinner to remove the smell of LP from the tank. Be careful. One spark and you have a potential bomb on your hands. You could be replacing (or combining) an explosive gas with an explosive vapor. May I suggest removing the valve and inserting a compressor hose to the bottom of the tank and letting it run for a while thereby clearing the tank. If that doesn't do it then perhaps a little febreze?

Greg N

Hey Laurent, I use the joe woodworker venturi model with my compressor and it works great.
http://www.joewoodworker.com/veneering/v2-about.htm
Contrary to what people say, it does not have to stay on all the time as it has a vacuum reservoir and a mac valve that opens and closes as needed. kind of like your compressor kicks on and off. when your vacuum drops 3 hg from where you set it, the venturi will open and the start drawing more vacuum. This equates to the valve opening for 30 seconds every 3 or 4 minutes. I typically get about 25 hg with mine.
I use the LMII clamp fixture but you could easily make one yourself as was demoed above.
Best of luck

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Tickle your guitar daily, and it'll tickle you back.

We had a great show and tell with a vacuum pump and the joe woodworker venturi at one of our New England meetings. My impression was that both worked fine but that the venturi evacuated much quicker. In terms of size, the joe woodworker thing with the reservoirs may have been actually larger and more expensive to source and build than the little vac pump (ebay deal). I was more into the venturi though and have plans to build one.

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Burton
http://www.legeytinstruments.com
Brookline, MA.

John and Burton, thanks for the feedback. I will go the venturi route.

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Laurent Brondel
West Paris, Maine - USA
http://www.laurentbrondel.com/

There are a million kinds of venturis and I have about 6 of them . None of ones I have are even remotely loud although there may be heavier, industrial types that are much louder. The ones I'm talking about don't make any more noise than if you breathe out making an "H" sound at about mid-effort. Mine all have exhaust housings that attenuate noise although they aren't noisy even without the exhaust housing. They are well below conversational db levels and are quieter than the JB reed type pump that I use most often.

I'd characterize it like this. If the compressor was totally out of the picture and the venutri was in a room next to you with the door closed, there's no way you'd hear it.

I'd also add that there is a great deal of flexibility with a venturi at a lower cost. You can set your vacuum level at any point within no-vacuum to full-vacuum with a venturi simply by putting a ball or needle valve in the input flow. The less through flow, the less vacuum appears at the vacuum port. Simple. With a mechanical vacuum pump you need a vacuum regulator on the vacuum line to have an adjustment. A simple valve on the vacuum line would only adjust the speed at which full vacuum is acheived and not the level of vacuum.

The setup is: compressor - needle valve (or you can use an air pressure regulator) - venturi pump - vacuum gauge (optional) - vacuum fixture. Here you have the ability to apply vacuum in any amount from zero to full potential with one valve.

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I read Emerson on the can. A foolish consistency is the hobgoblin of little minds...true...but a consistent reading of Emerson has its uses nevertheless.

StuMusic

Laurent,
I bought the EVS system from Joe the Woodworker. I got the idea from KMG guitars. I modified the plans by using four 4" pvc pipes about 24" long for the reservoir. I had to buy a few brass pipe fittings to add to what Joe sent me. This makes a larger reservoir, and the unit only turns on a couple times during the glue up. I use it to glue the braces to the top and back and also the bridge. You can make your own fixture for gluing bridges. You need a bag and a coutoured back board for the backs and tops. I dont even use a contoured back board for the top. You can do it without one. They come out fine. I still countour my braces and glue them to the top in the bag. When you take it out, it still has the contour you need. I got that tip from a well known luthier. Joe provides everything you need and the instructions. He will help you if you need it. I use it with my compressor. It is the cheapest and safest way to go. All the parts on this rig are available if something breaks. Mine goes to -21 HG. It turns off and holds that HG until it drops about 5 HG and then turns on and brings it back up to -21 HG again. This is refered to as a vaccum generator. Simple and effective. Not really that noisy. I can send you a picture if you like. Go to joethewoodworker.com
Mike R.

hey folks, I just wanted to add that air flows through maple like a siv. not a good choice for a vac fixture. unless you seal it well. A Collings mandolin in the white makes a hell of a bang as it implodes. After that we drilled the end pin hole before sticking the back on a vac holding fixture!

ow! just.... ow!

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Jim Hansen