Official Luthiers Forum!

The latest Luthier Tips du Jour video is on the air. The topic is Vacuum Fixtures. I dsicuss the use of vacuum in the shop and show a couple of fixtures I use in my shop.
As always, comments and discussion are invited.
Enjoy!

Thanks for that Robbie, very clear, Love your holding device.

One point though, When calculating clamping pressures for the bridge or other items smaller than the fixture, you should be using the area of the bridge not the fixture.

The figure you have calculted is the clamping force of the fixture to the guitar top, the force of the bridge to guitar top will be about a quarter of this.

I don't have any doubt that what you are doing is more than adequate, just the calculations lead the viewer to think all that clamping pressure you quote is on the bridge.

regards
Jeff

You are correct Jeff. I should have clarified this.

Hey Robbie,

Really like those vacuum clamping jigs. Would you happen to have a couple
of drawings on how to build these tools? That would be great, I've got a vacuum pump
and it would be cool to use it as shown.

Thanks - Luc

Luc,

I don't have any drawings of these jigs. Both of the ones I use in the video are LMI products. If you want to spend some bucks and some time you could make them. Since I am short on time I prefer to just purchase them and get on with building.

Hi Robbie,

Thanks for the info on the availability of these jigs, didn't realize LMI offered them for sale.

Cheers !

Luc

Where is the best place to get a vacuum pump...on the cheap? How much compressor capacity do you need for a venture set up.

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Jeremy Vonk

eBay for vacuum pumps. If you have the compressor capacity, Venturis suck down a LOT faster (which helps a lot with vacuum clamping, as all clamps leak to some degree). You can check out the air requirements at http://qualityvak.com/venturi.html

The Venturis are -really- easy to make, but calibrating the airflow and the airflow/vacuum ratio is a hassle so I'd say it's worth getting one from QV even though you'll laugh when you see how simple the parts are. I use the one that pulls 5.2CFM of vacuum. You can overdrive them a bit if you run them at 100PSI instead of 85, but there are no gains above that.

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Bob Garrish
Former Canonized Purveyor of Fine CNC Luthier Services

Moving pictures. You have to like them. Although a little more fumbling with the bridge clamps would have made for a good infomercial (tried of your old bridge clamps....) I have dibs on my refrigeration buddies soon to be replaced evac pump. I think it will work.

Have you ever had a problem using wooden bridge pins to glue your wooden bridge to your wood top using wood glue?

Still Watching and Thanks Again,
Danny

Whoow!
just looked on e bay at pumps
Diaphram, bellows, oil, oil less.
Whats a guy to do?
any recommendations as to type?

Peter

Okay, I normally don't consider buying anything from HF that plugs in, but how about this?

http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=98076

My only thought is, if it's for pulling a momentary vacuum on an AC unit, would it hold up for the 45 minutes at a time needed to glue a bridge?

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http://www.presnallguitars.com

Or if a guy had one of those nice units that hold the guitar and swivel all about.
You'd want it to hold indefinatly,not fearing it might release

Peter

You can wrap the pins in saran wrap. Also, when you remove the bridge clamp to clean out the squeeze out after 10 minutes you can remove the pins. If you don't get happy with the glue you are usually fine.

Not saying this is a good unit, but pulling a vacuum on an A/C unit is not a momentary thing. I have pulled a vacuum for over an hour, it just depend on the size of the unit and how much moister you want to remove. A good A/C vacuum pump just might cost more.

Todd

Okay! Thanks Todd!

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http://www.presnallguitars.com

Charles Fox wrote a good article about using vacuum in issue #88 of the GAL publication. I basically copied the fixtures he uses in his shop and use a pump designed for automobile A/C use. The system works great and cost less than $200 including the pump. I have run the pump for over 30 minutes at a stretch many times with no issues.

Chuck

Edit - My pump cost around $120 at the local auto supply store.