Official Luthiers Forum!

Is this the same one you posted about last July?
viewtopic.php?f=10101&t=37137&p=486605&hilit=+vacuum#p486605

I still think its leaving it on too long

Is it natural black rubber? If it is, seems like some of its color leached into the lacquer.

Kevin Looker

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I'm not a luthier.
I'm just a guy who builds guitars in his basement.
It's better than playing golf.

Ever use rubber clamping pads on a bar clamp? The pressure will often cause something to leach out of the pad. I would assume that it depends on the material but it wouldn't surprise me if lots of rubbers and plastics do this.

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http://www.chassonguitars.com

So here'sone for you guys too... I recently saw a guitar I built about 5 years ago and a discoloration has cropped up around the bridge perimeter. It's like a inversed sunburst! it's draker right at the bridge and fads out in about an 1/8 of an inch or so. My bridges are also vacuum clamped. The customers not really concerned about it as he's happy with the guitar and the bridge isn't lifting or anything, it just a cometic thing.
Any thoughts.

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Jim Watts
http://jameswattsguitars.com

You only need to leave it in the clamp for an hour, two if it makes you happy, but not disturb it until the next day.

It's quite possibly a "bleed burst". If the owner puts fretboard oil (e.g. that Dunlop stuff, which is a non-drying oil) on the bridge, some woods like Maccasar Ebony, Cocobolo amongst others, will release colour into the oil which then migrates though the bridge, through the glue line and into the soundboard, giving said bleed burst. So, if you must oil a bridge, make sure it's a drying oil that you use. This problem is unrelated to vacuum clamping.

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Trevor Gore, Luthier. Australian hand made acoustic guitars, classical guitars; custom guitar design and build; guitar design instruction.

http://www.goreguitars.com.au

Trevor, that's interesting and "bleed burst" is a good term for it. It's a Maccaser Ebony bridge.
I have no idea if it's had any type of oil on it.

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Jim Watts
http://jameswattsguitars.com

Why overnight? I have used this same clamp for years (bought it from Bob on the first batch he sold) Never a problem. I have used titebond, LMI and hide glues on new builds and repairs. Don't need to leave clamped more than an hour. I may leave them on longer as I am doing other things, but an hour is plenty of time.

Fillipo,
Have you thought about making a mask of saran wrap to go under the vacuum seal and isolate it from the finish? That shouldn't affect the vacuum at all, but would keep the seal from leaching into the finish,

Mike