vacuum holder marks my finish

[Mike Ryan]

I have a vacuum system and the billet aluminum tilting holder from LMI. It has about a 10 inch round holder with a rubber gasket for seal. I hated other methods for holding acoustic guitars.
I love this thing for holding for sanding, working on almost anything. I usually just hold on to the back to work on the guitar.
But there is one BIG problem.
My finish gets marked up by the vacuum holder.
I use em6000 water based lacquer and really like the stuff for ease of use and a nice finish. However, even after letting the finish harden for over a month, I can still see where the holder was as a ring after I use the holder. I can get the ring out but it takes considerable wet sanding and buffing.
I can't think of any way around it except using the vacuum holder less or putting up with the considerable finish repair by wet sanding. .

[JC Whitney]

Is it because the force exerted by the gasket is compressing/marring the finish? If so, increasing the width of the gasketing material would (in my pea brain's view) spread out the force over a larger area and in doing so impart less psi onto the finish. Ice skates vs snowshoes...?

[Mike Ryan]

excellent thought. I have actually tried that without success. Maybe try it again. Maybe look at it from a different perspective. Always hope it is lightbulb over the head going on time.
One of fears from experience is sanding through the finish although didn't have that problem this time. My experience with that has to do with mainly sides and upper bout at neck joint and several sanding through episodes. I made a bigger effort to get things flat regarding sides and back with new sanding techniques this time.

Are you familiar with this fixture from LMI for vacuum holding?

[Steve Senseney]

Another thought, would there be a plasticizer leaching out of the rubber holder that is causing the ring?

Especially if the finish has dried for a month.

[Randy Roberts]

Mike,

I have the same vacuum vise, and had the same problem ( although French polish rather than laquer).

The solution ended up being a good going over of the edges of the channel for the gasket. There is a burr left on the edge that, while you may not be able to feel it, does cut into the finish enough to leave a visible mark in finish,( though not, it seems, in wood), at least with mine. Hitting the edges of the gasket trough with sand paper eliminated the problem at least for mine.

I would not have spent the money for the fixture myself, but I got it as a gift from my Dad, and just love it. Definitely well designed and solidly built.

Sand down those edges and I think you will be happy.