Vacuum Chuck Question

[Dave Fritz]

I'm working on a small white oak plate and used a vacuum chuck to do the bottom. The chuck is a Woodfast one with a Rubber Chucky rim on it. I'm finishing it with Minwax tung oil finish. I find no matter how many times I sand it the ring from the vacuum chuck is still visible. It acts like fiber compression from the bevel of a gouge.

Has anyone else had this problem and if so what did you do to fix it? Thanks

Dave Fritz

[Tony De Masi]

Sure have. My solution was to use an old mouse pad between the chuck and the wood. Just cut a hole in the pad smaller than the diameter of the chuck. Problem solved.

[Eric Gourieux]

Yes, I've had the same problem. Tony's solution is a good one going forward. To remove the ring that you have on your current piece, just keep sanding. You may need to back up to 220 grit and move up from there. I have not found any other solution for removing the ring that you describe, but I have always been able to sand it out.

[Kyle Iwamoto]

Too much vacuum? Not familiar with the Rubber Chucky brand, but if you run too much of a vacuum, I could see crushing fibers, resulting in that ring. Don't know what your vacuum generator is either. Do you have a bleed valve?

It seems that you've finished and can't sand out the ring. You'll have to sand all the way through the finish to get to the damaged fibers.

[Dave Fritz]

Thank you, it's nice to know I'm not the only one with this issue. I wonder if I tighten the tail stock to much when first chucking it up? I keep the tail stock on as long as possible.

I have this system: http://www.jtturningtools.com/vacuumpumps-kits and usually the vacuum is between 15 to 20 on the gauge. I adjust to that level with the bleed valve.

I will sand away the finish and keep going until it's gone.

Thanks,

Dave Fritz

[Dwight Rutherford]

I also think it may be too much suction.
example;
at 15" of Mg. a chuck that is 3.5" diameter will be exerting 70.9 lbs of suction
at 18" of Mg. a chuck that is 3.5" diameter will be exerting 85.0 lbs of suction
at 15" of Mg. a chuck that is 5.5" diameter will be exerting 175.0 lbs of suction
at 18" of Mg. a chuck that is 5.5" diameter will be exerting 210.0 lbs of suction

If if you don't have a bleed valve installed, suggest you do.

If your plate is thin, at those pressures you risk implosion.

If all you are doing now is sanding you just don't need that kind of vacuum. I sand at 300RPM and use about 10lbs.
When using my vacuum and tailstock, the tailstock is gently brought to up to the piece after I have applied suction.

[Bob Bergstrom]

I find it hard to believe there are any crushed fibers if you were turning dry white oak. Sounds like the rubber duckie is burishing the wood. The bowl is spinning on the chuck. I would suggest leaving the tail stock engaged till most of the bottom turned with the vacuum on. Suction and pressure from the tailstock helps prevent spinning. If I have a ring I just power sand through a few of the finer grits with the bowl in my lap. Also don't use too big of a gouge. If the cut causes too much resistance the bowl will spin.

[David C. Roseman]

Agree with Bob that with dry white oak it's unlikely you're using too much vacuum. I use 25" Hg on cherry and mahogany without crushing the fibers. But whether it's the fibers being crushed from vacuum, or burnished from slipping against the rubber rim of the chuck, I would try dampening the ghost ring and the adjacent areas with denatured alcohol, or just plain water, to raise the wood fibers. Let the bowl sit for a short while until dry, then go back to sanding.

[Dave Fritz]

Thanks for the comments and suggestions. I am pretty sure the plate isn't slipping on the chuck. I'll change out the Rubber Chucky and try some other material in the future.

Dave Fritz