Porous Wood?

[John Trax]

Well I turned the first bowl using my new vacuum chuck and it did not work! When I turned the bowl around to attach to the vacuum chuck I could only get about 7" of Hg. Spent 30 minutes checking every connection for leaks. Finally took the bowl off and stuck my hand over the vacuum chuck and it instantly went to 26" of Hg.

I assumed there was a crack in the bowl so I set it aside and started on another blank. When I re-chucked it on the vacuum plate, same thing only 7" of Hg. But this time I noticed that dust in the air was actually being drawn to the surface of the bowl! Putting hands on the wood I could feel air going into the wood! In the first spark of intelligence all day I decided to try wrapping the bowl in something, found a roll of masking tape and wrapped it up from top to down where I needed to work at the bottom. Vacuum gauge now shows 16" of Hg, still not perfect but the best I could get. Used tail stock support and finished this one.

I was turning Red Alder on both of these. So the question is, is this common with other woods or did I just get unlucky on the first thing I turned?

[David Walser]

John,

Some woods, like red oak and ash, have open pores and -- depending on the thickness of the wood -- are difficult to vacuum chuck. A possible solution is to finish the inside of your bowl with a film finish, such as lacquer, before vacuum chucking. Assuming the film finish has cured (and has plugged all the pores), you should be good to go.

HTH.

[Richard Madison]

John, If you're using the vac chuck to just clean up the the center of the bottom you could wrap the rest of the bottom in thin plastic wrap. No guarantees, but might be worth a try.

[William Payer]

John,

I recently had the same problem turning a bunch of willow. The bowls were decently thick at the botom (about 3/8") yet the wood was so porous, my vacuum dropped to unusable levels. Since I was going to finish them with salad bowl finish, I put a couple coats on them (after sanding ) and all went well from there.

[Mike Minto]

Jim at Australian Burls gave me what I think is a simple, but brilliant way to increase vacuum on poorus wood - he places the wood on the vacuum chuck, turns on his pump, then with his other hand covers the outside/bottom of the form with sawdust. Plugs the holes in the turning. I haven't tried this yet, but am keeping it in my back pocket until I need it. I would think you'd have to check the filter leading to your pump after doing this, however.

[Doug W Swanson]

In the second Bill Grumbine video he uses masking tape to cover the bottom of a bowl. I don't remember the type of wood he was using but there must have been 3-4 layers of tape on it.

Doug

[Steve Schlumpf]

John - the only times I have had problems with vacuum was when there were small cracks, voids or when I had turned something really thin. I have used masking tape over voids before and it does work.

I do remember turning a small spalted birch bowl fairly thin and you could feel the difference in temperature between the center of the bowl and the outer edges. The vacuum was drawing air through the bowl and the wood was very cold to the touch! Remember thinking that it was interesting and something I had not expected!

[Leo Van Der Loo]

It is the endgrain that will leak with these open pored woods, sidegrain on them leaks hardly anything if at all, so using a chuck on the inside bottom or sealing the endgrain is the simplest way around this problem, things like cling wrap do work as a seal for that, HTH for next time ;-))

[John Trax]

Thanks for the suggestions everyone! I did use masking tape and I thought at the time I had thought of it myself but I have Bill Grumbine's second video so that is probably where I saw it done. Funny how the concept stuck but I have no memory of seeing it on Bill's video.

Alder is a fun wood to turn, although it gets a lot of tear out. I have been using Bill Grumbine's "vertical shear scrape" to finish with and that seems to work on the outside. Nothing for it but sanding on the inside. It isn't what I would call a 'pretty' wood but it's what I have for now and maybe by the time I get ahold of something else my skills will have increased to the point I won't be afraid to work on 'good' wood.