Vacuum question?

[swirlman]

Getting ready to do some stabilization on some spalted maple. This will be my first time at this. Have the HF pot and venturi vacuum pump. Did a test run with the pot empty and my compressor will get me approx. -25 vacuum. Will this be enougth to do the job? I wll be using the acetone/plexi mix to stabalize the blanks. Also how long should the blanks be under vacuum? Do I drill the blanks before they go in the pot? I've looked thru the archives and past post on this subject and didn't see any answers for my questions. If those that have used the HF pot set up could help me out I would appreciate any help/info. I'm fairly new at turning pens, have done about 75 and really like the look of the spalted maple but would like it to be more solid to cut down on the CA usage. Thanks, swirlman

 

[alamocdc]

Yep, that should be plenty good. If you're talking about the HF paint pot, I'm not sure what the acetone fumes would do to the rubber gasket. If that's the case, be prepared to replace it unless you are using a separate lid. Draw a vacuum and let it sit for about an hour then release and let it sit for a few hours and repeat the process several times. I don't use my paint pot for vacuum.

 

[swirlman]

Thanks Bill for the info. I didn't think about the acetone damaging the gasket on the lid but that makes sense. I think I'll go with a thick piece of plexi for the lid and save the original for casting blanks under pressure. I still would like to know if drilling the blanks before stabilizing would help the process. George R.

 

[loglugger]

swirlman, I drill before stabilizing.
Bob

 

[DocRon]

" I think I'll go with a thick piece of plexi for the lid"
Hummm. Plexi for the lid...acetone is the solvent for plexi ... pulling a vacuum, which vaporizes acetone from the solution... hummm.

Just wondering. I would expect that at the least the plexi lid would etch from the acetone fumes. Might it also stress crack under vacuum? Don't know, just wondering from a base of no experience at all. I do know that Lexan, aka. polycarbonate, will stress crack rapidly with acetone.

 

[mrplace]

What is everyone using for their vacuum reference, inches of water or inches of mercury?

 

[Russb]

"What is everyone using for their vacuum reference, inches of water or inches of mercury?"

Hg = Mercury

 

[Fred]

Swirlman... the HF pressure pot is acceptable for vacuum with modifications made to the PRESSURE gague that comes with the pot. PRESSURE gagues do not measure VACUUM and will often be ruined if a vacuum is applied. You must understand that vacuum reduces the ambient pressure within the pot and the lower pressure will cause the solvent in any mixture to "boil" off much faster.

I have found that a vacuum of 5-10 inches of mercury will allow the solution to penetrate the wood effectively IF the wood is (1) pre-drilled, and/or (2) less than 10% moisture content. I use my own mixture of MEK and dissolved clean white styrofoam to fill the wood pores. So far I am extremely satisfied with my results. If I apply full vacuum to the pot the MEK solvent boils off very rapidly and I am left with a thick solution that does not get pulled into the wood as deep as I want it to.

To avoid wasting the MEK (17.50 - 27.00 a gallon) I have resorted to the lower vacuum and allowing the wood to soak longer - around an hour or so under constant vacuum.

I pre-turn to a close diameter to my finished pen or whatever and always pre-drill to expose the interior wood to the mixture and vacuum. This pre-turning and pre-drilling have proven to be extremely benefical to the process and it has also lessened the time of the vacuum process. I redrill afterwards to allow the tubing to be glued in place ... the CA seems to hold much stronger also and I don't seem to need as much CA either.

The most important thing to remember here is that the wood needs to be dry - at 10% or less moisture content. Most acrylics do not mix well with ANY moisture and the results can be quite noticable.

BTW, an exploding pressure pot can best be compaired to the results as seen when a grenade goes off. Flying metal shards are just as deadly as grenade fragments. Applying any pressure to a glass jar - as some have stated they use - is just asking for trouble of the worst kind. If one insists on using glass I HIGHLY recommend that the jar be placed inside a metal bucket to contain the fragments IF and WHEN the thing explodes.

I certainly don't ever want to be near a glass jar of any kind when it explodes, nor do I ever want to witness an exploding pressure pot. Why do you think they put a PRESSURE RELIEF valve on these things...

The use of common sense goes a long way when dealing with presure or the lack thereof... you ever see an exploding gasoline truck or gas tank? If you don't know how or what you are doing ASK questions FIRST. Your life or eye or hand or whatever you save just might be yours or your kids or friend.

 

[johncrane]

Top posting Fred and some very good advise thanks a lot.[]

 

[KenV]

Failure under vacuum is called "imploding". Bucket is still a good precaution when using something that can bounce.