Pressure vs. Vacuum

[Padre]

I finally built my HF pressure pot so that it can do both pressure and vacuum. I can pressure it up to about 70 psi without any leaks. I can vacuum to about 18inHG, and that's as far as my pump will take it.

My main question is: when do you use pressure, and when do you use vacuum? I had some great success doing the 'coffee and cream' blanks using pressure.

Thanks in advance for any comments.

 

[lorbay]

Pressure for what you did with the coffee blanks and for worthless wood & Alumilte.
Vacuum for degasing resin before adding the catalist ( some of us will add the catalist 1st) and Vacuum for stabilizing wood blanks and dying.

Lin.

 

[Padre]

Thank you!

 

[Glass Scratcher]

Vacuum for degassing some Urethane resins before mixing, and if you are going to make silicone molds- for degassing silicone before and after mixing, before pouring over your mold plug.

 

[MesquiteMan]

I can pressure it up to about 70 psi without any leaks.

Chip, please see this thread here regarding my experience using a HF pot at high pressure: http://www.penturners.org/forum/showthread.php?t=51588&highlight=catastrophic

 

[gketell]

Yup, vacuum when you want to get the slow-setting resins (PR, fixative, etc) deep into the porous woods for stabilizing punky woods or "worthless wood" where the wood used has lots of little cracks and crevices. Then pressure to shove it further in (which is why you need slow-setting resins for this).

Pressure for everything else.

You never want to use vacuum only and leave it vacuumed while the resin sets. That just makes the bubbles that don't pop bigger than they would be without vacuum.