Vacuum chuck at altitude... what's a 'safe' pressure?

[rickjudd]

When I lived near sea level I could pull a vacuum in the high 20's. Now that I'm at 7,000' altitude naturally I don't get quite the vacuum... somewhere around 19-21. Any opinions on if this is safe or to be avoided would be appreciated. I get that it depends on the diameter of the chuck as well as size of the piece being turned.

Thanks!
Rick

 

[Jim McLain]

Maximum theoritical vacuum at your altitude is 23.27 according to the Turntex site so 19-21 be more than adequate to hold a piece in place.

 

[Dave Landers]

I live at 7750' and have no problems. My gauge is goofy so I don't have numbers. Main problems are the same as at sea level - bad seal or leaky wood pores.

 

[Gary Beasley]

The cfm rating of the pump plays in to the equation as well. Higher cfm gives you a bit more tolerance to leaks in the seals or the wood.

 

[rickjudd]

I'm using a Gast pump that has pretty good CFM. Haven't had issues but wanted to get y'all's thoughts. I guess the real challenge is when the power goes out .

 

[Dean Center]

You'll feel more comfortable about vacuum chucking when you've got a few more pieces under your belt. I like to have the pressure above 15, but not long ago the best I could get was about 10. All I had left to do was remove a tenon and sand the foot, so I went ahead and it worked out fine. Most of the things we do with a piece on a vacuum chuck are not really stressful to the connection--like sanding and nibbling off a tenon. We aren't generally rough turning a big bowl with a huge honkin gouge.

 

[Gary Beasley]

I'm using a Gast pump that has pretty good CFM. Haven't had issues but wanted to get y'all's thoughts. I guess the real challenge is when the power goes out .

If thats a concern for you put a ”storage” tank in the circuit somewhere. It will take longer to draw the vacuum down but will also take longer to lose vacuum in the case of a power failure.