Vacuum System Up and Running!!

[Jeff Paxton]

I received my Gast replacement pump today and switched it out. It seems to be working fine. Surplus Center promptly sent a replacement and a shipping label for the defective one. According to my gauge I am registering 25 with the Oneway 3.5 inch chuck. In researching past threads, 18-25 seems to be a good number. BTW, some say that are pulling so many "hg" and some say "inches." Could someone explain that? Also, what is a good (and safe) number to be pulling to do the bottom of bowls?

Just want to say thanks to Steve Schlumpf. I basically copied his system, with a few minor modifications, keeping everything on the same side like Bob Justin's. So thanks guys!

Jeff

[Nathan Hawkes]

Hg is the periodic table symbol for mercury. Pressure is commonly measured in inches of mercury, pounds per square inch, atmospheres ( 1 ATM= approximately 14.7 psi), and kPa (kilopascals--I'm not sure of the conversion here). Hope this helps.

[Nathan Hawkes]

forgot to add; I don't know the inches of mercury for normal pressure, as it I think is related to the atmospheric pressure at the time. They have a nice 4' tall mercury barometer in the chem lab at school with all the different scales on it.

[Steve Schlumpf]

Jeff - congrats on getting your vacuum system up and running! I am sure it will be worth the effort! There are charts out there that show you the pressure developed on the system but it all depends on the combination of vacuum in hg and the area/size of the chuck. For me, I have been running at 20 hg when using a 5" chuck and that puts the holding power somewhere around 200 pounds or so if I remember correctly.

If you need a chart - let me know as I am sure I have one around here somewhere.

Again, glad you got the system up and running! Looking forward to your review after you use it a couple more times!

[Russ Peters]

If it help that is what your blood pressure numbers are in except it millimeters of Hg not inches

[Tom Keen]

Congrats! I built a "Steve's Chuck Clone" also. Had to dip into the bandsaw fund but it was one of the best investments Ive made. Mine pulls about 22 with a 4 inch chuck. I routinely run my lathe at 500rpm with the vacuum chuck and I feel very secure. Watch out for catches..The weak point is the foam sealing ring.

[Jeff Paxton]

Steve,

Is this the chart you are talking about?

http://cnew.org/tips_techniques/vacuum_pressure_chart.pdf

I don't guess it makes much difference, but it is interesting to know how much pressure that little pump will produce. If this is not the chart you are talking about do you have the link?

Jeff

[Steve Schlumpf]

Jeff, found a copy of the info I was looking for but it is in Word Doc format. The info was originally sent to me by Tom Steyer when he was ansering all my questions about vac systems. The author of the chart is Curt Norman and all credits go to him for taking the time to figure out the numbers.

VACUUM CHUCK HOLDING POUNDS
2 INCH CHUCK ------- 31 lbs. @ 20 hg........ 45 lbs. @ 28 hg
3 INCH CHUCK ------- 70 lbs. @ 20 hg...... 100 lbs. @ 28 hg
4 INCH CHUCK -------125 lbs. @ 20 hg...... 170 lbs. @ 28 hg
5 INCH CHUCK -------190 lbs. @ 20 hg...... 275 lbs. @ 28 hg
6 INCH CHUCK -------280 lbs. @ 20 hg...... 395 lbs. @ 28 hg
7 INCH CHUCK -------380 lbs. @ 20 hg...... 540 lbs. @ 28 hg
8 INCH CHUCK -------500 lbs. @ 20 hg...... 700 lbs. @ 28 hg

(π X r² X ½hg = pounds of force)

The pressure exerted by the atmosphere is about 1/2 pound of force per sq. in. for every in. of mercury

Area in Square Inches of a Vacuum Chuck = π r² (3.14 X Radius Squared) Inches of Mercury = hg

Curt Norman 1/15/2006

Hope that helps.

[Gary Muto]

forgot to add; I don't know the inches of mercury for normal pressure, as it I think is related to the atmospheric pressure at the time. They have a nice 4' tall mercury barometer in the chem lab at school with all the different scales on it.

As I recall 1 standard atmosphere = 14.7 psi= 101.1 kPa=1013 mm Hg= 29.55 inches Hg