4x8 Vacuum Hold Down

[elogicca]

Ok, Now I need to build a vacuum hold down for my table, my power options are 220v/110v single phase. I will mill 4 zones maybe 5, what options are there besides a regenerative pump. It must run on 220 and support a 4x8 foot surface.

[harryn]

I am not sure about the area you live in, but around here, there are a lot of used vacuum pumps on the market. The semiconductor market especially uses a lot of them.

Almost any of them will pull at least 1/2 atm for high volume. Lower volume ones in reasonable sizes will go lower, but going to less than 1/10th of an atmosphere is probably not worth the size / price.

A single or dual stage oil filled pump will work fine. You might even get away with a small roots blower type.

There are a few higher end vacuum cleaners that have pretty strong motor / turbine setups - usually the canister types, like a Princess or some of the German house vacuum systems made with HEPA filters. (the one I am thinking of starts with an "M", but I cannot remember the name) These can be found mostly at small, local vacuum repair stores.

I have been told that some of the older Kirbys could pull the carpet away from the wall, so they had to "weaken" the suction.

I would not bother with ANY upright vacuum motor / fan setups. Even the pricey ones are not that powerful.

[elogicca]

I've seen quite a few vacuum pumps in the local ads, bu i'm not sure what i should be looking for in hg and cfm for a 4x8 surface area.

[Geof]

Originally Posted by elogicca I've seen quite a few vacuum pumps in the local ads, bu i'm not sure what i should be looking for in hg and cfm for a 4x8 surface area.

Go for the biggest you can afford and drive with your electric supply. It is difficult to give firm figures because there are many variables such as how porous is the material you a holding down, how severe are your cutting forces, etc.

Full vacuum, about 30" Hg which is impossible to get, gives you a hold down force of 14.7 psi or just over 2000lb over a square foot. A really good vaccum pump will pull 27", maybe a bit more, without any leaks. As soon as there is any leakage the vacuum is lost very quickly because it can take a very large pump to overcome even small leaks and give a good vacuum.