Vaccum Pump for my 36X24 DIY vac tableI

[Roy Esslinger]

I just got done making my vacuum table out of 2 pieces MDF and it turned out great. I hooked up my shop vac that has a 2 inch hose and it really sucks right through the top piece of MDF really strong but I don't think it will be quite hard enough force to hold my work in place. the shop vac is really noisy and if I can find a stronger vac pump then the next step is to make the base of the table out of phenolic material to seal the bottom section. Any suggestions will be greatly appreciated. So far I only have about a twenty dollar bill in everything.

[martin54]

Before you go to the expense of buying something else I would finish the project & try it. You don't need a huge vacuum to hold stuff in place, long as you have a way to block the holes that aren't covered by the work piece you may find the shop vac does a good enough job.

[rscrawford]

Remember, the force holding an object to the table is actually the atmospheric pressure. When you remove ALL the air from under an object, you get the full atmospheric pressure pushing down (not really possible, but it is about 29"hg or ~15psi, so about 15lbs of force on every square inch.) With a shop vac, you are probably getting a maximum of 3 psi. So if you want 1000lbs of pressure holding your piece down, that means the surface area of your piece must be 333 square inches (11" x 30"). With leakage, the pressure will decrease so you either have to cover up the rest of your spoil board, or get a vacuum source that has enough flow to maintain vac pressure at higher leakage.

If you are cutting whole sheets (4608 square inches), you will be getting over 12000lbs of hold down force from a shop vac as long as you leave an onionskin.

[mike1966]

would a dust collector work? Ive seen some at grizzly for $100 that have 650cfm

[rungemach]

Hello Roy

Shop vacs and dust collectors are usually low force high air volume devices, whereas vacuum pumps are high force (negative pressure) and low volume.
Vacuum pumps get expensive as you get into larger air flow volumes.

Shop vacs are tolerant of modest leakage because they can move a lot of air at their modest force level. So leakage is not as important in your fixture.

The force developed on a part is only developed across the area of the hole, not the entire area of the part unless you can seal the edges and have the trapped air underneath evacuated. for that reason, some folks chamfer the holes, or cut circular grooves that hey can place sealing material in, etc.

One general problem with vacuum hold down is that you are trying to prevent the work piece from sliding sideways by holding it down. You have to get a lot of down force to hold it tightly. Its like trying to keep a car from rolling by putting weight on the roof. So you may end up with a combination of vacuum for hold down and pins or adjustable side blocks to prevent sliding, rather that try and get total hold down with vacuum that is hard to keep at a high level.

I hope this info helps.

[Edmeaux]

I use a 6 hp shop vac for my vacuum clamp table. I have 6 air pickups between 2 sides of the base. I get extremely good holding power if all of the holes are sealed. The shop vac is lound, but I tried a borrowed 6 cfm vacuum pump and it just didn't compare. I'd like to try a bigger pump, but I'm certainly not going to spend that kind of coin on an experiment. Gotta find one to borrow for that purpose. I have brainstormed that my dental suction pumps at the office may be up to the task, but again those are really expensive and need a water line in & out to make suction. If I can find a used suction pump at a good price...

[ssflyer]

Keep in mind that shopvacs depends on air flow for cooling - If you are trying to pull a vacuum w/o any leakage, you will fry the motor...

[Edmeaux]

Keep in mind that shopvacs depends on air flow for cooling - If you are trying to pull a vacuum w/o any leakage, you will fry the motor...

That's been in the back of my mind during this process. Maybe a small strategically placed "leak" closer to the vacuum unit could help that.

[PaulRowntree]

There are spring-loaded poppet valves that might serve, or perhaps cobble up something similar.

https://www.swagelok.com/products/valve ... alves.aspx
Cheers!

[Joey Jarrard]

Try looking at this http://www.blackboxvac.com/

[Gundawg]

I have a shop built vacuum table and I use 2 built in house vacuum motors I bought the motors from Light House Vacuum supply they have a large supply. I have 6 zones and use Valtera knife valves for running my zones as needed I can also run 1 vacuum motor at a time or both in parallel. The piping is made from 3" & 2" ABS sewer pipe. The main trunk is 3" ABS and each branch is made from 2" ABS.

In my opinion there are 3 methods for holding work by vacuum on router tables.

1) Vacuum pucks or jigs and allowing very little or no leakage and running a vacuum pump with high suction HG and low CFM flow.

2) Using a bleeder board and high CFM flow but lower vacuum pressure but having a larger area to hold parts and using gasketing to cover areas of the bleeder board not covered by the material being machined. I have a much larger table with more vacuum zones that can be turned on or off.

3) Using a large vacuum pump 10 to 25 HP or more. This in my opinion is the most expensive and probably best way to go if you have the $$ and electrical capacity to run these large pumps they have both high HG suction and the CFM flow.

To me most home shop or small shop people will find type 1 or 2 a better choice. I cut plastic most of the time and I do not cut through my parts and leave a skin to keep from loosing too much vacuum pressure. This works for me but you will have to figure out what works for you. You cannot use a small high suction pump with low CFM flow to suck through a large bleeder board.

Mike