Recommendations for a cheap powerful vacuum pump

[Michael Thames]

This evening I whipped together a vacuum table clamp to hold down work on the CNC machine. I have a vacuum press and figured that I’d just hook that up to the new vacuum clamp. But alas, it doesn’t seem to have enough power to really do anything.

‘’Anyone have suggestions on where to find a powerful enough pump to hold down work? Thought of some kinda shop vac hook up but it might be hard to step down to a quarter inch hose going into the clamp. Thanks!

[David Falkner]

Cheap and powerful aren't often used in the same sentence unless there's a 'not' thrown in there somewhere.

A friend owns a cabinet shop and they have a beast of a CNC, 12HP main spindle with 4HP secondary for drilling holes, and it has three 5HP vacuum pumps to hold a full 4x8 sheet to the bed. So the vacuum pumps exceed the spindle power and I've seen that before, that it takes more HP to hold the piece than it does to machine it. That's assuming you want to provide clamping on the entire table. I've seen fixtures for specific pieces, like bridge blanks, where the fixture is large enough for the blank and the work piece is held by a shop vac. I guess it depends on how large an area you want to clamp, Michael.

David

[Jim Becker]

The smaller pumps like you and I have for vacuum press, etc., are usable for "pucks" and the like to hold down components for CNC milling, but as you note are not anywhere near capable of anything much larger. For small CNC machines, some folks do use high-performance shop vacs, but "real" vacuum systems for CNC "start" at a cost that is as much or more than you invested in your first CNC machine. These systems have enough air flow and pressure drop to pull vacuum through a spoil board.

I'll also mention that holding small parts is actually harder than holding large parts, the reason being that the more square inches of "part" you are holding, the more atmospheric pressure will be there to hold down the part at just over 14 lbs per square inch. There's a good, recent "mathematical" explanation about this in the Camheads forum. While I cannot directly link to it, if you go to camheads dot org, scroll down to the "Vacuum, work holding, dust collection" area and then visit a thread by member "Options" named "Vacuum", take a look at post #5 for a full explanation about how vacuum work holding, um...works.

[Kevin Jenness]

What sort of pump do you use for your veneer press? As Jim says, a low flow/high vacuum pump can be effective for clamping with properly designed fixtures.

I have a full table (4x8) system based on three central vacuum motors adding up to 21 amps/220 volts that pulls about 7 in.hg and works pretty well for full sheets and parts down to maybe 100 sq. inches if the rest of the zone is covered.

For small parts I have made fixtures using my 1/4 hp rotary vane pump. Initially I tried to use the small pump to pull the fixture down to the mdf spoilboard as well as the workpiece to the fixture, but the system lost too much vacuum to leakage through the spoilboard. When I screwed the fixture down using pins for location and confined the airflow to the top of the fixture holding the workpiece it worked fine. There is a balance between the cutting force and the clamping force- the smaller the part the harder it is to keep it in place.

[Michael Thames]

Thanks guys, I have a Mercury vacuum pump I bought probably 20 years ago. Tried to look them up but seems like they are long gone. I’d have to remove the casing to see the motor ratings. I have a table top press that opens and closes. I live in Santa Fe, NM at 7000 feet. I get considerably less PSI here than when I lived in Calif. But I digress.......

I just Just want to hold down a guitar top. I drilled the holes only in the area of the guitar shape, so not that big.

I really dont don’t want to invest in an expensive pump, so i’lll try and rig up a shop vac and see what happens.

[richard newman]

Michael, did you run a gasket around the perimeter of the guitar top? That will help avoid leakage at around the edges.

The other thing that might help is to have a tank as in a compressor, to create a rush of vacuum to pull it down initially. Once your part is "sealed down" your pump may be adequate to keep it down. Holding the top down with a flat board would help get that initial grip.

I've used a 3/4 hp Gast pump for vacuum chucks to hold large vessels on my patternmakers' lathe, but always with neoprene gaskets.

But you can't go wrong with a big ass pump, and if this is going to be an important part of your process, might be worth the investment.

[Michael Thames]

Hi Richard, No didn't use a gasket. I used Melamine two pieces 3/4 inch thick about 18x24 each and sandwiched them between a 1/4 thick MDF gasket I made a gasket rim and sealed it with a caulk/adhesive all around the perimeter. Then made strips inside with cut-outs for air circulation, and support in keeping the work table straight and level. I have a jig/template that I place on top of the guitar top and is heavy and holds everything down then use a router to rout out a couple mm's. When I get the CNC I'll route out the cavities with that.

Yesterday for the first time I ruined a guitar top, while routing out the recess, the wood loses its strength and acts like a piece of paper at .60 mm thick and starts to buckle up and then it has a very uneven cut, and I need an exact consistent thickness in that area of .60 mm. The cut has to be very even and exact at .60 mm no room for variation in the thickness. I thought for sure the Pump I had would do the trick.

[Brad Shipton]

If you post some pics of the pump I am sure we can help. It comes down to the max vacuum the pump can generate and cfm. The vacuum pump for my veneer press is rated for 5cfm and it can evacuate a 48x96 bag in about 5min or so for a stack of flat stock.

I would look carefully at your gasketing also. If your gaskets are not perfect, your vacuum constantly flows air. It takes a much larger pump then. I had problems with the pumps I use for pods and eventually I found it was mainly a problem with my gaskets. I make my gaskets with the CNC now, and they work much better.

[David Falkner]

This is something I have been wanting to try but haven't gotten to it yet, won't work for everything but doesn't look bad.



David

[Brad Shipton]

There are oodles of stories of homemade vacuums on the shopbot forum. You can find the basis of the hurricane vacuum Gary created by searching for his name or Brady Watson on that forum. I built a table vacuum myself based on the concepts posted there. Vacuum pumps made using the shop vac size motors are mainly for large pieces where you can get enough hold down with 7 - 10" of Hg. For small parts, pods or dedicated fixtures work much better.

[Kevin Jenness]

Michael, at .6mm (approx. .024") you are talking veneer thickness. It may well be at that thickness your material is too porous to be held down effectively with vacuum. You may want to try using tape instead. I am still searching for the holy grail of double-sided tape that holds strongly yet releases easily with no residue. One method I have used successfully is two layers of blue masking tape with ca glue between. For more precise thickness I have contemplated using aggressive double stick tape sandwiched between blue tape. Good luck.

[Michael Thames]

This is something I have been wanting to try but haven't gotten to it yet, won't work for everything but doesn't look bad.



David

Kinda what I came up with. I when to WoodWorkers Supply today and got some step downs. Of course I got the wrong size, I'll have to go back later this week.

I solved the pump issue, I simply used my big dust collector and stepped the 3 inch tube down to 1 inch into the clamp. Works like a charm, tons of suction I can barely move it when it on.

Made a short video too will post it later

[Mick Simon]

Thanks guys, I have a Mercury vacuum pump I bought probably 20 years ago. Tried to look them up but seems like they are long gone. I’d have to remove the casing to see the motor ratings. I have a table top press that opens and closes. I live in Santa Fe, NM at 7000 feet. I get considerably less PSI here than when I lived in Calif. But I digress.......

I just Just want to hold down a guitar top. I drilled the holes only in the area of the guitar shape, so not that big.

I really dont don’t want to invest in an expensive pump, so i’lll try and rig up a shop vac and see what happens.

If you're interested, I'm also in Santa Fe and teach CNC for woodworking at SFCC. I have a student who is making a vacuum fixture for guitar tops, among others. If you would like to sit in on a session, PM me.

[Michael Thames]

Here is what I came up with. A quick and dirty video, not as in-depth as David's. But, the big shop vac works great

[Michael Thames]

If you're interested, I'm also in Santa Fe and teach CNC for woodworking at SFCC. I have a student who is making a vacuum fixture for guitar tops, among others. If you would like to sit in on a session, PM me.

‘Wow Mark, I was thinking of looking up SFCC for courses in CAD and CNC. Yes, I’m interested.