Homemade Vacuum clamp

[ChrisA Edwards]

After seeing this video, I purchased the plans, but the plans did not specify any info on the air pressure to vacuum device or the size of the rubber seal ring.

Thought I'd ask here.


https://www.youtube.com/watch?v=OUJNfhnowog

[Bert McMahan]

The vacuum device should have the specs on required input pressure and flow. Do you have that device yet?

And the seal ring looks like caulk backer rod, something like this- https://www.homedepot.com/p/M-D-Building-Products-20-ft-Gray-Foam-Backer-Rod-for-Medium-Gaps-and-Joints-71480/202066515

It's available in a few sizes I believe.

Edit: Watching the video, it looks like it could just be a rubber tube? I doubt the size matters too much as long as it protrudes a bit and can squish down.

[Jim Becker]

If I'm not mistaken, vacuum sources for fixtures like that have to be able to develop a high static pressure because of the limited area of the parts being held in place while CFM optimized vacuum sources are better for holding large pieces of sheet goods on CNC machines because gravity helps "a whole bunch" at something like 14 lbs per square inch. For a fixture, it's the same thing as with a vacuum chuck on a lathe...something like a Gast vacuum pump (I got mine surplus) can be a good source. The same kind of pump can also be used for vacuum veneering so it's a good investment that has multiple uses.

[Jerry Bruette]

JSK is using a inline venturi vacuum generator. We used to use Vaccon brand at work but a quick search at McMaster and Grainger show other brands. You need a constant supply of air to operate them. Not sujre on how many CFM you'll need, but I'll guess you'll need a good sized compressor to run them.

You can get O-ring material in any length you need along with the glue to make up the seals from the same suppliers.

You'll need pretty clean air to run the generators because the ports in the venturi are pretty small and will plug with the finest dirt. Get the mufflers with the generators too or the constant hissing of the air will become pretty annoying.

You'll want to pick a diameter of o-ring based on the thickness of the blocks used in the fixture. 1/4 inch thick MDF or Masonite for the blocks would require an o-ring that's thicker than 1/4 inch. McMaster has special material for vacuum work holding plates https://www.mcmaster.com/products/o-ring-cord-stock/gasketing-for-vacuum-workholding-plates/.

[ChrisA Edwards]

I have a couple of vacuum pumps that I use on my lathe and when vacuum bagging. I was thinking I could utilize my air line rather than having to drag one of the pumps out and plug it in.

I'm also thinking I may may make a small, removable, hold down area on my CNC, maybe 12" x 24".

[Steve Jenkins]

For the gasket you can use closed cell foam weather stripping

[Alex Zeller]

Back in the day when I did lead abatement we used venturi vacuums to collect the lead paint. We did things like removing lead paint on bridges. Often a small spot needed to be stripped, not the whole bridge. The tools used were things like air powered needle scalers so it made sense to use air for the vacuum. They worked ok but we weren't using a 5hp air compressor. These were tow behind 210 cfm air compressors. I've never tried it with a smaller compressor but it felt like while it could go low it couldn't move a lot of air so you would need it to be sealed very well.

I was checking out my neighbors CNC. His has a 20hp vacuum pump and it just pulls the air out through the MDF. There's no holes or anything. It just pulls it right through the spoilboard. It's a 5x10. You just have to flatten each side to take the surface off of it (because it has a sealer applied to it). It sits on top pf a phenolic table with zones. I'm thinking for a small CNC a 5hp vac should be fine.

[Patrick Varley]

I have a couple of vacuum pumps that I use on my lathe and when vacuum bagging. I was thinking I could utilize my air line rather than having to drag one of the pumps out and plug it in.

I'm also thinking I may may make a small, removable, hold down area on my CNC, maybe 12" x 24".

Veneer Supplies/Joe Woodworker has a few venturi-based kits for sale, and those plans spec the CFM required. https://www.veneersupplies.com/categories/Vacuum__Press__Items/Vacuum__Press__Kits/

[Jim Becker]

I was checking out my neighbors CNC. His has a 20hp vacuum pump and it just pulls the air out through the MDF. There's no holes or anything. It just pulls it right through the spoilboard. It's a 5x10. You just have to flatten each side to take the surface off of it (because it has a sealer applied to it). It sits on top pf a phenolic table with zones. I'm thinking for a small CNC a 5hp vac should be fine.

A vacuum table is a different animal than a fixture and requires a different kind of source for vacuum. It's also not a good setup for small parts because...gravity can't help much with very limited surface area. I mentioned this in my original reply to this thread.

[Pat Hemen]

This brings back memories! I used to work for a plaque manufacturer, at the peak we made 20,000 daily, rectangular or square. Then at one point we added shapes. Our methods produced the shapes at a much slower pace, like maybe only 500 a day of a 12 by 12 size. We used a vacuum transducer that used air pressure to create a very high vacuum using Bernoulli's Effect. We had a steel jig made in the shape of a heart and used a rubber material that had adhesive on one side and stuck it to the jig. We used half inch MDF and found we had to order the MDF with a vinyl overlay on one side, because the transducer sucked air right through the MDF and we had trouble keeping a 12 inch by 12 inch blank on the jig. With the vinyl overlay, it held so strong you could not pull it off. Then we used table mounted routers to cut the shape of the heart shaped jig. The bearing on the router bit followed the jig and it actually worked pretty good. To release the cut out shape, the exhaust was directed by a hose to one of the handles to the jig, and by putting your finger over the end of the exhaust hose, it disrupted the vacuum and the newly cut shape would fall off the jig, and the process was repeated. We had a 2 stage air compressor and could run 2 to 4 stations at a time. I don't recall exactly how much CFM of compressed air was required but it wasn't an unreasonable number. We also made much smaller heart shapes, and found the vacuum was not strong enough to hold up against a router bit cutting through the half inch MDF, so we ended holding them to the jig by pre-drilling the back side of the blanks and using 2 locator pins on the jig to keep the blank from moving on the jig. I ended up buying a transducer for myself, but have yet to put it to work, but it was pretty cool how you could hold the blanks in place perfectly using compressed air to make the vacuum. My transducer is about 30 years old, so it may look a little different than the attached picture. I hope I explained this enough to add to the conversation.

[Maurice Mcmurry]

I always had trouble trusting the one at Franklin to hold a $10,000 to $20,000 dollar guitar. I see from this in fretboard journal that Nick's still works fine.

Reunion: Revisiting Nick Kukich of the Franklin Guitar Co. - Fretboard Journal (https://www.fretboardjournal.com/features/reunion-revisiting-nick-kukich-of-the-franklin-guitar-co/)

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[Bill Dufour]

Vac pressure is a maximum of 14.7 PSI. Less in real life. No way around it without a pressure chamber. Venturi maybe 10-11 PSI max
Bill D.

[John Kananis]

12 psi is quite a bit though. You're pulling ~25HG to get that kind of clamping pressure.

[Maurice Mcmurry]

That little air Venturi in the video posted by the OP is super cool! The Venturi and the jet engine supposably function based on physics. They sure appear to be magic to me. I need to get more educated on vacuum holding. The last fixture I tried is in the kindling bin.

[ChrisA Edwards]

I'm in the process of 3D printing a bunch of these for trial use on my CNC


https://hosting.photobucket.com/images/i452/cedwards874/VacuumPod.jpg



https://www.youtube.com/watch?v=vgbNrJ59w7c

[Wes Grass]

Very slick.

4x4" @ 12 psi is 192 lbs. Pretty hard to pull off, but depending on the part and fixture materials, keeping it from sliding around could be a problem. A spiral flute generates a little lifting force, but not enough to pull the workpiece up. But not much problem sliding it around, so some sort of 'keys' to fix it in place are a requirement.

[Michael Burnside]

A vacuum table is a different animal than a fixture and requires a different kind of source for vacuum. It's also not a good setup for small parts because...gravity can't help much with very limited surface area. I mentioned this in my original reply to this thread.

Agreed. I have one on my CNC as well, runs at 15A and 240V. It works great but for small pieces you have to cover up the MDF area with plexiglass or other non-porous material. I use it for larger parts and sheet goods but for small parts it's just a lot of overkill to use it. In that circumstance, I prefer my "MFT dog hole" spoilboard with a few t-track channels that is indexed when I place it down on my Phenolic bed. As the name implies, it has spacing compatible with Festool so I use a few MFT jigs/squares and a lot of TSO products (dogs and dog stops). I find a couple of small clamps to hold down is sufficient (barely needed if using a downcut bit) and the dogs/dog stops prevent everything from slipping.

[Bruce Wrenn]

Couple of thoughts. For gasket material, use the "O" ring from a five gallon paint buckets, and tire patching cement to join ends. Venturi used in most commercial small vacuum units is Air-Vac's AVR093H ($39.99) Bill Hylton's book, "Router Magic," has a section devoted to vacuum jigs, and their construction. Many years back, Shop Notes did an article on vacuum jigs. To make individual pads for vacuum block, make one and then use it with vacuum to hold others for routing on router table.