Vac-Clamp Dissappointment

[LazyMan]

I have single sided Vac-Clamp from http://www.vac-clamp.com/ and am using a harbor freight 8 gallon 2 hp compressor. Im using the whole surface and it just doesnt have much holding power. Theres no way im even generating 200 lb of holding power because it doesnt take much effort to pull it off even when using it with non porous material. My compressor doesnt get below 80 psi. I saw someone on cnczone who got great results.

Any ideas?

[bp092]

I'm not impressed with the vac clamp either. It works but I'm not sure its good for cnc situations, there are better vac clamps out there. But much of it has to do with two things; how well your gasket is and how strong your compressor is. I don't think an 8 gallon will keep up with the vacclamp. I would imagine that thing will be recharging itself constantly, 2hp or not harbor freight compressors arent that well made anyways. Ran mine on an industrial ingersol rand and a 150 gallon 8hp?(I think) compressor and it worked well. Could hold my body weight but still had too much give to it for me to want to use it on a cnc router. Great as an extra hand when manually routing stuff though.

[ger21]

With any pod type vacuum, you really need to use two to keep the part from wanting to spin or slide. At least from my experience.

[LazyMan]

Thanks for the input.

I suspected that the harbor frieght compressor was not doing a particularly great job, but everything seemed to run within the Vac-clamps specs.

I tried it again and its even difficult to get the clamp to stick and just simply hang on the material. I was hoping to cut stuff that was around 6x6inches. I guess thats just too little surface for vacuum system.

It just frustrating because the the stuff I been reading about this system made it sound as if it was better than sliced bread. With the performance I was getting from the vac-clamp, it's hard to believe it would be useful for any cnc work at all.

[ger21]

It honestly doesn't sound like it's working correctly. Our machine has 6x6 pods, and they will hold a part down while a 1/2" bit is cutting it, although it will move a bit. But that's with a worn out 10 year old pump. I'd expect the Vac-Clamp to actually hold better. Either the compressor isn't keeping up, your getting leaks, or the Vac Clamp may be defective, imo.

[LeeWay]

I don't have that clamp, but I have used venturi style vacuum pumps before. They work well for an air conditioning system to pull a vacuum, but just have a hard time generating constant vacuum once there is a leak. Even a minor leak.
I built a vacuum jfixture using aluminum and an old AC compressor. It would work, but did not have enough volume to hold a vacuum once a little air escaped.
I saw where another fellow mentioned using an aux. tank to maintain the vacuum.
Something like this might actually make your's work better too. Hook your fixture to one end of the tank and have the venturi pulling from the other end.
You would have to do some testing, I'm sure. It might hold just a little better than what you have though.

Otherwise a vacuum pump would surely do better.

[bp092]

Its strong I have held my body off the ground with a piece of prefin plywood one time to test its strength (screwed down to the bench.) However I believe Ger is correct; it has a lot of play, maybe two would work better as it would pin it at two points. It just has too much give because of the gasket material. But it definitely has a lot of holding power with the right compressor.

[LazyMan]

Well, theres got to be something going wrong from what im reading here. I suspect my compressor is defective or something because it just seems like theres not much that could go wrong with the pod itself, but I could be wrong.

Ill try to find someone with a compressor and see what happens. I really hope to get a working system because vacuum hold-down just makes so much sense for the type of work I want to do.

[Geof]

Can you rig a vacuum gauge to see what vacuum you are getting? Just a piece of 1/2" polycarbonate plastic tap for the gauge put on in place of your workpiece.

If your compressor is able to maintain 80 psi when it is running the vac-clamp I don't think it is the compressor. Vacuum venturi have two big limitations in my experience; they cannot move much air on the vacuum side so even the smallest leak overcomes them, and even when the system is sealed perfectly they cannot pull much better than 20"Hg which is only two thirds of a full vacuum, i.e. less than 10psi differential across the workpiece.

You would probably be better off turning your compressor into a vacuum pump like I did.

http://www.cnczone.com/forums/showthread.php?t=53796

[Rance]

Geoff,

I see the link to http://www.cnczone.com/forums/showthread.php?t=53796 and soforth but I don't ever see any details of the build, only that you did it. Is there more info. than that? Thanks.

Rance

Originally Posted by Geof ...You would probably be better off turning your compressor into a vacuum pump like I did. http://www.cnczone.com/forums/showthread.php?t=53796

[Geof]

Originally Posted by Rance Geoff, I see the link to http://www.cnczone.com/forums/showthread.php?t=53796 and soforth but I don't ever see any details of the build, only that you did it. Is there more info. than that? Thanks. Rance

The build was simple partly because the inlet and outlet ports are identical, both being 1/2" NPT on this compressor.

Originally there were two filter units screwed into the two inlet ports and the outlet were combined and connected to the tank through a non return valve in the top.

I took off all the outlet piping and removed the non return valve from the top of the tank; this left a 1/2" NPT connection at the top of the tank.

I moved the inlet filters over to the outlet ports; here they act as silencers.

Then as mentioned in the thread I just connected the two inlet ports to the top of the tank using copper water pipe. Near the cylinder heads in the first picture you can see the flanged unions that are used with copper pipe as disconnection points, there is also one at the top of the tank not visible under the motor mount. These just allow the copper to be disconnected if needed; I actually cut and fitted everything up and soldered all the joints in position.

[Vac-Clamp]

Dear Vac-Clamp users,
All of the products that we manufacture we stand behind. I invite all people whom have purchased Vac-Clamps and have had difficulties to contact us via email. (Goto www.vac-clamp.com and click on email us) We don't mind assisting users, and questions are usually answered within 24 hours, time zone difference permitting.
We have a lot of Vac-Clamp users that have had good results on CNC equipment. There is also a product developed specifically to help CNC users.