Need Help!- Building Vacuum Clamp and Mechanical Clamp Sub-Table

[automizer]

So I was using my machine this weekend and came across some all to familiar problems for holding down my material. I have a 50" x 100" Aluminum Table with Drilled and tapped holes on 4" centers. What I want to do is bolt down a piece of 1" Ply with holes drilled and T-Nuts pressed in I would like it on more holes then 4" centers gives but that I can work around. What I am having trouble deciding is the vacuum side of it. I want to split the table in to 8 zones at 2' square each. Now I'm undecided if I should cut out paths for air lines or should I just be carving out a path on the underside and let that become a chamber sucking the ply down to my top. As well I'm looking at the options of running an electric vacuum pump or a compressed air pump.
I'm looking at all options but I would like to start making the top with in the week.

[swarfmacdaddy]

You will never do it with a compressor , venturi type affair. Too much surface area.

[Gir]

You will never do it with a compressor , venturi type affair. Too much surface area.

I've seen people use vacuum hold downs with compressors and get good results. I'm not sure what the Venturi Effect has to with this, as well as surface area. Perhaps I'm just ignorant.

[ger21]

Originally Posted by Gir I've seen people use vacuum hold downs with compressors and get good results. I'm not sure what the Venturi Effect has to with this, as well as surface area. Perhaps I'm just ignorant.

You'll need a virtually perfect seal on the 2' x2' area to get the vacuum started. If you can't hold it very tight and flat for a few seconds, you'll have a hard time getting it started. A venturi pump might only draw 2-4 cfm, while commercial router vacuum systems use 15or more cfm, so it'll suck a part down quickly.

[Gir]

You'll need a virtually perfect seal on the 2' x2' area to get the vacuum started. If you can't hold it very tight and flat for a few seconds, you'll have a hard time getting it started. A venturi pump might only draw 2-4 cfm, while commercial router vacuum systems use 15or more cfm, so it'll suck a part down quickly.

Ohhhh, thanks. I was thinking of the Venturi Effect, which really has more to do with liquids. That explains a lot.

[swarfmacdaddy]

Check out joewoodworker.com A wealth of info on the subject.

[automizer]

Well I can agree with the need for a good seal and that will be key number one. I will be running a vacuum like the on found here
http://www.cnczone.com/forums/showthread.php?t=53796
I was hopeing to start today but I have run in to a problem with my machine and can't. But im going to do this in 2 stages a top and chamber to get the best results.
I have looked up Joewoodworker and there is some good info there, I think my idea will work but I wont know until I put it all together.

[w1cam]

Hello,

I'm new here and ran across your forum. There is a guy that sells vacuum clamps on Ebay for around 25 bucks for a set of four. They work really well. His user name for Ebay is dcad100. If you do a search in Google using
dcad100 you can get there too. As far as a venturi, it will work better using a vacuum pump. The venturi will run your compressor non-stop so it will be noisy and run up your electric bill. I have both but alway use the vacuum pump.

Good luck

[Vac-Clamp]

I beg to differ on a couple of points raised in this forum. We manufacture venturi units and vacuum hold downs. We have also made some custom units with a single venturi unit working with a 450mm square (18" x 18") pod, and they work extremely well.
Air consumption is about 1 cfm per generator, so they work with small compressors. They also are remarkably quiet. A good seal between vacuum pad and workpiece is essential, even if you have a large vacuum pump, and porous materials (MDF) will yield lower vacuum pressure.
I am wondering if the forum contributors have been working with inefficient venturis?
Vac-Clamp

[w1cam]

"I beg to differ on a couple of points raised in this forum. We manufacture venturi units and vacuum hold downs. We have also made some custom units with a single venturi unit working with a 450mm square (18" x 18") pod, and they work extremely well. Air consumption is about 1 cfm per generator, so they work with small compressors. They also are remarkably quiet. A good seal between vacuum pad and workpiece is essential, even if you have a large vacuum pump, and porous materials (MDF) will yield lower vacuum pressure. I am wondering if the forum contributors have been working with inefficient venturis?"

I've worked with all kinds of venturi and not found one that works like you describe. Venturi are air hogs typically require 80psi and for it to be a constant. Even a multistage venturi needs to create a vacuum from a large volume of air. Not enough air then not enough holding force. A router would just kick the part with your description. You may be able to hold a part so you can sand it but not cut into it. I checked your site and don't see them for sales either. If you need a powerful holding force, a pump is the way to go especially if it is a hole type grid table. A good hold starts at about 10CFM and 26 or more Hg.

[mlabruyere]

Originally Posted by Gir Ohhhh, thanks. I was thinking of the Venturi Effect, which really has more to do with liquids. That explains a lot.

Air is a fluid and is therefore subject to this effect.

[Papakel]

Hi all,
I have had great success using a 1cu ft refrigaration vac pump with home made clamps I used 25mm perspex plain and simple foam tape arround both sides a 10mm hole drilled into the edge between the tapes and a 20mm hole drilled through the centre connecting with the 10mm from the side which connecte to the vac pipe with an old gas tap controling the vacum flow. I have made several sizes and have used 2 or 3 together for larger jobs. I use 10mm plastic tube connecting them together with quick release Hep20 fittings. I hope this is usefull.