Vacuum Clamping

[John Sincerbeaux]

Hello everyone,
I fabricated a large vertical fence that I have been using on my slider for several production tasks. For clamping, I have been using my AirTight pneumatic clamps. The Airtight clamps are pretty stout contenders and are awesome. However, in this application(mounted horizontally), they are pretty cumbersome. I can’t help but to think about using vacuum clamping instead of pneumatic clamping.
Think a 24” X 12” vertical fence that is made from a CNC plate, table, chuck or whatever they are called? It seem the names are interchangeable?
Anyway, I was wondering if any of you CNC guys could shed some light on the best setup for this.
Compressed air systems vs. dedicated vacuum pump? I have seen both.
I can buy a pre made aluminum grooved (grid) plate with multiple ports that you can customize by using rubber or silicon tubing? I have a small pump that I use for veneering but don’t know if that would work for clamping?
Would a grooved plate hold wood strong enough for cutting on a Table saw? It seems most industrial CNC wood cutting is done using small individual cup-like pods that connect anywhere on a large vacuum table?

Any insights? I think Jim Becker has a lot of CNC experience?

thanks
John

[John K Jordan]

John,

My own CNC experience is small so I don't know how well this would apply, but the information at Joe Woodworker might be useful. He is primarily focused on veneering with a vacuum press but also caters to vacuum chucks for lathes and vacuum clamps. I bought everything to vacuum clamps for my milling machine but have not yet constructed them.

Joe Gorleski provides plans for building a quite capable vacuum pump system with reservoir and sells any parts needed at quite reasonable prices. (He is a real nice and helpful person too!)
Maybe browse the topics on the right side of his main page.
https://www.joewoodworker.com/veneering/welcome.htm

Some possibly interesting sections. I like his footswitch control.
https://www.joewoodworker.com/veneer...umclamping.htm
https://www.joewoodworker.com/veneering/EVS/concept.htm

JKJ

Hello everyone,
I fabricated a large vertical fence that I have been using on my slider for several production tasks. For clamping, I have been using my AirTight pneumatic clamps. The Airtight clamps are pretty stout contenders and are awesome. However, in this application(mounted horizontally), they are pretty cumbersome. I can’t help but to think about using vacuum clamping instead of pneumatic clamping.
Think a 24” X 12” vertical fence that is made from a CNC plate, table, chuck or whatever they are called? It seem the names are interchangeable?
Anyway, I was wondering if any of you CNC guys could shed some light on the best setup for this.
Compressed air systems vs. dedicated vacuum pump? I have seen both.
I can buy a pre made aluminum grooved (grid) plate with multiple ports that you can customize by using rubber or silicon tubing? I have a small pump that I use for veneering but don’t know if that would work for clamping?
Would a grooved plate hold wood strong enough for cutting on a Table saw? It seems most industrial CNC wood cutting is done using small individual cup-like pods that connect anywhere on a large vacuum table?

Any insights? I think Jim Becker has a lot of CNC experience?

thanks
John

[Jim Becker]

There are different challenges with using vacuum for work holding on a CNC table vs using vacuum with fixtures. The reason is because of surface area and orientation of stresses that will try to move something. I don't currently use vacuum with my CNC table, but have played with some smaller fixtures. Smaller pumps can be used with fixtures, but are not capable of servicing larger areas. Many CNC routers that use vacuum are configured with vacuum being pulled through an MDF or LDF spoilboard and hold a full sheet. CNCs that have gasket setups are most likely being used to machine specifically shaped object...like guitar bodies. Fixtures are great for holding small parts but I'm not sure how serviceable they would be for use on a tool like a table saw. I'd personally be more comfortable using vacuum clamps for that because they don't depend upon gravity and the weight of the atmosphere to keep work down.

[Kevin Jenness]

Your vacuum pump will work if you can get a good seal with little leakage. I have used a 4 cfm 1/4 hp rotary vane pump for clamping parts successfully using shop-made fixtures with neoprene tape seals at around 23 in. hg levels. My rudimentary universal vacuum setup on a 4'x8' table uses about 4 hp to pull 7"hg vacuum through an ldf spoilboard but most commercial users have 10 hp or more. I would assume that rail and pod cnc tables are used with good seals, low flow and high vacuum levels, while most cnc vacuum setups are based on high volume at a lower static pressure without positive sealing and require a lot of horsepower to hold small parts successfully.

[Brad Shipton]

I have used both a venturi to create vacuum and I have a couple of different vacuum pumps. Keep in mind the air demand for a venturi. My venturi used 3cfm if I wanted maximum vacuum, and it was quite loud when running at that level. In your case you are always aiming for a perfect seal, so the pump cfm is only important to determine how fast it will grab your parts. A small 1cfm Gast or other pump is cheap and that is what I would use. Cfm is quite a bit more important to CNC guys because we want to cut thru the stock to avoid tabs or something else that creates a follow up step. CFM demand goes up very quickly once you cut thru the stock with cutters.

I don't quite follow what exactly you are trying to do. If mainly you are clamping down a jig to hold stock when cutting, that is quite easy since you will have perfectly flat surfaces to clamp too. If you are hoping to clamp wood parts to the jig and then work it, that is something totally different. Any bow or twist in your stock (knots a problem too) will cause problems achieving a perfect seal. This is the reason gasket material comes in endless different thicknesses and hardness. It might not be too bad if you are only dealing with 8" - 12" wide stock using 2 jigs, but when I have been working panels needing 4 pods to complete the machining, I have had a few instances where I had some grief getting things to seal with the standard gasket I like to use. It was not a big deal, but something to think about it you are doing large runs and you don't want to stop to futz with things. If you want to see some of the gasket material options take a look at allstar adhesives.

[John Sincerbeaux]

“ If you are hoping to clamp wood parts to the jig and then work it, that is something totally different.“

That’s what I am thinking.

Steve Rowe AKA Extreme Woodworker did something similar. He uses two 6x6” pods attached to his shaper fence which holds various boards to be cut on the shaper. But I think his pods are non- configuring ie, one gasket around the perimeter of the pod which would required min 6” wide stock.
My idea is t use a Configurable grooved plate for a tall fence like 12 x 24”

John

[Mick Simon]

I see no reason why it wouldn't work. A gasket grooved pod with a central port that gives you flexibility to configure the gasket as needed would not require significant cfm, just adequate pressure, provided that the seal is good. The larger the area inside the gasket the longer it will take to pull the vacuum. But we're talking 3 seconds vs 2 not 15 or 20.

I do something similar with my vacuum bag pump and pods. There was a good article in Fine Woodworking a few years back. Here's a link but I don't know if this is a subscriber-only article or not.

[Brad Shipton]

I think it will work fine. There will be some details to sort out like tube management and the gasket material, but with 2 pods it could work quite well. I watched the Steve Rowe video, and that is a fairly easy application similar to what many use for sanding on a shop table. Make sure to have a vacuum gauge within eye site. It is easy to think you have full vacuum when you still have leaks. A small pump will not be able to keep up with fairly minor leaks.

The link below is an example of a popular ball valve. Joe has some as well, but I like these ones.
https://bettervacuumcups.com/bv1000-bvc-ball-valves/