Vacuum Tables and CDX Plywood?

[Howley]

You know I set up my 6 zone vacuum table and initially I'm just using a 6.5 HP Craftsman shop VAC as a vacuum source until I order my four lighthouse motors.
It's pulling about 5" of Hg. and if the piece of wood is 16"x16" or bigger and is a high grade veneer, it is unmovable, even with this small vacuum.

My question or comment is this.......Even with the lighthouse motors pulling over 10" of Hg... Will anything really hold CDX Pine 3/4" Plywood?

It appears to me that the surface is so uneven that you just can't get a great hold on it!! My current Vacuum would not hold cdx plywood at all, and I don't think that even with twice the HG and four times the CFM I don't think it will hold.

Any experience with CDX and Vacuum tables??:confused:

Thanks for any feedback!!

John

[cwshop]

When I first got my shopbot, vacuum holding was great’s thing that came to my shop. Unfortunately thru the years, I found that vacuum clamping wasn’t the answer for everything. I just go back to screwing them down or having some sort of clamping fixture.

[loriny]

I've had very limited success doing it with full sheets. I only run 2 vac motors though. if i would get the better side to have the crown oi the middle it works with 2 passes. (climb cut, then conventional skin cut pass)
Lorin

[dana_swift]

The air has to be getting around the ply or thorough it. Maybe both. I dont work with ply, but any part can have the problem. I use blue painters masking tape (3M) to seal around the edges of problem parts, that stops the leak there. If a not, or hole in the middle is causing the problem, I add some tape there. Eventually I get a good hold on even the worst troublemakers.

Most things just "pop" down and seal. But even once in a while I get troubles.. tape seems to do the most good on a generic hold-down.

The best of all is a dedicated fixture with gasket tape around the perimeter. I rarely have any trouble with those. So.. conceptually you could run a bead of gasket tape around the perimeter of the spoilboard to seal against the ply's irregularities. You would have to replace the gasket tape occasionally, but it would make setups fast. Just something to consider- if you do the same type ply regularly.

D

[Howley]

Thanks Dana, I'll give the blue painters tape a try, it's cheap and easy!
As far as a dedicated fixture, I thought about a scrap piece of corian with 1/8" groves 1x1 grid and a harbor freight vacuum pump. Then I can put the gasketing material where I need it, of course this would only be for carvings, no cut through.

Thanks to you and everyone for the advise !

[bcondon]

Hi John,

I think the answer to your CDX question will be much moe about the gasket material. The material from All Adhesive (resource list) comes in many widths, thickness and densities. I use it on my dedicated pucks and works great.

There is an explanation in their site which talks about density (soft, medium or hard) and the thickness. I would go for a soft or Medium density because it needs to mould into the crevices of the cdx but also the thickness is important to span or seal the gap.

I will give it a try on a piece of CDX hopefully tomorrow and get back to you. I have a Harbor Freight Vacuum pump and pucks with gasket material. Are you doing a full sheet or something smaller?

Thanks

Bob

[Howley]

When I cut cdx plywood, it's all the way through, so I can't use a small vacuum pump, it has to be a high CFM vacuum. Pucks and gaskets are ok for pieces smaller than 24"x24" that are bring carved on top with no through cuts. CNCs are easy, vacuum hold downs drive me nuts. Sooo many variables!!!

[bleeth]

4 LH motors should hold down just fine as long as you aren't cutting a lot of little parts out of it with a big bit. In many ways cdx is similar to Chinese cabinet ply in that it often has a pretty good bow. Usually we can overcome it with our small regen (7.5HP) just by putting the sheet on with the cup up in the center. Occasionally we need to add a couple screws or clamps in the corners, but that's about it. 4LH motors will suck better than my regen.

[bcondon]

I did setup a 24x24 piece on my 5x11 puck using the gasket and it held on as I expected. The gasketing did absorb the roughness of the CDX

I can understand your thinking. I set up small pucks and fixturing around my table and zero to that fixture and produce what I need. Some pucks have multiple features...

If ever piece is different, then your model will work fine... I would simply screw down the corners with offset blocks and let it rip.

If I had reproducible work, then I would place two or three pucks where I need them (to the table) and then do the cutting but fail to see the time improvement over just screwing it down!

Good luck!

Bob