Vacuum fixturing..........20x32 plate processing......where to start?

Still dreaming of a new larger VMC and I have some possible parts that lend themselves to vacuum work holding. 3/8" 6061 plate approximately 20"x32" that needs to be profiled w/chamfer top/bottom, drilled/tapped holes, and a few cut outs needing chamfering top/bottom. I obviously want to machine complete in one OP. What kind of vacuum workholding is out there for this? I can't do one flat vacuum fixture, I need the plate elevated to allow the chamfering top and bottom.

How many parts???? Sounds to me you need to make a custom fixture for the part, if you're making enough to justify it.

I use the Pierson vacuum chucks, the small size. Chamfering bottom edges isn't a problem if you use pallets. You can cut a pocket in the pallet for the chamfer tool clearance. Make the pallet whatever thickness you need. I cut them on a laser out of 3/8" 6061.

You could certainly do a large part like this. We ended up making a 34x30 plate (and pallets) for some larger parts.

I have several Pierson venturi units and make my own plates. You could easily make a plate with gasket around the thru pockets. Thru holes are not necessarily a deal breaker but are more difficult to mask around.

I buy 1 inch thick plate when I find good deals and keep it around to turn into plates. I can design and make a pretty complex vac plate with multiple steps in just a few hours. Once you get the basics down it goes pretty quickly.

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By my opinion you can us MDF board. Chipper and easy. Libor

I tried this SmartVac II Vacuum System – Pierson Workholding for a small part I was doing and had no luck.
If you end up trying this system I would sell mine for half of new. I keep waiting for that large flat plate part to roll in the door....
Gary

Cycle1000 said:

I tried this SmartVac II Vacuum System – Pierson Workholding for a small part I was doing and had no luck.
If you end up trying this system I would sell mine for half of new. I keep waiting for that large flat plate part to roll in the door....
Gary

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Unlike a vacuum pump system the Pierson requires a larger area to be effective. I don't know if I'm correct in saying this but I use a 14 lbs per square inch inside the gasket. If I make a vac fixture for a smaller part I typically add pins or clamps to keep the part in place.

David, with plates that big there are other ways, how many parts are there, ...........and do you want to spend $$?

Limy Sami said:

David, with plates that big there are other ways, how many parts are there, ...........and do you want to spend $$?

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Sami..............just pokin and proddin right now, but I hope to do a few hundred of these plates. I want to be able to do them in one op.......profile/cut windows.......chamfer top/bottom of profile/windows.....drill and tap. No sure how else I could do these in one shot......................................?

For this many parts I'd definitely be looking at making up a custom vacuum plate w/ o-ring stock used as gasket material to prevent too much vacuum leak. Pocket as necessary to allow clearance for profiling endmills and back chamfer tools.

How will you be generating the vacuum? Dedicated pump or veturi? If venturi, consider using an accumulator near the machine to hold a reservoir of vacuum in order to ensure clamping remains solid through the cycle. I've had to do that on a couple of vacuum-based processes I set up.

If this will be repeat work, consider a Datron machine. My company recently bought one and we love it - great for large flat work, especially aluminum and plastics.

Dear look on foto how we us MDF board. Regards Libor

For that many parts I too would make my own custom plate with orings. Dovetail the oring grooves so they don't come out when you blow the chips and coolant off the plate. Vaccum is vaccum, doesn't matter how it is produced. I like the venturi pumps for this type of work. I use the smallest that Vaccon makes, 27 inches at .4 cfm. It doesn't move much air but with a good oring seal it doesn't need to. I use an 8 oz coolant accumulator with a vaccum gage to see how well it is working. While venturi pumps will pass coolant that gets past the seals it does reduce the vaccum level significantly, other pumps can not ingest coolant without problems.

Bite the bullet once and be done with it. Get a big enough plate of aluminum and mill it out. Thicker is better if going wider. I like to groove mine out with a 5x5 mm deep groove and for a plate the size you need I would go with a grid about 1.25" on center. In the center of each square tap a hole for holding stuff down. Countersink hole so a dummy screw can sit flush and keep chips out when not using that hole. Edge drill this plate in a few places as deep as you can. You can edge drill CL on groove or square, if on square then plan on a shallow X groove on square top. Drill and tap entrance holes to the edge drill so you can seal the unused holes. I use a .25 x .75 counter bore on these holes and put a punched out piece of 3/16 felt in the cbore as an intake filter.
Air powered venturis work fine and as David said, get a bit weak when passing coolant (so do I). Larger venturis consume more air and are less affected.
Once you know your part you make riser plates to elevate your work piece. These plates will be made to bolt down to the mother plate and have their own gasket groove on top. In many cases they are sacrificial too.
So, start with faced plate and add just the grooves that you need, but make sure they are on the grid. As you use this more and more you can keep adding to the grid as needed. Or git it all done at once.
I use .250 EPDM cord stock as it easily squishes down flat to the surface under vacuum. O ring cord stock has got to be put in perfectly for the same result. Other benefit with EPDM is that as it sits much higher above the surface it makes it a lot easier for the vacuum to seal, pulling the part down flat. On a piece as big as your making you will soon find out what that means.