Matrix Table Upgrade?

[HuFlungDung]

Could a person make a table with a large number of small pockets cut in, say 3/8 material (or thicker), with one vacuum hole in the center of each pocket. I suppose the pocket could be what, 2" diameter? Then, countersink a seat at each vacuum hole location, and provide a single plastic ball that is captured within each cavity, but is just rolling around loose to start with.

When cutting the part opens a pocket to the atmosphere, then air flow tends to suck the ball over to the hole, where it plunks down into the seat and blocks it off. Wait a minute, this is giving me an idea for a household appliance........

[Scrit]

I can imagine this the other way round, sort-of, i.e. a cavity with a hole in the top where the ball is held against the opening by a weak spring. The spring would need to be strong enough to counteract the vacuum. When a work piece is placed on top the ball is depressed and the vacuum is "switched on". If there is nothing on top of a ball, then it is forced upwards by the spring, blocking the vent and the vacuum is "switched off". There is already a commercially-made system called the MiniMach / MaxiMach (by a firm called VTech, I think) which does this and you can buy kits of the parts in the UK. How would you stop the balls from being sucked into the hole, though?

I am beginning to wonder if the technique used by some of the plastics boys might be the best approach. Acrylics are supplied with a thickish self-adhesive paper coating on both sides and the guys I've watched have the matrix set-up to draw down over a number of cells (divided up by foam rubber coird) over the maximum area they can. They set-up their cuts so that they skim the paper with the final pass, but don't pierce it. It believe that this requires the matrix bed to be regularly reskimmed, though

[HuFlungDung]

The problem with the spring and plunger though, is that the cutter would have to totally clear the material overlying the exact plunger position, in order to free it so it would spring up and allow the ball to seal the hole. You also might have the danger of cutting the plunger.

The vacuum hole does not need to be large enough to "swallow" the ball, this is what the countersunk seat provides, is a place for the ball to sit, blocking a small hole in the center of the seat where vacuum is applied.

A bit of wind from the cutter bit might cause the ball to fly around, or even get out of the cavity, so maybe a small "ball cage" (screen cover) would have to be provided to prevent this possibility, and to keep the ball down safely out of the cutter tip zone.

Another approach might be to use a "reed flapper" over top of the vacuum hole. The trick with this system is that you would need perhaps a secondary, but completely isolated vacuum grid system to each pocket to perform the initial evacuation, from another hole in the pocket, on the "top or air side" of the reed valve. This would then allow the reed valves to stay open. At that point, then the secondary system would be disconnected, and the vacuum redirected to the initial vacuum grid. Then, because no air is left in the pocket at this stage, the reed valves would not move until the integrity of the chamber was breached.

The reed valve would have to have enough natural stiffness that it would lift off the vacuum hole when the state of vacuum exists in the pocket.

[ger21]

The pods on our Masterwood have the ball and spring. Although it's only half a ball with a pin on the bottom to go in the center of the spring. very soft plastic, or hard rubber to seal good. Remember that you'll have to seal each of your pockets, and if you cut through this seal or the ball, you'll lose vacuum.


Gerry

[HuFlungDung]

Would it be possible to improve the efficiency of a small vacuum pump system by zoning off areas that have been exposed to the atmosphere? This would take a series of solenoid valves that could be called by M functions, to disconnect or reconnect certain zones back to the pump. The connection to the various zones could even be cycled on and off as necessary to support the work whenever the cutter is in that zone.

[skippy]

I'm an Australian living in Belgium and last time I went back home to Oz I was amazed to find someone using MDF as the sacrificial board (vac system on a cnc router). The MDF there was much lower density and therefore allowed the air to pass through it. The MDF here in Europe wouldn't let any air through at all I'd imagine.
Phil

[ger21]

You can get regular MDF and low density MDF, which is probably what you saw. But even regular MDF will let some air through, as long as you seal the edges.

[nemi]

We are a OEM that manufactures plenums, grid tables and vacuum pods.
We have made several plenums and grid table that are placed on
a pod and rail machine or point to point.
Please check out the below links for plenums, grid tables and vacuum pods.

http://www.nemi.com/plenum_table.htm

http://www.nemi.com/vacuum%20grid%20table.htm

If you have any questions please email or call.
Have a good weekend.

[charlespricefur]

Originally Posted by Scrit Does anyone have experience of replacing pod bar type tables with matrix beds? In particular, what is the ideal size for the "islands" in a matrix bed and how much vacuum draw down is required? We curently have a Biesse Rover 335 PTP router (3 x 7.5HP HSDs, 24 vertical and 8 horizontal boring units) and we'd like to replace the pod bars with a system which could draw down small plastic or wood compononens, preferably only a sacrificial bed of MDF or similar. Any thoughts gratefully received.

Hi will you be disposing of your vacume pods and rails as i have a biesse rover 335 and im in need of some spairs.
regards
steve

[craigy85]

In my work I always just use MDF a a cover sheet, i have also cut down a 'C' Cramp and welded a plate to it which can be screwed down or slid up the slots in my matrix bed. it works well to provide a little extra grip to small areas.

Anyone got any good links to websites for self learning on cnc's and CAD/CAM software?