sizing a vacuum pump

[netsol]

i anticipate cutting A LOT of small printed numbers (1-5/8" squares) from polystyrene with drag knife
IF I FABRICATE a small vacuum table 24" x 48" how do i size the vacuum pump to hold my sheets?
i know when i look at the specs on a gerber sabre it seems like i could power the east coast with what it takes to run their pump

 

[Evan Gillette]

Hard to say exactly because it depends on the type of pump and table setup. But basically in your case, you are looking at pressure/vacuum differential. Basic idea is this: pressure/vacuum exerted by the pump/table to pull the sheet against spoilboard, friction is what is holding the sheet from moving around as it is being cut. You can increase friction in two ways, more pressure or surface conditions/materials. A good setup might include side rails on two sides to help with lateral movement. Most pumps are sized by flow, think of it as a pipe system, and each change point in the system needs an adequate cross-sectional area to reduce losses. Ultimately the other end of the "pipe" is the holes in the table and the sum of their area. The more leaks you have in/around your sheet the more air flows through, reducing pressure differential and force on the sheet which equals less friction. The reason most industrial tables have such large pumps and selectable zones is that they need to maintain vacuum even when 1/2 or more of the holes are open and allowing flow. Hope you can sort out my rambling and it helps break it down into manageable concepts

 

[johnnysigns]

We added tile gasket https://store.allstarcnc.com/tile-gasket to our spoilboard on our AXYZ for a polycarbonate job we did months ago and it's been a life saver. Technically I'm supposed to put my sacrificial mat on top of my spoilboard for knife cutting, but I'm eager to try knife cutting right on top of the tile gasket. We run the 1/32" thick stuff and the performance in vac power has been astounding considering the weak vacuum the AXYZ machines seem to suffer from with their plenum based vac supply. I'd bet you could use a shop vac, tile gasket and get some outstanding results. Thinner substrates will dimple where the holes are in the tile gasket. I would imagine if you didn't want to cut all the way down to the MDF you could at least score and break any parts that ran over the dimples. It's a pretty small investment for the performance you can gain.