You should contact tech service. You get the alarm due to insufficient vacuum threshold set by the factory. That is adjustable(at least it is on other machines I have worked on). Find out how and dial it down.
We have been buying 1/2" but I'm going to try 3/4" from here on out. I had another CNC machine my last 1/2" to 3/8" and I get better holding power on my 1/2" so I'll try 3/4" to see how it holds. My tooling and machine are VERY accurate so I can make a new sheet last for months.
I've pursued that a little. Seems the less ports I open on the matrix table the more concentrated the suction is where it is open...and again, the mdf is so open it shows even less vacuum overall. I almost wish I could turn down the HP on my pump. I think I'll just resort to getting a new piece when needed.
On Thermwood machines we use a 3/4" Table Board (32Lb per cubic foot recommended density) as a base with a 1/4" Wasteboard (48 lb per cubic foot density) on top This eliminates a lot of the bleed through. We replace the wasteboard when it is surfaced to .17"
You should probably look at the CFM of your pump to see if it is moving enough volume of air. The piping to the pump and the table matrix are also factors. The pump can be rated for a lot of suction but if it can't move enough volume of air it won't hold your parts.
Dirty air filters in the pump can also reduce its efficiency.
Not to be rude, but my problem lies in having too much suction. The mdf I'm trying to resurface isn't even seen by the machine as my pump sucks THRU it so well.
Apparently this isn't a big issue for smaller pumps (like the four other CNC machines at our other facility).
I can't just make a massive spoil board as most of what I do runs on pvc/uhmw pods directly on the table and I have to take my spoil board on and off as necessary. 90% without it so making it massive isn't going to work as I have to lift it off and on manually.
Suction, is what happens when you restrict the flow of air through your spoilboard.
If your spoilboard is allowing too much flow of air through it then the pump needs to move a greater volume of air (CFM) to create suction.
Give us some more info about the pump.
If this is a low plenum pressure alarm, I would really look at the simple and most likely things first because 3/4 standard MDF should be working just fine with just about any pump and any machine.
Have you carefully and thoroughly checked for leaks in your vacuum line? Like Kerry says blockage can reduce the pressure and set off this alarm, but the opposite is true as well, leaks reduce the pressure and the sensor will trigger the alarm. If you have really eliminated this possibility Mike and Chuck are dead on, your sensor may be bad or mis-set. Contact tech and get the real answer, your problem is not likely the MDF.
I went from a 10HP Becker to a 30HP rotary screw. I had to lower the switch setting with the rotary screw to get rid of the low vacuum errors. It's likely the high cfm that is causing you the problem.
If you can't adjust the vacuum switch, jumper it out when resurfacing, or, depending on where the switch is, put a ball valve between the switch and the table so you can restrict the flow and increase the vacuum the switch sees.
Check your gaskets make sure you have a dood seal on the edges. Sometimes our board will start to warp and won't lay flat and leak, so i have jumped up on the table to weight the high spots, once it grabs it will hold.
Change brands of material. We had something similar and discovered the material was the culprit along with a bow in the product. If we have vacuum problems we often will cover the table with a roll of polyethylene to find out where our leaks or problems exist. It becomes fairly easy to trace whistle sound when you restrict the draw with the poly.
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