Hand-Coding to Engage CNC Vacuum

      In case the operator forgets to turn on the vacuum, you can code to have the machine do it automatically. November 11, 2006

I'm training someone new to run our new CNC panel router and he keeps forgetting to engage the vacuum to the table after he loads a panel. We are starting to develop a small pile of "panel art" in the corner of the shop. Now on our Stratos/SUP, it won't run if the vacuum doesn't register a certain amount, I think at least 20". But with our vacuum (which holds parts just fine), the meter on the machine only reads 15-20", so I have to have the vacuum override on. Is there a way to change the minimal vacuum amount so I don't have to have the vacuum override on?

Forum Responses
(CNC Forum)
From contributor N:
The vacuum system is designed for safety purposes. The override is to run material where the vacuum bleeds through the board but the board is secure. If the operator canít remember this, shutting the override off this will force him to engage the vacuum. If this still doesnít work, try someone that will understand.

From contributor M:
Pretty easy. I am assuming a Stratos is an Anderson and you are using Alpha Cam to program. You can put anything you want at the beginning of a program, usually called safety blocks. Put the M-code that opens the vacuum valve(s) in the post processor where the safety blocks come from. I did this for my machine at work after one of my guys launched a board into the wall. If you are not comfortable editing your post, have the guys at Anderson do it. It is a very minor change and will eliminate the problem.

From contributor G:
Deduct the cost of each panel that is ruined from the trainee's paycheck. He will not forget to engage your vacuum system.

From the original questioner:
I use MV and I know I can edit the post to open the vacuum valve, I'm just hesitant to. We primarily use imported plywood and sometimes it takes a little work to get the warped sheets to suck down. If I just let the operator load the table and run the cycle, some parts may knock loose during the nesting. We are using a 5x10 spoil board, which leaves a large area open when nesting 4x8 sheets, lots of bleed through. So far we haven't had much of a problem with the extra bleed through other than having to keep the vacuum override on. Currently we are running 20 units of melamine, so I can edit the post for this job. From my experience, around 20" of vacuum seems to be the line; anything below that, I get an alarm and have to switch the override on. Is there a way to adjust this?

From contributor M:
I think you misunderstood my meaning. Put the code in the post so that the valve gets the signal to open when the cycle start button is pushed. I didn't mean to imply that the operator shouldn't first apply the vacuum manually and check for a good seal. If the operator remembered to open the valve manually, the result of the M-code to open the valve will be nothing. If he forgot again, then you have a prayer of holding the part. Oh, and by the way, for best results, use some offal or something to cover the bleeder board areas that aren't covered by stock.

From the original questioner:
Thanks for your posts. I will put the m code in as soon as I know what the code is. Unfortunately, it's not on my m code sheet. Do you know the code? Are codes for Fanuc controllers universal?

From contributor M:
Generally M-codes are assigned by the machine manufacturer, not the controller builder. You will have to contact the distributor for that. Since the same control is used by different machine brands and types, there is no practical way to assign codes universally.

As a side note, some folks like to release the vacuum at the end of a program with an M-code, but I like the parts to stay in place until the vacuum is broken manually. The exception to that is when using custom pressure fixtures or pendulum machining using each table independently for quicker cycle times. Remember, for whatever reason, some guys just never make good operators. It seems that some people are more suited for a work station away from the automated stuff, and vise-a-versa.

From contributor J:
If you are going to use an M code to turn a vacuum valve on/off, be sure and use one that will not reset on E-Stop. If the M code resets, it will turn the valve off. Usually M codes like M71/72 do not reset and are useful for applications like this. You might also want to put an M00 right after the vacuum valve on code that will give the operator another chance to make sure the part is held after pressing the start button. Then, after the M00, pressing the start button again will continue the program.

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