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CNC vacuum cfm4/13
We are looking at purchasing a new cnc router and are comparing the cfm on the vacuum pumps of 2 different machines to see which one will give us the best hold down so that our parts will move the least. One vacuum pump produces 635cfm and one produces 600cfm. In our particular applications of boards we use 11/16", 1", 1 1/8" HPL and Thermally Fused boards that are cut on an mdf spoil board. The majority of our material is 1 1/8" thermally fused. The majority of what we cut is larger than 24"x24", but occasionally we cut parts that are 1 1/4" tall by 15" long out of the 11/16" material
Below I created a chart that compares each pump and the cfm that is pulling the board. The numbers are derived based upon the board size vs the zone size of each machine. IE a 4x4 board placed on a 4x8 zone
4x4 318cfm vs 240cfm
Now logic would dictate that the bigger number is the best choice. However what I am wondering is should I not look at the machine with the smaller pump because my parts could move or does the smaller pump still produce enough vacuum?
I think you are confusing CFM with the vacuum force (generally given in inches of mercury, or inches of water column)
CFM doesnt vary with square footage of part. The CFM is the maximum flow of air the pump will move without any restriction. Either 600 or 635 CFM should be negligible difference in practice. But it depends upon the vacuum. If both are pulling the same vacuum, they will perform similarly.
I will assume this is from a regenerative blower/vac? Prob about 16 or 17 HP?
I use a 10.5 HP regen vac pulling close to 400 CFM at what amounts to 4.5 PSI - which on my 48" by 48" CNC holds even smaller parts like the narrow piece you describe, quite well with a down spiral, or compression bit. Your cutting strategy is just as important to work with the available vacuum, in order to keep small parts from moving. Larger parts no issue.
you have to look at the air flow and the vacuum force to make a choice IMO.
Are you nesting on the router?
does the router have automatic zoning?
router table is 5'x10'?
what sheet sizes are you running?
how many hours a day do you think the pump will run?
What type/brand of pumps are you looking at?
There are serious differences in short and long term costs that need to be part of the equation.
We are running a nested based router.
One machine has 4x8 and 5x10 zones, the other machine has automatic zones that adjusts based upon the board size in the program.
Our table is 5'x10'.
As said below we run 4x4, 4x8, 4x10, 5x8, 5x12 size sheets depending on the job. The sheet sizes vary through out the day and we can have multiple sheet sizes on a job.
The pump will probably run somewhere between 15-17hrs a day.
One machine will use 1 Travaini 600s-1a liquid ring vacuum pump. The other machine will run 3 Busch mink pumps.
Thatís a lot of hours a day, I would consider maintenance costs of the units as a deciding factor. You didnít mention vein pumps which I would have deterred from you running that hard as repair cost add up.
If my quick math is right you are looking at over 30 hp worth of pumps, that on a 5x10 should be more than plenty, overkill even in my opinion. Worst case maybe tab small parts if needed.
Potential electrical costs might even need to be considered. I don't know the Trivianni well but the Busch pumps are very good but expensive.
You also mentioned 12í material, how to you run that on a 5x10 table?
Sorry that was a typo. It was supposed to read 5x10. I have 4x12 and 5x12 on my mind because we are thinking about potentially adding them to our inventory. This of course would mean that we would be jumping up to a 12' machine. I'm not sure if that would change the situation at all, but I didn't want to ask because we are just in the investigation stages
How many CFM a pump can move only matters as your leakage approaches the point where the work will move. Maintaining a sufficient level of vacuum to hold the part is related to CFM but CFM is dictated by leakage. A perfectly flat sheet on a sealed edge waster board that perfectly matches the work & table will require very few CFM (to start.) Different pump methods produce considerably different curves for CFM VS level of vacuum. The level of vacuum required goes up as the size of the parts goes down. At some point you are forced to go to onion skin/tab no matter how many hp your pump has. The condition of your spoil board has a significant affect on lost vacuum. It is probably possible to mathematically determining the minimum part area that can be held, IF you know all the variables. Your software needs to be set to switch to tab/onionskin at a point you have determined by trial & error. That point is also variable based on what you are cutting, condition of spoil bd. amount of tool path.... Onionskin cuts take twice as long so you don't want to have more than needed. More art than science!
we use a quincy 15hp rotary screw on a 5x12 flat table, The quincy does a nice job and sips amperage compared to a huge 40hp shotgun style pump