CNC Bit Choice and Dust Collection

      Will an upshear bit improve dust collection effectiveness on a CNC? November 26, 2007

We use our CNC to rough shape 3/4 PB for countertops, sometimes with laminate applied. Our local machine salesman hooked us up with straight cut bits and said they would be all we would need for our purposes. He seems to be right, as they cut the material just fine. However, these bits eject the chips sideways, and for the most part down into the bed. Would I notice a large difference using upshear bits, which would draw the chips up where the suction could better pick them up? I have a bit of CNC experience, but maybe what I need is some more CNC specific tooling knowledge. It struck me as strange to outfit our changer completely with straight cuts.

Forum Responses
(CNC Forum)
From contributor Z:
The up shear bits will pull the sawdust up, but it will cause chip in the pieces that already have the laminate supplied. We use compression bits for everything we cut to get the best finish top and bottom.

From the original questioner:
I suppose the compression bits would be the same as a straight cut for dust extraction? What I'm curious about is if we'll have considerably less cleanup using upshear. I realize the potential for chipping, but likely anything with laminate we would just run upside-down so the upshear would actually be compressing it.

From contributor Z:
Do you have a dust shroud or hood around the base of the spindle? This will dramatically increase the dust extraction. If you don't, there are a few ways to make one yourself. I know that Woodworkers Wholesale sells them.

From contributor K:
If you always machine the parts with the laminate face down, you should use an upshear tool. This will pull the waste up, and if your dust collection is good, you should have a clean table after the program is done. One possible downside to using an upshear tool is that it will tend to lift small parts, so be aware of the part size. If you are cutting a double clad panel, I would use a compression tool, and if you still have considerable dust on the table, make a second pass with the upshear tool to clean out the tool path slots.

From the original questioner:
Yes, the CNC head has a hood and shroud. I suspect it is set up perfectly, except for the bits we are using. The straight cutter throws dust backward down the line it has just cut. Sounds like upshear would be quite efficient at pulling the dust up into the exhaust shroud.

From contributor M:
Good shot of chips being removed with a 30 degree upshear. The dust hood is in the up position for the shot, but you get the idea of what the helix on the tool produces.

Click here for higher quality, full size image

From the original questioner:
Thanks, that picture is perfect. I suppose I should also be sure our machine has suction for the dust. Right now we have a collector dedicated just to the CNC at the back of the shop. Calculations weren't done before we got the system, it was just conveniently available from one of our branches. I believe it is a 10 hp motor with one 12" galvanized pipe going straight to the CNC with about an 8' hose and 2 elbows. Does this sound about right?

From contributor M:
Wish I could help you there, but I am no expert when it comes to dust extraction. What I can tell you is we put a booster fan in between the router and the indoor collector at the back of the shop and that keeps our static pressure up pretty good. I'm told that static pressure and cfm are different, but both are important for extraction. Keep asking and someone is bound to know the answers. We just brought in a pro to do it for us.

From contributor C:
Yes, the upcut would extract the chips upward. But you could have a problem with the part lifting. We [Southeast Tool] recommend Slow Spirals.

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