Compression Bit Size: What's Best

Half-inch bits run faster, but the 3/8-inch size wastes less. April 10, 2005

We currently run 1/2" mortise compression tooling as our main cut out tool on an Onsrud CNC. We are primarily cutting particle board core melamines at 750 inches per minute. We are looking at changing to 3/8" tooling. I'm wondering what everybody else is using and the pros and cons of 1/2 versus 3/8 inch tooling. Also, if you are using 3/8 tooling, what kinds of cut speed are you maintaining?

Forum Responses
(CNC Forum)
From contributor A:
I'm using 3/8" 2 flute compression for nested cabinet parts, mostly pre finished plywood but some melamine. We run at 18000 rpm and at 750 inches per minute, getting about 60 sheets per bit.

From contributor B:
For that tool and rpm, increase your feed rate to 1260 IPM and you will see a larger sheet count per tool.

From contributor A:
Would quality of cut suffer at all? What do you base your recommendation on?

From contributor C:
Most firms that have switched to a .375 compression are doing for yield purposes. With a .375 tool you are losing about 10-20 sheets worth of cutting. As the gullets are smaller than the .500, chip evacuation is not as great. Also when servicing these tools, the maximum services are 10% of the diameter, meaning 1-2 fewer sharpenings. On 3/4" material 750IPM at 18000 RPMs are OK on the .375 tool.

From contributor D:
I would think about this very seriously before switching. You will be able to run a higher feed rate with the 1/2" bits. The yield will be lower with the bigger bits.

From contributor E:
Flip a coin - they'll both work great at those feeds and speeds. The only viable reasons for switching are material utilization and yield or for a little better parts holding. The 3/8 opens less kerf and thus you lose less vacuum through it. With the 40HP pump you guys have, that's probably not a compelling reason to switch.

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Comment from contributor F:
I switched from 1/2 to 3/8 a year ago. I cut mostly 5/8 melamine, and I find that I can run just as fast if I do not re-adjust the speed. I have a lot less waste and bags to empty.