Half-inch Versus Three-Eighths-Inch Cutters

      Larger bits can work faster. To choose RPMs and feed rate, calculate the desired chip load. June 30, 2007

I've been running our CNC for four months now and I'd like to standardize and/or consolidate the tooling some. I need some input on the value of using 1/2" tooling versus 3/8 when cutting PB, MDF, mel and Plam sheet goods. A big day for us is 30 - 35 sheets, so speed helps, but not critical. Will the 1/2" last longer than 3/8"?

Forum Responses
(CNC Forum)
From contributor F:
For sheet goods with 3/4" core, I exclusively use 3/8" diameter tooling. Mainly for the tighter nests vs. the 1/2" tool. I can still cut over 1000ipm with a 3/8" diameter tool with excellent life. For your production output you wouldn't have to change bits for a couple of days if you started a shift with a new one. I use a 3 flute mortise compression tool for perimeters, rabbets and some dadoes. For 3/4" wide or greater dadoes or cut outs that are pocketed, I do change over to 1/2" tool to take advantage of the wider diameter. Still, my 3/8" and 1/2" 3 flute mortise comp bits are my main tools for sheet goods.

From contributor D:
There are many factors that determine what is the best tool for your machine. Horsepower - the more horsepower, the larger tool you can use. Achievable feed rates - if you can achieve high feed rates, you may want a 1/2" tool to prevent snapping or tool deflection.

The best way to determine what tool is best for you is to calculate chip load at the speed you wish to achieve. Feed / RPM / # of flutes. I find I get the best tool life and speed if I run around a .026-.027 chip load. To achieve that I am running 950-1000 ipm/18000 rpm/ 2 flutes. Now if I want to speed up my ipm and get the same chip load I can do a couple things - increase my spindle rpm or add another flute or both. Keep in mind that a smaller diameter tool will not handle high speeds of feed through thick material as well as a large diameter tool. Just plain strength of the tool also plays into the equation. And what speed your machine is capable of. The best thing to do is do the math.

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