# Endmill vs Spiral bit



## Timberwerkz (Jan 1, 2010)

As a cabinetmaker turned machinist. I've been using endmills (look like spiral bits but with potentially more flutes up to 6) at work. I was wondering what the difference was. I can get a n endmill with 3" flutes for cutting tenons for the same price as a straight bit that can only cut 2.5". One of my co-workers gave me a 4 flute bit to bring home and play with the only thing I noticed was that it required a slower feed rate, but left a better finish. I'm guessing that the feed rate difference is from the extra resistance from the extra flutes. Any help understanding the difference would be greatly appreciated .

Chris


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## grobinson6000 (Jun 22, 2010)

Hi Chris,

I've been using endmills on plastic and MDF for a while, and basically more flutes equates to a better finish because you're cutting off a smaller chunk each time. I tend to stick to spiral bits and 2-flute endmills because the higher flute counts tend to create a bit more heat and melt the acrylic.

AFAIK Difference between a spiral/endmill and a straight bit will be the action of the cut: the straight bit is cutting like a chisel straight across the face of the timber (horizontally), whereas the spiral shape of the fluted cutter has more of a continuous scissor-like diagonal action. As the blades tend not to hit the wood as abruptly this way, the bit doesn't vibrate, the wood doesn't tear, and you'll probably get a better finish. The straight cutter will in general be a lot faster though.

Other advantage of an endmill is you tend to get a pretty good facing finish too, although the straight cutters tend to do ok here too.

George


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