acme thread for large wood screw

bob wrote:

If you're using a form tool--a cutter shaped exactly like the profile you are cutting away--then you likely have zero rake on the top of the cutter, and you are just scraping instead of slicing as wood likes to be cut. That may be OK with maple or other woods of similar hardness if you take light cuts for each pass. But if you're trying to hog a lot of wood in one pass, the result will be chipping and tearing, especially in oak.
If you were to slice the wood instead of scraping it, the cutting edge needs to be keener, or have much less of an included angle between the front or side of a toolbit and it's top face. Only way to do this is to have a seperate cutter for each flank (right and left, plus the root)--unless you are skilled enough to grind a cutter tip with positive backrake on all three edges (not very easy).
So you're back to the flat-topped cutter, taking several light cuts, or a rotary cutter in a router which I would recommend. Elm or maple are much better choices for wood, as others say.
Ken Grunke
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