bob wrote:
I want to make a wood screw for a vise(2in. dia). I have tried using
dried and green oak and 3 tpi. The threads for the nut cut very nicely
but the outside threads are a mess. Lots of chipping and tearing. Is it
the wood, the tool grind ,or me? I have also tried cherry and it was
worse than oak. My brother ground the tool for the inside threads and I
ground the tool for outside and am a relative clutz so I hope it is
just the grind.
Anyone with experience doing this?
Thanks,
Bob


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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