Since some people are very sensitive to thread drift, I will start a new thread pertaining to the recent thread on threading. This quote came up on the previous thread.
Every description of tool form that I have read calls for no rake in any direction on the top of a threading bit. On some bulletin board, a poster provided all the geometry to show how top rake changed the thread form. A statement very similar to this quote was recently made on the Logan board, so now I am questioning my own opinion.
What do the experts say?
Brass and steel cut completely different with regards to tool rake angle. Typically brass wants less rake angle and steel wants more. I have more questions than answers at this point but I would start with the tool bit top relief angle assuming you have the rest of your settings dialed in correctly.
As far as the tool bit for steel goes: 60 degree included angle, slight radius on the end (no thread has a sharp V) and the top relief angle should be around 12-15 degrees. Stone all of the sides to remove burrs. Your tool bit appears to be mostly flat on top. Great for brass, bad for steel.
Also, is your compound set to 29 degrees? and are you infeeding with the compound and not the cross slide?
Every description of tool form that I have read calls for no rake in any direction on the top of a threading bit. On some bulletin board, a poster provided all the geometry to show how top rake changed the thread form. A statement very similar to this quote was recently made on the Logan board, so now I am questioning my own opinion.
What do the experts say?