Re: Threadmill

Joe,

You're correct. But, it can be done (sort of) by grinding a relief
on the back of the remaining flute so that you only have a very small
land left from the original tap flute, maybe as small as .010-.020"
wide.

Another consideration is to use a tap with the smallest helix angle
that'll do the job. For instance, a 1/2-20 tap and a 1/4-20 both
have the same pitch, but the 1/2-20 has less helix angle due to it's
greater diameter.

One other point.....the quality of thread milled holes decreases as
the diameter of the tool approaches the finish diameter of the
thread. As the diameters near each other distortion of the thread
profile becomes more pronounced.

Doug

--- In CAD_CAM_EDM_DRO@y..., Joe Vicars <jvicars@c...> wrote:
> You cannot use a tap to mill a thread. If you ground all but
one flute off you would probably get passable results.
> A thread mill is the same form as a thread chasing tool, it has
no "lead", only a certain number of teeth per inch of a certain
> form. Taps have "lead", they are helical in nature.
> Take a thread mill and just bore inside a hole with no helical
interpolation and you will get a nice set of ridges that look
> like the teeth on the tool. Do the same thing with a tap and you
will get a mess
> You can use an internal thread boring bar to mill threads, and
you can use a thread mill on a lathe to cut threads (of the same
> pitch as the threadmill). Advantage of the thread mill is speed
(and usually better finish than single point tool) , and the
> advantage of the single point tool is that you can cut more variety
of pitch with the same tool.
>
> Ref page 1852 machinery's handbook 25th edition.