re: mill threading

Tony,

Thanks for the tip! I've learned a lot from several trips to your
website. I have an HSS conical tip engraver, inspired by your engraving
on your rotary table. Now if I can find a suitable carbide cutter
here! And I think I "feel" what you're talking about in regards to the
swarf, I must have some in my fingers too!

Alan

Tony Jeffree wrote:

>
> At 08:17 15/11/00 +0000, you wrote:
> >Alan M wrote:
> > >What if I setup my rotary table and a tail stock on the Sherline
> > >mill, and use a 60deg. conical point (or something else?), by
> > >driving the rotary table and the 'X' axis, I should be able to cut
> > >threads on the mill!
> >
> >Yes. Be aware of the low cutting ability of the point of the cutter
> >when used this way (low, to no cutting speed) Grinding (or buying) a
> >cutter with the point "dubbed off" and made into cutting flutes will
> >increase the cut you can take (or the materials you can cut; depends
> >on how you look at it)
> >
> > >one should be able to cut an ACME screw?
> >
> >Yes. Just use an appropriately shaped cutter.
> >
> ><snip>I haven't sat down to figure out how to do it in CAD/CAM.
> >
> >Draw a taper(angled line, really) with the x scaled to y by the ratio
> >of steps per rotation to steps covered linearly per rotation. So on a
> >sherline with 8000 steps per inch, and a rotary table of 1440 steps
> >per revolution, to cut ten threads per inch: (we'll just go around
> >once)
>
> This technique works very well - I've used it on my Taig CNC mill with a
> CNC dividing head - see 2nd photo from the end of this page:
>
> http://www.jeffree.co.uk/Pages/divheadmk2.html
>
> As Ballendo correctly observes, use a conical point engraving cutter with
> the tip ground to a sensible (non-zero) diameter - my local supplier will
> grind solid carbide cutters to any tip angle and diameter that you specify.
> The drawback with this approach is that you can only get within 1/2 cutter
> diameter of a shoulder - so preferable to use small diameter (say 1/8")
> cutters if this is a problem, or run a die over the thread after milling to
> get the last couple of threads cut. This is probably a smart move anyway
> to clean up the thread form.
>
> One major drawback - the cutting action produces large quantities of very
> fine, needle-sharp swarf - for a week or so after cutting the thread shown
> on my web-page I was still feeling the effects of a couple of dozen of
> these particles embedded in my hands.
>
> Regards,
> Tony