re: mill threading was re: as simple as 1,2,3... ENCODER/JOG

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)

We'll step the linear axis 800 steps (.1 inch) WHILE we output 1440
steps in y. Two ways to go here: If your S/L y axis is also set to
8000 steps per inch, we need to figure out how long the line is (for
1440 steps) 1440/8000= .18

So you draw a line that rises (or falls, this will be LH vs. RH
threads) .18 for each .100 it goes across the screen. This should
give you 10tpi with the numbers assumed.

If the rotary is set in the cnc s/w for 1440, then the line will rise
(or fall) one inch for each .100 across the screen.

This all assumes you have no rotary axis capability in your cnc S/W.

>The nuts are going to be a little harder to crack, er, machine!
>Alan

The nuts will be easily made with a programmed helix and a
Threadmill. These can be expensive to buy. A single point tool ground
from a boring bar, can work well here. I'd call it a boring tool, but
I've never seen one of those :-)
Or for larger threads, a flycutter type single point tool.

Of course, you can machine the male threads this way too! You will be
limited by the length of the tool shank though.

Hope this helps.

Ballendo

P.S. On the sherline (with the rotary and tailstock setup) you could
tilt the head (so it clears the work while using a small diameter
cutter) and use something like a dovetail mill to cut threads. This
would be one way around the "vee-point" limitations mentioned above,
since you will be cutting with the tool periphery.