Threadmilling success...

I tested a Micro 100 TM250 single row thread mill today by milling a
couple of 3/8-24 threads without much trouble.

I drilled a couple 21/64" pilot hole using a G78 canned cycle. The
holes were a bit oversized because I had the feedrate a bit high.

I installed the TM250 in a collet and called the thread milling cycle I
just wrote for TurboCNC. It machined a beautiful thread. My call was:

G222 Z-1 D0.384 Q0.312 K0.41666 I0.010 F4 P1
Where:
Z = final depth of the thread
D = final OD of the thread
Q = starting diameter of the thread
K = thread pitch (1/24 = 0.041666)
I = feed increment for the radius path milling
F = feed rate in IPM
P = 2 finishing passes at the final diameter.

I ran it at about 150% feed override, ie 6 IPM. It was kind of slow,
but yet it was done quite quickly, being that I didn't have to manually
cut the thread or load/set any special tooling. I didn't optimize the
feedrate or depth of cut at all, I just ran it at that. Future threads
might be cut quicker.

I didn't know where to set the final OD. I measured a 3/8" tap and
found the OD to be 0.379" A cut at that OD would start the bolt on the
taper, but it wouldn't thread in. Adding 5 thou made a pretty good
thread. A cut at 0.390 is a bit sloppy.

I've got to cut a thread 1-9/16" x 18 TPI for a ballnut. Does anyone
know how to calculate the starting hole diameter other than to subtract
the pitch from the major diameter ? ie 1-9/16" - 1/18" = 1.5069" BTW:
I've got a helical milling routine written too, so I'll cut the hole
that way. Ie I don't have to buy a drill bit exactly the right size to
cut the (oddball) hole size for the thread.

--
Kim Lux <lux@...>