Re: Rigid Tapping--How is this accomplished?

--- In CAD_CAM_EDM_DRO@yahoogroups.com, Kim Lux <lux@d...> wrote:
I just can't fathom how one could drive a tap from the
> top to the bottom of the hole without reversing it and without
breaking
> it.
>
> Kim

Kim,

Try using thread forming taps. No chips. But you have to be
careful of the tap drill size.

Since the threads are formed by displacing material from the hole
diameter to create on-size threads you need to make sure the hole
size is held within a much closer tolerance range than for a cutting
tap. Threads are measured by pitch diameter and percent of thread.
A .001" difference in hole size can make a significant difference in
percent of thread with smaller thread sizes. Sometimes there may
not a drill of the theoretical size available so reaming the hole to
size is an option.

A tension/compression holder works well for mill tapping. Calculate
the needed feed rate based on spindle rpm and tap pitch. Run a test
in soft material to verify (soft plastic is a good choice).
Depending on how fast your spindle reverses you may need to account
for spindle "coasting" once the programmed depth is reached. Some
mills are setup with a spindle brake that's energized on an M05,
this helps hold accurate depth.

Here's how I program the process:

G97 M03 Sxx Txx
G00 Xxx Yxx Z.1
G01 Z-.50 Fxx
M05
G01 Z.1 M04

On my mill the M05 brakes the spindle.

Doug