Re: [CAD_CAM_EDM_DRO] Rigid Tapping--How is this accomplished?

From: "jmorrphd2" <jmorrphd@...>

> I would like to know how rigid tapping is implemented. I know
> that the Z-axis feed and the rpm are synchronized such that the
> Z-axis feed (in distance per minute) is equal to motor rpm x thread
> pitch. How does the drive motor "measure" its angular displacement
> or speed? Is the Z-axis speed adjusted continuously as a function
> of motor speed variation? Or, is the motor angular momentum such
> that there is no appreciable decrease in speed over the length of
> the cutting of threads?
> Finally, I imagine that there is more than one way to implement
> rigid tapping. Any comments appreciated. Thanks, Jim

On the big machines I've used, the Z and spindle just run at the speed
you tell them for the tap cycle. I don't know how the software / hardware
handles it. On the older machines we use to use a spring loaded tapmatic
head, it has clutches to slip, springs to make up for the spindle and feed
not being totaly matched and gears to reverse the tap when the head starts
to go up. The other way we tap the holes with the cnc is to use a tapping
cutter, IE you want to do 1"-10 tpi the cutter would be around .75 and have
10 theeth per inch but straight cut, you would feed it into the hole, feed
it out .125 then do a 360 deg circle dropping .100. That way you cut all the
threads at once.