Re: Rigid Tapping--How is this accomplished?

--- In CAD_CAM_EDM_DRO@yahoogroups.com, Kim Lux <lux@d...> wrote:

> Thanks for the tip about the spindle brake. Our mill uses a VFD on
> which we can adjust the deceleration. I'll turn that way up if we

use a

> floating tap holder. I was worried about spindle coasting. With a
> coarse thread, ie 10 TPI, one doesn't get many turns with 0.5" of
> compression.(5 to be exact...)
>
> The thing about coarse threads is that they are usually on large
> diameter holes and I can use thread milling to cut those threads.
>
> Kim
>

Kim,

Spindle coasting isn't much of a problem on coarse threads since you
have the torque of the tap acting as a spindle brake. It's the 10-
32's and smaller where there's very little torque involved.

Yes, a 10tpi doesn't have much room to coast with a tension holder,
but I don't think you'll be able to tap the coarse pitches like that
anyway. Check the tapping capacity of commercial machines sometime,
it's always smaller than you'd expect based on the spindle hp.

Another type of tap holder I use in the CNC lathes is a releasing
type, once the depth is reached and feed stops the tap self feeds
slightly more and then spins freely. By reversing the spindle the
mechanism catches again and screws the tap out. These have a
slightly less axial movement than the usual tension/compression
type. I'm not sure if these work in a mill where the holder is
rotating as opposed to the lathe where the holder is stationary.

Doug