Re: Rigid Tapping--How is this accomplished?

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "Damon" <damonfg@y...> wrote:

> For that size range- I'll tell you what I am doing. Take it
> with a grain of salt- but it works like a champ for me...
>
> I can't actually post the code we use, but here's the nutshell.
>
> Tool change to a morse adapter, morse adapter contains a tap
> driver, and also a tap. 3/8" spiral point coated for this
> example...
>
> Spindle forward at 60 RPM, flood coolant on, z down through
> the hole.
>
> Stop the Z motion and stop the spindle rotation. Z stops
> instantly, spindle coasts to a stop. It probably only turns
> maybe 2 rotations as it is in low speed (reduction) and has
> the drag of pushing the tap through it. The tap *will*
> continue to thread ahead in the material for those couple of
> coasting turns. The square shank of the tap pulls forward a
> bit from the holder. Still stays engaged though, no problems
> there.
>
> deliberately pause in the code so that the spindle is
> guaranteed to stop.
>
> start the spindle in reverse, and Z-up. Same way the tap
> follows up. The axial (z) travel in the holder lets the
> tap go back up while the spindle is coming up to speed.
> That whole acceleration profile is compensated by the slip
> in the holder.
>
> How well does it work?
> I used to spend 2.5 hours hand tapping each part (18 holes,
> 3/8-24, in 4140 CrMo). I would break a hand tap every 25
> holes or so.
> Using the tap holder setup, I can thread the same part in
> about 6.5 minutes, and lost a tap every 100 or so. Backing
> the spindle speed (and Z) off a bit, I ran an entire shift
> on one tap...
>
> Spiral flute taps are great! I will take them anytime over
> hand taps. NO QUESTION! Much stiffer !!
>
> -Damon
>

Damon,

I follow what you're doing, essentially you're using the tap driver
as a non-spring loaded tension/compression holder.

Do you manually push the tap back into the driver seat after each
part? I can see a problem if the rpm/feed are not perfectly
coordinated from part to part where the tap might not return exactly
to it's fully seated position.

This is a nice solution for machines with a limited spindle to table
distance. Even a T/C holder is longer than your setup, but still
not as long as a self reversing tapping head like Tapmatic, etc.

But, if you have the room wouldn't it be simpler and more fool-proof
to use a T/C holder?

Doug