Re: [CAD_CAM_EDM_DRO] Re: General Tool Life Question

Most CNC type tap holders "float" axially to compensate for the difference
in Z-feedrate/RPM's, and the actual thread pitch. When I ran a MAZAK V7.5
Machining Center, we always used to calculate so the tool holder would
"float" downward (we'd feed a little less in the Z-axis than calculated).
BTW that 7.5 stands for spindle H.P., and I used taps (damn good taps) down
to 4-40 size in 4XXX alloy steel. (Sure we broke some, but we got jobs that
nobody else would touch!) p.s. we also had an EDM tap burner, because we
broke so many!

Ray Heckert

If what you're living for
Isn't worth dying for,
Then what you're living for
Isn't worth living for!

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> From: Fitch R. Williams <frwillia@...>
> To: CAD_CAM_EDM_DRO@yahoogroups.com
> Subject: Re: [CAD_CAM_EDM_DRO] Re: General Tool Life Question
> Date: Thursday, January 17, 2002 6:39 AM
>
> On Thu, 17 Jan 2002 07:10:27 +0000, Jon Elson <elson@...>
> wrote:
>
> >I use a Procunier "CNC" tapping head, that has clutches and
> >gears to drive the tap forward when down feed pressure is applied,
> >and reverses the tap at 2 X spindle speed when upward pressure
> >is applied. The spindle of the CNC machine controls depth.
> >I use Alum-Tap when tapping in aluminum, it works amazingly
> >well.
>
> Jon,
>
> This sounds like a wonderful capability. I have some projects coming up
> where that capability would be a huge help. However I get nervous
> speculating on what happens if there is a mismatch between feed rate and
> rpm? I don't have a good accurate way to set spindle rpm - although I
> could probably adapt one of Sphero's digital tachs to my spindle some
> way if I had to. The mill spindle has a variable speed pulley with hand
> crank, and to complicate things (add uncertainty) it is fed from a VFD,
> and the speed has to be manually adjusted each time it is turned on -
> the Anilam control I have doesn't have a spindle on-off output, not even
> a contact closure other than from the big red panic button (darn it).
>
> I can do the basic arithmetic to calculate what tap rpm and feed rates
> would go together, and what the hole depth would be, etc., that's not
> the issue.
>
> My concern is for the following situations when using a tapping
> attachment like you listed on The Animal:
>
> Case 1: This seems like the worst case. Spindle RPM is slower (for
> whatever reason) than the tap needs to keep up with the selected feed
> rate. In this case the spindle will over run the tap and push (hard) on
> the tap. It might damage something.
>
> Case 2: RPM is faster than the tap needs to keep up with the feed rate.
> In this condition, the tap will gain on the spindle - the tap will pull.
> I would think that if this is the case the tapping head would reverse or
> disengage (?) momentarily then re-engage and keep tapping.
>
> Case 3 is when spindle speed and feed match, but that one takes care of
> itself of course.
>
> With that as a background, I have some question and would be interested
> in your experience with this. The questions are: Does case 2 work as I
> described? If so, do you always make sure your spindle is a bit faster
> than required so that you are operating as described in case 2? If so,
> how much faster?
>
> Fitch
>
> Addresses:
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