As I was about ready to send the following statements as a follow-up post to
earlier questions, I think I determined a basic need for a signal to
monitor/track the rotation of a tap.
If the tap needs to re-enter the hole during the tapping operation, knowing
the rotational position of the tap would matter, so the tap is in sync with
the previously-cut thread.
Since CNC tapping isn't generally a pecking-type operation AFAICT, how often
would the signals from a high count encoder be any more practical than a low
count model?



My curiousity was wrt the importance of one count out of 4096 being of any
significance to the rotational position of a tap.. in real life.

I wasn't trying to suggest that tapping should be done at higher speeds in a
home shop.

If a large diameter (12"+) workpiece such as a division plate for a critical
timing or positioning application were being machined, then a 4096 count
encoder (on a rotary table, for example) would be more practical, for radial
positional accuracy.

My question, is why would anyone care if a tap's rotational position was
within 1/4096th or even 1/1024th out of position?

For testing, it's good to know if the encoder signals are being accurately
counted, but in terms of the depth of thread or almost any other tapped hole
parameters, the high count encoder rate is not significant.
It's not as if a thread needs to start at a specific position, generally.
Tapping a blind hole could require an incremental change in where the tap is
stopped, I suppose.

I could see having a relatively high count encoder on a CNC lathe spindle,
for example, to allow incremental stops for a thread or groove, but not for
a tap in a mill.
This example would be where a cutting tool on a lathe is started or
retracted from the workpiece at a specific rotational position.

As far as encoder count rates, a lower count per rotation would be more
desirable for very high speeds.. low enough as to not exceed the CNC
circuit's effective counting rate (input signal frequency).

Having such a high count for a mill spindle's rotational position doesn't
seem to have much significance (to me), as far as milling, tapping or
drilling are concerned.

As I suggested earlier.. wouldn't a low count (100 or even less) encoder
serve adequately for a mill spindle's rotational position?

--
WB
..........


"Ignoramus30138" wrote in message
...
On 2010-12-18, Wild_Bill wrote:
Wouldn't a low number of counts.. 100 counts (1 = 1%), or 360 (1 = 1
degree)
be adequate for the rotational position of a tap?

I suspect that 100 counts would be far more reliable at high (or low)
speeds, even though HSM tapping isn't an especially high speed
application.

Assuming the 4096 encoder was already purchased, it would work to test
the
application, but there isn't really a need for that high of a count per
rotation, is there?

I have a US digital encoder. The encoder disc that provides pulses is
replaceable and is not very expensive, whatever it is, $10-20 or so.

Replacing the disc is easy and cheap. Mine is 1024 pulses (4096
counts). Very possibly, a lower count would work even better, say 500
counts, and could let me tap at high speed.

At this point, tapping at 500 RPM is just fine with me and I do not
feel that my needs would be served better if I could tap at 4,000 or
even 1,000 RPM. In fact, to do motor reversals with the VFD, at high
speed, is kind of taxing and I overshoot the tap position a lot. And
at 500 RPM, my encoder works fine, as evidenced by my trial today.

i