On 04/17/2021 04:50 AM, Gene Heskett wrote:
Depends on which gear Jon. I have switches on the knob, and I switch
encoder scales in some hal stuff according to the switches. The
effective scales are something over 7000/1 in high gear, and a similar
fudge factor over 14,000 in low gear. This was determined by recording
the encoder count at turn 3, stopping the count at turn 103, and subbing
the first count from the second and dividing by 100, in each gear. But
thats never changed as I always tap in low gear. And I've got taps up to
7/16" in my tap hats.
OH, you have the encoder on the other side of a gearbox from
the spindle?
The backlash in the gears is probably 25X worse that the
error from direction change,
unless that encoder situation is accumulating. Or, of
course, you could have some kind
of a noise issue.
On a quick reverse, I hear the iron in the motor
chirp from that limiter, but the reversal is contoured by a limit3 in
front of your pwm-servo, in both directions, to stop z following errors
at reversals. I could reverse faster, but z can't keep up. In low gear,
the spindle motor inertia is the big lag, so turnaround times are about
400 milliseconds running wide open in either gear. At tapping speeds,
500 or less, 100 milliseconds and no chirp.
Since I don't seem to have a problem with torque, I tap with
the belts in the highest-speed setting, and let the motor
run slow, at about 20 Hz or so from the VFD.
I do use Alum-Tap, which is a truly magic tapping fluid.
You can EASILY feel the reduced torque
when hand tapping aluminum, maybe half the torque as when
using cutting oil.
Not stocked locally. Wish it was.
I have no idea if the company is even still in business.
But, I imagine there are other aluminum tapping fluids that
are just as good.
One other issue, could there be backlash in your Z drive? I
have less than .0015" backlash
in my Z drive.
Last time I checked last fall mine wasn't up to 2 thou yet.
This could also be related to the post itself being out of square which
has the obvious effect of pushing the tap sideways as it descends into
the hole. I need to buy a circular square, grab the post with the hoist
I use to move that bs-1 around, and pull its bolts and ream the holes
one size bigger so I can adjust it plumb like it should be. Cheap
chinese mill. Thats been on my todo list for 3 or 4 years since I
discovered it wasn't square. It might even need a reynolds wrap shim to
plumb it for and aft too. Won't know till I get the square, or make one
on the sheldon. But I don't have stock that big.
Yes, that should be adjusted, for sure. My method of
tramming was to write a program to
mill a circular path in a piece of scrap with a small end
mill. Step down in Z a few thousandths at a time until it
mills all the way around. Then, move to the center and
mount a dial test indicator in the spindle. You then sweep
the circle and look for high and low spots at 0, 90 180 and
270 degrees. I have to worry about wear on the ways, so it
actually gives a saddle-shape.
But, after adjusting the head, I can get it well under .001"
deviation at the opposite points.
That's as good as you can get it with wear on the ways.
Jon
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