spindle speed error and rigid tapping - [acorn can compensate - works well - vids attached]

[rk9268vc]

How well does acorn compensate in Z speed if the spindle rpm (measured by encoder) is off from commanded rpm?
Or does it compensate at all?

Like if I tap at 640 rpm and the motor is actually turning 700 rpm will it just plunge faster so the threads are "fine"?


My spindle motor is an ancient brushless dc servo and all the tuning is done by analog potentiometers and an error of about 50 rpm is the best i can get it dialed in.
It is only off by about 20 rpm at full speed (4300 rpm), but it is off by 60 ish rpm at low speed (500 rpm)

for acorn mill

thanks

[tblough]

Centroid uses the exact speed measured by the encoder to calculate the Z feedrate.

[rk9268vc]

Centroid uses the exact speed measured by the encoder to calculate the Z feedrate.

I was reading the tech bulletin 304 and it was saying to have the rpm match commanded within 1 rpm.

but if what youre saying is true, that is pretty neat

thanks!


"Making Threads Notes:
a.) Be sure to check the RPM accuracy at 640 RPM in high range. Using the VCP turn on AUTO SPINDLE
MODE; and with the Spindle speed OVERRIDE at 100%, in MDI turn on the spindle at 640 RPM (use this
command “M3 S640”) Now with the spindle running. Adjust the maximum frequency of the VFD so the actual
spindle speed is within 1 rpm of 640 RPM for best Rigid Tapping results and remember to use High Range to
Rigid Tap! Typically tapping RPM is 640 RPM for most all taps."

[rk9268vc]

Works Great!
It is able to compensate for the rpm error no problem

Here are some videos
PM-30MV
old school brushless servo with analog pot adjustment
3D printed pulley for encoder off of low range belt pulley
Tapping 1/4-20 with spiral tap
Using tormach compression tap holder for safety - because i didnt know how well it would work





Here is a look at my 3D printed pulley. Couldnt find one to buy that is the right OD and ID so printed it. works great

Threads looks good. Great fit on the 1/4 -20 bolt