THREADING CHECK – LONGER THREADING
Mach3 version 3.042.27 and using a SmoothStepper.
For checking of how longer threading is functioning in Mach ( or my lathe ? ) a microscope was attached to the carriage for viewing and measurements.
The tube was finished down to a .7500” diameter, then the surface was colored blue with a permanent marker. A very pointed sharp tool ( no radius ) was used to scribe the lines on the shaft as it was cut.
The threading was as follows:
PITCH: 0.050” and 29 degree angle ( basically there is no step change in the Gcode for Z as it just cutting radial)
PASSES: 60 @ 0.0001”
TOTAL DEPTH OF CUT: 0.003”
RPM: 402 / 20 IPM
Picture #57, 58 show the setup and scribed material after the threading cycle.
Now it is quite obvious that the pitch is changing as the threading is progressively getting longer.
I guess that has not been fixed yet in MACH! On the starting end of the thread there are five cuts in a space
0.005”, then in the middle there are 5 cuts in 0.011”, and at the end of the 2” thread there are 5 cuts
in 0.019”. This is shown in picture #60 and then enlarged to show the cutting grooves at the end of the threading as shown on picture #61.
Each groove measured 0.003” deep ( I have .0003” backlash in the X ) but the widening / changing of pitch is not do to the Z mechanically ( I have 0.0006 to 0.0008” backlash in the Z ). The rpm is not changing.
The steps per unit a correct.
In the last post a ¾-13 x ¾” long thread was cut and there were no lead problems. If this thread was
cut was 2” long only ¾” or maybe 1” would have been usable. I didn’t get any X & Z combination moves,
but, as shown in the pictures, somewhere in the threading cycle there is still something causing a change in the Z such that one bigger cut is “always” done somewhere in the cycle. On a punny lathe the thread may be ruined but on bigger machine you would just have a wider cut and may not even notice that quirk!
More threading tests need to be done but did notice that the affect is not as pronounced as in a smaller
thread. Maybe Mach4 will have have it fixed, but until then, there are still problems with threading on the lathe.
Till next time…….keep the threading short,
RICH