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« on: November 10, 2013, 04:24:10 AM »
OK,
I had assumed that because it appeared to work for me, that CSS capability was an undocumented feature of Mach3. You have aroused my curiosity, so I performed some measurements.
This is what I did.
Setup some stock in the chuck and calibrated the X Axis.
Using the MDI, I issued the command G96 M3 S50
From the MDI, I requested G01 X50, X45, X40, X35, X30 , X25, X20, X15 in succession
At each of the diameters listed above, I recorded using an independent tachometer, the actual Spindle RPM, and the reported RPM from Mach3 DRO (S True)
Listed below are the results:
Ø (mm) Calculated RPM Measured RPM Mach3 DRO RPM Reading Tangential Surface Speed (Metres/min)
50 318.31 348 349 50
45 353.68 380 380
40 397.89 420 420
35 454.73 471 471
30 530.52 540 540
25 636.62 636 636
20 795.77 785 785
15 1061.03 1034 1034
Calculated RPM is from the formula:
RPM = Surface Speed (in Metres per Minute x1000) / π*Diameter
I repeated the measurements at a couple of random diameters and the results were totally repeatable. I also noted that the speed transition was very smooth, regardless of whether the diameter was increasing or decreasing.
I think the measurements prove that my combination of Mach3 and USB Smoothstepper is capable of at least approximating CSS. I am happy it works for me.
One thing that annoys and frustrates me is that at the first use of Mach3 Turn, CSS does not work as intended, and the spindle speed drops to below the Mach3 low speed limit. The workaround for this is to stop the program, rewind and start again. The lathe then behaves normally for the rest of the working day, even if I change part programs. I think this is a result of my initial conditioning code, and I haven’t solved this problem yet. I have simply learned to live with, and expect, this behaviour.
Regards
Chris Humphris
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