Problem- C6 SPINDLE RPM PROBLEM

[neilw20]

When turning threads, Mach3 uses a pulse from the spindle to control the Z-Feed. As it is once per revolution (most likely) it is important the the timing of the signal is consistent from one revolution to the next.

1. Timing will change if the spindle speed is not constant.
2. Timing will change if the signal level from the sensor is not good.

By not good I mean, that with the supplied opto interrupter, it can only sink fairly low current. If the BOB, or more likely the port on the PC presents too low an impedance to the signal, the timing will be corrupted because it becomes level (and hence noise) dependent.

After this much time you guys should have fixed this.(hehe)

[gio1976]

we are almost there neil.

i tried brass and it looks better, only a few minor tweaks and we're there.

its in the timing and constant spindle rpm. sometime during threading spindle slows down a bit. but i think the timing recovers. threads do not overlap as before. does backlash got something to do with this? i tried modifying the backlash lately, i think it was not at the same value with the standard check list that came with the machine.

any tips on precisely gauging the backlash of the C6?..

[neilw20]

Backlash usually won't effect your threads, at least not noticeably.
To measure backlash, turn off backlash compensation in the config area.

Mount a dial indicator you can move the axis to with the jog keys. Set to small increments using the the tab key first.
Gently move the axis until the dial indicator is measuring.
Zero the DRO.
Now move back the other way until the dial indicator moves.
The value on the DRO is the backlash.

Check it in both directions a few times for each axis.

If you are turning radii then the backlash being enabled will muck up the arc when an axis changes directions.

As for your threads, fix the motor speed control. The current limit maybe set too low.

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The following information is specifically for SIEG MACHINE PCB part number XMT-2325

If it is the speed control I have seen there are 3 pots on it marked IR,CL and R3.

The one marked IR is to compensate for winding resistance losses.
If is set too far one way the motor speed will slow with load. (probably your problem)
If is set to far the other way as you load up the spindle the speed will become unstable.

CL will be the current limit. If set to low then the motor will slow once it gets to a certain load, but at less load the speed will be stable.

R3 is to set the range of the speed control so it works nicely through the range.

I am only saying this from memory looking at a PCB so I might be telling some lies.

CAUTION: All of the motor circuit is live at mains potential including the connections on the speed control potentiometer.

If you connect an oscilloscope to the circuit you must use an isolating transformer or special high voltage isolated probes.
BE CAREFUL. If you are not sure, ask an expert.

[gio1976]

thanks a lot sir neil.

i think this will be very helpful. i'll go check the PCB.

BTW i tried threading on a 1050 steel rod @ 600 rpm 14TPI 10mm dia. 0.03mm per pass, set infeed angle to zero and thread looks better now, pitch is good. just not that better looking compared to a conventional lathe thread. Anyway its a lot of improvement. if infeed angle = 29 degress (as default) spindle slowsdown during cutting.

to think that we are about to upgrade the spindle motor to a higher HP,(if we can find the same motor dimension with higher HP.)

maybe i'll post a photo of our PCB here for a better view, hehehe.


thanks again. i'll update later.

[neilw20]

gio1976

Thanks for the picture. It is a different model PCB than the one I have but the instructions I gave (which are my best guesses) still apply.

Search to see if you can find any documentation, and if not try my suggestions.

Neil

[gio1976]

HI:

anybody here ever tried to upgrade their c6 spindle motor to a 3 phase induction motor? we are planning to do this but have doubts. i think that the weakest link in a lathe machine should be the cutting tool and not the spindle motor or steppers. our c6 is only cutting a 1045 steel shaft at 600 rpm 0.3 DOC, 30 mm per minute feed. any attempt to increase DOC or feed trips the spindle.

any insights, opinions, suggestions will be very much appreciated. thanks.

[neilw20]

Torque is proportional to the current.
Have you measured what current it trips at?
Until this is corrected or the IR compensation is set correctly expect poor results.

[gio1976]

i havent tested yet the current. i ll try today.

what current should it trip at?

are the machining settings (0.05mm/rev 0.3 mm DOC 600 rpm 1045 steel) appropriate for the c6 or or too high?

[neilw20]

Power = Current times Volts.
so
Amps = Voltage divided by Power

Look at the name plate to find the power, and initially use your line voltage.

Plug them in to the equation and see what you get.
Those feed rates and RPM should work.
It should not even slow down noticeably.

[john_t_h]

Originally Posted by peu I think the problem is related to config, try in Config>general config, lowering the debounce parameters good luck

I was having the same problem and I set the Interval to 200 and the index to 25 and now Mach3 displays the correct RPM checked against a digital tachometer. Pablo saves the day