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Mach4 General Discussion / Re: Thinking of doing a lathe build and need some basic questions answered.
« on: December 12, 2022, 05:12:07 PM »
Hi.
lathe threading is a realtime process and it largely enacted by the motion controller, not Mach4 at all.
Mach4 provides the numeric parameters to the motion controller, and the motion controller handles it from there. Mach4 is at best a supervisor.
There are a couple of variations of the one theme, but the idea remains the same. If the spindle is rotating at some fairly slow but known and constant speed
then its index pulse is used to start the thread. This allows multiple passes as you cut one thread....so your spindle must produce a single index pulse per spindle
revolution. In addition you can use either an index pulse or, depending on the motion controller, an encoder to measure the exact speed of the spindle.
Ideally the spindle speed would be constant, but as the cutting starts it will slow a little. The controller needs to know the reduction in speed so it can slow the Z axis advance
to have the thread retain the programmed or desired pitch. For example if the spindle is rotating at 600rpm, or 10 revs/second and you wish to cut a 1mm pitch thread
then the Z axis must advance 1mm per rev or 10mm/second. If as a result of the cutting the spindle slows to 550rpm the Z axis advance needs to be slowed to 9.166mm/second
in order to maintain the same pitch. Clearly a absolutely constant and rock steady spindle speed is very VERY desirable for threading.
Some motion controllers use the spindle speed as feedback to try to maintain the spindle speed constant.
I'm not familiar enough with the Hicon to be definitive but believe it has this feature. The ESS with which I am familiar definitely has this feature, that is to say that it can use
either an index pulse or an encoder pulse to slightly alter the PWM to the spindle drive to secure constant spindle speed for threading. This feedback feature may help with
underpowered spindles, but still there is the HIGHEST possible advantage to a powerful spindle of significant rotational inertia for lathe threading.
Craig
lathe threading is a realtime process and it largely enacted by the motion controller, not Mach4 at all.
Mach4 provides the numeric parameters to the motion controller, and the motion controller handles it from there. Mach4 is at best a supervisor.
There are a couple of variations of the one theme, but the idea remains the same. If the spindle is rotating at some fairly slow but known and constant speed
then its index pulse is used to start the thread. This allows multiple passes as you cut one thread....so your spindle must produce a single index pulse per spindle
revolution. In addition you can use either an index pulse or, depending on the motion controller, an encoder to measure the exact speed of the spindle.
Ideally the spindle speed would be constant, but as the cutting starts it will slow a little. The controller needs to know the reduction in speed so it can slow the Z axis advance
to have the thread retain the programmed or desired pitch. For example if the spindle is rotating at 600rpm, or 10 revs/second and you wish to cut a 1mm pitch thread
then the Z axis must advance 1mm per rev or 10mm/second. If as a result of the cutting the spindle slows to 550rpm the Z axis advance needs to be slowed to 9.166mm/second
in order to maintain the same pitch. Clearly a absolutely constant and rock steady spindle speed is very VERY desirable for threading.
Some motion controllers use the spindle speed as feedback to try to maintain the spindle speed constant.
I'm not familiar enough with the Hicon to be definitive but believe it has this feature. The ESS with which I am familiar definitely has this feature, that is to say that it can use
either an index pulse or an encoder pulse to slightly alter the PWM to the spindle drive to secure constant spindle speed for threading. This feedback feature may help with
underpowered spindles, but still there is the HIGHEST possible advantage to a powerful spindle of significant rotational inertia for lathe threading.
Craig