G-code to control double threading!

[samirnashef]

Hi, I'm having a problem cutting a double-thread with a lathe using two cycles of G-76. After cutting the first thread through the first cycle, it is supposed to go to the next cycle with the tool half the lead away from its initial position, but the problem is that it seems that the machine is missing the required synchronization between the turning head and the tool so the resulting teeth are having different widths.

Does anybody have an idea on how to force the machine not to lose this synchronization?

Thnaks

Samir

[HuFlungDung]

I trust you are keeping the spindle speed exactly the same for both cycles, and that feedrate override settings are cancelled out for threading.

It sounds like you have physically moved the Z position to the midpoint before calling the second cycle. That should work, too, so long as the spindle encoder rotates at a whole number ratio to the spindle rotations.

Some controls have the option to control the start angle of multi-start threads with a parameter set in the G76. Do you have this option?

[out2thow]

try posting your program sequence with the threadding in here, so we can see what your doing......my initial thoughts are that either you didn't calculate the lead correctly or didn't enter the start position for the second lead correctly. also changing anything like RPMs and start points will affect where the thread starts.

If the machine cut the first lead without crossthreadding, then i highly doubt that it's a machine problem.

[M-man]

Mabe try to use g32 and Q will be the degrees between thread entry..

[tobyaxis]

Originally Posted by samirnashef Hi, I'm having a problem cutting a double-thread with a lathe using two cycles of G-76. After cutting the first thread through the first cycle, it is supposed to go to the next cycle with the tool half the lead away from its initial position, but the problem is that it seems that the machine is missing the required synchronization between the turning head and the tool so the resulting teeth are having different widths. Does anybody have an idea on how to force the machine not to lose this synchronization? Thnaks Samir

This definately sounds like a synchronization problem. Just to give another option try G92 type A thread cutting cycle. To my knowledge there really isn't a way to Force Synchronization between the Spindle and Turret. This may need a Tech to fix the problem machanically or a Parameter Change. Also check your control programming manual because in the past I've had machines that wouldn't perform Triple start threads due to the fact that it was not capable. Which doesn't make any sence?