I'll try explain what I need to do:

I have a 4th axis and want it to move continously at a constant feed while performing a couple moves in another axis.
Is this possible?

I want to move X axis along a cylinder and then back all the way while rotating the cylinder with the 4th axis to make an endless screw that goes back and forth. I would do it something like:
G0 X0 A0
G01 X10 A1800
G01 X0 A3600
But the A axis is not constant because it "waits" for the X axis to decelerate at the change in direction.  I need the A axis to be completely constant.

Is there a way??

Thanks for any help!

No on the seperate moves. BUT your code runs FINE here. IF you want a symetrical screw then you need to comp the ends a little to make a smoother transition to the opposite direction. I do something similar to build a level winder for winches.

Are you running backlash comp? That is the only reason I can think of for the "Wait".  With backlash comp ON the machine has to Cycle out the backlash BEFORE it changes direction.

Just a thought, (;-) TP

Thanks for your reply.
When I say that A axis "waits" it is not that it stops, but that it decelerates accordingly with the X deceleration with the change in direction.

"IF you want a symetrical screw then you need to comp the ends a little"

What kind of comp   That is basically what I need to achieve a smooth transition.

Have you tried putting a dwell in between the G1 lines?

Are you running CV? With CV on there will be no lag the moves will all blend in to a smooth continous motion.

Just a thought, (;-) TP

jrobson: mmm a dwell I don't think so, because what I need is constant axis move instead.

BR549:  Yes I am using CV. But the X axis makes a 180° move so it has to stop, so it has to decelerate... and then the A axis decelerates accordingly. Thats the problem.  / :   The X decelerating is ok because it would give the smooth return for the screw, but the A should go on at continuous feed.

WHen the X slows the A HAS to slow as well to maintain a coordinated feed (;-) You cannot have one axis running independant of the other. Besides IF it did your screw would not be accurate at all.

The angle change at the ends will NOT be 180 deg (;-) think about it.

The axis will maintain a proper "cut" if it is coded correctly

You must have really SLOW accelleration on the axis's.

Are you running radius comp on the A axis?

Attached is an example of comping the ends for a smoother transition to return. Note that IF you are looking for a true constant velocity of the screw feed then this is not the way(;-) as the linear feed of the screw will slow as it reaches the ends

(;-) TP

That's exactly what I need! A round smooth transition.   So you mean using radius compensation, I didn't get when you said comp the first time.
Going to try it that way.

Thanks!!!!

There is another way to do what you want........

you can do a "Swap Axis" VB command and swap your Spindle (which is constant velocity), and your A axis.
see the VB customizing manual on how to use swap axis.

scott

>you can do a "Swap Axis" VB command and swap your Spindle (which is constant velocity), and your A axis.

That seem great for this and many other 4thAxis-as-lathe jobs!