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Author Topic: Motors / DRO not moving to issued pos  (Read 127 times)

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Motors / DRO not moving to issued pos
« on: August 07, 2019, 10:05:36 PM »
I was starting to test my Mach3 / Y axis setup and have the motor steps set correctly based on the setup I am using. I can issue a G0Y12 and it moves to the 12” mark just fine. The issue I am having or not understanding something is if I write a quick test script to move from Y0 to Y12 and back then loop (M47). It moves from 0 to about 10.5” and the DRO on the screen matches then moves back to 0 and repeats. For some reason it will not move to 12 where I have the Gcode moving to. If I manually issue the same commands via the Input box, it works. If I add a G4 P0.5 after the move to Y12 before the G0 then it works also. Almost like the planner isn’t giving the moves enough time before moving back (based on accel and max speeds). What am I overlooking?

G0Y12
G0Y0
M47

Moves from 0 to 10.5~ and back and repeats, showing the same positions on the Mach3 screen.

G0Y12
G4 P0.5
G0
M47 works

G0Y0 then enter on the Input box followed by G0Y12 moves to 12 correctly.

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Re: Motors / DRO not moving to issued pos
« Reply #1 on: August 08, 2019, 01:10:25 AM »
If you add a G61 at the start of your code it will work OK.

Perhaps read up on Constant Velocity, Axis Velocity and Axis Acceleration for just how it affects the toolpath.
Success consists of going from failure to failure without loss of enthusiasm.  Winston Churchill.
Re: Motors / DRO not moving to issued pos
« Reply #2 on: August 08, 2019, 10:07:45 AM »
Will do. This is what I needed. I figured it had to be related to path planning and I am coming from the 3d printer side and things seem to work differently.

If you add a G61 at the start of your code it will work OK.

Perhaps read up on Constant Velocity, Axis Velocity and Axis Acceleration for just how it affects the toolpath.
Re: Motors / DRO not moving to issued pos
« Reply #3 on: August 09, 2019, 04:47:25 PM »
Hi,
CV, or constant velocity mode is the normal operating mode for CNC mills. The software tries to keep the machine moving as fast
as possible.

When it comes to a right angle corner for instance it will slow as it approaches the corner in preparation to stop exactly
at the corner. In CV mode however it will not stop but take a shortcut and round the corner slightly before accelerating
away from the corner at 900 to its approach.

You can stop the corner rounding by going to 'Exact Stop' mode, which exactly as described would stop at the corner before moving
away in the new direction. This tends to result in the machine jerking around and long cycle times. For this reason CV mode is
preferred.

There are a number of settings that can be made to CV mode that will allow somewhat closer toolpath following but the
single most important measure is machine acceleration.

If a machine is to cut a right angle corner accurately and quickly it will need to decelerate quickly and the accelerate quickly
away in the new direction. Thus you are encouraged to build and tune your machine to exhibit the highest acceleration your motors
and machine construction can attain without flexing.

Acceleration is probably more important than maximum axis velocity with respect to cycle times and is certainly more important
to tool path following.

Craig
My wife left with my best friend...
     and I miss him!