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Author Topic: Mach3 Z Axis Travel Not Complete for Next Instruction.  (Read 1648 times)

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Mach3 Z Axis Travel Not Complete for Next Instruction.
« on: July 14, 2016, 01:47:09 PM »
Hello,
I am new to Mach3 but have been picking it up quickly.
I am currently seeing a problem and am not sure where to look to resolve it.  When my Z axis goes to position it is not quite completely at the exact cutting depth when Mach3 sends the next instructions so I am seeing a little bit of a ramp occur when it starts to cut.  I am using this to etch circuit boards at a 0.1mm resolution and this is causing a problem when the GCode picks up and moves the cutter to the next location it isn't quite reaching complete cutting depth on its way back down which is causing it to not cut all the way through the copper just at the start of the X and Y movements for like .1mm.  I am not sure if this is related to how far I am coming off the board between cuts or how deep I am going, or related to deceleration so that Mach3 is sending the next instruction just before the Z axis has completed its travel.  I have tuned the motors and have excellent accuracy however I keep seeing this one problem with just the Z Axis.  I keep thinking Mach3 should be waiting for the depth to be reached then moving, which is why I think the machine just hasn't caught up to Mach3.  However the distances traveled all match up to Mach3 in the end, Mach3 just isn't waiting quite long enough to accomplish this.  Can someone tell me if my thoughts are right, or way off, and how I should go about testing and resolving this.

Thank you for any help.

Offline Tweakie.CNC

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Re: Mach3 Z Axis Travel Not Complete for Next Instruction.
« Reply #1 on: July 15, 2016, 01:35:54 AM »
Assuming your Z axis down movement is on it's own line of Gcode then changing the Motion Mode to Exact Stop (Config. / General Config.) will cure the problem but it may slow down the overall execution of the complete run.
Another possible solution would be to increase Acceleration (perhaps reducing Velocity if necessary) for all axes (not just Z axes).

Tweakie.
KEEP SAFE !
Re: Mach3 Z Axis Travel Not Complete for Next Instruction.
« Reply #2 on: July 15, 2016, 02:48:44 PM »
Thanks for the response.  You are correct each are on a different line of code.  I don't tend to have any issues with the corners rounding for what I have done with the X and Y axis, and I hate to slow down the job at all.  I wasn't thinking in the Constant Velocity area since what I was noticing was specific to the Z axis and most references refer to X and Y with Corner Rounding.  I guess I was thinking in the wrong dimension. :)  It makes sense though somewhat.  I was thinking Mach3 would make sure the cutter was at the right depth before moving on, unlike the CV rounding, but to Mach3 it is just another Axis.  Is there a way to have it perform Exact Stops for movements on just one Axis, instead of all?  I have been afraid to try the exact stop option, but for Circuit board etching that might be better.

I followed the info I got with the machine on the Motor Tuning, which has worked well up until now, but I don't know too much about that and the rest of the info I received hasn't always been accurate for the machine.  School of Hard Knocks Lessons.  The Z axis is set to half the velocity, but the same steps and acceleration then the X and Y even though they all use the same mechanics and motors, I guess because of weight, but you would think that would affect Acceleration not velocity.  I have made the Z velocity the same to see if that would help but haven't tested etching yet, but it does seem to move it up and down fine with the same velocity set.  Do you have any links or helpful info on finding the right Acceleration/velocity for each axis, or do you find that depending on what you are working on you need to change this to fit the project.  I had thought about reducing the FeedRate as well, but wasn't sure that would have any effect since it slows down all the Axi uniformly.  I have been trying to keep all the Mach3 machine settings to a generally good range so regardless of what I work on it will work well, but maybe others have different profiles for different types of work.  I am new to Mach3. :(  Also do you think that BackLash could be a factor at all?  The movements from what I have measured all seem to be to a 0.01mm resolution, but I am not sure if under any pressure it is off at all.

Thanks for all your help.

Offline Tweakie.CNC

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Re: Mach3 Z Axis Travel Not Complete for Next Instruction.
« Reply #3 on: July 16, 2016, 02:07:08 AM »
Just some rambling’s…

I don’t think there is any defined method for establishing Velocity and Acceleration other than by ‘trial and error’ where they are each individually increased until the point of stall then reduced by 30 %.
If your machine is going to be used for substantially different tasks (eg. Wood routing / pcb engraving / etc.) then it makes sense to create and use different profiles with each, individually set to optimum performance (Velocity / Acceleration / etc.) for the intended task.
I am not aware of any means of setting Exact Stop mode just for the Z axis movements. You could, of course, use G61 / G64 before and after each Z axis line of Gcode but that would also slow down overall program execution speed. You could also perhaps consider modifying your post processor to add a G4 dwell (P #) following each negative Z movement, the delay being great enough to allow complete axis travel.
Another option and one that I would do, is to reduce the clearance Z height above the pcb. Assuming everything is flat then 1mm clearance would be more than adequate.

Tweakie.
KEEP SAFE !

Offline rcaffin

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Re: Mach3 Z Axis Travel Not Complete for Next Instruction.
« Reply #4 on: July 18, 2016, 05:42:24 AM »
Mach3 drives the electronic driver which controls the motor.
If Mach3 thinks the motor can accelerate faster than the driver is set up to handle, then Mach3 might assume the Z axis has got up to speed before it has. But this is not your problem: your problem is at the deceleration end. Even so, if Mach3 is expecting more performance out of the driver than it can give, you may still experience problems.
I dunno, but it would be worth your while to check the acceleration settings in Mach3 and in the driver.

Cheers
Roger