cutting in air

[ZASto]

If your acceleration is too high, you will loose steps, resulting in incorrect positioning.
Even with your car you can not speed up to 60 if 1 sec
If your max speed is too high, the same as above, pushing motor above its limits.

[JAZZCNC]

The reason you will be losing position in this manner is 99% likely to be because your Step pulse is falling on the wrong side of the slope. This happens often and often goes unnoticed because it only shows on longer jobs or jobs with lots of direction changes. On Profile jobs or short jobs, etc it often goes unnoticed.

The solution to this is an easy fix.! In ports-n-pins / motor outputs toggle the "Step Low Active" to the opposite of whatever it is set to now.

If you want to test for this the write a G-code file which moves the axis back n forth a few 100 times then ends by coming back to zero, you don't need to move far 10mm will be enough and you can use G0 moves so travels at rapid speeds. Just make sure the last move is back zero. Something like this repeated 200 times will do.
G0 z-10
z0


Before you run the G-code Zero the axis and mark a point on the axis. When the code is finished it should return to the mark. If it doesn't then change the Step Low active and repeat the test. (don't forget to Zero and remark)

Do this test on each axis individually.

[RichardR]

Thanks, I have been looking G0 Z10 Z0 at a you tube review of Todd Flemings JS Cut, and realise that there is an adjustment that can be made to the plunge rate, I had my profile programme set really fast, so I am going to reset that and try it. If that fails then I will try your suggestion, I am very reluctant to alter my Mach3 settings as you know how long it took me to get to where I am. While I am writing, even though this may not be the right place to ask, I watched a JScut review with Todd Fleming where the programme showed more options for setting the job up. like width and settings for different type of cutting on the one job, which is not on the version that I get on the web browser, am I missing something? as looking at that version it will be much more versatile
How would I write or add to G0 Z10 Z0 to repeat a few hundred times without doing it manually, I have not got into writing G code as I just let JS cut do it for me :-)

[JAZZCNC]

How would I write or add to G0 Z10 Z0 to repeat a few hundred times without doing it manually, I have not got into writing G code as I just let JS cut do it for me :-)

Just use a text editor like Notepad and use copy n paste. To change for other axis just use the find n replace option ie: find Z and replace with X.

When writing the G-code you only need G0 Z-10 on the top line only because it's what's called a Modul command and the G0 which means travel at max velocity will stay in effect until another command comes along like G1, which is a commanded feedrate move.

So you can write it Like this, then just copy and paste the last 2 lines over and over, or if you're clever you'll do 10 or 20 lines then copy n paste those.
G0 Z-10
Z0
Z-10
Z0

[RichardR]

I would like to say Thank You to JAZZCNC for his help, the test programme showed a problem, with some odd noises and the Z crashing into the limit switch.
A really BIG thank you to Mike (Doddy) who after chatting with and suggesting to swap the leads at the back of the control unit so X was operating the Z axis the problem was cured, however not satisfied with just leaving it at that after several texts he advised me to set the step pulse and Dir pulse to 5, they were set at 1 also to slow the acceleration as it was a tad too fast, all this in the motor tuning within Mach 3, I swapped the Z and X leads back to where they should be and did several tests using my Vernier to measure the start and finish positions of the Z axis, which was good.
Today I did a job that took approximately 1.5 hours and it was perfect, so it looks as if the problem has been solved.
All I need to sort out now is a strange sort of squeaking noise on the X axis as it travels along, just started during the job I have just completed. it has always been lubricated at regular intervals with a silicone lubricating spray, (not WD40)