Hi
 
I have machine setup fine and running ok except the Z axis has a problem.
 
I set the postion of the tool on the start position of the board and set all axis back to zero and then regenerate toolpath and press start all looks good but what happens is if the machine needs to stepdown it machines the first layer slightly deeper than told too then when it comes out of the board to the safe zone then goes back into the board to machine the next step down it’s gaining about 2-3mm each time.
 
For example.....
 
tool stepdown 1mm
 
machining 2mm deep
 
first machining 1mm deep
 
second machining deep 4-5mm
 

I also ran out a program the other day in a 12mm board and maximum depth of machining was 9mm, stepping down 1mm each time, I had to quickly stop it when the depth should have been 8mm it had started to machine through the bottom of the board so had gained 4mm

Can you suggest anything please

Sounds like you are skipping steps on the z up moves or your steps per are off.  Try retuning your z axis motor with about half the accel and velocity it is set to now to see if that fixes it.  If not, have a look at these topics.

http://www.machsupport.com/forum/index.php/topic,12513.0.html#new

http://www.machsupport.com/forum/index.php/topic,12512.0.html#new

http://www.machsupport.com/forum/index.php/topic,16315.0.html#new

You may also have a mechanical problem like a loose pulley or coupling, tight spot in the z causing skipped steps, etc.

Brett

Ok thanks for replying, its a small engraving cnc so the movement are very slow

I would think its more to do with the links, i assume they are to do with calculating how much the screw turns to move the Z axis.

I've just looked at all three links and understand what it is trying to achieve but its gone right over my head as I wouldnt have a clue on any of the figures for my machine.

is there somewhere I can just enter a figure and trial and adjust number until its right or is there a simple way I can get the figures to enter into that backlash spreadsheet?

Thats not a backlash spread sheet, it is for steps per unit.  These numbers really should be known if possible.  That is the only way to know for sure you have it right.  You can set your steps per and measure a move using a dial indicator and commanding a move of a set distance from mdi, compare the two and adjust your steps per in motor tuning according but what if it skips steps while testing?  What if there is backlash and you have not allowed for that?  Can you not find the specs for the machine?

Brett

Ok thanks i'll e-mail the supplier and see if they can provide me with the specs and will let you know

Just found the velocity and acceleration settings in config and they are set to the default in mach3, I haven't altered them at all.

for Z axis they are...

steps per      640
velocity        799.8
Acceleration 100

Should I be dropping these figures?

Regards

The supplier should have recommendations for you I would think.  Did you buy the machine complete?

Brett

Yes I did

Its a TS3040c-H80

No idea if this is correct but may help.

http://www.joyfay.com/us/media/import/EnglishMaualforCNCrouter.pdf

Brett

Hi that's great that you found that, thankyou and it has the steps per etc etc in there which I will change later.

So does the steps for control the amount of screw rotation to achieve a specific set distance?

Thinking about it I would think it is to do with these settings as if it was mechanical then the machining depth would vary across the board but even though too deep it is constant and the fact that the settings I have in mach3 are default and are twice the amount that is recommended in the file you just sent me.

I had an e-mail back from suppler attaching the same pdf as you just linked to. Bloody typical, Why they didn't let me have it before I don't know.

I'll change settings and see what happens and let you know.

Thanks for your help, really appreciate it. 

Regards