Quote Originally Posted by Davidh
Here's the progress



Careful study has revealed this is a backlash setting problem of some sort. When I uncheck 'enable backlash comp.' then the trouble is completely gone. Full speed any which way I like.
Mechanics, electronics, hardware, power supply, printer port, motors,accel, steps, duration, everything is proved good by this although I am still in the soft stuff as I need backlash comp.

The backlash speed % was 15% of full, I put it there after a quick run on the day I commissioned mach3. playing with this has shown 6%-8% makes things a lot better than they were. Though the x y motors are still doing something funny when pushed.

A bit of sniffing about, there are words like 'CV mode', 'shuttle acceleration' appearing. This is where I will look next.

Thanks for all the pointers
BFN

Hi there,

glad to hear that you've located the lockup problem.. but I must admit to becoming a little concerned in terms of whats going on with your machine.

you say that backlash compensation was the problem.. another new revelation... but I can't understand how you can compensate for backlash if you didn't run the axis calculations beforehand... you may not have a backlash problem to compensate for in the 1st place. If you spotted positioning errors and put them down to backlash they may have actually come from an incorrect steps per rev setting... which you "reverse engineered" using a ruler.

running at speed without lockup can't be taken as "everything is proved good" i'm afraid. What you need to first establish beyond all doubt is positioning accuracy... based on what you say in the posts to date you don't have this at the moment. You mention CV mode and shuttle acceleration as being your next areas of investigation in resolving problems... I think you may be getting into a bit of a goose chase here.. at this point you don't have any factual basis on which to address any of the issues. "Looks OK" or "good enough" won't really do it, you need some facts.. hard data... measuable errors... to which you can then apply measurable solutions...

I would seriously suggest going back to 1st principles and setting the machine up frtom scratch on the basis of the parts spec and the results of the mach setup calculations. Having accomplished this I would then run the dial-gauge test described in the mach manual to establish actual positioning accuracy/errors. Forget about speed for the time being. First get accurate, then get fast. You can run as fast as you like but if positioning is not there machine is effectively unusable for anything serious.

Once you've established the degree of error/backlash you can then apply the correct amount of compensation and be secure in the knowledge that the setting is correct. However, I would say this is a worst case solution. Backlash compensation can deal with some problems to a degree when motion is in particular direction.. usually parallel to the compensated axis... but it is of zero benefit once the motion departs from this plane... like it will on a real cut. You would be much better off if you are able to deal with any backlash by mechanical means. This would function in all directions of motion and you would have a better machine.

Having been through the learning curve of building and running a CNC machine I can say that you will soon have enough to deal with in terms of getting the GCode and setups right without having to chase problems in cuts down to the machine mechanics. This is the last thing you want. Might seem a pain but the fact is you would save yourself so much grief and aggravation by getting your positioning sorted... then address speed... then you can cut accurately.. and fast.. which is the whole point....

hope this helps