Originally Posted by
nicubila
Hi all
I am scratching my head around an issue for which I cannot detect the cause but only witness the effects.
I have been running a cnc touter with Delta nc300 controller, asda2 drives with absolute encoder motors. The router is stiff, steel, rack and pinion, with almost no backlash (alpha gearboxes), meaning around 0.01mm. Axes A is slave of Y. Motors are absolute single turn encoder (Delta has no multiturn) and run with 3.6V batteries. Spindle very little run out.
For the production I make I need both gantry perpendicularity and repeatability (0.05mm max positioning error). I have to make 2 drill holes (3.175) in the table in 2 still plates, so that I use those holes to guide the aluminium composite panel sheet I machine.
Lately I observed random errors with the repeatability. If I change the steel plates and make new holes, machine works ok, production works ok. After a few hours of work I send the router to do again the same holes, and goes through the procedure very precisely, No steel is removed, and after that the 3.175 shank of the bit still goes inside the hole very precisely, no play.
If I turn off the router, then start it again. and try to do the holes again....surprise. they are off about 0.2-0.3mm , sometimes even more. it goes off on both Y and X axes. This drives me crazy, because it i have to turn off the router in the middle of the work, i have sometimes to scrap a 100eur sheet.
So my takeaway are:
- indeed spindle has no runout, so it cannot be because of it
- general mechanical repeatability is ok because the machines returns to holes
- thermal expansion is excluded as a cause
I run with compensation in the controller as the racks are not that exact. now when i am writing this I think that maybe if i should disable the compensation, do the holes, restart the router and check if router return to holes. Could be path.
The batteries on the absolute encoders are ok, actually new. No error pops up as normally does when batteries are low (or too high voltage). I do not think this could be the problem.
there are no other compensation setups that could affect the setup.
because the repeatability problem is on all axes, I think it is not any single of the motors or drives defective. Rather in controller something.
So if anyone has further ideas where to search for, it would be appreciated. I can post further settings of the controller and drives if that helps.
thank you
Marius