goaran wrote: @PCW: no I have not tried inverting the pulse, however the motors seem to move totally normal ig the slight drift over time.
How could that be a result of inverted step pulses?
@BeagleBrainz: it seems to be with all axis, however a bit more on the longer one.
No its not a linear error. If you move one axes and measure the distance, then the measured distance is totally fine within some few microns.
The error only occurs when milling for lets say half an hour and then measuring the position against the start position.
The coupling between the motors and the lead screw is done with those couplings that have red rubber in between.
The bearings at the end of the leadscrew are the bearing blocks that come with the leadscrew. I have tested pushing as strong as I can against the bearings and also moving the axis in between, that does not seem to have any effect on them.
The "procedure" I used for testing is. Measure the position of the tool in one axes. Then mill something. Measure it again. This results in an difference of up to 0.5 mm after half an hour of milling. Since 0.5mm is really a lot i cannot imagine how this could be from the leadscrew backlash.
The error is kind of random therefor I habe not tested from different start points.
Generally that's not the accepted method for testing backlash. Depending on the amount the leadscrew is changing directions it will eventually add up.
I would suggest using google to search for methods to measure backlash.
One backwards & forwards test really wont show much, the more you can repeat this procedure the more the commutative error will be.
Whilst you may measure "within a few microns" with one iteration, that will change to "within a few tens of microns" over 10 iterations, ie this measurement will be 10 times greater. Backlash can also come from the coupler itself. If you have a low quality coupler that can contribute to the issue. A good quality coupler from a reputable supplier\manufacturer with help mitigate the issue. A good quality coupler is not cheap. They cost somewhat more than the types you get from most ebay stores & "maker stores".
A little bit of looseness here some there and some more else where will add up.
It may even be that there is a non linear section of the leadscrew that could be enough to add to other issues.
Any tests you make should ideally be done with a dial indicator. It can be painful and time consuming to chase these issues.
One thing that comes to mind is that some of the cheaper bearing blocks use standard bearing and not angular contact bearings, I have 2 sets of bearing blocks that I bought at different times from different suppliers. On set has angular contact bearing on the fixed block and the other has plain bearing on the fixed end.
Then if you add issues with latency..............
