I have HUGE issue with two K8400 printers. I ordered them a month ago, fully asembled, runned few tests. And after about 30 hours of great printing, they started shifting layers in Y and X axis (both printers). From this moment, both of printers started to do it often and often.
I alligned all cariages using this tool: thingiverse . com/thing:606083
I made shure that all pulleys arent moving on rods (they were tightened correctly)
I noticed, that X belts are a bit too lose, so I used that tensioners: thingiverse . com/thing:19892
But none of this steps helped me.
I turned printer upside down, and noticed, that all DRV8825 were way too hot (about 80deg C). I measured their reference voltage, and it was about 0.925V, which means that they drived 1,85A. I checked on pololu . com/product/2133/specs and there was said, that maximum current without radiator is 1,5A, so I mounted radiators on all of them (dedicated stepstick radiators, using thermoconductive tape). I also moved bottom fan to blow directly into stepsticks using this adapter:thingiverse . com/thing:734288
It helped a bit, but not enough, so I put whole printer on cups to make more space for airflow under printer and added office fan: instagram . com/p/BZD06N4lSfq/?taken-by=mosi2323
Now problem happens not just after starting print, but after about hour. I started reading about stepper motors in K8400 and found, that they got maximum torgue at 2.5A - http://img.auctiva.com/imgdata/1/5/3/0/7/1/2/webimg/788063055_o.jpg but I also known, that even properly cooled DRV8825 can be set to maximally 2.2A, so I’ve done it - I rotated potentiometers to 1.1V. After hour of printing, stepsticks got about 90deg C, and motors got about 60deg C. And layer shifted (fuck!).
I turned printer off, and manualy pulled every belt to check if there is any bigger friction while moving printhead - there wasn’t any bigger problems. After loosing my mind, I even tried to change Igus Drylin tubes into LM8UU linear bearings in one printer, but I keep having trouble with both printers still, no matter if there are igus or lm8uu.
I found, that microstepping configuration on mainboard is 1/32 (all three pins connected). Comparing to this chart: static.micromo . com/media/wysiwyg/Technical-library/Stepper/microstepping_chart_table_1.jpg motors have only 5% of their torgue. I decided to change microstepping to 1/8, and comparing to this table: doku.radds . org/wp-content/uploads/2015/02/MicroStepping_Modes_tbl.png I had to disconnect MS3 pin. On K8400 there’s no microstepping switches or jumpers, so I just physically cuttend one of goldpins on every x/y stepstick to disconnect it. It worked, and now printer was traveling 4 times longer distances, so I changed steps_per_mm parameter to 4 times smaller. After that, printer should have bigger torgue, but prints got still layer shifted. From this moment, without changing everything, I was just changing stepstick voltage from 0.65 to 1.3 (current from 1.3 do 2.6), but with current under 1.8, printers wasn’t abble to even do auto home properly, and with currents over 2.2 stepsticks was overheating in a few minutes. And currents between 1.8 and 2.2 was giving me better results, but all tried (1.8, 1.85, 1.90 etc) was giving me failture without completing 3hr print.
Remove spaces from the links, because velleman forum tells me that I can use maximally 2 links in post…
In addition, I have built and worked with about 10 K8400 printers in my career, and never had such a problem. This time, I bought and built two of them and both gave me problems.
Please help me ASAP.
Regards, Maciej Mosak.