Author Topic: My 3D Printer 1000hr service.  (Read 190 times)

Offline Joules

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My 3D Printer 1000hr service.
« on: July 28, 2018, 09:33:54 PM »
Maybe quite a bit over the 1000hrs, some printed parts had started showing poor surface finish and layer slip (the PLA pattern for casting being one and some of the props).  I have 3 printers that are the work horses of my designing.   What I learnt on the first machine was applied in mods on the other two machines as soon as they got unboxed.  My first printer has over 2000hrs on it and still running, but a little more battle scarred.  One of the main mods I did was to clean all the linear bearings from the start, strip them off the machine and clean in an ultrasound tank, then re grease.  During this current strip down none of the linear bearings show any sign of wear, and once the bars wiped clean, the bearings still lubed the bars again.  They need no further attention.  The Z screw has some wear in the brass nut, but nothing that affects its operation as it works against gravity.  The leadscrew clocks as true over the top couple of inches where most wear would have occured.

The layer slip shown below on the left hand print can be seen in the uneven edges of the gear teeth and the flat spot on the front, compared to the new test print after service.   This can be belt slip/stretch or bearings binding.  I used my jig tools made for the first printer to check the printer for racking.  Sure enough, a piece of paper was needed to keep both bars in place, something had given, time for full strip down.  This was a fairly low cost printer at the time, but with careful setup from the start it can be made to perform well above its pay grade.

What I did find was some belt stretch and a failing bearing (marked with red circle) on one of the belt guides.  If you grip belts tightly at one end and stretch them out, you can see if they have any miss alignment at the other end.  I have 0.010" and 0.012" difference to a new belt over the same length.   That isn't as bad as it seems as the belt is stretched a bit anyway when installed, the difference is an issue.  It pointed to the bad bearing that had started the gantry racking and this was causing random layer slip and poor geometry due to backlash where the printer cycles direction.  A flange bearing was tight and on its way out this also added to the backlash in the system.  Replacing that bearing got things running smoothly.   I could have replaced the belts, but decided to swap over the left and right belts.  A design flaw in this machine is that the drive goes through one belt to a line shaft that then drives the next belt.  Any backlash accumulates in the two belts, if they had put the line shaft direct on the motor coupled pulley, backlash in one belt wouldn't be passed to the next, especially as the failed bearing was at the end of the drive train.  Oh well, it's sorted now.  Always pay close attention to the belt in the pulley, if you see the belt rise as they rotate backwards and forwards by hand, it doesn't have enough tension and this will cause backlash that can appear as uneven layering.

Upon reassembly the jig tools are used to set the gantry square, this is shown with the jig rods both set and not dropping out.  Cycling the motion a few times and replacing the jig rods gave the same result so the racking has been removed. I used some current work for test printing as it was easy to measure and see if the geometry was correct.  I had a little under extrusion to take care of as the nozzle is due replacement, this I dialled in using the onboard printer settings rather than my software settings.  That way reprinting old and new model will produce the most accurate results.

Errors are fine as long as they are consistent and you note where you corrected them.  Too easy to end up chasing your tail between hardware and software, and all your old design library needing tweaks as they don't print accuratly anymore.

These printers give very good results for having steel chassis and small bed volumes, this helps with overal rigidity, again reflected in the print quality. 

Just get doing and make swarf, you can decide what its going to be later.   :thumbup: