Extruder clicking fixed, vibration stuff

Created on Tuesday, October 10, 2017.

Extruder clicking fixed

I made three changes to the hotend part of the machine:

  1. I removed the beefy tensioner arm spring that I installed last night and replaced the original, stretching it out slightly first to get a bit more force. I felt that the beefy spring was just too much for a plastic arm assembly and was probably distorting that part of the extruder.
  2. I ran PID autotuning:

     M303 S220 C5 ; Run Marlin's PID autotuning at 220 C, for 5 cycles.
         Example returned values:
         Clasic PID
         Kp: 28.97
         Ki: 1.41
         Kd: 120.01
     M301 P28.97 I1.41 D120.01 ; Set the above Kp/Ki/Kd values for the hotend.
     M500 ; Commit to EEPROM.
  3. I increased print temperature by 10 °C, as Micro Swiss themselves suggested in their installation instructions:

    For PLA, you might need to increase extruder temperature 10-15 degrees.

This has entirely stopped the extruder clicking problem, and my solid layers are actually solid now.

‘Drylin’ bushings arrived

Those AliExpress RJMP-01-08 bushings came in the mail today, and the plastic does feel extremely slick and a bit oily, so things are actually looking good.

What’s not looking good is that the bushings are actually 1 mm OD larger than normal LM8UUs, so I can’t put them into the stock bearing blocks. I had a look for some new ones on Thingiverse, but a lot of people are using blocks that are only half the length of the stock ones, and therefore only secured through two holes. I want more rigidity in mine, so I have to make my own. My first attempt was basically a beefier version of the stock block:

But I found that the size of the M4 nuts and their closeness to the bushing created some thin wall areas that are not ideal. I was also a little unhappy about the amount of compression that the design exerted; IGUS recommends an H7 bore, which describes the tolerance of the bore in relation to the nominal shaft OD. In the case of the 16 mm RJMP-01-08, a 16 mm H7 bore is 16.00–16.02 mm to get the correct compression, or else the bushing will be oversized. I was thinking of rolling with a shape like this to clear the M4 nuts:

But I am concerned about the amount of compression such a short block can provide. I think in the end I will have to use a big ol’ box-type block, but I will design mine so that it compresses properly and does not need a retaining collar.

Y carriage bearings replaced

I replaced all of the LM8UU bearings on the Y carriage today when I found out that the new RJMPs would not fit for now. The old bearings were running very loose, rattling when I shook them near my ear, and revolving freely on the shaft. The new ones do not rattle or revolve, but they still run cleanly. I also dropped the Z endstop so that I could keep as much tension in the bed springs as possible. This seems to have removed my vertical vibration artefacts, although I can still very faintly see the diagonal vibration artefacts.

Since the diagonals occur on all faces, it’s likely related to a source of vibration on the extruder block, mostly the part cooling fan (see yesterday’s post) but also probably the X axis bearings. I used my mechanic’s stethoscope to listen to every part, and the long LM8LUU sounds like it’s rattling a bit too. I have enough RJMPs to replace this axis also, but I may need to design a whole new extruder backplate, unless I do some test prints of the ones that I found on Thingiverse.

Plans for a rigid bed

I would still like to switch to a rigid bed assembly to finally rule out the bed springs from my vibration troubles. I need to remember to print grips for M3 nylock nuts now that I have them.

I guess the basic idea is to have two nylock nuts per levelling screw, one below the carriage and one above. The above nylock is used to adjust the bed height, and the below nylock is used to lock it in.

That's all there is, there isn't any more.
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