KP3S Pro Bed Levelling Thumb Wheel Clip

Update This design is for the original KP3S pro with the pulley wheel drive for the Y axis. I have another design for the new bed carriage which comes with the Y axis linear bearing upgrade which you can find here

The thumb wheel adjustment mechanism for the print bed is problematic; the thumb wheels will always tend to loosen. In fact after my first bed levelling, one of the wheels fell off completely during a 4 hour print. I know I should have ensured that they were pushing the springs up a bit tighter, but nonetheless the undoing tendency will always be there.

So, I designed this clip in Fusion 360. It was designed from scratch but was inspired by wheel clips designed for other printers, notably monsieurglad. I also chose to replace the thumb wheels for these by McFly, the clip will also work on the original thumb wheels, but I find these McFly wheels much easier to use.

These McFly wheels have six indents and so six positions where the wheel can be locked. A M4 screw has a lead of 0.7mm, so each click advance or retract of the wheel will move the bed roundabout 0.1mm. Is that differential enough for fine adjustment? I think probably yes.

I printed the clips (and the wheels) in PETG. I checked their temperature in use whilst the bed was at 60°C and they were at 30°C so that's ok I think. I haven't printed PETG on this printer yet, but if it keeps a 30°C difference that should be fine also.

I printed them on a MK3S in PETG, at the Prusa 0.2mm quality setting, modified with 3 perimeters and 20% infill.  I printed  all four in one print and used the “complete individual objects” option in “Output Options” in Prusa Slicer to cut down on stringing between them. It takes about 1hr 45minutes to print all four. I've included a print file option for this if you want to try it.

There is a bridge and some 50° overhangs on the underside of the clip, but the MK3S coped with those with needing no supports.

Rather than take the bed completely off, it's probably easier to install them one at a time. The left rear is going to be the most awkward - such is life.

I would loosen all the thumbwheels, then take one off, remove the bolt wheel and spring, slide the clip onto the bed prong, insert the bolt through the bed, replace the spring, ensuring that it is on the bed through the hole in the clip, then lift the clip tag upwards to clear the thumb wheel and tighten the thumb wheel. Repeat this for the other corners. Or, do it your way :-)

When levelling the bed, I did it first whilst the bed was cold and went round three times for each corner getting the gaps right. Then I did a final adjustment when the bed and nozzle were at 60°C and 150°C respectively. There is a tendency to grip the tag of the clip and the bed together with the thumb and forefinger, if you do the levelling this way then you get most of it done without to much heat on your fingers. Again, or, do it your way :-)

The Fusion 360 design file is a bit of a dogs breakfast at the moment, I did rather hack my way through at the end with constraints and such. If, or when, I make it respectable I'll publish that too.

Enjoy! And watch those springs!