Prusa Mini Square Helper

After printing 4 years with my Prusa Mini I am still happy with the printer BUT I am still annoyed that my squaring is only for a short time and then must be redone.

So, what‘s the problem?

Even a small force, like squishing the filament, presses the printhead up. If the print head is on the far left side then this force has the whole x axis as a lever and introduces a torsion at the right where the X-axis ends. This produces again a torsion at the bottom of the Z-axis which has a further lever to produce a torsion in the right bottom beam. Even when a 30x30 beam looks sturdy, it can not hold this force and will be twisted. If you print heigher objects things go even more worse, the total lever comes up to 40cm which makes a small force quit big. To counteract this torsion this lever makes again an upright force from the torsion and presses against the left beam, so the twisting will be much less and as a result the Z-axis gets stiffer in X direction (and a small bit in the other diections too). As a side effect the 4 screws  which hold the right beam don‘t have to hold the full torsion force and resquaring is not nesserary so often.

Parts Needed

• 7 T-nuts for 3030 with 5 mm thread (M5)
• 7 screws flat head 5 mm x 8 or 10 mm (M5)
• 1 screw M6 x 70 or 80 mm
• 1 nut M6
• 2 washers M6
• 1 M3 x 12 allen screw (optional)
• this print
• allen key for the screws, two 10 mm wrenches for the M6 screw
• some craft skill

Print Parameters

• 3 Perimeter
• 30% gyrofill infill
• 5 top and 5 bottom layers
• some painted supports under and between the clamp (short arm) and between the clamps (long arm)
• Print the parts laying on the side, this makes them more robust.

I used PETG for the print.

Assembly

The thread for the M3 screw needs to be cut into the plastic (refer the pictures) and can be used to adjust the squaring. Before you screw the M3 screw in loosen the 4 screws of the right beam which holds the Z-axis. Use some pressure for moving it into the right direction. The screw can be used if the X-axis is too high on the left side (opposite to the Z-axis) which is the usual case if you have printed some time with the Mini.

1. Screw the short part from the bottom to the left beam. Use the single screw first.
2. Position the long arm on the beam with the Z-Axis in a way that it moves into the clamp from the short arm. Already installed T-nuts at the bottom makes your live easier (see picture).
3. Press the long arm into the clamp of the short arm
4. Fiddle in the screws on the long arm which goes horizontal (needs some time..)
5. Install the M6 screw from back to front but leave it loose now.
6. Square your mini (optional with the help of the M3 screw). Remember to loose the screws which hold the beam which holds the Z-axis.
7. Tighten the M6 screw and the beam holder screws if you are satisfied with the squaring.

Ready to print

Additional off-topic tip

After 8-10 kg of filament printing my bowden tube was worn and I had a lot of problems with my retraction settings. I replaced it with a cheap 1.9 mm inner diameter tube and the problems are gone.

Happy printing!