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Free Z-Axis Worries Me

I recently installed an old lead screw to the Power ARM prototype and I am more than a little concerned about the free wobble in the z-axis farthest from the lead screw. It isn't supported by much and the linear bearings are perhaps overly loose leading to 1-2mm of sag. In theory this should not impact print quality as the Ender 3, Ender 3 Pro, Prusa Mini, and other similar cantilever printers aimed to compete with do not suffer from this problem and still have respectable print quality.

Just in case this problem causes quality issues, I am going to prepare some back up plans:

  • Add a second lead screw, motor, stepper driver, anti-backlash bearing, top lead screw stabilizer, extensively redesign the free Z-Axis to accommodate the new pieces. Now I might be able to get away without the additional stepper driver but this upgrade will certainly add quite a bit to the final price of the machine. Money aside, supply for proper lead screws is really tight and I am not even sure I can get more right now.

  • Add a third linear rod and pair of linear bearings to the free Z-Axis and extensive redesign. This is a fairly obtuse solution but much more economical as I have plenty of linear bearings in stock and linear rods can be quickly resupplied. This would mostly solve the sagging issues as well at perhaps a third the price increase of adding a second lead screw and motor.

  • Reverse angle the z-axis linear bearings. This is a risky modification but adds not additional cost to the design and can be done almost immediately. Basically I angle the linear bearings by 1-2 degrees against each other in the support and this creates an aggressive anti-backlash at the cost of more stress on the bearings. The bearings should last indefinitely with proper lubrication so the stress is more of an issue with people that don't lubricate bearings but I am not entirely convinced this can solve the sagging.

For those that do not know, I once worked on a printer called the "one-up" printer and it had more extreme sagging at about 5-10mm. Nonetheless, it printed surprisingly well. I will be very curious to see how test prints turn out.

Bonus: the sagging makes it harder for the nozzle to scratch the build plate or damage the nozzle.


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