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MPCNC Part Repairs Z Nut Lock

mpcnc part repairs #1

MPCNC part repairs were needed when several pieces cracked during final assembly.

It turns out that I made a mistake when printing the Z-Nut Lock. This plastic part fits over a 5/16 inch coupling nut which attaches the threaded rod to the middle joiners, and also holds the middle joiners together. It turns out that there are two different sizes of coupling nut diameters. My nut was 11 millimeters across the flats, but I printed the larger nut lock. As a result, I was trying to tighten down too much.

Since PLA is quite brittle, there was too much compression stress. This caused the nut lock to crack, as shown on the left of the above picture. So, I printed the correctly sized nut lock in ABS, as shown on the right. The fit was very snug and little tightening was needed. All is now well. The gantry now moves smoothly on the threaded rod.

MPCNC Part Repairs – Rigid Coupler

A similar problem took place with the rigid coupler. This coupler connects the stepper motor shaft to the threaded rod. Again, over-tightening caused a crack, and resulted in more MPCNC part repairs.

mpcnc part repairs #2

As shown in the picture, the cracked part on the left was replaced with a new ABS plastic part, shown on the right. I sized this part to fit the shaft and rod more snugly, and that did the trick. Combined with the extra strength of ABS and a snugger fit, this replacement should work fine.

The lesson to be learned here is that PLA is more brittle than ABS, and not at all flexible. If you are printing parts that need some flexibility, use ABS or maybe PETG. Unfortunately, I still have not figured out how to get PETG to print properly, so ABS will do for now.

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