Improved locknut for Lamicall phone holder

Designed using 100% open source tools

I am proud to say that this rather complex design of a thread that narrows down as it winds, was done using 100% open source tools. First I measured the thread as precisely as I could and designed the fitting female thread using stl_tools, running on a RaspberryPi (actually the one that controls my Pursa Mini). To be honest it took me a few iterations to get the thread perfectly fitting. Then I designed the outside form of the locknut in FreeCAD, including the inside hole that narrows down.  Then I fused both parts together and exported them to PrusaSlicer. There I exported the part as .stl, as I found that this creates trouble-free .stl files, which is not always the case with other tools.

Improvement over the original part

This design makes a big difference. The original locknut does not have a thread that narrows down, therefore the ball mount is never really locked. It may be strong enough to hold a phone in position on a well suspended motorbike. But on a mountain bike, or when riding rough roads on the motorbike, the weight of the phone will make it come down more and more with every bump. This effect could be completely eliminated with my improvement, the phone holds it position even on very rough terrain. 

Select your version of the lock nut

There are not two versions of the lock nut. One has four grips, like shown in the pictures. If you have enough space around the lock nut, I clearly recommend that one. 

If you have limited space however, go for the version that says “slim profile” in the name.

Printing

My recommendation is to use 4 (or more) perimeters, to make the part strong at the thread. I have found 25% infill to be sufficient if you print it from PETG. 

It might work in PLA as well, but that is not tested. Keep in mind that PLA “floats” over time if it is under permanent mechanical load.  So when printed in PLA, the locknut may become loose over time. 

I have printed my parts on a Prusa i3 Mk3S, because the precision it gives helps to create a perfect thread inside the locknut.

Happy printing!