Problem solved!

I am happy to confirm that we have solved our issue and we are glad to have seen it before the launch. Some words on what happened...

As you know, we want to have a precise and reliable assembly of the extruder for everybody. To achieve this, one of the thing we do is to use well selected tolerances and shapes to self center the motor (with the 17T gear) with the bigger 50T gear. Unfortunately, it was not 100% right and one of our developer had a problem while all others testers didn't. One of them has even put more than 750 hours of printing with this extruder without a single issue. We had the gears too close from each others.

The problem is that the spacing tolerance on spur gears are very small (those gears have a 0.5 module for those that are curious) and our first design was not using appropriate tolerance. One simple solution is to make the spacing adjustable but it is hard to feel the perfect distance (even for us) and it makes the assembly harder. We really wanted to keep our self centering feature!

After several testing, the first fix that was partially helping us was to take into account the shrinkage of PETG for the gear spacing. We did some researches to make this properly as well as providing a reliable way to apply shrinkage factor for other materials like ABS. You can find more details on our calculation here: https://github.com/gregsaun/maker_cheatsheet/blob/master/3d_printing/calculators.md#part-scaling . We will later build a guide on how to perfectly scale your parts in the slicer (nothing special but always good to have a guide as reference).

We still had the issue after the PETG compensation applied to the gear spacing. However, when we were scaling the original part directly in the slicer instead of CAD with the same factor we were not having the issue. We found later that the self centering shape and dimensions were not good and were deforming the part and reducing the gear spacing. You can see the difference applied around the motor and bearing holes on the last two images (it might sound easy but it is very thin there). And voilà, problem solved!

While we were trying to understand were the issue was coming from, we could see that the 17T gear is never perfectly centered on the motor shaft. This is not really a problem, you need some tolerance to be able to slide the gear on the motor shaft and those were appropriate. We are working on an LDO optimized stepper and to increase the precision we will press the 17T gear on the motor shaft during the manufacturing. This will also reduce a bit the weight, simplify the assembly and save some space.

The good news is that with the refined tolerance and shape, the extruder is now running even smoother than before (which is good for 602) and we could keep our self centering feature making assembly and maintenance very easy and reliable!

Thank you all for your patience, we hope to release tomorrow.

Enjoy :)