This is the new model but it is still untested, but after comparing it to the old version I can see that most issues are fixed.

In the full assembly you can see the addition of screws and standoffs. The screws are to hold the middle and translucent section together and the standoffs are to hold the top disk (the one that the encoder screws to) to the middle section. I also found that the knob didn't sit parallel with the middle section, not sure if that is because of the encoder coupler but it seemed like a very good fit, it could be that the coupler itself is not sitting perpendicular inside the knob. I will be making a new knob with a better mould, details are in the next paragraph. 

The new mould should hopefully fix a couple issues I have with the current mould. 

1. Trying to push the top disk onto the cement is difficult because the seal is very tight between the disk and the PVC walls. New version has indents around the circumference in order to let air through. 

2. The bottom disk which forms the cavity for the encoder coupler left a cavity which was too tight and made it hard to insert the actual coupler. New version will leave a bigger cavity.