It’s my post, I can make bad puns in the title if I want to, so there nyah *Thhbbbtttt!!!
After recieving a tip, I was finally able to source a pair of 5mm oldham couplings that didn’t look like they were made out of tinfoil and cheese and would crumple at any second. The part number is s50xuvm20h05h05
Why did I replace my couplings you ask? Simple. Helical coil couplings are just flat out the wrong coupling for the application we are using them for, and have been for years on every single 3d printer you see them on. In the beginning, they were used because they allowed the leadscrew to flex side to side and front and back, to eliminate signs of Z banding. Once more printers started to properly constrain the z axis, like on a Taz, they got left in place, probably because they are inexpensive and don’t really cause that many issues, but theyhave 2 fairly major flaws. 1, they aren’t 100" zero lash. There is a spring effect, very very tiny, but when you turn the motor, the leadscrew turns slightly later than the motor shaft. It catches up when its at speed, and it’s the Z axis so it doesn’t really matter since the XY print doesn’t generally start until after the Z travel, but its an area we can improve upon. The other serious issue is that the spring actually can pull the leadscrew or the motor out of allignment and actually cause banding.
An oldham style coupling has zero lash on startup, and exerts no force on the leadscrew aside from rotary motion. As you can see from the pictures you can misallign the shaft quite significantly if you want and still have a usable machine.
There are two downsides i have seen so far. One is the cost, this upgrade will set you back about $70, the other is the noise. The spring couplings acted as a vibration damper for the z motors. Rapid motor travel during Z home is much, much louder than it was. I think a pair of motor dampers on the Z motors should take care of that issue though.
Am I seeing any improvements in print quality from where I was already at? on my machine, no. But my couplers were already well aligned and my motors were lined up right with the leadscrews, so I wasn’t expecting to see any either. This modification may slightly improve the life of my leadscrew tailshafts and the leadscrew nuts themselves by removing potential leadscrew deflection caused friction.
if you are seeing any signs of Z banding on your taz, this is one thing you will want to consider, possibly before the Anti wobble projects. if you aren’t seeing any signs of banding, you can probably ignore this one.