During my tinkering time with the printer, trying to improve the print quality I noted that something seemed a little ‘off’ with the Y axis movements……
A picture’s worth a thousand words so, have a look at the title picture for this blog post.
The Stepper motor mount at the rear of the printer has the Drive wheel centred at the top of the 4040 extrusion
The centre of the Idler at the front of the printer is raised above the 4040 extrusion by about 12mm….
This means that travelling from front to back, the Belt drive has to form an odd shape as the front is higher than the back by about 12mm…..
What this means for performance
Something has to stretch / give when the bed moves, which flexes ‘stuff’ and raises / lowers the bed height
- The bed is constrained to a single plane of travel only, the Y axis, front to back. It doesn’t go up, down, left or right
- The Bed is fixed to the driving belt by two fixed bolts – it should only ever move parallel to the base
- If the bed is fixed and the motor mounts are fixed, the belt forms a sort of triangle –
- The Hypotenuse of the triangle is a fixed length
- The Adjacent and the Oposite sides vary in length depending if the bed is at the front or the back
- when the bed is at the front, the belt is almost parallel with the bed, there’s little up or down force needed
- when the bed is at the back, the belt needs to stretch upwards, or the bed mount needs to pull downwards.
I believe that this poor design is part of the reason why people experience bad levelling on the D9. I also believe that this is the cause of the inconsistent layering often seen on D9 prints…….
A better performing system has both lengths of the belt in parallel, Kind of like below……
I’ve designed a new motor mount (currently in Version 6) you can download it on Thingiverse
This does two things
- Much stiffer than the stock motor mount
- Raises the stepper motor by 6mm – only 1/2 of what’s ideal, but avoids any interference with the bed mounts
The mount’s been used successfully by many people in the D9 facebook groups