update 20120103: The machine was commissioned some time ago, and this has been working great! (see picture). I'll adapt this system in all future designs. It will work with belts up to 10 mm wide.
This is part of a small audit I am doing of the current Mendel structure for the utter lack of stiffness of some key parts. The general aim is to have a superior Mendel while still keeping plastic (here: only 27 + 16 grams) & vitamins needs at moderate levels . Any help, comments, contributions and evolutions of the design most welcome!
The aims of this torsion box mount are:
- to put a mercy end to the y axis motor sorry flexion on its mount (and the consequent lack of parallelism that has the pulley and belt doing very unwanted things)
- to provide support to the Y axis pulley on both ends, thus reducing the forces exerted on the stepper motor bearings
- to improve the general ability to correctly tension belts and improve stiffness, precision and fight backlash.
The design uses one 28x12x8 bearing.. Clearances are OK with or without a printed idler / bearing cover. Lately I have switched to two bare 608 bearings side by side.
There is a 16 mm wide space inside the box for the idler and all the washers that will fit.
The starting point is the dxf from Adrian's mods.
Note: a similar "treatment" will be applied to the X axis in the near future.
This is easy and straightforward to print!
I am using a vitamin aluminium machined pulley from eBay (that determined the bearing's diameter), but it should be very easy to adapt an existing printed pulley design, and also to adopt a different type of bearing.
Check the clearances with your particular setup first.
I printed this with 4 solid layers, 3 extra shells and 60% infill in hexagonal pattern.
slip in place, add washers as needed, bolt on, also secure with nuts on the M8 threaded rods, re-tension the belt. Enjoy!