This is version 3 of my CobbleBot X Axis mod. Don't bother looking for verison 2, I did not post it. This has completely removed the issue of X backlash for me and I can now properly print with my printer.
This mod basically attaches a drive shaft to the X stepper motor that then drives two belt pulleys. One at the top of the X plane and one at the bottom. This keeps each end of the Y axis moving as one. The stepper is mounted outside the frame of the gantry and the drive shaft runs just underneath the gantry. The coupler for the drive shaft is inside the stepper mount. There is a slot in the stepper mount for turning the set screws on the coupler.
In addition to the printed parts you are going to need four 625 radial bearings, two idler pulleys, a 5mm drive shaft, two 5mm pulleys, and a 5mm to 5mm coupler. Here are the ones I used:
Bearing - http://openbuildspartstore.com/ball-bearing-625-2rs-5x16x5/
Idler - http://openbuildspartstore.com/smooth-idler-pulley-wheel-kit/
Pulley - http://www.amazon.com/gp/product/B00THZJNTI?psc=1&redirect=true&ref_=oh_aui_detailpage_o01_s00
Coupler - http://www.amazon.com/EnPoint-Flexible-Aluminum-Coupling-Backlash/dp/B016F2E92G/ref=sr_1_7?s=industrial&ie=UTF8&qid=1447884138&sr=1-7&keywords=enpoint+5mm+coupler
The drive shaft is a 5mm drill rod that I got from McMaster Carr, but their website doesnt allow me to directly link to it. It is literally 5mm which the hole in the bearings are actually a little smaller than 5mm. To compensate for this I had to put the drill rod into a drill and use sand paper to take off a few thousandths to get the bearings over the drive shaft.
You will also need screws and t nuts to mount everything to the vslot rails.
As always I have included the google sketchup files so people can easily make changes.
EDIT: Added some additional pictures of the motor mount. You can see the slot on the top for accessing the set screws for the coupler.
- Modified the X-Axis-Idler-Mount so it can get closer to the rails
- Modified the X-Axis-Drive-Shaft-Mount so it can get closer to the rails.
- Modified the X-Axis-Drive-Shaft-Mount to strengthen the area around the bearings.
- Created a new X-Axis-Drive-Shaft-Mount that is very different than my other design. This design can be printed without supports and with the bearing holder laying flat. The print quality is much better with it. You should print four of this one, two of which you should invert so the bearing mount is on the other side. This allows you to spread the bearings out evenly along the drive shaft rather than just at the ends.
- Change the X-Axis-Idler-Mount so that the tension is adjustable and prints without supports. Requires 2 35mm M3 bolts and 2 M3 nuts to hold the two halves together. For the Idler adjustments you need 2 15mm M5 bolts and 2 M5 nuts plus a 30mm length of 5mm diameter rod.
- Redesigned the X-Axis-Drive-Shaft-Mount mount yet again. This time in Fusion360. The part is stronger and has two attachment points instead of one. It can still be printed without supports. I recommend at least 50% infill for strength. You will need 2x M4 nuts and appropriate t-slot bolts for mounting. I added a chamfer to make pressing the bearing in easier. I recommend a C clamp for that.