J-Bot Core-XY?

Work in progress. I really liked the initial D-Bot Core-XY setup http://www.thingiverse.com/thing:1001065, but there were a few things that I changed. I made it ride on both the back and the front rails and shifted the lead screws towards the center, added a part to connect the belts together so that z steps aren't lost, beefed up some of the parts, and changed the bed mounting brackets to something a little more rigid.

I added an optical end stop for the z axis because it is a lot more precise to alter the first layer z height in firmware than with a screw. There are a few things you need to modify in the firmware to use it. I have attached two photos of what you'll need to edit in the firmware. The first photo is changing the endstop to trigger when the visual field is broken. The second picture is where you adjust the manual home position. You adjust the z value to change first layer height.

Optical end stop: http://r.ebay.com/M1UBdX

The belt tensioner uses a 860mm GT2 ti