Im thinking about the Z axis for my self built CoreXY printer. Usually you see somehing like the second picture, but because of missing space I want to move the Z drive to the corners of the printer.There will be 2 motors driving the bed (the cubes) and two 8mm guiding rods. Are there any reasons not to put the guiding rods with a greater distance between them? Thanks for your tips!
if your gonna have two motors.
why not just have four rail, two on opposite sides.
The problem is, that I have no room on the back and one the two sides, only on the front corners. Also the front have to be free over the width of the print bed…
Maybe a solution for you!
https://plus.google.com/u/0/112467558426863470913/posts/gPF7ezm9sww?pid=6128273548638538050&oid=112467558426863470913
@Mark_Rehorst unfortunately there’s just no room on the sides to mount the motors, but the idea using a belt seems good 
My current self built printer also uses two steppers with threaded rods and works quite ok. I don’t want to buy anything, because I already have all parts here and want to reuse them. The link from Erich looks also nice Thanks for your feedback!
Sputz! There’s only 10mm space between the Y carriage and the case, not enough room for an 8mm rod with a part holding it. But maybe I’ll use 3mm rods for the bed, should be enough for a Z axis…
@Volker_Klaffehn , I would take recommend you use the thickest rods you can, preferably something like 10, 12, or even 16mm smooth rods for your z-axis, especially if the bed is cantilevered like this. The 4th power rule basically says the relative stiffness of two rods is proportional to the ratio if their diameters, so a 16mm rod is 16x stiffer than an 8mm rod. Would it be possible for you to mount the motor at the top of your machine, and drive the screws from there, if it saves space?
Take a look at the CoreXY i built http://www.thingiverse.com/thing:313095
That shall give some ideas
X any Y are almost finished, and that Z drive unfortunately wont fit (already looked at that page before), but thanks!