Sorry John, since I don't have the right software and didn't create the step files I can't help you there. @1972 Can you help here?

 

That is giant. You'll definitely need to use some upgraded Z axis and frame rigidity modifications. That control board looks great, should work fine (realizing that you need to power the heated bed separately as that 15A circuit isn't going to cut it). Make sure you go through AK Eric's blog (linked in my printer description/front page), he has had to tackle some issues that I didn't face with my smaller bed and nozzle.

 

I was using 5mm for my attempt (see a page or two back). Basically increase retraction until you are happy with the results or start jamming. Obviously if you jam you will have to back off the amount of retraction. You can also drop your hotend temp to help with oozing.

 

Alright, who wants to design a light single nozzle direct drive extruder carriage?

 

Do I have a guinea pig?

 

I am concerned about the moving mass of two stepper motors. Sharp corners and other large acceleration/decelerations will create a lot of vibration and cause ghosting. You'd really have to clamp down on those limits.

 

Here ya go. Beta version, please provide recommendations on changes and note any fitment issues. I have not used or even printed this.
It is meant to be used with a bowden tube to guide the filament to the carriage and a short length of tube to guide it down to the nozzle from the direct drive extruder.

 

What do you mean? Have it move there at the end of a print? If so, yes. Just add some custom gcode in slic3r to the "End G-Code" section.

Something like:
G90 ; Switch to absolute coordinates, should already be there though
G1 Z200 F1000 ; Linear move to program Z=200mm at a speed of 1000mm/min

Where in this example your lowest bed position is 200mm from origin.
At a speed of 1000mm/min it will take 1/5th of a minute to go from origin to max Z position.

 

If you are thinking of not moving the bed at all then you must get your Z movement by either:
Moving the hotend up and down like this:
Maximus 3D Printer | OpenBuilds
Or moving the entire Z assembly up and down like this:
CoreXY W/ Fixed Build Plate & Enclosure | OpenBuilds
Or some other inventive means.

I don't prefer the first as it makes the carriage assembly very heavy for a coreXY belt system, it is better suited for a heavy lead screw/ball screw driven CNC with a heavy tool assembly.
The second is just much more complicated and I don't see any benefit from adding that complexity (though neat).
If you really don't want a moving bed then a delta printer is hands down the way to go.
I would do something similar to this but redesign it to use my 3D printer plate system instead of aluminum ones and use a 10" or 12" round bed.
Delta-Six | OpenBuilds

Personally I don't have an issue with it moving in the Z direction as it only moves once per layer. Even if you have nozzle lift enabled then it only moves slightly. Much better than a constantly moving Y axis bed which deals with large inertial direction changes.
If it is a cantilevered bed like mine then it has to be rigid enough to handle the forces. As folks have exceeded my original 8" canteliver, improvements were necessary.

These came in the form of two solutions:
1) spread the forces over a large distance. The rear moving Z bar was changed from 20x40 to 20x60 extrusion. Could even go to 20x80 but it also impacts usable Z height. The bars supporting the bed can be upgraded as well. Additionally I have seen the brackets holding these together be beefed up.
2) move the motors from the very back to the 1/4 or 1/3 closer. Uses an extra piece of extrusion but all the same parts.

 

@AK Eric Have you given it a try yet? The only issue I see is a risk of left/right stability. The V wheels may be enough though. I like that you added a cross piece on the bed frame, I actually had that my original design (though at the midpoint), but forgot to actually install it.
I like the way @trublu832 modified it slightly better as it reduces the canteliver but still stabilizes left/right. It costs a piece of extrusion, but it also allows easy adjustment on that bar to align with the bed frame.

 

I think the little dollup you are seeing is from the nozzle lift movement. I had the same, but it does help clear the print during nozzle movements and with oozing.
Hopefully @AK Eric will have some time to test and debug the design soon Feel free to help him out though!