Concerning my concept for mounting the Y axis motor inside the chassis I have made a few tweaks.

First off my thought is that a perfectly centered motor would not need flex couplers. A solid coupler would be better. Solid couplers can be made smaller and this would address the issue of the couplers taking up too much room. So I have drawn up printable couplers that are 14mm in diameter and 20mm long. The set screw holes would need to be tapped for 3mm set screws. I don't know if I have the diameter of the set screw holes correct for tapping. These couplers still may not clear the Z axis guide rods though they are at least closer to doing so. Someone may know of an existing coupler for 5mm to 6mm that would work better.

In order to align the motor properly we need to be able to adjust the alignment in both the Z and the Y axis. I have changed the motor mount holes to slots with .5mm play in both directions of the Y axis. I have changed the chassis mount holes in the motor mounts to slots to provide adjustment in the Z axis. This should allow the motor to be perfectly aligned.

I don't have a dual shaft Nema 17 motor. This plan is based on a motor model that I did not create. So final placement of the motor in the horizontal plane is not final at this point. This needs to be known before the rectangular hole can be cut in the chassis.

With the holidays coming up it may be some time before I can come up with the few dollars to order the motor. So someone may beat me to trying this mod. As a fair warning to those interested, this is only a concept at this time. I have not done this mod. This mod is design for the SD3. I don't think there is enough room to do this on the SD2.

I haven't split out the coupler and motor mount parts from the drawing because they are still concept parts. While you need two motor mounts and two couplers, they are identical so there is only two parts, but you need two of each.

If you have sketchup (it's free) you can select the parts, copy them (Ctrl C) and paste them into a new drawing to isolate them for modification and printing. There is a free plugin extension for sketchup to import/export STL files.

Have fun.

This requires a dual shaft Nema 17 motor, two couplers, and the two motor mounts in the drawing.

This is just a concept drawing, not a working model. While it is close enough to determine whether it will fit, it is not a built and tested mod. Hope this helps anyone interested.

I don't think alignment will be too difficult.  Besides, there is always a little play in the mounting holes.

Have any of you who have tried this already had any problems with the motor wobbling on those spacers?  I would be concerned that the torque from fast changes in direction could cause the whole thing to twist and introduce a new backlash problem.  Instead of metal spacers, why not design a printable rectangular spacer so that the motor can't rotate at all?  I was thinking something like this, but taller: http://www.thingiverse.com/thing:11429/#instructions

P.S. Never mind... the y axis is a Nema 17 and it is too big to line up with the shaft from inside the case. They do make dual shaft Nema 17's I'm not seeing a way to align it to the shaft. They do make higher current Nema 14's, maybe a higher current version could drive it?

...here is a pretty good test for circle calibrations.

I gave it a shot. My settings probably have to be adjusted. I don't know if it makes a difference if it's ABS or PLA and how the material shrinks after it cools for this test. I'm using ABS though and it was pretty tight so I had to give the nickle a good wack to get it in there. If there's any deformities, there's a chance I may have stretched them out around the nickle.

The coupler came as you see in the picture, all three pieces. No separate insert was ordered. A longer shaft is necessary for it to extend to the coupler so I had to order an SD3 6mm shaft for my SD2.

someone said you used a spider/love coupler. It seemed like you order those with a separate insert. Thanks for the info.

nice mod indeed on the y-axis.

is there any reason for the spider style coupler instead of a rigid coupler? Is it just impossible to align things well enough for a rigid coupling?  I assume the spider/love-joy introduces backlash.

The reason for the coupler I chose is because I didn't want any compression or expansion as with other couplers. Looking back at it, I also didn't want it fully rigid because I didn't know how well the motor will align with the rod.

It's a 5mm / 6mm coupler. I'm not sure what you mean by the insert. Coupler is made of three pieces.

I'll try to make some prints over the weekend and post the results.

nice mod indeed on the y-axis.

is there any reason for the spider style coupler instead of a rigid coupler? Is it just impossible to align things well enough for a rigid coupling?  I assume the spider/love-joy introduces backlash.

Actually it doesnt, thats what makes it nice. Hard couplings have no backlash, but HAVE to be aligned. Helical couplings do not need to be aligned, but flex so much they have backlash. Spider coupling has no backlash and does not need to be aligned. But nothing holds it together either, the mounting needs to hold the coupling together.

is there any reason for the spider style coupler instead of a rigid coupler? Is it just impossible to align things well enough for a rigid coupling?  I assume the spider/love-joy introduces backlash.

You can give this mount a try and use a dial gauge to test the backlash in the Y axis - http://www.thingiverse.com/thing:69029