Long story short, the McMaster bearings were a bad choice.  I had to trim the flange and the bolt holes ended up being pretty close to the coupler.  Then the aliexpress bearings showed up and they would not need trimming, are shorter, and would be an overall better fit.  But I got it done so these will have to do for now.  Some pictures:

http://imgur.com/a/Bv8UB

The bracket was printed very quickly with a large nozzle because I thought it would be a prototype but then when it worked I just went with it.

I made the direct drive bracket in openscad so it would be easy to adjust hole diameters and offsets if I wanted to change something.  The main benefit of this part is that it used the same holes as the bearings so it minimizes holes to be drilled in the case and make it so there are only 2 points along the axis that have to align.  I hope that makes sense but basically this design eliminates the issue where the motor shaft ends up at an angle to the drive shaft.  Files are attached.  I will be updating this bracket to use with the (better) aliexpress brackets in a couple weeks but if someone wants it sooner, it is easy to figure out the file.

The "8mm bearing cut template" files is just a template for marking your frame for drilling.  The frame was too big for my drill press table so I just did it with a hand drill.  A steady hand helps so you don't screw it up and have to redo a hole and end up with one horrible hole and almost ruin the frame like me.

I will put it up on thingiverse after I change it to use the aliexpress bearings, which I will be doing for my SD2.

And my 8mm bore pulleys got here too.  The McMaster bearing holders do conflict with the 8mm Y rod collars, so it looks like I will pop the hose clamps off my SD2 and use those on the SD4.  Then put the collars on the SD2 for now.  I've never had a problem with hose clamps.

I got tired of waiting on epacket shipping from china so I just cracked open my wallet and bought some from McMaster a couple days ago and tracking says it was delivered this morning.  Still not bad at ~$11 each:

http://www.mcmaster.com/#1434k33/=zun124

It looks like these ones are a little bigger, 31.8mm width, so half that is 15.9... I'm thinking I will take my dremel cutting wheel to these and just trim the flange a little bit so I can fit them inside the case.  I think that is preferable to cutting the case and then I can avoid moving the drive rod more forward where it may conflict with the Z rods and/or reduce my bed space in the back.  I hope to get this done this weekend and will report back!

Also, I'm tired of waiting on my 8mm bore GT2 pulleys too so I think I'll just take my 8mm drill bit to some 5mm bore pulleys I have laying around and hope for the best.

Good luck! +1 on modify the bearing flanges rather than the frame. Low load application here, and that's the non-bearing-load side. With the GT2 pulleys, might not be much meat left on the hub for the set screw thread after they're drilled to 8mm though, so be cautious with your expectations. Also if you have or have access to a drill press rather than a hand drill, you'll get a cleaner better-centered hole. Lathe even better haha.

http://www.mcmaster.com/#1434k33/=zun124

It looks like these ones are a little bigger, 31.8mm width, so half that is 15.9... I'm thinking I will take my dremel cutting wheel to these and just trim the flange a little bit so I can fit them inside the case.  I think that is preferable to cutting the case and then I can avoid moving the drive rod more forward where it may conflict with the Z rods and/or reduce my bed space in the back.  I hope to get this done this weekend and will report back!

Also, I'm tired of waiting on my 8mm bore GT2 pulleys too so I think I'll just take my 8mm drill bit to some 5mm bore pulleys I have laying around and hope for the best.

http://www.ebay.com/itm/261352535116?_t … EBIDX%3AIT

I'd hazard that with the stiffer driveshaft you probably don't need intermediate bearings to support it - the back of the case just bows in (it's not at all rigid in the normal axis) so they'll provide very little support. The sides of the case though are in-plane, so bearings in there will take all the load quite happily I think.

* Flanged bearings in the sides will be fine.
* Adding the KP08's will do little to improve the stiffness of the driveshaft, which is not very necessary as it's already 8mm and you're going direct drive.

If you want to use the KP08's instead of the flanged bearings:

* Mount those as close to the outside of the case as you can (location of pulleys etc. into consideration)
* If they're too low, stick a piece of aluminium underneath them to shim them up to an acceptable height.
* Get a piece of 50x30mm (or thereabouts) aluminium C-section or even angle from the hardware store, and bolt that right across the back of the case (just bolt it on with the KP08 mounting screws). Should be flush or overlapping the outside edges. This will be much more rigid than the back of the case, and will transfer the belt tension force into the side plates of the case where it's in-plane.

So, are flanged 8mm bearings in the side enough, or are pillow blocks required?  I'll be going direct drive.  Thanks!

no big secret. they are just pressed in and have a small ridge to keep them in place.

when I replaced mine with bearings, I used a longish bolt* with a fender washer and a small length of pipe large enough in diameter to allow the bushing to pass thru on the outside of the case, washer & nut on the inside, tighten the nut to push the bushing out. worked great.

* bolt needs to fit thru the bushing...

used the reverse to pop the bearings in.

Hey, that worked pretty good!  Thanks. 

http://imgur.com/EPm0CPj

when I replaced mine with bearings, I used a longish bolt* with a fender washer and a small length of pipe large enough in diameter to allow the bushing to pass thru on the outside of the case, washer & nut on the inside, tighten the nut to push the bushing out. worked great.

* bolt needs to fit thru the bushing...

used the reverse to pop the bearings in.

Is there some secret to removing the 6mm bushings from the frame?  They seem pretty firm in there and I don't want to go wacking on it with a hammer if I can avoid it.  It would suck to bend the frame.  It looks like the 6mm bushing holes and big enough and will line up only slightly off centered of the KP08's, so that I won't have to cut the frame.  However, has anyone designed a direct Y motor mount for an 8mm rod held on KP08's? The Y motor mount that I'm using before probably will not quite line up.  Surely somebody has switched this rod to 8mm and direct drive before and has encountered this?

Thanks!