The XY motor mount and brace seems to be sorted, at least for now. Did a fit test for the matching pulley mount and brace. Have a print running.
Dropped the print speed from 150mm/s to 100mm/s (still at 20% infill), as simply too many print fails. The print times as now in the eight-hour range.
Designed the top-side and bottom braces (one per corner). Would be faster at this point if I had more printers, so I could do test prints in parallel. If you want to mock my newly acquired CAD skills, you can monitor my progress in OnShape:
https://cad.onshape.com/documents/b58ba100b14b2669a4081d50/w/ba4121935e115d3ac6584892/e/439f9921cea12b8cc057cc6d
Note: your motor holder can be melt by the hot motor.
Is the same corexy construction? -> https://www.thingiverse.com/thing:2138286
@Jan_Dwinger Yes, this a concern. Will the motor get that hot? Should I use active cooling, or a more temperature tolerant plastic?
Will find out.
i did not own a 3d printer, but want to build my own, too!
i read a lot about issues with 3d printer, so some people wrote, that they cannot touch the hot stepper motor. Just watch it.
maybe you are not affected. (i’m not an expert)
i think a stepper would normally work at about 50C but getting them to about 80C is not hard at all…
At rated current with five sides exposed in open room-temp air, a stepper will probably run somewhere around 75C surface temp. PLA’s glass point is 55C. You can see the problem, right?
Various solutions:
- Print actual production parts in a higher-temp plastic like PETG
- Use a cork isolator or stepper damper to insulate the part from the motor (btw dampers are awesome)
- Drop the motor current to around 50% of the rating and give up some torque/power
- Add a really impractical amount of motor cooling (a simple heatsink and fan helps but not a huge amount because it only cools one end of the motor, and the iron stator lamination stack doesn’t conduct heat all that well, so the shaft faceplate side still gets hot)
What is that print filling the diagonal of he print bed?
@NathanielStenzel Probably the mount for the pulleys. (The print for the motor mount is similar.)
@Ryan_Carlyle Thanks. I have a spool of ABS. Matterhackers is about a mile from my front door. Nylon is possibly an even better choice. After checking the RepRap wiki, apparently I could print with weed trimmer filament.
Sticking with PLA until there is reason to do something else.
Pretty sure I have options, after the rest is sorted. 
A good part of today went to experiments … that largely did not work. This is perfectly fine, as a part of the learning curve.
Pretty much just have a bunch of prints to do. More of the first-round parts landing in the discard pile.
Now that the bottom is fully braced, the top is notably rigid, even with one still unbraced corner. This with light (20% infill) braces.
Will cycle through the prints for the top corners, then the bottom corners (replacing four prints with one). Should take a few days.
Printing and installing braces for the bottom corners. Also printing fit-tests as iterating toward the design of the XY gantry. Will do another top-level post in a few days, when there is reportable progress.
My pile of discarded prints is growing. 
@Ryan_Carlyle Replying on an old thread…
As a point of information, the stepper motors during a long print on a cheap-Chinese CoreXY printer (a TronXY X5S) are only warm to the touch. The stepper for the extruder is closer to hot, but not uncomfortably so. Not sure why the difference from you expectation. At that price point, not expecting anything exotic as drivers.
For now, I am assuming that using PLA for the motor mounts is not going to be an issue.
@Preston_Bannister that’s good and fine, just means the motors are being run with much less than their nominal rated current. Perhaps the drivers are sending 1A actual instead of 1.5A motor rating, or whatever. 3d printers tend to have enormous torque safety factors so it’s not really a problem if you give up 30-50% of the rated torque in order to get cool motors.
