And let it rest on the 2040 rails that look 5 mm shorter:
And attach the corner plates with 15mm screws to the C-beams and with 12mm screws t-nuts in the 2040 rails:
Attribution and credit: picture copied from https://www.thingiverse.com/thing:2538752/files from file “WorkBee-Screw-Assembly-Manual.pdf” as made by Ooznest and made available under Attribution-ShareAlike 3.0 Unported (CC BY-SA 3.0) license (link: https://creativecommons.org/licenses/by-sa/3.0/ )
At the backside of the machine, also add the 2 stepper motors for the Y axis, and attach the leadscrews to them with flexible couplers:
Attribution and credit: picture copied from https://www.thingiverse.com/thing:2538752/files from file “WorkBee-Screw-Assembly-Manual.pdf” as made by Ooznest and made available under Attribution-ShareAlike 3.0 Unported (CC BY-SA 3.0) license (link: https://creativecommons.org/licenses/by-sa/3.0/ )