K40 Motorized Bed

I've been using for some time the really good motorized bed made by Jean-Philippe Civade but thought some things could be improved:

• the use of thin M5 threaded rods made the whole assembly a bit fragile and prone to seizing if they were not perfectly straight (which can end up being hard to source…). Also I found the pitch/lead being a bit low.
• it could be a bit wobbly due to the placement of the pulleys at each corner and to how the threaded rods were constrained by the belt
• the stepper support felt a bit weak
• no built-in way to compensate for an uneven K40 floor

I decided to look at other motorized beds but they either had some other weaknesses (eg.: the belt going inside of the danger zone) or required a lot of parts I didn't have on hand.

So… I started working on a new one that fits my needs.

It is made of:

• 4x 100mm smooth rods to make sure the bed is going straight up without any wobbling
• 4x 100mm T8 lead screws because sourcing straight ones is easy/cheap
• 8x 608 bearings to constrain the lead screws with almost no friction
• 4x optional F4-10M thrust ball bearings
• 4x LM8UU linear bearings for the smooth rods
• A 6mm GT2 belt (between 1240 and 1310mm. In my case a 1240mm one was perfect but that depends on the size of the final bed and the available space behind it, I recommend buying an open one and closing it yourself using something like https://www.printables.com/model/417805-gt2-belt-jig-diy-closed-loop-belts)
• 4x 8mm bore / 6mm width GT2 pulleys for the lead screws
• 1x NEMA 17 stepper
• 1x 5mm bore / 6mm width GT2 pulley for the stepper
• 2x 5mm bore / 6mm width toothless pulleys
• some 15x15mm / 1.5mm thickness squared steel tube (2x310mm + 2x280mm + 4x165mm, but I recommend measuring the available space before assembling the whole thing, depending on your K40 you may have to reduce the Y axis a bit - don't forget to take the space required by the stepper into account). You can use the following jig if you plan to cut it using a hack saw: https://www.printables.com/model/613718-15mm-square-tube-cutting-jig
• A steel expanded metal sheet (~360x260mm)
• 4x M8 hex screws, washers and nuts that act as adjustable feet (or anchors if you want to)
• 8x M3x16 round head screws for the lead screw nuts
• 8x M3x35 hex socket cap screws + nuts to assemble the bottom corners
• 4x M3x5 round head screws to hold the NEMA 17 stepper
• 2x M3x50 screws + nuts for the tensionner (you can use shorter screws depending on how much you need to tighten your belt)
• 2x M3x25 screws + nuts to attach the stepper support to the square tube
• 2x M2x6 screws + nuts to attach the tensionner to the pulleys support