K40 Motorized Bed

CHANGELOG:

• 2023-10-13: Improved the “Stepper Support - Support” part to prevent nuts rotation

• 2023-10-14: Reduced the global footprint and fixied various issues with the stepper support

• 2024-01-09: Added some holes in  the “Stepper Support - Tensioner” part to make assembly/disassembly easier + a new variant that can hold a long lever end-stop microswitch

• 2024-01-17: Updated “Stepper Support - Tensioner - with microswitch support” part to make the microswitch seat a bit higher

• 2024-02-08: Added the STEP files

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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 (8mm diameter) 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