These bed holders/corners aim to solve the dreaded XY wobble arising from crooked threaded rods. They also prevent the upper bed from shaking with respect to the lower bed on the 3 sprung M8 bolts. Finally they allow fine bed height adjustment at 4 corners rather than just 3 points.
This is version 15 of my design and the best so far, but it does not remove wobble 100%. I am very receptive to ideas to improve it. To give you an idea of my early designs, here is a youtube video of version ~8:
Installing these will be a hassle the first time as partial disassembly is required to remove the original bed holders. However my replacements are designed to be easily upgradable so please bare with the pain :)
I realise there are a lot of steps below, but it is quite simple and a lot of it will be obvious just by looking at the photos. The only tricky parts you need to obtain are 12x linear bearings (the same type used on the X and Y belt idlers) and 8x 35mm-long M3 bolts. These quantities are for a full installation of 4 bed holders, which I recommend as it would be tricky to mix and match these with the original bed holders.
PS I have quite a few bearings and 35mm M3 bolts left over, if anyone in Australia wants some, just send me a message.
- Remove entire bed
- Loosen Z belt
- Remove Z threaded rods and original bed holders. This is easy to do for the 2 smaller corners (on Rapman 3.1 and 3.2) but harder on the other 2 as they are fixed to the corner rods. If you have installed my replacement corners (http://www.thingiverse.com/thing:4398) then it is a 2 minute job, otherwise take your time to either dismantle the upper corner or simply break the acrylic holding the corner rods (if you have faith in my design :)
- Remove bed holders from threaded rods but BE CAREFUL and aim the bed holder at the ground as the nut will fly off due to the spring.
- Replace the 2 nuts onto the threaded rod and put the spring aside.
- Reinstall the threaded rods and reassemble the corners if necessary. MAKE SURE the Z belt goes around each threaded rod, but DON'T fit and tighten the Z belt just yet.
- Cut 4 lengths of 12mm-diameter rod (wood, aluminium, etc) to 365mm in length.
- Drill 5mm-6mm holes 7.5mm in from each end of each rod. The centres of these holes should be 350mm apart.
- Wind the 2 nuts on the threaded rod so they are just far apart enough for the small bed holder parts to fit around them. Secure loosely with M4 bolts at the bottom (refer to photos)
- Insert rods and secure loosely with more M4 bolts.
- Tighten bottom M4 bolts first, then top bolts on the rods. The "inner assembly" is now complete.
- Install linear bearings onto the larger bed holder pieces with M3 bolts, nuts and washers as shown in the photos (3 bearings per corner).
- Back to the print bed: Disassemble it and prepare just the lower part.
- Assemble with the lower print bed piece on the printer, and sit it on top of the inner assembly. Tightening the 2 halves together will clamp the 3 bearings on the guide rods.
- At each corner, insert the springs in the spring receptacles.
- Install long M3 bolts from underneath and compress the spring before fitting a nut. A nyloc nut would be ideal, but a standard M3 nut with a bit of loctite also works well (you don't want it to shake loose)
- Install the top part of the bed onto the bottom part, omitting the springs as the corners now provide the spring action. You may need a spacer depending on clearance.
- Level the 4 bed corners by turning the Z rods at each corner, then re-fit the Z belt.