Saturday, December 9, 2017

Replace cheap LMU bed bearings for smoother operation.

   I love my aluminum 2020 framed 3D printer. But one thing I noticed rather early on was the bed bearings needed constant attention. There was always something getting on the rods or bearing and the grease or oil was regularly needing reapplying which involves basically tearing the whole lower end of the printer apart. That and the cheap LMU bearings running on the 8mm rods was usually rather sloppy and inaccurate, oh, and very loud! I came up with this method of replacing them with wheels and Openbuild's 2020 V Groove extrusions for a MUCH smoother and quieter operation. Been over 6 months now and it's been about the most reliable part of the printer since. This isn't complicated, but not exactly easy either, I'm guessing people will likely come up with slight improvements or easier methods of installing. If you do, please share! this is all part of the awesomeness of the 3D Printing community!

 Purchased Parts-
  •  2 - 2020 V groove extrusions (length is going to depend on you printer and such but it needs to go at least the length of the frame and I recommend getting a few extra mm's front and back. )
  •  8 - V groove mini wheels (Openbuilds, yes, mini wheels, not the standard larger V groove wheels!) 
  •  8 - M5 bolts (25mm long at least) and lock nuts (Openbuild supply the lock nuts with the wheels generally. use the lock nuts, please don't use regular nuts as you'll likely regret it... )
  •  8 - 2020 extrusion mounting 90º angle brackets
  • 16 - M5 Tee nuts
  • 16 - M5 8mm long screws 
  • ** one aluminum bed platform if you don't already have one (don't reccomend doing this with an acrylic or other plastic based bed)
 Printed parts-
  • 4 - Wheel mounts
  • 2  - turn buckles (2 left thread, 2 right thread 2 centers) 
STL files -

Optional - Will align the belt path for much smoother, more accurate and just all around better operation
  • Bed carriage mount
  • Y/Bed idler wheel mount
  • Y motor mount

Tools -

  • 5mm  drill bit (and drill obviously)
  • Allen/Hex tools for screws (sizes very depending on screw/bolt brands)
  • Open end, box, socket or adjustable wrench to fit the M5 lock nuts (generally a 8mm socket/wrench)
  • Calipers

   First off print up the 4 wheel mounts, and also the turn buckle parts. Do to all the threading I highly recommend taking the extra time and printing these in a higher, well smaller, layer height for better accuracy and fit. At the standard 0.2 height it's a bit rough I've found to work smoothly,  0.16 or lower seems to work well for me.

Test the threading on the turn buckles, screw them all together and make sure they run smoothly, just working them in and out a bunch helps usually, (also found a bit of rubbing alcohol seems to smooth them out easier if you used PLA) 

Locate the holes you want to use in the aluminum bed plate and drill out to fit the M5 screws/bolts, they need to slide through, but preferably not be too sloppy.

Assemble the mini wheels, (make sure you put the washer in-between the 2 bearings, made the mistake of forgetting a couple myself and it makes them useless!! DUH!)

Now assemble the wheel and wheel blocks. Slide the mini wheel onto the M5 bolt, then a washer, (supplied with wheels usually) and screw it into the wheel block. The block is threaded, tighten the bolt until the wheels rolls smoothly still but has no wiggle or play, give it an extra 1/4-1/2 turn but don't over tighten!!! If you strip the threading, you've over tightened. Do all four blocks installing two wheels per block.

Slide block and wheel assembly onto the bed plate through the holes you drilled out. install the lock nuts onto the bolts and tighten by turning the nut while holding the bolt in place, remember the blocks are threaded and turning the bolt will increase the tension on the bearing. Tighten these good but again, don't over tighten. You want the wheel and blocks to be firmly mounted, but not to crush the printed mounts. Install all four wheel/block assemblies.

Now take the two 2020 V-Groove extrusions and set the bed on top of them, push out on the 2020 extrusions till the come in contact with the wheels.  Now assemble the turn buckle units with a left, right and center piece. slide the turn buckle unit in-between the 2020 extrusions and, while aligning the tabs into the 2020 grooves, snug up the turn buckle to the extrusions. Do your best to keep both sides equal in length.

Slide the bed to the approximate center of the 2020 extrusions, and making sure they are generally square and equal in placement, keep tightening the turn buckles a small bit at a time doing both equally. Make sure the wheels are in the V groove of the 2020. Get the 2 extrusions and the bed assembly loosely setup so the wheels are rolling in the v grooves.

**The bed assembly only sits 1mm above the extrusions, make sure everything is clear and set. If it is riding too low you may need to add an extra washer between the wheel and the blocks to compensate for printed layer height differences of your printer. **

Take the bed and roll it back and forth on the extrusions. "feel" the movement, you can tell if one side is too tight or too loose. Get as good as you can by feel, then take the calipers and measure the distance between the extrusions on both ends. Adjust the turnbuckles so both sides are as exact to each other as possible and the bed is riding smoothly in the grooves but not so loose it had wobble or play.

Once you have the 2 extrusions set and have the bed rolling smoothly, and evenly, now just pick it up and place on you printer frame in place of the old rods and bearings. Use the 8 angle brackets  along with the screws and tnuts and mount the assembly to the printer frame. once the brackets are locked down you can remove the turn buckles and install the belt. done, enjoy the smoother operation of your printer.
 Accompanying video

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