Bronze Bushings or LM8UU Bearings
The standard Prusa builds (and most other 3D Printers, CNCs, engravers etc) use LMU88 linear bearings for all linear rod movements. They are the go to part when you use 8mm smooth rod as your axis guides and are cheap, easy to use and readily available. The quality of these bearings however is a mixed bag, and you can either pay for high quality ones, or get a pot luck bag of cheap ones – where you will find some work fine, some bind up and some fall apart (that ominous tiny ticking sound you hear as one of the bearings’ balls fall from their track and bounces away under your desk, never to be seen again! Arrgh!). They rely on several tracks of these tiny ball bearings moving round and round as the bearing moves, so they naturally make noise as they work.
To eliminate this noise and potential mechanical failure of cheap LMU88 bearings you can opt for other types of bushings and bearings, such as Igus Drylin bearings or sintered bronze bearings. I won’t go into detail to the technology behind all these, but following Toolson’s experience (and his designed parts) I have decided to go with sintered bronze bearings as my axis rod guides. I was going to go with LMU88 bearings for the X and Y axis, but after finding a cheap supplier of the specific ones Toolson uses, I changed course and went for the bronze ones.
I even got as far as printing the y-axis bearing clamps for the LMU88s, perhaps I will do a audio and friction test one day!?
Where to get bronze bearings?
The bronze bushing/bearings used on Toolson’s parts are 8mm*12mm*12mm. So the 8mm is the hole, 12mm is the outer diameter and they are 12mm in length. There are a lot of 15mm length ones, but Toolson’s parts are designed for a 12mm length. Either adjust the parts yourself, or cut down the 15mm lengths to 12mm. You can find the exact ones I purchased from AliExpress here – 8x12x12mm bushings. I’d highly recommend the seller Peugeot bearing, with prompt postage and great little bushings.
Printing The Bronze Clamps
Beautifully designed bearing clamps for the bronze bearings to sit in by Toolson. All his printed parts can be found on his blog – http://scheuten.me/. He doesn’t put them on Thingiverse anymore, but they are available in a zip file on his blog, thanks Toolson!
All four clamps and their “nut plate” parts printed fine and without issue. If you look at the STL they are a real work of art!
After printing you need to add in a couple of M3 nuts to the nut plate. I always do this using a pair of locking pliars – you can adjust the final lock gap and apply accurate pressure just where you need it to press the nuts into the plastic. I opted for nyloc M3 nuts to reduce the chance of them vibrating loose. I noticed that from Toolson’s MK1 to MK2 design for the clamps he added the nut plate part and reversed the direction of the M3 nut and bolt. I assumed this was for ease of maintenance – as now the adjustable bolt is on the underside of the y-carriage, and not hidden between the top side of the carriage and the print bed where is will be difficult to access. Hats off to Toolson for these tiny amends which are down to his working experience of his existing setup (I assume!).
To keep the bearings secure in their clamps you need to add in a retaining fastener. You can use an M3 bolt and a washer, just enough to touch the bearing, but not go over the inner hole. I opted for an M3 5mm screw with built in 7mm washer, the same used for motherboards and hard drive mounts – nice and simple! You will need to drill and tap the small holes with an M3 tap, otherwise they WILL split. Be careful as the walls are thin.
And that’s the clamps done, all ready with their retaining nut plates to be bolted onto the y-carriage…. or so I thought….
Click on the next page to find out what issues I had with these clamps, and the YouTube video of the whole process.