P3Steel Build Log (#06) – Y-axis Carriage Clamps

By chunkyadmin,

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Bronze Bushings or LM8UU Bearings

lmu88-stack

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.

bronze-bearingTo 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!?66692738ff47a080f223219def5eefb2_preview_featured

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!

IMG_7022

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!).

IMG_7023

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.

IMG_7024 IMG_7025 IMG_7026 IMG_7027 IMG_7028 IMG_7029

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.

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  Comments: 5


  1. Hi, it’s me again 😀

    Short question: did you add some grease to the rods? I don’t think that it’s neccessary, but I ask you to make sure that I do not ruin my bearings…


    • Hi Chirs,

      This has an interesting answer, and not a quick one either! 😵

      Bronze bushing should not need lubrication, as they are supposed to be impregnated with carbon or oil to make them self lube. I was in the same thought as you though – and thought they should be lubricated too.

      Initially I used some lithium grease (spray) but this ended up creating loads of black residue (assume it is lithium oxide??) powder which seems to stain anything it touched. It also ended up making the rods “sticky” to a point and they were not smooth.

      I then switched to silicone spray and this seemed to clear up the black residue and the rods did run smoother. After a few applications of several weeks the residue I think is now gone – I am hoping that it was due to the lithium(??) Every so often I will wipe the rods down with a cloth which is sprayed with silicone grease. I don’t know if this helps or not?! It does seem to make the bed ‘feel smooth’ when I wizz it back and forth.

      Finally – I am not happy with my bushings (for the y-axis). The x-axis runs smooth and has never caused me any issue. But I think with the weight of the y-axis frame, the bed and glass – those little 12mm x 12mm bushing are under too much strain and wearing down. I can now “wiggle” my bed up and down slightly and the bushings have too much play. I have just got some orange PETG and in the middle of replacing all my orange PLA parts with PETG, but am doing an experiment with returning to LMU88 bearings for just the y-axis. Then I am then going to look into getting longer bushings (like the ones used on the Ulitmaker) and try those under the bed, with some newly designed brackets to hold them. All of which should/will be documented no doubt!!

      It never stops….! 🤓

      Steve


  2. Thanks for your reply! I tend to use some kind of lubricant also. I got some grease with PTFE, but the viscosity seems pretty thick, so i am not sure if it will work. Maybe I will get some silicone spray, too. I finished printing my P3Steel Toolson Parts on my Prusa i3 and I am going to assemble it the next days. I will let you know which way I am heading, and how things are going. Is your P3Steel Toolson up and running?


  3. Do you have a BOM for the fasteners ?

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