Making a 3D Printer (cheaply) – Linear Bearings

This page is to record all my detail and findings on using linear bearings (good or bad).

Using 8mm rod salvaged from old printer/scanner:

This rod measured 7.98mm diameter.Its leading edge was chamfered and it was lightly oiled with a low viscosity oil.

Cheap Ebay LM8UU 8mm bearings.   There was a high level of friction which decreased after working the bearing back and forth. This however grooved the 8mm rod. I raised this with the Ebay seller who instantly offered me a refund and said they would inform their suppliers…top marks to that seller. A few days later whilst inserting the rod for other tests I ended up with some small ball bearings in my hand !

Hot Melt Glue.    I extruded holt melt glue from a gun directly onto the 8mm bar and when it had set I gave it a sharp tap to free it. Initially it seemed to work really well with little friction. However when left standing for an hour or so the friction increased dramatically. After it had stood overnight I couldn’t budge one of the test pieces. I can only assume the glue absorbed some of the oil and swelled. After freeing up the friction dropped back down again.

Glass Fibre and Hot Melt Glue.   Wrapping a small amount of glass fibre plasterers scrim (which is what I had available) around the rod, making sure the self adhesive side faced out, I was then able to add a layer of hot melt glue. This worked well and didn’t appear to ‘swell’ up like the pure hot melt glue bearing did. I also made a test pice by potting the above sleeve into a short length of copper pipe using epoxy resin.

Polyethylene (PE) Sleeve.   I took some from an old milk carton as I know that stuff has a low friction coefficient. I initially tried wrapping a slither tightly around the 8mm bar and adding hot melt glue. This didn’t stay tight and the hot melt glue didn’t adhere to the PE very well. I tried super glue….which didn’t take at all (that’s a good sign).

Then I tried heating the PE after wrapping around the 8mm bar. This was in varying degrees of success and needs looking at further. The PE melted on some to make a good bond to the layer below. Sometimes on cooling the PE sleeve was too hard to move.

My last attempts were using a sleeve of PE wrapped around and melted using a hot blade (heated in a candle flame). This held the PE slither at the correct tightness to the 8mm bar. I then wrapped around some glass scrim (as that stuff doesn’t stretch) and coated that with some hot melt glue.

This sleeve has low friction and doesn’t have any noticeable play.

..pictures and other notes to follow.

The rest of my 3D Printer build can be found here

 

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