Friday, March 23, 2012

Shapelock Linear Bearings

It's pretty difficult to get reasonably priced linear-bearings in Canada, due to the markup that Canadian distributors apply and shipping/export fees when importing from the US.  In spite of this, I ordered a set of shaft supports and pillow-block linear bearings from VXB via Amazon.  The shaft-supports are okay, but the bearings are deafening when they move.  For a CNC mill this would be fine, since the cutting noises will probably drown out the bearing noise.  However I'd like to be able to swap out the spindle for a plastic extruder to make a 3D printer that I can use in my apartment.

So I set about trying to make quiet, modestly accurate linear bearings from scratch, using only handtools.  Here are the results:

The body of the bearing is made from Shapelock, with a brass tube insert for the contact surface.  They're not the most accurate, with about 4 thou (0.1mm) of play, but they're dirt cheap and pretty easy to make if you're patient.  Higher accuracy is possible if you can find brass-tubing with an ID that matches the OD of your linear shaft.  In my case, the best I could find for 8mm linear shaft was 11/32" OD brass tubing with an ID of 8.1mm.

I decided to use the existing shaft supports as forms.  I started by sliding the brass bushing over the shaft and clamping one shaft support on either side.  I then used a clamp to hold two corner brackets against the shaft supports.  The aluminum sheet underneath is not necessary, but conducts heat well and does not stick to the Shapelock (unlike my counter-tops), which I've found makes the process faster and easier.

After that I heated up the Shapelock and started cramming it in from the top and bottom, cooling it in the sink under running water afterwards.  Be sure to add more material than you need, since you can always cut off excess.

After remove the clamp and prying off the corner brackets, the result had a lot of flashing:

After cutting the excess away with a box-cutter, I had the final parts.  Now all that is left is to drill mounting holes.

These bearings run much more quietly on the 8mm shafting than the LM8UU pillow-blocks that I ordered.  They don't bind much when torque is applied and run much more smoothly than the pillow-blocks, at least with low-load.  The pillow-blocks can hang vertically on the shafting without moving, while these lighter bearings will start to slide if the shaft is tilted by about 15 degrees.

Unfortunately they have more play than the pillowblocks, this is largely from using 11/32" OD brass-tubing which has an ID of slightly more than 8mm.  Finding 8mm ID tubing should fix this however.

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