I wanted to upgrade the Y-Axis rails on my Taz 6 to make them more firm. The stock rails are 10mm, so I purchased 12mm rails like are used on the X-axis of the 6, and wanted to mod the bearings and Y-feet to accommodate.
There are a couple of upgrades listed on Thingiverse for this purpose already; however, unfortunately for me, none of them seemed to be "quite right" in terms of fitment for me when printed with ABS (as the factory ones are). Holes wouldn't line up or the Igus bushing would fit too tightly. So I modified user 'piercet's thing 1549505 to widen the hole on the Y-legs to allow for ABS print tolerances, and redesigned the Y-Bushings entirely.
Printed in ABS with a 0.35mm layer height on a 0.5mm nozzle. Igus bushings should just slip in and finger-compress-to-lock (no need for a hammer!) in the ring. I'm actually using this mod so I can confirm it will fit properly when printed in ABS. If you print the legs with PLA or another plastic, there will likely be too much tolerance in the holes and you'd be better off using one of the other mods listed on here instead. If you print in ABS - this should be right-on!
As always, this is done at your own risk. I accept no responsibility for this mod whatsoever and it likely voids your warranty. You will need to purchase 4 x 12mm Igus bushings to use.
Please note: This mod reduces your Z-Print-Volume by a few millimetres. Not sure by how much, didn't bother to check because it's not an issue for my needs, but it's probably dropped ~5mm or less. This mod may also change your Z-Offset values, so to ensure that you don't break something on your printer, you're going to need to watch your Z-Offset on your first print /very closely/ and adjust as needed.