See the explanatory thread I posted for more details http://www.shapeoko.com/forum/viewtopic.php?f=11&t=907
Basically, when the washer is too thick, the outer races of the bearings do not have continuous contact with the v-wheel's inner lip. Forum member jimw posted a video which demonstrates the problem http://www.vimeo.com/51734462
These upgraded spacers are sized 0.98 to 1.01 mm, much more snug than the 7% over/undersizing that can be seen in the supplied washers.
Similar notes on the problem can be found on these two posts
http://www.shapeoko.com/forum/viewtopic ... lit=#p5746 and in Improbable Construct's notes
http://www.shapeoko.com/forum/viewtopic ... 0&start=20
They may not look they'll change the world, but they make a world of difference.
Notice how very flat the surface is and how clean and perpendicular the hole is. The opening is sized to snugly fit the bolts just like the included precision washers do.
They come ready to install. We've got fully finished (as pictured) sets grouped depending on how many you would like upgraded on your machine. I recommend at least replacing the eight spacers found on the eight wheels on the gantry. If you would prefer to do the work yourself, you can purchase unfinished blanks in sets as well. These are a great deal less expensive since you will need to remove the burrs and extra material. Unfinished blanks are approximately 1.025 millimeters thick, allowing material to be removed to yield a final 1 mm thickness.
Both finished and unfinished are available in the shop http://www.bit.ly/reactshop
With regards,
EJ