SO3: Y Carriage Eccentric Tensioning Question

Hey, so I am currently assembling my XL Shapeoko 3, and while I am new to at-home-CNCs, I am fairly mechanically inclined, so I have a general understanding with what I am doing, but I am struggling to accurately tension one of the wheels to the V of the rail (I was able to successfully tension the other wheels).

The wheel seems very tight so that it does not want to rotate regardless of the position of the eccentric. I have loosened the screw portion relative to the eccentric nut, and while this has provided some freedom for the wheel to rotate, I am having a tough time tensioning it properly. The closest I have gotten allows the wheel to rotate when the carriage is moved (relatively) quickly, but continues to slide when the carriage is moved slowly. Further, none of the other screws seem loose at all and I’m concerned I am affecting the spacing by loosening the screw. I may be attacking this in the wrong way.

I have tried untensioning the other eccentrics, but that hasn’t helped.

Any advice?

I can provide additional information as needed.


It the wheel binding against the metal plate? Maybe it needs a washer or other tiny spacer?

Or, perhaps it’s a bad washer?

The custom SO3 extrusions are pretty much the same as MakerSlide (which in turn was a custom extrusion which made what commercial profiles provided more affordable), so the instructions for it ought to apply:

You guys are good. It looks like I’m missing the small washer that abuts the carriage plate on the wheel-side.

I’m guessing there’s nothing proprietary about the washer and I can pick one up from the hardware store. Is the correct washer size listed anywhere? If not, I can disassemble one of the other wheel assemblies for reference.

Official B.O.M. here:

Crowd-sourced version here:

Details on and discussion of parts here:

Just get a metric one which matches the bolt in question.

@SwapmeetPete The washer (shim) between the v-wheel and the plate is the equivalent of an M5 washer that is 1mm thick.

We recently began sourcing precision shims that are within a thou of the 1mm specification, but a regular M5 washer will be fine so long as it’s not cupped or happens to have a burr on any of the edges.

Related note - we now have a test for the vwheels before we pack them! If they spin, they’re good. If they dont… we forgot the shim! Sorry for the inconvenience.