Mitre Slot Adjustable Zero-Clearance Rail Runner - Fully Parametric

Edit 2026-05-04 - Version 1.1

• Added additional 4x washers with different chamfers which let you increase the expansion to span a larger gap between the wall of the runner and the mitre slot.

I modelled this based on the design from here:

https://www.amazon.com.au/OSKOOL-Miter-Runner-Slider-Crosscut/dp/B0D3GJR

The model consists of:

• a runner

• 4x expansion washers

The expansion washers sit in the 4x pockets in the runner attached with short M4 screws screwed directly into the threaded holes in the model. The washers have a split in them to allow them to expand in diameter when pressure is applied by tightening the screws. This allows the width of the runner to effectively increase, thus providing zero-clearance.

The washer allows for an expansion of ~1mm which should be plenty if you dimension the width correctly.

The base model was for my cheap Makita MLT100N contractor's table saw which has significantly smaller dimensions of its mitre slots, however the model is completely parametric (see screenshot) so you can update this to suit your needs.

I have included a model for the Makita, as well as a generic one for a slot that is 19mm x 9.5mm (approx. 3/4" x 3/8")

I've included the original Fusion360 file so you can edit the params yourself.

To assemble, you'll only need some screws:

• 4x M4 countersunk screw per runner. Height should be just shorter than the depth of the runner (Makita ~4mm, Generic ~ 8mm) -- you will likely have to cut a longer screw.

Note:

• the length of the rail is actually excluding the tapered nose... I added this after and didn't update the parameters and modify the dimensioned sketches / features to suite. You will need to add 15mm to get the total length. The models I've given will print on a 256mm bed like the Bambu A1.