[JesseK]

The endcaps are press-fit for normal 1/8" wall, or snug-slip-fit for VEXPro extrusions. Turns out that normal 1/8" wall extrusion just needs some filing (for a taper) to get it started on the endcaps, then a rubber mallet does the rest. The shoulder of the endcap that goes into the extrusion is somewhere between 1/8" and 1/4" - I don't remember.

We could make additional endcaps for other-sized tubes if we CNC them often (e.g. 2x2 for telescoping what-nots). For now though, we'll just clamp the tubes down to the table like we did last year.

The tricky part about the construction of the endcaps is that both sides must be perfectly symmetric about the hole they rotate. Otherwise the two sides of the rail will not precisely align if doing mirrored CNC cuts after the 180-degree rotation (which is the point of this particular design). An easy way to check is to see if, after a 180-degree rotation on the jig, the spindle has to be re-zero'ed.