Centre Finder

Beta This jig is in beta: the files are generated and checked, but the design may still change. Check the drawing against your instrument before you cut.

What you need to buy

Designations, not links: a shop link dies within months and a dead one reads as a recommendation nobody stands behind any more. Every part here is a standard item you can search for.

Part	How many	What it does, and where such a thing is found
623ZZ	2 (one at each end of the beam)	Deep-groove ball bearing, 3 × 10 × 4 mm; it is what rolls along the board's edgeOn its dowel, under the beam's end. Pushed on from below; nothing retains it but the fit.
Ø3 × 16	2 (one per bearing)	Steel dowel pin the bearing turns onPressed into the beam from the top, through to the bearing below. No screw, no nut.
Pencil	1 (your own)	Any pencil or marker between 4 and 9 mm across; the centre hole is printed to the size you enterThrough the hole at the middle of the beam.
PLA or PETG filament	As needed	One printed part: the beam. Nothing in this jig flexes, so either materialThe beam.

The printed parts are not on this list — you generate and print those. This is what has to arrive in a parcel or come off a shelf.

Start with the coupon