O-Ring Splicing Jig

Splicing O-rings is very useful if you don't have the correct size in stock or need a custom size, but doing it without a jig usually yields a poor splice.

Both ends must be cut in a perfect right angle and must be perfectly aligned when gluing them.

The jig has holes with the following diameters:
1.8 mm for 1.6 and 1.78 mm cord
2.0 mm for 2 mm cord
2.5 mm for 2.4 mm cord
2.7 mm for 2.62 mm cord
3.2 mm for 3 and 3.18 mm cord
4.0 mm for 3.53 and 4 mm cord

Cutting is done with a single edge razor blade (0.009" or 0.012" thick).

The jig has V-grooves all around, for alignment of the cord ends. You may want to pad the groove with masking tape to prevent the O-ring from sticking to the jig.
Use a rapid-set cyanoacrylate adhesive for gluing the cord ends (Loctite 404 is recommended but others work well too).

The slot for the razor is only 0.3 mm wide, any blobs or zits may clog it.
There's a version with "seam traps" inside the slot, that prohibit the seam from protrud