There are a lot of details below, but in summary, this is how I prefer to make one:
material | Only steel is acceptable — aluminum is softer than a steel utility blade, so is liable to being scratched, allowing the blade to climb and travel over the straight-edge, posing a hazard to your fingers. |
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width | 1½" is great, and 2" wide is acceptable. 1" is probably too narrow, as it doesn't give enough room for fingers to keep the straight-edge steady while avoiding risky situations with the knife. |
thickness | 3/16" thick is much better, though ⅛" thick can work too. (0.1875" or 0.125")
What I learned is that the heavier, the better, because this helps keep the straight-edge in place. |
anti-slip backing — thickness | I like varying thicknesses:
Thicker rubber can accommodate bumps and protrusions with ease, but feel like they would be less accurate due to the fact that the straight-edge can rock side-to-side. If possible, the rubber should be firm, especially for the thicker pieces. Note that you can put different thicknesses of rubber on each side of the straight-edge, which gives you a choice of which one you want to use for each cut. |
anti-slip backing — material | You want THE grippiest material you can find.
I've had luck with rubber that describes itself as "Buna-N rubber", AKA nitrile rubber. [1] Supposedly silicone is the grippiest rubber available. Bonding silicone isn't the easiest; here's some advice. (Worst case — either use UHMWPE to "stitch" the silicone onto the steel, through holes in the metal; or find a way to cure raw silicone in situ against the metal, known as 'overmolding' or 'insert molding') |
adhesive | I tried super glue, and it sort of works, but it had decent-size sections that didn't adhere properly. 0/10, do not recommend.
Maybe try contact cement? Rubber that is manufactured with adhesive on the back is great, it's much simpler/quicker to use than using your own adhesive. |