Corradi Three Square File

Three Square files by Corradi are what we use to file the BT&C Hardware Store Saw and Gramercy Tools carcase saws. They are admittedly much more expensive than the regular saw files - their design means their teeth need careful aligning and cutting - but we choose them because they're faster and we get a smoother finish on the teeth. The narrow arrises mean deeper gullets and faster sawing. (Also the Hardware Store Saw has teeth that are really too big for the 4 1/2" file.)

The files get their name from the three equal sides that form a triangle, tapered slightly toward the point. The faces are double-cut, designed to remove material efficiently. We’re stocking different styles that vary in the number of teeth. Cut 0 (Coarse): Fastest material removal, roughest finish. Used for heavy stock removal. Cut 1 (Medium/Second): Medium removal rate, standard filing. A versatile, general-purpose cut. Cut 2 (Fine/Smooth): Slow removal rate, smoothest finish. Used for precision shaping and final smoothing before polishing.

The files have uses beyond the saw filing for which we use it, with applications for lutherie, workshops and jewelry-making and goldsmithing. Corradi recommends them for soft metals, iron, gold, silver, annealed steel, tempered and hardened steel (note aluminum is not listed) and wood.

And their use is noted in Moxon (in his description of how to sharpen a saw in Section 26 of the joinery chapter):

“With a three-square File they (the Workmen) begin at the left hand end, leaning harder upon the side of the File on the right Hand, than on that side to the left hand; so that they File the upper side of the Tooth of the Saw a-slope towards the right Hand, and the underside of the Tooth a little a-slope towards the left, or, almost downright.” - Joseph Moxon, Mechanick Exercises