Benching is the leveling and tensioning of the saw. When a band saw is run on a mill, it is it stretched with thousands of pounds of force. With so much force, the cutting edge will heat up during operation, causing the saw to become deformed. Benching will deform an un-mounted saw in a way so that it will counteract the operating stresses allowing the saw to pull flat and cut straight when in use. Benching is a hard process to learn and can take months to accomplish correctly.
Benching is generally done in a dark room with a stretcher-roller machine and flat anvil. A saw filer will usually use a single light at the benchman’s work station, along with ground gauges, to measure the level and tension of the saw.
A crossface hammer and stretcher-roller adjustment is used in leveling. A filer will carefully dress up his/her crossface hammer, which are available in left and right hand versions.
For checking the tensioning, a stretcher-roller is used. This machine consists of hardened rollers above and below the saw. This machinery slowly rotates and pinch the saw when a lever is cranked. It rolls a thin strip through the length of the saw to stretch the metal where it was rolled. Careful placement and force of the rolls deform the metal so that it counteracts with the forces put upon the saw during operation. More rolls are placed in the mid-section of the saw.
With resaws, the back is pulled to counteract the uneven heating of the cutting edge. For this, the non-cutting edge back of the saw is rolled. The back is measured with a three pin gauge at around .003" per three feet curved.
Benching basically involves the simultaneous solution of multiple deformations to the saw so that it counteracts the predicted stresses of the saw in operation. A benchman can easily recognize variations in steel batches.