A circular saw must be tensioned to operate properly; the larger the saw is, the more important it is to have the proper tension. As the saw comes up to speed, the rim stretches much more than the center of the saw, due to centrifugal force. An untensioned saw will be loose and floppy at speed and will wander out of the cut and heat up. Tensioning is done by "Hammering"; the saw is placed on a saw anvil, mounted on a "hammering horse" and controlled blows are applied in a specific manner to adjust the tension. Almost all hammering is done equally on both sides of the saw, preferably with the hammer blows exactly corresponding. Blows applied INSIDE the center of the radius of the saw will add to the tension, blows applied OUTSIDE the center of the radius will lower the tension. A saw that is going to be run at higher speed will have to have more tension than one operated at slower speed. The person doing the hammering must know exactly what the RPM of the saw is while in the cut, how much power is on the mandrel, and whether the mill is Left or Right Hand. (The "hand" is determined by which side of the sawyer the log is on as it enters the cut; if it's on his left, the mill is Left Hand)
Once the saw is properly tensioned, it's a good idea to remove all the lumps in the plate. This is done on an anvil that's padded with very thin leather or several layers of heavy paper. The saw should have no shiny spots on it after it's been in operation for some time. A well-tensioned saw will stand up to the cut in fine fashion, even if the bits are slightly dull. A saw that needs work will wander out of the cut, especially if it's not perfectly sharp. That causes poor lumber and heating of the saw.
Besides the anvil and hammering horse, the blade smith must have an
accurate straightedge, a tension guage, and a dog-head
hammer. The tension guage looks like this from
the front. Notice the little wedge and how the bottom is a seperate
piece of metal, riveted to the main body. Pushing the
wedge to the right makes the bottom very slightly curved. On the back
side is a 'leg' to allow the guage to stand on the saw while the 'smith
peers under it to see how his work is progressing.
Sharpening can be done by several different means, starting with a hand-held file. There are gadgets that hold the file for you, keeping it square with the plate, other outfits that use a little crank to turn a wheel with pieces of file on it, and the Jockey Grinder. This is how it's used on the saw; the Jockey Grinder used to be sold in both electric and flexible-cable (hand-cranked) models. I doubt that the latter is available anymore.
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