Part II - Lump and Cup Removal

On saws that have been kinked repeatedly or severely, it’s common to achieve a straight cutting edge by hammering and tensioning as I described in the previous installment, but still not have a saw that will cut smoothly. 

This Disston #16’s cutting edge was hammered straight, but you can see a small bend remaining in the saw’s back and what appears to be a cup or lump remaining that will bind in the kerf during sawing and cause the saw to wander.

A short straightedge run down the blade allows chalking the lump’s outline on the concave side.  Turn the saw over and transfer the marks to the convex side of the lump.

Any tension in the concavity is removed using a small, convex-faced hammer, hammering on the marks from the outside of the circle inwards. Each mark represents two light hammer strikes.

Flipping the blade to the convex side, the lump is hammered out using the large hammer in exactly the same sequence and locations as in the previous step.

The blade is checked again using the straightedge and while there are still lumps and hollows, they are smaller. 

Rub out the old chalk marks and use the straightedge to make new ones, then repeat the same marking and hammering sequence of using the light hammer on the concave side and the heavy hammer on the convex side.  Stop when the straightedge makes full contact with the blade.