This is the sixteenth entry in a nineteen part series that covers the construction of one of my saws from start to finish. For links to the other entries, please see the full chronological index. -Ed.
Fitting the back & blade
As I mentioned in my last post, the blades are held in their backs by friction that is generated by squeezing the slots closed. The back’s hold on the blade can be incredibly tenacious, capable of rendering its removal nearly impossible. For this reason, all shaping and test fitting of the parts is done before joining the back and blade.
The two parts are assembled by driving the back onto the blade with a cast iron hammer with wood faces. The blade is clamped tightly between two pieces of wood, leaving just enough of the blade exposed so that the back can be seated. I use paper between the wood and the blade to help prevent scratching.
Before installing the back on the blade, I run a feeler gauge through the slot to ensure that no debris is trapped within. Any material there can prevent the blade from fully seating, leading to either a crooked back or warped blade.
I start by tapping the handle end of the back onto the blade, then check to ensure that it is properly positioned (from front to back) before proceeding further. Adjustments are very difficult to make when the back is further installed.
I continue to work down the back, always striking behind the point where the blade enters the back. When needed, I hold the free end of the back so that the slot remains aligned with the blade as it enters the slot. The rounded edge that was filed on the back of the blade also helps guide the blade into the slot.
When the whole length of the blade has entered the slot, I begin working back and forth to ensure that the entire length of the blade is seated to the full depth of the slot. It is easy to see when the ends are fully seated; the middle can be checked by sighting along the back or with a straightedge.
If the blade is fully seated in the middle, but not at the ends, you will notice bowing, or oil-canning, at the toothline. If the bow pops to the other direction when you push on the convex side, the toothline of the blade is in compression. This can be remedied by driving the ends of the back further onto the blade or by driving the center of the back off of the blade. If neither of these helps, there is little choice but to remove the back and try again. Likewise, any wrinkles near the back necessitate removal and reinstallation of the back.
It is common for the blade to have some twist in it, and this will be removed in the next step. For now, consider any blade that is installed without oil-canning or wrinkles a success.