Friday, July 3, 2009
Half-Back Saw Blade
I had a old saw blade kicking around for a while, and I decided to use it. I've always wanted to make a backsaw, but I hate cutting teeth. Also I didn't know if what I had in mind for a spline would work. I decided to make a prototype. It actually worked! There was only one problem, the saw blade was funckily shaped, too thin and short for a panel saw, too thin for a tenon saw. So I made my own saw: a cross between a table and a halfback saw. To begin I had to take off about 2" from the top of the first part of the saw. I did this with a thin cutoff disk in a drill, guided by scrap wood, all in a vise. Then I cleaned up the edges with a small grinding wheel, and roughly cut the transitional curve with a hacksaw, refining with the wheel. Then I cut the profile at the end, refining with files. I then moved onto the spline. It is cut out of a brass door plate. Leif Hansen has a very good write up on bending splines, and an alternative way(by lamination), is shown by Tim Hoff. The final way, that many modern companies use, it to mill a slot in solid brass, but that is impossible to do without proper tooling. My method is very simple, and requires little tooling, or jigs. I first cut out the brass approximately 1 1/4" by 5", and scored a line down the middle (the tip of a spade bit works very well for this). This is not to make a place where the back will start to bend, it is just a guide for bending. Do this on what will be the INSIDE of the back. To start the bend, use a brake, a nifty metal bender, or simply put the brass in a vise, the top of the jaws lining up with the scribed bending line, and bend it slowly using pliers, working from one side to the other. With a slight bend established, I moved to the metal working vise, using the clamping pressure to bend. The next few shots are what it looks like after a while. Now the brass is ready for hammering, an anvil is handy, but not essential, I used the flat area behind the jaws of my metalworking vise. Medium hammer blows focused at the top do the trick. With the back bent, I tapped the spline off so I could work on it, beginning with the end detail, and flushing up the bottom. I then moved on to cleaning off dents and scratches, this took a long time. With the back polished to 220 grit, I cleaned off rust from the saw blade, unfortunately it was pitted, and did not all come out. Some advise: use a rust-free blade to save yourself much trouble. I then hammered the spline back onto the blade, starting at the handle end, making sure not to make anymore scratches or dents, and then polishing to 600 grit. Now all that's left is the handle.
As always a great saw resource-Old Ladies