Sunday, September 6, 2015

Making a saw blade knife

Saw blade knife with padauk handle.
I made this knife from a circular saw blade. There is an internet myth that claims circular saw blades are made from low carbon or mild steel, or just junk steel, nothing could be further from the truth. Saw blades spin at over 3,500 rotations per minute and endure significant stress while cutting wood, the steel must be high quality and very tough. Unfortunately blade makers are not very forth coming with what steel they use and the resulting speculation breeds all sorts of rumor. Many people believe these blades are made of L6, a common tool steel known for it's toughness and impact resistance. A few have sent blades for metallurgical analysis and the results confirm an alloy that is very similar to L6. Still there are a number of people who for whatever reason insist these blades are garbage steel. I'm not a metallurgist and can't say what steel is in any particular saw blade but neither can anyone else who isn't the manufacturer of that blade. What I can say is that many people have made knives from circular saw blades and in testing those knives are very tough and hold an edge well. If you need a disclaimer, here it is: cheap things are cheaply made. I believe that if you use a good quality blade from a respected manufacturer then you're likely to get good steel but this is recycling, there are no guarantees.

Step one was cutting the rough shape from an old Delta saw blade using a 10" cut off wheel in a chop saw. This steel is hardened and cuts very slowly. It is so hard near the tips where the carbide is brazed that I had to break it, even the cut off wheel wouldn't cut it. Usually you will see knives made from annealed (softened) steel which is later hardened then tempered. Since this steel is already hardened and I do not have proper heat treat equipment, I chose to keep the factory heat treat and just be careful to keep the blade cool while cutting and grinding; that meant lots of stopping and waiting.
 

The handle material is padauk, a South American hardwood often used for xylophone keys. It is hard and somewhat oily. The red will "bleed" out when the wood is wetted, especially with any kind of solvent. Normally the handle would be attached with pins but this steel is too hard to drill with normal drill bits so I have to rely on epoxy.

The handle scales clamped while the epoxy hardens.

The handle was shaped with disc and spindle sanders, then hand sanded with 120, 150, 220, 320, & 400 grit sandpaper. Sorry, no pics of the sanding.

The finish is shellac and wax. Not an especially good choice for a knife but the padauk is tough wood and would be fine without a finish but the shellac stops the red from bleeding.

Top down shot of the handle.

No trouble with a Roma, fresh from the garden.

See through radishes!