How to Inspect a Saw Blade
Ripped Shoulders and Tip Loss
Why we chose Tenryu, Popular Tools and Everlast
Sometimes a piece of saw blade will come off with the tip still attached. In this case the steel was made brittle during the brazing operation and was not tempered afterwards.
The heat of brazing is enough to change the structure of the steel so that it can get very, very hard and very, very brittle. This does not have to occur but often does. There are two ways to address this issue. First, you control the heat so that you do not heat the steel that much. Second, after the saw blade is brazed you can temper it back to a softer, stronger condition.
The following drawing shows the shoulder of the saw tip with three areas marked A,B and C.
When the steel is hardened it goes from a Rockwell C scale measurement of around 40 – 45 to a Rockwell C scale measurement of around 60.
Since you have to get the saw tip, the braze alloy and the steel all up to the same temperature a little hardening is inevitable.
If the hardening is confined to section A then everything should be fine. The deeper the hardening goes into section B, the more likely you are to have trouble. Once you hit the dotted bottom line and get anywhere near section C trouble is almost inevitable.
The separation between the two areas, the hard and the soft area, is often called the chill line. This is very obvious when manufacturing a saw as there are distinct color differences.
The heat affected, hardened area will be much darker. At the edge of the heat affected area you can often see a rainbow. The area that is not affected by the heat will still be the standard steel gray.
Typically the chill line is considered to be the edge of the rainbow on the side next to the steel gray. You can make a good case for moving it about anyplace in the rainbow.
This color doesn’t show up on finished saw blades because they’re sandblasted to clean them up.
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