Saw shop tech: cracked circular saw blades.


Vern Burke, SwiftWater Edge Tool Works

I’ve been seeing a lot of questions regarding cracks in circular saw blades coming through to the blog and the website as search engine hits, so I thought I’d take a bit of time and talk about this tonight.

Any type of circular saw blade, from skil saw blades to table saw blades to the largest cordwood saw and sawmill sized blades can be susceptible to cracks. Cracks are a serious issue, since they can eventually cause a complete failure of the blade, resulting in the spraying of sharp chunks of metal at high speed. Any circular saw blade should be thoroughly inspected at sharpening or after any event that could damage the blade (running in to metal in the wood being sawed) for the start of cracks.

Cracks in circular saw blades normally start in the gullets between the teeth and/or the blade’s heat expansion slots. There are several reasons for saw blades to crack:

1. Physical damage

Running into metal in the wood being sawed (spikes, random junk the tree may have grown around) is probably the most common culprit. Running diamond blades until they wear all the diamond off and are cutting on the steel or knocking carbides off and trying to cut on the steel are both blade failures waiting to happen.

2. Sharpening mistakes

Amateur sharpening attempts using flat sided mill files usually results in notches in what should be a nice, curved, gullet between the teeth. Every notch is a potential starter for a crack. On large blades such as cordwood saws, I use a Dremel tool with a pink chainsaw sharpening stone to hog out the gullets while maintaining the nice smooth shape, as well as fixing gullets that have been chopped up by other sharpening attempts.

3. Overheating

There’s not much to say about this one. If you see the blade smoking or the teeth or any part of the saw plate discolor blue/black, the damage is done.

So, you’ve got a crack. How do you fix it? The short answer is, there’s no really safe way to “fix” a cracked circular saw blade.

Drilling a stop hole at the end of the crack will certainly stop the crack from spreading, but drilling a saw plate is fairly difficult and you don’t know how badly the blade is already compromised (how many other cracks are there that you havn’t found yet?).

Play it safe and deep six a cracked blade. The price of replacing a blade is nowhere near as high as dealing with the aftermath of a high speed disintegration.

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