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Sharpening band saw blades

Band saw blades last quite a long time, but they don’t stay sharp forever. Probably most people throw them out when they get too blunt to use. They just put in a new blade. That makes sense. Who has time for sharpening all the teeth on a band saw blade?

A blunt blade isn’t safe (though nor is a sharp one if care is not taken!) because it makes you push too hard to force the cut. Blunt blades shouldn’t be used. Re-sharpening means a potential saving in cash if not in time. And it can save delay if you don’t have spare blades to hand.

My Startrite 352 has a blade 112″ long, and I normally use a 3/8″ or 1/2″ blade with 3 teeth per inch. That’s 336 teeth per blade. Despite this, I like to sharpen them. It only takes a few minutes, and the sharpened blade cuts about as freely as a new one.

Reasons not to re-sharpen blades

I can’t sharpen the teeth very accurately and uniformly without proper equipment, so the re-sharpened blade is not as good for precision cutting. But that is rarely necessary for the rough work I do. It would be possible to make a jig with a click detent to ensure proper tooth placement, and stops to limit the grinding depth. Sharpening does reduce the amount of ‘set’, so the kerf will be narrower.

The blade isn’t new after sharpening. Blades eventually break, sooner if they are thicker and the bandsaw wheels are small. Metal fatigue makes the blades brittle. There is usually some warning that a blade is about to break. A crack develops, and you may hear it clicking as the crack goes through the guides. You may also see the blade moving backwards and forwards in the guides when not actually cutting. If you carry on cutting, there will soon be a loud bang as the blade breaks. A bit scary, but it never seems to do any harm. If you re-sharpen a blade it will extend its life, but you are then more likely to have it crack and break in use. It’s possible to repair a broken blade, but the whole length will be brittle and I don’t think it’s worthwhile. It will soon break again.

Sharpening options

The teeth on the band saw blades I use alternate with left set, no set and right set. They are all sharpened straight across at 90 degrees to the blade body, regardless of their set.

Over the years, I’ve tried various methods for sharpening band saw blades. Here are some of the options.

The first choice is whether to sharpen the blade in the machine or out of it. Doing it in the machine means the blade is held securely and can be moved on to the next tooth without losing alignment. However, access is better when the blade is removed.

Sharpening in the machine

Hardened teeth cannot be filed, so grinding is necessary. You can grind the leading face or the back of the tooth. You can use a small diamond or carbide burr in a Dremel tool inside the tooth hook. I found that the diamond burrs wear quite quickly. If you choose their diameter to suit the tooth shape, another blade may have teeth of a different profile. You will probably have to work from the right of the blade (access may be difficult from the left), which means the burr turns toward the point of the tooth. That makes it prone to climbing over the point, which damages the tooth. I’ve also tried cylindrical stone grinder points, but they wear too rapidly even if you slide them across the tooth to even out the wear.

This method allows you to put the burr into the tooth gullet and use it to lift the blade to the next tooth during the sharpening of the first tooth. They are quite fast and effective when all is going well. But if the burr is too small, it’s easy to grind the hook without actually touching the point. The tooth is pointing down, so not easy to see the result of grinding. If the burr is too big, or you slide it to reach the point, that’s when it climbs over the point and ruins it.

Grinding the back of the tooth

The back of the tooth can be touched up in the machine too. You can use a small grinding disc in a Dremel to cut back the point until you remove the wear. This can work well too. The difficulties are maintaining a consistent angle, taking off the same amount from each tooth, and making sure the following tooth doesn’t touch the grinder until it is in the right position.

If you grind a tooth more than its neighbours, it won’t touch the timber so won’t do its share of the cutting. I’ve found it very easy to take the point off the following tooth by mistake. You need a steady hand, but you can make up a simple jig to hold the Dremel. It can slide along the fence or in the table T slot. This controls the angle, but doesn’t stop you taking too much off, and the blade has to be advanced manually to get to the next tooth. Again, I found it easy to grind the point off by mistake. Here is an example of such a jig.

Visibility is better when grinding the backs of the teeth in the machine.

Sharpening outside the machine

If you lay the blade on a flat surface you can sharpen either the hook or the back of the tooth, using a Dremel. You can see what you are doing, and I found it easier to avoid mistakes this way. The burr can run off the tooth points, so is less liable to spoil them.

I preferred to use a bench grinder for sharpening band saw blades. I set the grinder platform to 90 degrees and turn the grinder at an angle to the bench top (making sure it is secure) to allow the blade to take the proper angle to the wheel. You can easily make an angle setting jig to ensure accuracy. An error in the platform angle might cause the blade to drift when cutting. Depending on the position of the grinder you may not have to turn it.

Then I hang the blade over the platform at an angle to suit the tooth and touch the back of each tooth against the wheel. This is a quick process and visibility is good. If I rush too much, mistakes do happen, but a small number of badly ground teeth have little effect on performance. Even with a fine wheel the grinding action is aggressive, so a slow speed grinder would be ideal.

I found a thin grinding wheel and set it up in the lathe. With a diamond wheel dresser, I shaped the wheel profile to fit the tooth gullet. Then I could drape the blade over the toolrest, set at the proper angle to the wheel, and quickly sharpen each tooth. This worked better than using the bench grinder, though it was necessary to rig up supports to keep the blade horizontal.

I have now started to use a cheap chainsaw sharpening machine (which I bought to sharpen chainsaws, but it didn’t work very well for that). It has a click detent for moving the blade along, a slot for the blade to fit in, and an adjustable stop for the grinding wheel. The machine is largely made of plastic and not made to high precision. None of the adjustments are very repeatable. But the grinding wheel comes down at the right angle to sharpen the tooth gullet, and the indexing is quick. It should be possible to improve the repeatability. Even as it is, the result is the best yet. The sharpened blade cuts smoothly and well.

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