Typically, a corner-cutting machine will come with more than one blade so that you can cut different-sized corner radii. Changing the blade isn’t complicated, but it can be a little bit fiddly to get right if you’re not used to working with this type of machine. There are three important parts of the machine to consider when you are changing the blades: the upper (moving) blade, the lower blade (sometimes called a button or anvil), and the jig. The upper and lower blades are a matched pair, so if you’re going to fit a 10mm radius upper blade, you’ll also be fitting a 10mm radius lower blade. The cutting edges of the blades should match up perfectly when the cutting lever is pulled down. Fitting the upper blade is usually just a matter of removing a machine bolt and swapping the blade over. The lower blades sometimes perform multiple duties, with a single button being radiused to match two different blades. You’ll have to make sure these are the right way around and positioned correctly by fitting the lower blade in place loosely, slowly bringing the upper blade down, and then adjusting the fit to match the curve of the upper blade. Once the upper and lower blades are properly aligned, tighten the bolts and double-check nothing has moved.

With the upper and lower blades aligned, you need to adjust the fit of the jig. The purpose of the jig is to hold the piece that you want to cut in the right position as the blade comes down. This position will change whenever you change the radius of the cutter. Normally, for right-angled pieces, you’ll want the angle between the two sides of the jig to be 90 degrees, with a 45-degree angle to the direction of the blade. That means the point of the corner should hit the midline of the blade. You’ll also need to make sure that the jig is set so that the edge of the blade contacts at the edge of the material. The easiest way to do this is to use a square to set a 45-degree angle on your jig, and then set one side by eye so that the point of the material touches the midpoint of the blade. Slide the material forward and nibble away at the corner using the blade, until the blade touches the outer edge of the material. Then without moving the material, lock both sides of the jig into place flush with the edges of the material. It can be a bit fiddly and some fine adjustment might be needed, but the end results are well worth the effort. 

Warning!

Sharp blades

As well as plastic and paper,  a corner-cutting shear will carve a neat radius into human flesh if you use it without due care. Watch your fingers!