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How to Sharpen a Plane Iron

One of the most familiar hand tools to most woodworkers is the plane. While there are several types of planes, all of them work on the same principle. The bottom of the plane is a flat surface with a slot in it. The plane iron or blade extends through this slot just enough to allow the plane to shave small amounts of wood from a plank as the plane is pushed over its surface.
To do good woodworking, the plane iron needs to be sharp.

In order to do a good job, the plane iron needs a razor sharp edge. The plane iron is made of tempered steel so that it will hold its edge for an extended period of time. Most plane irons need to be sharpened after just a few uses. This is especially true if it is being used to plane a seasoned hardwood like oak. Once the plane iron is removed from the plane, the process of sharpening it does not take a lot of effort to master.

The end of the plane iron that is sharpened has a bevel.

Most planes come out with the bevel already having been ground on the plane iron. If you would happen to need to create this bevel due to damage, the recommended angle is about twenty degrees for softwoods like pine and twenty-five to thirty degrees for hardwoods like maple or oak. The bevel can be ground on a bench grinder. It is possible to do this freehand, but if you have have an attachment for your grinder to hold the plane iron and set the angle, it is easier. Use a protractor to measure the angle for the correct pitch.

When grinding the plane iron, the wheel should turn toward the blade with the bevel side up.

It is a good idea to wear safety goggles when grinding any steel. By turning the plane iron so that the bevel side will be up, most of the debris from the grinder will be driven away from you and your eyes. The length of the bevel should be about 2 ½ times the thickness of the blade. Avoid applying too much pressure to keep from overheating the blade. It is a good idea to dip the iron into water frequently to keep it from loosing its temper. If you are grinding the plane iron freehand, move it back and forth slowly over the grinding wheel. A small burr may form, but this will be removed during the next sharpening step.

Use an oilstone for the final sharpening.

The final sharpening can be done on any type of whetstone, but an oilstone is the easiest to use. The stone should be coated with an oil that is a mixture of one half machine or shop oil and one half kerosine. Usually just a few drops along the surface of the stone is sufficient. Push the bevel of the plane iron across the oilstone at an angle of about thirty to thirty-five degrees while keeping a firm and even downward pressure on the blade. For best results, push and pull the blade along the length of the oilstone.

After several strokes, remove the burr on the opposite side of the plane iron.

The sharpening should be complete after six to ten trips forward on the oilstone. Flip the blade over and hold it nearly level with the oilstone. Slide the blade back and forth without too much pressure with the burr against the oilstone. A couple of trips should be sufficient to remove the excess metal.

The plane iron needs to be tested for sharpness before putting back into the plane.

There are two simple ways to see if the plane iron is sharp enough. The first way is to hold the blade with the bevel up and push it gently over your thumb nail. If it slides over the nail without catching, it is not sharp enough. If you feel it bite into your nail, stop pushing. The blade is sharp. The other method is to wet the hair in a small patch on your leg or arm. Use the plane iron like a straight razor. If it shaves the hair, it is sharp and ready for use. Put the plane iron back into the plane and get to work.

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