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How to flatten and sharpen
bench plane irons?

Shop for Woodworking Hand Planes
Non-bevelled side of a bench plane iron If the non-bevelled side of a plane’s iron is not perfectly flat, and the cutting edge razor sharp, the plane’s performance will be compromised.
Blunt bench plane iron can cause tear-out An uneven blade will replicate the unevenness in the cuts it makes. A less than sharp blade will make planing more difficult, and could cause tear-out, leaving serious blemishes in the workpiece.
800, 1000 and 1200 grit waterstones For the following procedures, you will need sharpening water stones in three grades – 800, 1000 and 1200 grit. They are readily available from DIY stores.

Flattening the iron

Even a new hand plane iron may not be perfectly flat Even a newly-purchased plane iron doesn’t necessarily have a perfectly flat back. Fortunately, “lapping” the back of the iron is a process you’ll most likely only have to do once.
Separating the iron from the chip breaker of a hand plane

Step 1 – Prepare for lapping

Remove the iron from the plane and, if there’s a chip breaker attached to the iron, remove it by undoing the stubby screw that goes through the slot of the iron into the back of the chip breaker.

Part of hand plane iron to be flattened by lapping You need to flatten only the first inch or so of the non-bevelled side of the iron, measured from the cutting edge of the blade.
Lapping the back of the bench plane iron

Step 2 – Start lapping

With the area of the blade to be flattened held firmly and perfectly flat on the 800 grit stone, slide it backwards and forwards along the stone. This is called “lapping” the iron.

This action has the effect of “polishing” the iron where it is in contact with the stone.

Checking progress of the bench plane iron flattening procedure

Step 3 – Check progress

After lapping for 30 seconds or so, turn the iron over and inspect the newly “polished” area.

When the polish is consistent all the way across the iron, covering an area about 25mm (1″) from the cutting edge, the iron is flat. Repeat lapping on the 800 grit stone if necessary.

Repeating bench plane iron flattening procedure on higher-grit stones

Step 4 – Repeat on higher grade stones

Now repeat the lapping process on the 1000 and then the 1200 grit stone to achieve a very smooth polish.

The blade should now be flat and ready for sharpening.

Sharpening the iron

Primary and secondary bevels of hand plane iron The cutting end of the iron will already have a bevel at an angle of about 25 degrees to the non-bevel side. This is known as the primary bevel. Sharpening – or honing – this bevel in effect creates a second bevel, known as the micro or secondary bevel.
Diagram of a honing guide There are several different approaches to honing irons, but using a honing guide, like this one, is perhaps the most accurate way of achieving the correct angle for the micro-bevel, consistent across the width of the iron.
Hand plane iron secured in honing guide ready for sharpening A honing guide is a small jig which rides on a roller. The iron is clamped to the jig and the angle at which the iron is to be sharpened is set. The guide is then rolled backwards and forwards along the sharpening stone with the cutting edge of the iron pressed down onto the stone, producing a secondary bevel at the desired angle.
Primary bevel of a typical bench plane iron

Step 1 – Check primary bevel

First, check that the iron’s primary bevel is angled at 25 degrees to the non-bevelled side of the iron.

If the angle of the primary bevel is incorrect, you may need to grind a new bevel using an electrically-powered grinder, or take your iron to a professional workshop to get this done.

Bench plane iron fits into honing guide bevel down

Step 2 – Secure iron in honing guide

Assuming the primary bevel is correct, fasten the iron into the honing guide, with the bevel facing downwards. This usually involves turning a knob to tighten a clamp onto the iron.

Setting the angle of the honing guide tp sharpen a bench plane iron

Step 3 – Set angle

Now follow the honing guide’s instruction leaflet to set the angle of honing to 30 degrees – that is, 5 degrees less acute than the primary angle. This means that the honing will affect only about 0.8mm to 1.6mm (1/32″ to 1/16″) of the primary bevel – and this is all you need!

Honing a bench plane iron using a honing guide

Step 4 – Hone iron

Sprinkle some water on the 800 grit stone and begin honing by rolling the honing guide backwards and forwards along the stone while pressing down quite firmly near the cutting edge of the iron.

Cambering the cutting edge of a hand plane iron

Step 5 – Camber iron

Some types of planing call for a slightly cambered (rounded) cutting edge. For instance, when smoothing wood faces that are wider than the iron, a slight camber on the cutting edge helps avoid leaving ridges on the surface with the sharp corners of the cutting edge.

Camber the iron slightly while honing by increasing finger pressure on first one side, then the other side of the iron.

Check secondary bevel of hand plane iron for size and sharpness during sharpening porocess

Step 6 – Check progress

Check occasionally that you are getting a secondary bevel of a consistent size right across the width of the iron. Gently run a finger across (not along!) the cutting edge to check if it is razor sharp.

Burr on a hand plane iron following sharpening

Step 7 – Remove burr

A burr is a fine roll-over of metal, in this case from the secondary bevel to the opposite side of the cutting edge, created by the sharpening action.

Removing the burr from a bench plane iron Remove it by turning the iron over and, holding the non-bevelled side of the blade flat on the stone, sliding the iron along the stone. Burr is usually quite visible and you might see particles of it on the sharpening stone after it has been removed.
Repeat bench plane iron sharpening process on higher grit stones

Step 8 – Repeat on higher grade stones

Repeat steps 4 to 7 on the 1000 grit stone, and then on the 1200 grit stone until you have a razor sharp, polished and, if desired, slightly cambered, secondary bevel.