giant Cypress

Tap Tap Revenge

Oops.

Tonight I conducted an unintended experiment to see what the impact resistance of a dropped Japanese plane blade vs. a concrete basement floor would be. Without getting into all the theoretical physics, the punch line is that the floor won.

Ouch.

As it happens, I’ve been waiting for an opportunity to write up how to tap out a Japanese plane blade, but none of my planes were going to need this process for a while. Until now. So I decided to make lemonade out of the lemons that the woodworking gods gave me tonight.

The first order of business is to get rid of the nick. I did this using the Tormek that I have. Japanese tools are pretty sensitive to losing their temper if ground on a dry wheel grinder, although I am sure that there are some people who can do this without screwing things up. I don’t think I’m that talented, so I use a Tormek for any grinding needs. I started by grinding down the nick by placing the plane blade at a 90º angle to the wheel, deliberately blunting the blade.

Then I worked the bevel side on the Tormek until I had raised a burr.

As an aside, Tormeks are often criticized for being too slow for grinding. This took me 15 minutes to do. A dry wheel grinder would be faster, but with a Tormek I don’t have to worry about messing up the temper of the plane blade, and I don’t have to worry about sparks in a small shop area. For those two reasons, I’ll gladly spend the 15 minutes.

Of course, by the time I had ground this much of the blade away, I had advanced into the hollow area on the back of the plane blade.

I need to reestablish the thin flat area at the edge of the plane blade. This needs to be dealt with by tapping out the blade.

Of all the mysteries surrounding Japanese planes, the tapping out process seems to be the most daunting. Perhaps this is because there is really no equivalent to this process for western planes. Most of the other aspects of using a Japanese plane have some sort of equivalent in the western plane world. Bed angle and bevel angle issues are pretty much the same. The idea of conditioning the sole of a Japanese plane is kind of like lapping the sole of a flea market Stanley. The need for sharp blades is the same for both types of planes, of course, and if you get past the mechanics of pulling or pushing a plane, at the end of the day both planes can be used by simply putting the workpiece against a planing stop. But tapping out a Japanese plane blade is a completely different animal.

The process itself is really pretty straight forward. The back of the plane blade is placed on a suitable surface, and a small hammer with a pointed tip, like a tack hammer, is used to strike the soft layer on the bevel in order to push the front of the hollow area down. This pushes the hollow down towards the back of the plane blade and lessens the amount of metal that needs to be removed from the back to reestablish the flat area at the edge of the blade.

This is what I use as an anvil for the tapping out process. It’s a rusty general purpose body dolly used by body shops to deal with dents that I found on eBay. The curved surfaces make it ideal for this task.

Alternatives that I have heard of include any sort of anvil with a gently convex surface, a short piece of railroad track, and a chunk of any suitably hard wood with the end grain facing up, carved to provide a similarly convex shape. I used a piece of white oak in this way for tapping out before I found the body dolly.

The plane blade is placed on the dolly so that the hollow area is firmly in contact with it. I then start tapping on the bevel side with a small hammer with a pointed end, trying to stay in the top half of the bevel, well within the soft layer of the plane blade. I’m not hitting the plane blade too hard. The amount of force that I’m hammering with is about the same as what I would use to start a finish nail in a piece of pine.

After a little while you can see the hammer strikes accumulating in the soft layer of the plane blade.

And here’s where the rustiness of the dolly comes in handy. The rust transfers to the back of the plane blade, and it clearly shows where the plane blade was touching the dolly. Not that you have to have this, of course, but it really helped me in checking that I had the plane blade in the right position.

After some hammering is completed, I flatten the back of the plane blade on the coarsest sharpening method that I have handy. For me, that means an Atoma 400 grit diamond stone. After a little while you can see the flat area starting to come in from the sides.

I’ll flatten for a while, then tap out for a while, then go back to flattening. After just a few rounds of this, the flat gets reestablished.

The flat is pretty thin, a bit less than 1/16”. But that’s all you really need for the plane to work. As I sharpen the blade more, the back will be flattened further, which will widen the flat area. Eventually, tapping out will probably be needed again.

The only thing left to do is to sharpen the bevel and back sides as you would normally do, working up through the grits until you get to your finest waterstone. Most of the hammer marks quickly go away from working the bevel side of the plane blade. You can see the residual hollow left by the Tormek, which will disappear after a few more sharpenings.

Since the blade is now shorter than it was, I needed to do some fine tuning to the bed of the plane just like I would if I was initially setting up a Japanese plane. I also needed to grind down the corners a little to make sure that they seated inside the throat of the plane, as that geometry changed due to the shortening of the plane blade. But this plane is ready to go again.

And here’s the obligatory gratuitous plane shaving shot.