Super-specific Smoothing Plane Specs

When I teach people how to sharpen and set up a handplane, I can jabber endlessly to little effect. Sure, I’ll get in a few jokes about lemurs and frogs (and their forbidden love), but I really don’t earn my keep until I start the “show and tell” section of the lecture.

That’s when I take apart each of my handplanes and pass the individual parts around. The students can see how curved the iron is. They can observe how tight the mouth is. And, later at the bench, they can pick the tool up and see how well it works.

When you write about handplanes for a living, it’s difficult to pass around the parts of your planes to your 200,000 readers. So today I’m going to take apart a plane that works extraordinarily well and try to describe its features using measurements that you can use.

About the Plane
If all my handplanes were repossessed and I had time to stuff just one in my pants (believe me there’s room. See this photo from Popular Woodworking for proof. My wife has offered to buy me implants for my birthday.) before the repo man came through the door, it would be the above plane.

It’s the Lie-Nielsen No. 4 in bronze with a 50Ã?° frog. I have more miles on this plane than any other, and I have it set up exactly how I like it.

How do I like it? Let’s see:

The Curve of the Iron
I like a smoothing plane’s iron to have a slight camber. This curve keeps the corners of the iron from digging gutters into your work, and it produces a beautiful finished surface that has a subtle undulation. How much curve?

That’s the problem. If the curve is too pronounced, you’ll take a very narrow, thin shaving at the middle of the mouth. If the curve is too flat, the corners will dig in.

There are math formulas that tell you how much curve you need , it varies depending on the width of the blade and the angle of the plane’s bed. For this plane with a 2″-wide iron, I like to get a shaving that is a little more than 1″ wide, .001″ thick and tapers to lace at the edges. That is what is shown in the mouth of the tool above. That’s a good shaving for general work.

I could describe the curve in terms of its radius (40′ feet perhaps), but that’s not helpful. Instead, I measured how much the corners of the iron were swept away at the edges of the iron. I did this by placing the iron against a square and measuring the gap with a feeler gauge (it’s just like checking the gap on your spark plugs).

On this plane, the corners were swept back by .006″.

The Chipbreaker
Two things are important about the chipbreaker. One: I keep it about 3/64″ from the cutting edge and I keep it fairly polished. I’ve written a lot about breakers, so I won’t bore you here. This setting prevents the tool from clogging and provides efficient shaving ejection.

I polish my breakers with a Klingspor hand block. The hand block removes the gunk that builds up on the breakers and polishes the bevel of the breaker. You can use sandpaper, too. Anything abrasive (except, perhaps, your personality).

The Mouth
I actually thought my mouth was tighter than this. When I measured it with feeler gauges it was .009″. I’m going to try to close it up just a little more. Sometimes the mouth will get changed when I disassemble the tool and demonstrate how the frog moves.

The one thing I cannot demonstrate here that it is really important is how much pressure is applied by the lever cap. It’s probably less pressure than you think. If I had to guess, it’s about the same amount of pressure you apply to open a typical car door.

However, as someone who owns an old Volkswagen that requires a Kung-Fu Grip to get into, that’s really not all that helpful.

– Christopher Schwarz