Lost Art Press

Somehow, during the course of about five years, I became a math dolt. When I left high school, my SAT scores for math were near perfect – far higher than my verbal score.

But after four years of studying intransitive verbs, subjunctive mood and zeugmas, my math skills withered to the point where – no lie – I couldn’t figure out the formula for the perimeter of a pentagon during a college class we all called “Math for Trees.” My wife still mocks me for this.

So I’ve always been at a loss to explain to readers the different curve required on the blade of a bevel-up smoothing plane vs. the curve required for a bevel-down smoothing plane.

The brain-dolt answer was always: The bevel-up planes require more curve to take the same shaving as a bevel-down smoothing plane. But that was about as good as my explanation got.

A couple weekends ago, David Powell explained the math to me during a presentation at the Northeastern Woodworkers Association’s Woodworkers Showcase. I retained the explanation and formula only until the next morning. (Honest: I had only one beer that night. Perhaps is was the lamb korma.)

In any case, I took notes during the presentation that are useful for the shop. If anyone wants the formulas, you can probably ask Powell himself. Powell was the founder of Diamond Machining Technology (DMT) and is now the maker of the Odate Crowning Plates. The plates are diamond stones with a curve built into them so you don’t have to use finger pressure to create the curve on the blade.

Powell’s numbers assume that the iron has a curve created by one of his diamond crowning plates. The plates are dished to mimic a 37-1/2’-radius circle. Powell’s numbers also assume you are using 90 percent of the iron of the tool during the cut.

So here goes: A bevel-down No. 4 handplane with a 2”-wide iron that is bedded at 45° will take a .002”-thick shaving if it has an iron that is sharpened with the Odate crowning plate.

Now let’s take a bevel-up low-angle block plane with its 1-3/8”-wide iron bedded at 12° and the iron sharpened at 25° (the angle of attack is therefore 37°). Powell says this plane will take a .0005”-thick shaving if you use 90 percent of the iron in the cut.

How about the very popular bevel-up jack plane? It has a 2-1/8”-wide iron and also is bedded bevel-up at 12°. If you have a 25° bevel sharpened on the iron, it will take a .0008”-thick cut. If you have a 38° bevel sharpened on the iron, the plane will take a .0006”-thick cut. And if you have a 50° bevel sharpened on the iron, the plane will take a .0004”-thick cut.

While these numbers don’t tell you how much extra pressure to put at the corners of your iron to make that extra curve, there is a good piece of data here. And here it is: Use the same curve for all your smoothing planes.

A plane bedded at 45° is best suited for mild woods. So its .002”-thick shaving is about right.

Planes bedded at higher angles are used for curly, exotic or just grumpy woods. So the best strategy is to take a thinner shaving (thinner shavings help reduce tear-out in my experience). So a shaving thinner than .001” is an excellent choice. And that’s exactly what you’ll get with a high pitch.

So all that math boiled down to this: Don’t bother with the math. Just stick with the same curve for bevel-up or bevel-down and you’ll be OK.

— Christopher Schwarz

Aside from eBay descriptions, photographs might be the biggest fibbers in the world of tools.

I’ve just finished judging a toolmaking contest sponsored by WoodCentral and Lee Valley Tools. During two days, I and two other judges examined, used and quarreled about more than 70 amateur-made tools. Our task was to award three prizes: the best-looking tool, the one that displayed the highest craftsmanship and the tool that worked the best.

As the entries came in, Ellis Wallentine of Wood Central posted pictures of the tools that were snapped by the makers (you can see those pictures here). I checked back every week or so to take a look at the entries and get a head start on judging.

Judging this contest, I thought, was going to be a cakewalk. We’d wrap it up in a couple hours and hit the Irish pub near the Lee Valley headquarters and spend the afternoon yucking it up.

It didn’t work out that way. In fact, the Lee Valley folks had to gently push us out the door after the first day of judging.

Here’s what happened: Photos are sometimes deceiving. Though some tools looked as good as they worked, other tools that looked like a million bucks in photos couldn’t cut a soggy toothpick in half. Tools that looked like they came over on the Mary Rose were so sweet they would almost do the job themselves when you went for a bathroom break.

And then there were the “ugly” tools. The tools that looked like they were made in a style that you had to wear either a black beret or Big Smith overalls (and no shirt) to truly appreciate. These tools managed to bore their way into your heart like a tapeworm in an Arkansas rice paddy.

So we argued about the tools. We almost abandoned any hope of awarding a prize for aesthetics. We were just too far apart. The craftsmanship award, however, was a little easier. There were lots of well-made tools, but some required more varied skills to make than others.

And function? That was the easy prize. When the steel hit the wood, it was quick to see which tools cut the mustard and which should be used only for resawing the mustard. In the end, using these tools radically changed my view of them. I didn’t care if the photos looked like junk or they had been professionally shot. When I looked at the pictures I saw only a tool that worked or didn’t work. As a result of all this, I was really pleased that we judged this contest in person and not via the photos. I think we got it right.

I cannot say yet which tools I personally liked or which tools I didn’t, but I’m including a few photos I snapped during the judging to break up the awful grey page generated by my typing prowess. When you take a gander, just make sure that you remember that pixels can be a crock of poo.

— Christopher Schwarz