Chris Schwarz's Blog

Bevel-out or Bevel-in? Good Question

If you haven’t surmised it yet, one of the themes running through the Spring 2008 issue is the fact that accurate sawing has a lot more to do with accurate chisel work than anything else. When you cut a tenon shoulder, it’s the chisel that cuts the part of the joint that shows , the saw just removes the waste below.

Several readers have picked up on this theme, and they’ve also pointed out (politely, I might add) what looks like a contradiction in my instructions about chiseling.

In the article on the Stickley Tabourets, I’m chiseling the joint line for the half-lap joint with the bevel of the chisel facing away from the waste (you can see this on page 10). A few pages later (page 19) I’m chiseling the shoulder for a tenon with the bevel of the chisel facing into the waste.

Have I finally taken one too many sips of La Fin Du Monde?

Perhaps, but I did have a good reason for what I did , I just didn’t have the room in the issue to explain it. So here goes:

When you deepen a knife line by striking it with a chisel, there are two important things to consider. First is what shape the resulting knife line will be, and second is how much the chisel will shift when you rap its handle with a mallet.

The first part is easy to understand. Chisels are wedge-shaped. They have a flat face and a bevel. So when you knock the tool straight down into your work it makes a “V”-shaped cut that is a photocopy of this shape. One side of the V is straight up and down. The other side of the V is sloped.

The second part also has to do with the fact that chisels are wedges. When you drive a chisel with a mallet, it doesn’t want to travel straight down in a line that’s parallel to the flat face of the chisel. Instead, it wants to travel at an angle that is halfway between the bevel and the flat face. So if you have a 20Ã?° bevel on your chisel (as I do in the paring chisel shown in the articles), the chisel doesn’t want to travel at 90Ã?° (straight down), it wants to move at 80Ã?°. (This assumes you have wood pushing back equally on the bevel and the face of the chisel.)

This is why when you are chiseling out your waste between dovetails that the chisel is always trying to move toward (and even cross) your baseline.

Whew. With all that on the table, I can now explain why I did what I did.

When chiseling a tenon shoulder, the shape of the line created by the chisel is critical. I want it perfectly square so it will close tight with the stile. So I chisel the joint with the bevel facing the waste. If this so happens to shrink the overall length of the tenoned part by 1/128″, I can live with that. I want the joint to be tight more than I care about its final length.

When chiseling a half-lap joint, my considerations are different. This isn’t a show joint, so I just want it to be tight and structural. The shoulder line isn’t as critical. That’s why I chisel with the bevel facing away from the waste. The chisel will then drift into the waste a tad. So when I saw the joint, the notch made by the chisel will encourage the saw to cut a half-lap that is just a tad tight. Then I can plane the piece’s mate to get a perfect fit.

This might be a little fussy for you. If so, I apologize. A chisel seems so simple (it’s a steel and wooden corndog!), but it actually is a subtle instrument (like a corndog with chorizo inside). Play around with the tool. Try it with the bevel out and then with the bevel in. And let us know what you discover.

- Christopher Schwarz

9 thoughts on “Bevel-out or Bevel-in? Good Question

  1. Mattias in Durham, NC

    What Francois said. Except the part about the beer: I don’t do beer. And Good Afternoon, not Good Morning. But you get the idea.

  2. Christopher Schwarz

    Brad,

    They both work very well. I don’t prefer one over the other for chisel work — though the Veritas also is a good assembly mallet. The Glen-Drake gets props for its compact size and nice handle shape.

    Really, either are excellent tools.

    Chris

  3. Brad

    Is that a Glen-Drake chisel hammer in the first photo? I’m just curious about your impressions of it and how it compares to the Veritas mallet.

  4. Paul Kierstead

    One of the finest beers in Canada, in my opinion. However, it must be said that it doesn’t take many sips to be too many. But man, is it tasty.

  5. David

    There’s good reason these "naturally fermented" beers aren’t in every grocery store. Because they’re not pasteurized, they have to be kept refrigerated at all times, and at least in NC, the big beer distribution companies that keep the large grocery stores filled can’t garantee that refrigeration. And if you’ve ever tried one of these that hasn’t been kept cold at all times, you’ll know why the bigger grocery stores won’t carry them – think skunk that’s been run over by an 18 wheeler and left in the sun for 3 days in July.

  6. Christopher Schwarz

    Dave,

    Heck, I can get them at the grocery store in Cincinnati. And our local bars that Maudite on tap!

    Just look for the big bottles! They are everywhere these days.

    Chris

  7. Christopher Schwarz

    Francois,

    I’m glad the explanation helped.

    And I don’t know of anything I like as much as Unibrou products (except Piratt on occasion). The Unibrou No. 17 ale this year is near perfect.

    Chris

  8. Francois Fournier

    Good Morning Chris,

    Thanks for the clear explanation regarding your chisel work. I admit that it I raised an eyebrow when I read the article, but now I understand the logic much better. I also commend you on your selection of fine french canadian beer!

    Francois (from Quebec city)

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