Author: fitz

I was flattening some panels by hand the other day (too wide for my machines), and that got me thinking about plane blade camber. If you search online for discussions of blade camber, you’ll find that a great many electrons have been spilled on the topic. One common thread in these discussions is frequent confusion over the fact that a bevel-up blade requires more camber (i.e., the center of the blade needs to protrude further beyond its corners) than a bevel-down blade to have the same effect.

On the one hand, everyone seems comfortable with the notion that as the blade’s bedding angle decreases, the effective radius of curvature of its edge increases. This is easy to see. First, find yourself a thin disk (e.g., a CD or DVD) and hold it up at arm’s length:

When the disc is perpendicular to your line of sight, the apparent radius of its lower edge is equal to its actual radius (2-3/8″ in the case of a CD/DVD). But start tilting it from perpendicular, and the curve flattens; its apparent radius increases:

Tilt even more, and it keeps increasing:

From the point of view of the wood fiber that’s about to have its head chopped off by an oncoming blade, the greater the tilt from vertical, the greater the apparent radius of curvature, and consequently the less the depth of cut at the center of the blade. And since the blade in a bevel-up plane is tilted further from perpendicular, its apparent radius of curvature is larger than that of the bevel-down blade unless we make its actual radius of curvature smaller (i.e., increase its camber). Easy.

On the other hand, we’ve also all seen diagrams of bevel-down vs. bevel-up planes seated on their respective frogs:

The resulting cutting geometries in the two cases are identical. The blade’s cutting edge comprises two intersecting planes, one formed by the back surface, and the other by the bevel. The only difference between the two configurations is that these two planar surfaces switch roles.

This is where I think some people get confused. If the two setups are equivalent, why can’t we measure the blade camber in the same way with both? In truth, we sort of can, but there’s a difference between the bevel in a cambered blade vs. a straight blade. When the camber is small, that difference is also small (and negligible), but with a strongly cambered blade, such as one we might use in a fore or scrub plane, it’s not. With a cambered blade, the bevel is not planar. In fact, the bevel is a section of the surface of a cone:

That’s where the equivalence breaks down, as it’s no longer possible to directly superimpose the cutting geometry of a bevel-up blade onto that of a bevel-down blade. And so we go back to always measuring the camber with respect to the back of the blade.

Anyway, is any of this important? Only to the extent that you get a feel for how the different parameters interact, so that you’ll know how much to camber your blade to achieve a given depth of cut.

I’m avoiding the math here, because it’s been covered before (such as here and here), but I did put together a little online app that lets you plug in some numbers to see how this all works. Here’s a screenshot:

You can find the app here. To use it, enter your bed angle and blade width, and one of the other three values. The app will compute the other two corresponding values for you, dynamically updating the display as you modify the values. The bed angle is in degrees; the other values can be in whatever length units you choose, as long as you’re consistent (inches, millimetres, furlongs, it makes no difference).

Now, I know that someone is going to read this and then get out their micrometer and measure their blade camber to three decimal places, to which I say,

STOP!! PLEASE STEP AWAY FROM THE PLANE!!

The point of the app is intuition, not prescription. The precise value of camber that you end up with is largely irrelevant, as long as you’re in the ballpark.

Don’t worry, plane happy.

–Steve Schafer

In case you haven’t looked out your windows for a while, it’s the middle of winter. (Californians and South Floridians are exempted from noticing.) Everything is gray, the trees have no leaves, and no one in their right mind would go out into the woods to identify trees this time of year, right?

So what are we waiting for? Let’s go! I live in Athens County in southeastern Ohio, in the Appalachian foothills, so we’ll begin by taking a look at some of the trees in my yard.

First, I have to admit that I lied about the trees having no leaves. A few kinds of trees do hang onto their leaves until very late in the winter, which makes them easy to pick out. I managed to get three species into one photo:

In late fall and winter, the leaves of red oak (Quercus rubra) are a rich brown. White oak (Q. alba) has leaves that are paler and grayer. American beech (Fagus grandifolia) has very pale, almost yellow leaves, and as you walk through the forest in winter, the sapling beech trees are obvious.

The overall shape of a tree can be useful in identification, but it can also be misleading. A tree growing in isolation (in the middle of a pasture, say) has a characteristic shape that varies quite a bit from one species to another. Forest trees, on the other hand, are much more similar in shape. For that reason, features of the bark and morphological details (e.g., branching pattern) are much more useful in the forest.

Red oaks are some of the most common trees in my yard, and they invariably have a bark pattern that is both unique and easy to spot:

The bark consists of a smooth(ish) medium gray (sometimes slightly brownish) ground interrupted by ragged vertical grooves that are considerably darker. On larger individuals, the bark near ground level may be much rougher than this, but you can always find this pattern if you look at the upper limbs.

The bark of white oaks is very different, a very pale gray (hence the name), flaking off in scales:

That particular tree has relatively small scales; here’s another (about the same diameter) whose scales are much larger:

Both red and white oaks are generalists, found in a variety of habitats. There are many other species of oak in Ohio, but most of them have specific habitat requirements. One of these specialists is the chestnut oak (Q. montana):

Chestnut oaks are found only near ridge tops, most often on the south-facing slope (which happens to be exactly where I live). The bark of the chestnut oak is dark and deeply furrowed. If you picture a cross section of the tree, the profile of the bark ridges would look something like the teeth of a gear.

Another very common tree in the yard is the red maple (Acer rubrum):

Red maples have a split personality; the bark of young trees is pale gray and very smooth (much like American beech, which I don’t have a photo of here). As the tree grows, the bark starts to split and darken, becoming much craggier. In a large tree, there is no trace of the smooth gray on the bark near the ground, but you can still find it if you look up. The bark of the silver maple (A. saccarhinum) is similar, but silver maples are restricted primarily to bottomland, where the soil contains more moisture. (Red maples, like the two oaks above, are generalists.)

Sugar maple (A. saccharum) has a medium gray bark that flakes off to expose an orangeish background:

The appearance of the bark is intermediate in all respects, so other than the orange background (which you sometimes see on white oaks, too) there really isn’t any one thing that tells you it’s a sugar maple. It’s kind of a process of elimination.

By the way, late January/early February is the time of year in this part of the country to tap sugar maples for making syrup and sugar. The best sap flow occurs when temperatures cycle above freezing during the day and back down below freezing at night. The prime tapping season is progressively later as you move north, as late as April in southern Canada.

There are two species of ash common in this area, white ash (Fraxinus americana), and green ash (F. pennsylvanica). (To confuse matters, green ash is also known as red ash.) White and green ash have very similar bark, fairly pale overall and consisting of narrow vertical ridges that often cross over each other, forming “X” patterns:

I believe that this example is a green ash, but I can’t be sure without getting a close look at the leaves, and unfortunately the lowest leaves on this tree are about 50 ft. above the ground.

As you may be aware, most of the North American ash species are seriously threatened by the introduced emerald ash borer. It is expected that over 99% of green ash trees will die over the next several years. White ash fares slightly better, but populations of both species (along with black ash, a more northerly species) are being devastated. A small number of individual trees appear to be resistant to the borer, so there is some hope that they will eventually be able to recover.

One of the most important forest trees in this area (Liriodendron tulipfera) goes by many names. The name preferred by the US Department of Agriculture (USDA) is “tuliptree,” but woodworkers know it as “yellow poplar,” “tulip poplar,” or even just “poplar” (which is especially misleading, as it is unrelated to true poplars):

(EDIT: As pointed out by “A Riving Home” in the comments, this is actually a mockernut hickory. I had taken photos of both it and the tuliptree, then decided to save the hickory for a later post, and managed to get the two photos mixed up.)

The bark of tuliptree is much like that of ash, with narrow vertical ridges, but is overall quite a bit darker, sometimes appearing almost black. This particular individual has a lot of the same sort of “X” pattern that ashes do, but not all tuliptrees show this. Tuliptree is one species where the overall shape of the tree is useful in identification, even in the forest: tuliptrees are arrow-straight (usually the straightest, most vertical trees in the forest), and the branches are restricted to the very top of the tree.

Here’s another tuliptree, with a big problem:

During the summer of 2015, we had a spell of very hot, dry weather. Many of the tuliptrees in this area and neighboring West Virginia were weakened and eventually killed by the drought. Some of these dead trees are now exhibiting this odd pattern of flaking bark.

Not every tree loses its leaves in the winter, of course. American holly (Ilex opaca) is primarily a tree of the southeastern forests, but there are a few scattered small hollies in my yard, such as this one, which is about 8 ft. tall:

I haven’t been able to figure out whether these individuals are native, at the very northern limit of their range, or escaped from cultivation. There is no record for Athens County for the species in the USDA PLANTS database, but there are records from some of the surrounding counties.

Incidentally, a good place to see much larger (and definitely native) American holly is along the Baltimore-Washington Parkway in Maryland.

The leaves of American holly make it easy to identify:

The leaves are a dark, shiny green, about two inches long and with very sharp spines along the margins.

Another bit of green in the yard comes from a scattering of eastern redcedar (Juniperus virginiana):

Redcedars are normally more conically shaped than this, but this is what happens when your yard is overrun by deer. As the scientific name suggests, redcedar is not actually a cedar, but a kind of juniper. The wood that is sold as “aromatic cedar” comes from this species.

Interestingly, redcedars have two kinds of foliage. On the upper part of the tree, the foliage has a typical juniper-like appearance:

But seedlings and the lower portion of trees that have been ravaged by deer have a much different foliage:

This juvenile foliage is quite prickly, and is an apparent attempt by the tree to dissuade browsers. It seems to work for the seedlings, which don’t get munched too badly, but it obviously doesn’t for the larger trees.

In addition to the large trees that make up the forest canopy, there are smaller trees that form the understory. One of the more common understory trees in the yard is flowering dogwood (Cornus florida):

The trees are small, usually less than 6″ in diameter, and the bark is broken up into numerous small roundish plates. But the easiest way to identify a dogwood in winter is the flower buds, which are usually plentiful and have a characteristic turban-like shape:

That’s it for now. I hope this inspires you to take a walk in your own woods. (Did I mention that there’s going to be a test later?) If you do, a couple of cautions:

• Remember that poison ivy (poison oak in the west) is plentiful in the forest, especially around openings, and like the trees, sheds its leaves. Be careful what you touch.
• Before walking in the forest, check with your state wildlife agency to determine the deer season dates for your area, and be sure to wear appropriate orange clothing if there is any chance of being in the same forest at the same time as a hunter.

–Steve Schafer

As some of you will recall, I last reported from Ecuador back in August, when I showed you the workbench that I had completed. Since then…nothing. What happened? Well, as it turned out, a variety of events and situations conspired to the extent that I ended up with virtually no time to do any actual woodworking. I did get started on a project, but wasn’t able to finish before we had to leave.

You will at least be happy to know that the bench found a good home in the workshop of the architect friend who earlier pointed me in the direction of wood merchants in my neighborhood.

And I did learn a few things along the way:

Lesson 1 – Colorado (aka Lyptus®, Eucalyptus grandis x urophylla) is not a hand tool-friendly wood.

Lyptus is very hard, about the same as hard maple or the very hardest of white oaks. And it has interlocked grain, which tears out readily no matter which direction you try to plane it in (even cross grain!). I eventually figured out how to plane it: with my plane set to a 60° cutting angle and taking extremely thin shavings, I was able to achieve a surface that could later be sanded smooth. But removing 1/16″ of tearout a thousandth at a time is not my idea of fun.

The wood reminds me of sapele, which is similarly hard and also has interlocked grain, although it’s more brittle and doesn’t tear out quite as much. Like sapele, it’s very difficult to get a decent finish without a considerable amount of sanding.

Lesson 2 – At some point, a baggage handler will drop your tool case very, very hard.

The damage shown here occurred when the lever cap knob of my Veritas low-angle jack plane punched through the bottom of the tray from below. Given that when the trays are stacked together there is at most 1/2″ of play before the knob contacts the tray bottom, I don’t want to think about how far the case must have fallen in order for this amount of destruction to occur. Fortunately, it appears that all of the tools are okay.

Lesson 3 – An outdoor woodworking shop in Tumbaco may not be the best idea.

This one was completely unexpected, and it’s the fault of these guys:

The soil in Ecuador is virtually all volcanic ash, in some places hundreds of feet deep. Very fine, very abrasive volcanic ash. Add to that the fact that the climate in Tumbaco is dry, and afternoons are usually windy, and you begin to see the problem. I would finish up one day and come back the next to find everything covered by a clearly visible layer of ash. Ash that wreaked havoc on my tool edges.

The ash ends up indoors, too. We had a housekeeper that came to clean every week, and still the pile-up of dust near windows and doors was impressive.

I’ll have more to write about our adventures in Ecuador (plus a couple of weeks in Peru) soon, so stay tuned. But for now, I have some pent-up woodworking to attend to.

– Steve Schafer