Popular Woodworking 2008-10 № 171, страница 54

a steep mountain. You don't make the road go straight up the mountain, you build switchbacks so the \-chicles can actually make it up the incline. Skewing rcduccs the amount of work required -both to plane a board and to climb a hill.

Howmuchdocs skewing reduce yourangk of attack? Skewinga 45°-pitch handplanc by 30° will reduce your cffcctive angle of attack to 40.9° - that's significant.

So here's the problem: If high planing angles reduce tear-out. and skewinga plane rcduccs your angle of attack, then how can skewing the plane reduce tear-out?

Hint: The answer is in the branches.

To explore this seeming contradiction. I did a little experiment. I took a short piece of ash with pronounced grain direction - that is. there was no questionabout which way the grain was traveling in the board.

1 cleaned up one face with a smoothing plane and then turned the board around so that I planed against the grain, which is when you arc more likely to encounter tear-out . Then 1 planed the board with a bevel-up block plane. This plane is bedded at 12° and the iron is sharpened with a 35® micro-bevel, so itsanglc of attack is 47°. The mouth on the plane is wide open, so it's not much of a factor. The tool is set to take a shaving that is about .002* thick.

First I planed the board against the grain without skewing the tool. This cleaned up the board just fine with no tear-out. Then I skewed the tool by 30° (which lowered my effective planing angle toabout 43°) and did the same operation. I tried skewing both to the left and to the right. Twoarcasofthc board tore out grotesquely.

Then I cleaned upthc board againand tried skewing the plane at 20°. Tear-out occurred at the same two places but not as badly. So I tried skewing the plane at a variety of angles. And without fail, the more I skewed the plane, the more tear-out occurred.

So how can skewing reduce tear-out?

You have to remember that trees a re not manufactured items. They are giant cones made of fibers that grow indifferent directions asthc tree responds tons environment: a hill, a disease, a wind storm. Then we slice them up into shapes suitable for building things, regardless of how the fibers arc traveling through the tree.

In some boards, grain can change directions on you a couple times. And the graincan be at odd angles -you cannot assume that all

\o skew. iVo tear-out. Planing with no skew resulted in no tear-out on this ash board.

Skewing and tearing. Ptaning nHh a Wskrsvtboth skewing Ml and skewing right> created this ugly patch oi torn grain.

And at 20*. Planing M a 20'skew tboth skessing Ml and skewing rightt created a little tear-out.

>ixir boards will have grain running from one end to the other - the grain may be traveling at a 20*directionalongthe face of the board and 10° along the edge. And the grain might be in the shape of a shallow wave.

So t here arc t i mes whe n skew i ng t he pla nc puts the edge in the right position at the right lime to deal with that patch of grain.

In my example board above, the two places where the tear-out occurred were at places where the grain rose quickly. So how did I deal with this board? As I encountered the arcasthat tore out. I straightened out the tool - no skew. When I worked the areasthat didn't tear out. I skewed the tool to reduce the effort required lor planing.

So the t rick with skewing takes us back to the No. 1 way to reduce tear-out: The best strategy- is to select the best wood possibk and karn to read the grain so you can begin to predict how your tools will behave. Sometimes, the best strategy isto not skew the tool.

Or put another way: Because grain isirtcg-ular. sometimes skewingthcplaneallowsthe Made tocncountcr the grain at a non-skewed angk - and to therefore you can plane it without tear-out. PW

(hrittoprier n the edine oi this magt/toe and the author ol' Wixtixrx/x-v Irom Dmgn A theory to Comtruc-lionS Lbe.'You can read more about traditional took M hoWogattostArtfrewxom.

m (19