Compound Miters for Dummy Woodworkers

Cutting a bevel with a table saw

Sometimes our staffers are just about to move on from the post they're reading when, halfway down the page, some bit of bogosity catches their attention. If there's anything we've learned by now, it should be that DotD candidates can reword part of a resource correctly and then go bonkers with the rest. That may be what happened with WiseGEEK.com contributor Dale Marshall, whose post "What is a Compound Angle" (now at niche site InfloBloom.com [and later moved to niche site AboutMechnics.com]) started out OK and then went awry.

Right up front, we'll point out that Dale may have misinterpreted the question, since he went straight to woodworking's compound miter instead of the trigonometric meaning¹ of the phrase "compound angle." Fair enough: how did he do on discussing compound miters? Well, he started out OK:

"In carpentry and woodworking, a compound angle is formed by cutting a piece of wood at an angle to both its horizontal and vertical planes."

Except that he's discussing a compound miter, not a compound angle, Dale's correct. It's when he expands on that statement that he begins to get off-track:

"Compound angles are important components of many different structures, including such diverse things as buildings, crown molding, and picture frames. Many rooms, boxes and frames are irregular — that is, the walls or sides don't meet at 90-degree angles — and to ensure snugly-fitting [sic] joints, the ability to cut accurate compound joints reliably is essential."

We aren't sure why you need a compound miter to accommodate out-of-square "rooms, boxes, [or] frames"; those corrections are modifications of the standard 45-degree cut instead of adding a bevel to a miter. You might well need compound bevels for framing a roof or building furniture, but a box? a frame? They're not usually "irregular" unless designed to be. Marshall's concept of a compound angle is apparently different from that of our staff woodworkers, who disagree with his notion that,

"...anything built with more than four sides, or fewer, will generally require compound angles at some point in their [sic] construction."

Well, no: once again, a miter joint that isn't 45° isn't the same thing as a compound miter. And then there's Dale's rather strange belief that,

"...many carpenters and woodworkers can produce accurate compound angles in dimensional lumber with table saws. Compound angle cuts in larger pieces may require the use of a hand-held motorized circular saw."

Just about anyone with a table saw can create a compound angle if they have a miter guide. As for the "larger pieces"; we aren't sure where Dale thinks sheet goods require compound miters, but we suppose that's right-ish. There's also his claim (about hand-cut miters) that,

"Specially designed wood or plastic miter boxes, with pre-cut slots corresponding to some popular [sic]² miter angles such as 15, 22.5, 30 and 45 degrees, as well as 90 degrees, are also available, but rarely can be used to produce a compound angle with any accuracy..."

We differ with Dale there: to our knowledge, no traditional miter box is designed for cutting bevels, much less compound miters. And finally, Dale claims that,

"Cutting accurate compound angles with a table saw... will require the use of clamps, fences, and jigs..."

Too bad Dale didn't seem to know that cutting a bevel with a table saw requires that the motor and blade be tilted. That might well obviate the need to use jigs. But, then, it's fairly obvious that our Dumbass of the Day has never cut a compound bevel on a table saw, and probably never on a power miter saw.

¹ "A compound angle is an algebraic sum of two or more angles."
² Don't you mean "common," Dale?

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