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ompound angles add vi- sual interest to a piece. Instead of building a cradle that looks like a stiff box, you can angle the sides to give it a more subtle, inviting appearance. Angled sides are used in many types of wood- work, from simple serving trays and win- dow boxes to the high-style bombé chest, with its flat, sloped case and drawers that are carved into a bulge on the outside. A compound angle occurs at the inter- section of two sloped sides, and there are a
number of joints that can be used to con- nect them. The most basic and fundamen- tal of these is the butt joint. Miter joints and dovetails are more complex options. At North Bennet Street School, where I teach, we’ve found an easy tablesaw method that handles all three variations required, with some handwork for dovetails. To form a compound angle on the table- saw, both the blade and the miter gauge must be angled for crosscutting. The prob- lem is that you cannot get those angle set-
tings from the standard views on drawings. When any piece features surfaces that are not perpendicular to the line of sight, there is distortion in their size and shape. Take the front side of a simple box. If each side slopes outward 10°, the front and side views will show a slightly shortened front side, and the crosscut angle at each end will be dis- torted. The top view is also deceiving—you are not looking straight down on the top edges of the box, so you can’t read the true bevel angle of the butt joints.
64 F I N E W O O D W O R K I N G Photos: Asa Christiana
C
By beveling the edges of a wood block at the desired slope for your sides, you create a work- ing model of the box or tray and all of its angles. Used alone, laid on its side, the block gives you the blade and miter-gauge angles for a butt joint; add a 45° triangle (above), and you have the settings for a miter.
Work from a model
Simple set-up block dials in
tablesaw settings for accurate
butt and miter joints
B Y S T E V E B R O W N
Compound
Angles
Without Math
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There are a few traditional approaches to calculating these two angle settings. The first involves drafting a corrected view that shows the true dimensions and angles of each side of the box. The second is a math- ematical solution using trigonometry. However, while working through these traditional solutions with our students, we became dissatisfied with their complexity and potential for inaccuracy. There are chances for error when drawing or making calculations and also when you turn those numbers into actual tablesaw settings. This led us to rethink the problem and eventu- ally figure out a simpler method for deter- mining and cutting compound angles on the tablesaw.
Set-up block is a simple solution To carry out this method, you need to know only the slope angle for the sides. This slope is also usually the blade angle used to rip the top and bottom edges of each side. If the slope is 10°, for example, most designs call for a 10° bevel along the top and bottom edges. The basic trick is using that same blade angle to bevel the edges of a set-up block, which then becomes a working model of the box and all of its angles (see the photos and drawing at right). That’s it. The edges of the block represent the sides of the box. Simply flip the block on one edge and slide an adjacent edge against the blade to find the appropriate blade and crosscut angles for an accurate butt joint. This approach lets you walk up to the saw with any slope in mind and quickly create tight joints. Start by ripping the box parts to width (or height, depending on your perspective) with the appropriate bevel on the top and bottom edges. Next, joint and plane a block of wood flat and square on all sides. Make the block roughly 2 in. thick by at least 3 in. wide by 10 in. long, for reasons that will become apparent later. Next, crosscut each end of the block and rip at least one side at the same blade angle you used to bevel the sides. If necessary, you can hold the box parts in place against the block to see if the slope suits your tastes. You now have your set-up block.
Cut the basic butt joint At this point a butt joint is easy to produce. Set the blade angle first. Lay the block on one of its beveled sides and change the
Transfer that angle to the blade. This is a good time to rip the top and bottom edges of the box sides, which usually are cut at this angle.
From a drawing or an existing piece, find the slope. The actual degree reading does not matter.
To make the set-up block, you need to know only the slope of the sides of the box. Set the sawblade to that angle and bevel three edges of a long block. The block becomes a working model of the box and all of its angles and can be used to set up the tablesaw to cut the joints.
Now make the set-up block. Mill a flat, square block roughly 2 in. thick by 3 in. wide by 10 in. long. Then rip one edge (above) and crosscut the two ends at the slope angle (inset).
P I C K A S L O P E , A N Y S L O P E
Drawings: Kelly J. Dunton
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ends of the boards were not crosscut with the blade at 90°, from that angle (looking straight down on the sloped sides), the joint is square. That’s why you can lay a square across the beveled top edge of the set-up block or the box itself and find a 90° angle between the sides. Likewise, a miter on this compound-angle joint will actually be 45° when viewed from the top. By plac- ing the triangle flat across the top side of the set-up block, you are using this phe- nomenon to find the right blade angle for a
perfect miter. The blade will not actually be 45° from the table, of course, because the triangle itself is being held at an angle. If all of this doesn’t make perfect sense to you, don’t worry; the procedure will work anyway.
With this technique you’ll never have to fear compound angles. You can cut a butt or miter joint at any angle. You can even set adjacent sides of a box at different angles and still determine the tablesaw settings for perfect joints. Also, with the butt joint in your repertoire, dovetails are just a layout procedure away.
Steve Brown is the head of the cabinet- and
furniture-making program at North Bennet Street
School in Boston.
Miter-joint clamping strategy. Rip some scrap stock at the current blade angle and glue these blocks onto the workpieces. Use these clamping cauls to draw the joint tightly together. The blocks can be pared away later.
C O M P O U N D - A N G L E M I T E R J O I N T
To turn the butt joint into a miter joint, simply add a 45° triangle to the front face of the set-up block and reset the blade angle. The miter-gauge angle stays at the butt-joint setting. Place the triangle flat against the front face of the set-up block. Angle the blade to meet the edge of the triangle.
To learn how to lay out compound-angle dovetails, see Master Class on p. 96.
Again, lay out and label the sides to keep track of the cuts. Workpiece creep is espe- cially a problem with these sharply angled cuts, so clamp on a stop block, or a stop stick.
