how to use a combination square

Man looking at Square

A good combination square, properly used, is worth its weight in gold. Let us show you eight practical uses.

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Little tool for big results

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Often underappreciated, a 6" or 12" combination square--we keep both on hand because they're handy for different project and tool-setup applications–does far more than just help you draw perpendicular lines. Here are some great ways to get the most from your combo square.

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1. Locate and lay out joinery precisely

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Because the head acts as a stop (compared to a floppy tape hook), a combo square measures more consistently and precisely than a measuring tape. And you'll know your layout lines are always square to the edges and ends.

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2. Make a short rule work like a long one

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For long layout lines, forget about marking two distant endpoints and then finding a long straightedge or messy chalk line to connect them. Instead, simply adjust your combination square so the rule's end indicates your layout line. Then hold a sharp pencil in the cup-shaped groove at the rule's end and slide the square and pencil together to connect the endpoints.

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3. Accurately set heights for blades and bits

Fingers holding up square by bit

The photo on the first slide shows a method we like for setting tablesaw-blade and router-bit heights: Lock the head on the rule at the desired height, and then raise the cutter until it just kisses the head. Be sure to hold the rule end on the table surface rather than the throat insert. Adjust the blade or bit up or down as needed. Or, place the combo square's head on the table and slide the rule up against the cutter, as shown here.

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4. Calibrate a tablesaw's blade-tilt stops

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You can only rely on your tablesaw's 0° and 45° blade stops if you've set them accurately to begin with. Use your combo square to set each angle precisely, adjusting the 0° stop before moving to the 45° stop. Place your square's head on the cast-iron top, as shown, rather than the throat insert for maximum accuracy.

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5. Align your tablesaw for clean and safe results

Copy on photo, Hold head against this edge of slot

A combination square helps with two critical tablesaw alignment steps: paralleling the miter-gauge slots and rip fence to the blade. To adjust the miter slots, raise the blade at least a couple of inches, place the square's head against the miter slot, and adjust the rule until it touches a tooth at the front of the blade. Slide the square to the back of the blade, and rotate the blade until that same tooth touches the rule. Adjust the top or trunnion (depending on the saw) until the tooth just ticks the rule front and back. Now, likewise align your saw's rip fence parallel to the miter slot.

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6. Parallel a router-table fence to its miter slot

Hand adjusting large know on router fence

Nearly all router-table fences have independent locks on each end, and the fence doesn't self-square to the miter slot. But parallelism proves critical if you use a miter gauge in conjunction with the fence, such as for routing coped door-rail ends or dadoes in narrow stock, using the fence as a stop. Begin by locking your square's rule to the desired length. Place the square's head against the inner wall of the miter slot and bring the end of the fence forward until it touches the rule. Repeat for the other end, and then lock the fence in place.

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7. Set the limits for stopped router-table cuts

Hand putting flat side a square against router bit

When making stopped cuts on the router table, you need to mark the stop points, or clamp stopblocks to prevent routing past those points. To do that, use your combination square to mark both stop points, as shown. Extend the marks on the fence above the workpiece thickness, again using your square resting on the tabletop.

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8. Square the chisel and fence on a mortiser

Chisle bit going into wood

Before cutting mortises on a dedicated mortising machine, you must square the hollow chisel to the fence to ensure that the necessary repeated cuts are parallel. With the chisel (and its matching drill bit) snugged in the chuck, use your combination square to set the distance between the chisel and fence while simultaneously squaring the chisel against the rule. Then lock in both the fence and chisel.

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