Every crooked drawer front starts with a fence that was "close enough"….. and on a crosscut sled, close enough gets copied into every part you cut, all day long. Most sleds get squared once with a framing square, screwed down, and trusted forever. Here's how to square one properly with the five-cut method, so you square it once and quit checking every cut.
Why it matters: A sled carries the work past the blade on two runners, so the cut can only be as square as the fence and only as true as the runners are tight. Lon Schleining put it plainly in Fine Woodworking: if the sled's fence isn't 90° to the blade, every cut will be inaccurate. The trouble is that a square can only read the error over the length of its own blade, and a good sled's error is smaller than you can see that way. The five-cut method runs one board around the blade four times, so the error stacks up four times over and shows up in a strip you can measure with calipers. In William Ng's own example the fence was out .0135″ across a 24″ cut. That's about three hundredths of a degree, and no square in my shop would show it. In the boat shop this is the jig I cut cleats, frame stock and thwart blanks to length on for the dory, and on the GC side it's cabinet parts and trim. Square ends on parts mean glue lines that close and frames that stand plumb.
Materials
- A flat base. Bob Van Dyke (Fine Woodworking) builds his everyday sled on ½″ or ⅜″ Baltic birch, about 30″ wide by 18″ deep. Jonathan Katz-Moses uses ¾″ plywood sized to his saw top. Flat matters more than thick.
- Front fence stock, straight and stable. Van Dyke laminates flatsawn mahogany strips into a riftsawn fence 1⅛″ thick by 5⅛″ tall by 29¾″ long. Katz-Moses glues up three layers of plywood.
- Back fence stock. Van Dyke uses 6/4 or 8/4 poplar, 24″ long. It doesn't need to span the whole base.
- Runner stock: hardwood (Katz-Moses likes maple), Baltic birch plywood ripped and planed on edge (Van Dyke: ⅜″ × ¾″ × 18¼″), or UHMW plastic strip (the Popular Woodworking sled).
- #8 washer-head screws for the pivot and adjust screws, flathead screws for the permanent fence screws, and round-head screws for the runners. Van Dyke warns that a flathead's tapered head can spread a runner as it's tightened.
- A test board: the biggest flat plywood or MDF panel the sled will take, with clean, smooth edges
- Scrap for a safety (exit) block and a stop block
- Paste wax or paraffin
Tools
- Digital calipers. You'll read to the thousandth.
- Feeler gauges, or strips of paper stacked up and measured with the calipers (the Katz-Moses fallback)
- Two or three clamps
- A square or drafting triangle you've checked, for the first rough setting
- Drill, Forstner bit and countersink
- A planer or hand plane to size the runners, plus a shoulder plane or a 120-grit sanding stick for tight spots
- A soft pencil for finding those tight spots
Steps
- Measure the miter slots. Calipers, both ends of each slot. Most full-size saws run about ¾″ wide by ⅜″ deep, but measure your own. William Ng's read .752″, a hair over ¾″.
- Fit the runners with no slop. Van Dyke planes his runners on edge until they fit the slot with absolutely no slop and are just loose enough to slide freely. Keep them a little shy of the slot depth so they never ride on the bottom. Ng cuts his 5/16″ thick for a 3/8″-deep slot so sawdust down there can't lift the sled. With UHMW, the Popular Woodworking sled drills the screw holes a bit oversize (9/64″ for No. 6 screws), because otherwise the plastic bulges around the screw and binds. Van Dyke lays ⅛″ plywood strips in the slots under the runners so they sit slightly proud while the glue sets under the base. If the sled is tight, rub pencil graphite on the slot walls, slide the sled, and skim the shiny spots with a shoulder plane or the sanding stick. Then wax it. Slop in the runners is the one thing no formula can fix.
- Know which fence does the work. The front fence, the one closest to you, is the reference. You push the work against it, so it's the one you square. The back fence just holds the two halves of the base together once the kerf is cut, so it doesn't need to be square to anything. Screw the back fence down. Attach the front fence with only two screws for now: a pivot screw near one end (Van Dyke goes about 1″ in) and an adjust screw in a slot ¼″ to ⅜″ long at the other end. Keep the permanent screw holes at least 1″ either side of the blade line. While the base is easy to get at, measure from the pivot screw to the far end of the fence and write it down. That's D.
- Cut the kerf and rough it in. Raise the blade and cut through the base and the back fence, stopping before the blade reaches the front fence. Wedge a snug spacer in the kerf and set the fence square to it with a square you trust. Clamp it and tighten the adjust screw. That's your starting point, not your finish.
- Make the five cuts. Number the test board's edges 1 through 4. Start on the longest edge. With edge 4 on the fence, trim edge 1, and cut the full length of the edge every time. Give the board a quarter-turn so the fresh edge rides the fence, and trim edge 2. Same direction every turn: edge 3, then edge 4. Now edge 4 is back on the fence. For cut five, take a strip about ½″ to 1″ wide off edge 1 again. Save that strip. Mark its far end (away from you) A and its near end B.
- Measure and do the math. Read the strip's width at A and at B with the calipers, the same distance in from each end. Measure the strip's length, L. Then:
Move = (A − B) ÷ 4 ÷ L × D
Why divide by 4? Each of the first four cuts carries the same small fence error. By the time edge 1 comes back around to be cut again, it holds that error four times over. The fifth cut only slices it off where your calipers can find it. Ng's worked example: A = .896″, B = .842″, L = 24″, D = 28.5″. The difference is .054″. Divide by 4 and you get .0135″, the real error over 24″. Divide by 24 for .00056″ per inch, and multiply by 28.5 for a .016″ move at the adjust end of the fence. - Move the fence with a feeler gauge and a block. Here's the pivot-screw-and-clamp trick, the way Katz-Moses lays it out. Leave the pivot screw alone and work at the far end. To swing the fence away from you, hold the feeler gauge (set to your move) against the end of the fence, clamp a scrap block tight to the gauge, pull the gauge, back out the adjust screw, and swing the fence out to the block. To swing it toward you, clamp the block right against the fence, back out the screw, slip the gauge between them and push the fence back against it. Either way, clamp the fence and drive the screw into a new hole. An old hole will pull the fence right back where it was. Which way? If the strip is wider at the far end, the fence end on the work side of the blade is sitting too far forward, so swing it back toward you. Wider at the near end, swing it the other way. Calculators online word the direction differently depending on which side the pivot is on, so trust the second test, not the arrow.
- Repeat, then screw it off. Run five more cuts to check. If the taper grew, you went the wrong way. Katz-Moses figures two or three rounds does it, and says once the calculated move is down to a few thousandths of an inch, take it and run. When you're there, clamp the fence and drive the permanent screws.
- Add the safety block and a stop. The blade comes right through the front fence when you push the sled, so attach a wooden block to the fence's front face, right where the blade exits. Van Dyke calls it a simple safety device you shouldn't skip. Fine Woodworking reader Chris Durkee points out that the main danger with a sled is your hands in the way of that exit point, and he adds a travel stop so the sled can't be pushed far enough for the blade to come out the front of the block. Then add a stop block for repeat lengths. A square scrap and a clamp works, and a T-track stop is quicker.
- Use it like you mean to keep your fingers. Fine Woodworking's table saw safety list says to set the blade with the teeth no more than ⅜″ above the work, to never put your hands or fingers in the path of the blade, and to stand out of the path of the blade and the workpiece. On a sled that means keeping your hands on the fence well off to the side of the kerf line, both in front of the fence and behind it, and never standing square behind the blade where an offcut can come back at you. Push through until the blade is buried in the safety block, switch off, and let the blade stop before you clear offcuts or reach past the fence.
MOAM's shop note: The most common mistake I see is fussing over the math and ignoring the runners. If the sled wiggles in the slots, every set of readings comes out different and you'll chase your tail all afternoon. Get the runners snug first. The second mistake is touching the pivot screw. It never moves. Pro trick from Van Dyke: drill a hanger hole and hang the sled on the wall instead of leaning it against the saw or the floor. He says a sled cared for that way will last decades and stay square. In a damp Marblehead boat shop in January, that's not optional.
Sources: Bob Van Dyke, "Simple Crosscut Sled" (Fine Woodworking #308); Lon Schleining, "Squaring a Crosscut Table Saw Sled" (Fine Woodworking); Chris Durkee, "Small stick stops crosscut sled in safe position" (Fine Woodworking #314); Fine Woodworking, "Safety Manual: Table Saw"; Travis Larson, "The Ultimate Shop-Built Crosscut Sled" (Popular Woodworking / American Woodworker); William Ng, "5 Cuts to a 'Perfect' Cross-Cut Sled" (William Ng Woodworking School, YouTube); Jonathan Katz-Moses, "Make an Ultra-Square Crosscut Sled" (Katz-Moses Tools); Kevin's Workbench, "Table Saw Cross-Cut Sled Setup"; Wind Ridge Wood Crafts five-cut calculator.
MOAM Out.
Tools for this tip
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- Starrett 12-inch combination square (11H-12-4R): first-pass squaring of the fence
- iGaging 6-inch digital caliper: measuring the five-cut test strip
Use whatever you already have in the shop; these are just the ones that fit this job.
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