How to Use a Marking Knife for Tighter Joints (and When a Pencil Is Fine)

A joint can't fit any tighter than the line you laid it out with….. A pencil line sits on top of the wood and it has width. Chris Becksvoort (Fine Woodworking) figures even a fine pencil line can run 1/32 in. or wider, and WOOD Magazine puts a carpenter's pencil at about 1/16 in. Saw on the wrong side of that and the shoulder's off before you've even started. A marking knife doesn't draw a line, it cuts one. It severs the fibers, and that cut gives the saw tooth or the chisel edge a wall to sit against. That doesn't mean the pencil goes in the trash, though. Half the trick is knowing which line gets which tool.

Why it matters: Wherever two parts meet (a tenon shoulder, a half-lap, a dovetail, a hinge leaf), the width of your line turns into a gap. Paul Sellers calls the knifed shoulder a knifewall: it's the guideline and the wall that separates the waste from the wanted, and saws, chisels and planes register against it. Yoav Liberman (Popular Woodworking) adds a shallow chiseled ramp on the waste side to make a little "V" that nests the saw for the first few strokes. The saw falls toward the square wall the knife made, not down the middle of a fuzzy line. The flip side: Becksvoort still draws his first layout in pencil, and at North Bennet Street School in Boston, Steve Brown teaches a sharp No. 2 for tracing dovetails and hinge mortises, because there a knife would cut into wood you mean to keep. Knife the lines that mate. Pencil the rest.

Materials

• A planed offcut (pine and oak both teach you something) to practice knife walls on before the good stock
• No. 2 pencil kept sharp, or a 0.5 mm or 0.7 mm mechanical pencil for a line that stays the same width
• Carpenter's pencil or lumber crayon for rough-sawn stock and cut-list layout
• P220 sandpaper to bring a pencil to a finer point, or 120–150 grit to flatten it into a wedge for tracing

Tools

• Marking knife: single-bevel (comes in left- and right-hand) or a double-bevel spear point that works either way
• Combination square or try square
• Marking gauge, preferably a cutting or wheel gauge, for lines parallel to an edge
• Bevel-edge chisel for paring the V on the waste side
• Backsaw or ryoba
• A flashlight held low (raking light makes a knife line easy to see)

Steps

1. Rough it out in pencil. Lay out lengths, part locations and the first lines of your joinery in pencil. These are lines that will get refined later, and pencil is quick, easy to see, and erasable if you change your mind (Becksvoort). On rough-sawn boards, a lumber crayon or carpenter's pencil is the right tool (Tom McLaughlin, FWW). Mark the waste with an X, or with the arrow or squiggle Rockler suggests, so you never cut on the wrong side of the line and come up a kerf short.
2. Put the square on the keeper. Lay the square's blade on the piece you're keeping and hold the stock tight to a true edge. That way, if the knife wanders, it wanders into the waste (WOOD Magazine). To carry a line around a corner, set the knife tip in the line, slide the square up to the blade, then cut.
3. Knife the line: flat to the square, bevel to the waste. With a single-bevel knife, keep the flat back tight against the square and the bevel facing the waste (Liberman; WOOD). With a double-bevel knife, lean it so the bevel riding the square sits plumb, which keeps the wall on the keeper side square (Sellers). Take a light first pass to set the track, then a few more with more pressure, to roughly 1/32 to 1/16 in. deep (Liberman).
4. Gauge anything parallel to an edge. Tenon cheeks, lap depths and dovetail baselines all get the marking gauge, not a square and a ruler. A knife-type cutter (a cutting or wheel gauge) slices cleanly across the grain, where a pin tends to tear (McLaughlin). Hold it by the head and start with light strokes so it doesn't wander (Bob Van Dyke, FWW).
5. Pare the V on the waste side. Set a chisel, bevel up, about 1/16 in. into the waste at roughly 45° and push down toward the knife line so the chip pops out at the wall. Work along the line until you have a clean little ramp (Liberman). Sellers does the same thing with the chisel angled low into the knifewall to make a step-down.
6. Saw or chop against the wall. Nest the saw in the V, square face against the knifed wall. Keep light pressure on the spine for the first strokes and ease off once the kerf is about 1/8 in. deep (Liberman). For chisel work, the final paring cut drops right into the knife line, which gives the chisel a seat (McLaughlin).
7. Cut to the wall, work up to the pencil. A knifed line is the finished edge, so you saw and pare right to it. A pencil line on keeper wood, like Brown's traced dovetails, is something you work up to but not into. Anything that'll be planed, sanded or sawn away later can just stay in pencil.

Where the pencil belongs

• Rough stock and first layout: cut lists, part locations, first passes at joinery (Becksvoort; McLaughlin).
• Curves and chamfers where you don't want a scored line left in the work (McLaughlin), and fair curves run off a batten.
• The loft floor. WoodenBoat's lofting primer runs lines in pencil (colored pencils to tell the views apart, with erasers in the kit), because a line on the loft floor gets checked, faired and redrawn.
• Machine setup marks, where the fence and stops do the precise work (McLaughlin).
• Tracing one part onto another when a knife would cut into keeper wood: Brown's dovetails and hinge leaves, with a No. 2 sharpened on P220.
• Boat shop: station marks and bevel numbers on rough dory frames and rough planking stock are pencil work, since that wood gets planed and faired anyway. Save the knife for the fitted joinery.

MOAM's shop note: The usual mistake is laying the square on the waste side and leaning the knife the wrong way. The bevel's bruise and any wander end up on your keeper, and you've traded a pencil's width of slop for a knife's worth of tear-out. Square on the keeper, bevel to the waste, light first pass. Pro trick: if a pencil is the right call, keep it sharp. Becksvoort found a freshly sharpened soft No. 1 wears down to a 1/16 in. line in just 6 to 10 in. of drawing on hardwood. A No. 2 or a 0.5 mm mechanical holds a line. And when you can't see your knife line, don't cut it deeper. Just put a flashlight down low across the board and it'll show up.

Sources: Christian Becksvoort, "What's the Best Tool for Accurate Layout?" Fine Woodworking #179; Steve Brown, "Layout: When Pencil Beats Knife," Fine Woodworking #224; Tom McLaughlin, "A Woodworker's Layout Tools: Marking," Fine Woodworking #280; Bob Van Dyke, "Using a Marking Gauge," Fine Woodworking #261; Paul Sellers, "What's 'Knifewall'?"; Yoav Liberman, "An Intro to Marking Knives: Part One," Popular Woodworking; Rockler, "Measurement Advice: Accurate Measuring and Marking"; WOOD Magazine, "Measure and mark for better accuracy"; Karen Wales, "Lofting: How to Loft a Simple Boat Plan," WoodenBoat.

MOAM Out.

Tools for this tip

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• Narex double-bevel marking knife: knifing shoulder lines and transferring joint layouts; lean it so the side against the square rides plumb
• Starrett 12-inch combination square (11H-12-4R): the steel blade the knife rides against, laid on the keeper side of the line
• Taytools wheel marking gauge, solid brass head: gauging lines parallel to an edge: cheeks, lap depths, dovetail baselines
• Narex Premium bevel-edge chisel set (4 pc): paring the small V-groove on the waste side of the knife wall
• Gyokucho 9-1/2" ryoba razor saw for hardwoods: sawing with the teeth seated against the knife wall

Use whatever you already have in the shop; these are just the ones that fit this job.