the craft · draw · EP-055

Screw, Nail, or Glue? (How to Choose by Load and Joint)

Every wobble is a lost argument.

General home-repair education, not a substitute for a builder or the hardware's own instructions. Anything that holds a person — a stair rail, a grab bar, a gate at the head of a stair — goes in with the hardware its maker names. For the wood facts behind a fastener or a glue joint, check the USDA Forest Products Laboratory's free Wood Handbook. Nothing on this page is sponsored.

Study II — The Craft.

the draw

What this draw covers.

Screw, nail, or glue? The answer is a reading skill: nearly every joint in your house is being pulled in one of two dominant directions — sideways (shear) or straight apart (withdrawal) — and each fastener has a direction it handles best. This episode teaches the two directions, each fastener's genius and its failure, how to choose by the load and the joint instead of by guesswork, and the pilot hole that prevents the split. Your wobbling chair is a lost argument; this is how to win it back.

What follows is the draw as spoken, line by line, with the gold line that sat under each.

On this page: the draw, in order · sources

as spoken

The draw, in order.

  1. Every wobble is a lost argument.

    Somewhere in your house tonight there is a chair that wobbles, a drawer front working itself loose, a towel bar that leans out from the wall a little more each month. None of them failed at random. Each one is a joint losing an argument with a direction.

  2. Read the pull before the parts.

    Today you draw a craftsman's tool from the well: how to choose between screw, nail, and glue. Which turns out to be a different skill than it sounds — the skill of reading which way a joint is being pulled.

  3. Two directions rule every joint.

    So before we touch a single fastener, learn the two directions that do most of the work. Nearly every load on a joint in your house resolves into one of them, or both at once — and a joint being twisted or levered is only these two, arguing at an angle.

  4. Shear: the sideways slide.

    The first is shear — the sideways slide, one piece trying to skate across the other. Picture the shelf pressing down across the bracket that carries it, the picture-frame corner sagging under its own weight. Where the fastener runs crosswise to the pull, the load runs across it, the way a river runs against a bridge piling.

  5. Withdrawal: the straight pull.

    The second is withdrawal — the straight pull-apart. The towel bar hauled toward you every morning. The lid pried upward. Where the fastener points along the pull, the load runs its length, trying to draw it out of the wood like a splinter. Lever a bar or a rail and the far fasteners feel this hardest.

  6. The nail forgives sideways.

    Now the nail. Fast, cheap — and in shear, brilliant. Framers nail a wall together, and a nail under sideways load is a steel pin that would rather bend than break. Under shock, under the seasons, it forgives.

  7. Smooth shanks surrender to the pull.

    But a common nail's shank is smooth, and a smooth shank holds only by the wood clamping around it — the fibers squeezing the steel they were driven past. Pull a nail straight and that grip surrenders by degrees; there is a reason the claw on your hammer makes the job look easy. Don't ask a plain nail to resist a straight pull for years.

  8. Threads are shelves cut in wood.

    Now the screw. Its threads are a spiral of small shelves cut into the wood — and against withdrawal, those shelves grip like a rooted thing. It is also reversible on purpose: what a screw joins, a screwdriver can un-join without wreckage.

  9. Hard snaps where soft bends.

    But hardness is bought with brittleness, and many screws — especially the hardened ones — have made that trade. Under a sharp sideways shock a screw can snap clean where a nail would have bent and carried on. Hold both in your hand and the screw feels stronger. Against shock, it is often the weaker one.

  10. Good glue can outmatch the wood.

    Glue is another creature altogether — and across broad, well-mated faces, in the right conditions, it is the strongest of the three. A good glue line on a properly fitted face can outmatch the wood beside it: force the joint and the wood itself often tears before the glue lets go.

  11. Glue bonds what already touches.

    But glue dictates terms. It wants surface area — long grain mating flat, not end grain butted. It wants clean bare material, the right glue for the stuff being joined, and clamp time while it cures. And ordinary wood glue is no gap-filler. Some adhesives are formulated to bridge a gap; the bottle on most shelves wants contact. It bonds what already touches.

  12. Sideways, nail. Pull, screw. Faces, glue.

    And now you can read any joint like a sentence. Load running sideways: nail it — or bolt it, if it is heavy or may someday need to come apart. Load pulling straight out, or both at once — a hinge, a bracket, a drawer front: screw it, into solid wood or a stud, not bare drywall. Broad faces mating, grain running the same way: glue it — and often glue and screw together, the glue to carry the load, the screws to clamp the cure.

  13. Not weak. Mis-assigned.

    Here, finally, is why things wobble. A joint set against the wrong direction loses its argument a little every day, and every rock of the chair reams its hole a little rounder, which loosens the joint, which deepens the rock. Most often the joint was never weak — it was mis-assigned.

  14. Wood breathes with the seasons.

    Remember too that the wood is alive to the seasons — it swells in the damp months and shrinks in the dry, and nearly all of that movement runs across the grain, not along it. So never pin a wide board tight at both edges; leave it room to move, or it will make room by splitting. Some winter creaks are only the house breathing.

  15. The pilot hole disarms the wedge.

    One habit prevents most of the grief: the pilot hole. Before driving a screw near any edge or end, drill a hole narrower than the screw's solid core — the shaft inside the threads, not counting them. Wood splits because the screw arrives like a wedge; the pilot removes the wood the wedge would have shoved aside, and leaves the threads their bite.

  16. Say the direction out loud.

    Here is your bucket to carry home. Before your next repair, say the load's direction out loud — sideways, straight out, or both — before you touch a fastener. Then find the one wobbling thing in your house, and re-fix it this week by matching the fastener to the pull — unless it holds a person: a stair rail, a grab bar, a gate at the head of a stair. Those get the hardware their maker names. A glued chair joint gone loose wants its old glue cleaned out and fresh glue in — a gap-filling glue if the rocking has worn it slack — not a nail.

drawn from

Where it comes from, and where it stops.

Drawn from: plain mechanical fact as the USDA Forest Products Laboratory's Wood Handbook sets it out (FPL-GTR-190, public domain) — shear versus withdrawal loading, the smooth shank's friction hold versus the thread's mechanical grip, glue joints exceeding wood strength across properly mated long grain, seasonal wood movement across the grain, and pilot-hole sizing.

General home-repair education, not a substitute for a builder or the hardware's own instructions. Anything that holds a person — a stair rail, a grab bar, a gate at the head of a stair — goes in with the hardware its maker names. For the wood facts behind a fastener or a glue joint, check the USDA Forest Products Laboratory's free Wood Handbook.

read alongside it

From the shelf.

As an Amazon Associate I earn from qualifying purchases. The commission costs you nothing and bought none of these; the whole shelf is on the reading page, and how that works is on the about page.

  1. Understanding Wood: A Craftsman's Guide to Wood Technology — R. Bruce Hoadley

  2. Structures: Or Why Things Don't Fall Down — J.E. Gordon

  3. Why Things Break — Mark Eberhart

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