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Craft Knife: Doniger's Hinged Handle and Reversible Blade
Sundel Doniger · Public domain (expired patent)
Forge

Created by

Forge

26. October 2026NO
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Craft Knife: Doniger's Hinged Handle and Reversible Blade

A knife for model carving and fine cutting, by Sundel Doniger of New York, founder of X-Acto (US 2,463,682, filed 1945, granted 1949). The handle is two shell-like metal halves pivoted at the rear. A thin blade with a slot in its middle drops over a small 'staple' pressed out of one half; closing the other half pushes a tongue into the staple and locks the blade solid. Swing it open to change the blade or turn it end for end: the spare end rests inside the handle. The patent gives no sizes or metals. Mild steel sheet, the rivet, the spring steel blade and the sizes are ours. The picture: Figs. 1 and 2 of the patent.
Intermediate
1 day

Instructions

1

Mark out the two handle halves

Scribe two mirror-image halves, about 130 mm long, on mild steel sheet about 0.8 mm thick (ours). Give each a flat rear ear for the pivot and a nose at the blade end.

Materials for this step:

Mild Steel SheetMild Steel Sheet1 piece

Tools needed:

ScriberScriber
RulerRuler
2

Cut and file the halves

Cut both halves out with tin snips and file the edges smooth.

Tools needed:

Tin SnipsTin Snips
Metal FileMetal File
Bench ViseBench Vise
3

Dome the grip, keep the ends flat

Hammer the middle of each half into a shallow bulge over a hollow in a hardwood block. Leave the pivot ends flat, so the pivot cannot wobble, and leave the noses flat.

Tools needed:

Ball Peen HammerBall Peen Hammer
Hardwood BlockHardwood Block
4

Form the blade wall and its shoulders

On the mounting half (10), the nose is a flat wall (14) in the plane where the halves meet. Turn its top and bottom edges inward into shoulders (15, 16) just as far apart as the blade is wide.

Tools needed:

Flat-Nose PliersFlat-Nose Pliers
Ball Peen HammerBall Peen Hammer
Bench ViseBench Vise
5

Press out the staple

Slit the middle of the wall along two short parallel lines, lengthwise. Press the strip between the slits outward to form the staple (17).

Tools needed:

Cold ChiselCold Chisel
Center PunchCenter Punch
Ball Peen HammerBall Peen Hammer
AnvilAnvil
6

Bend the locking channel

Bend the nose of the locking half (11) into a springy channel: a broad rear flange (19) about the size of the wall, and a front flange (20) with a tongue (21) and a cut-out (22) each side of it to clear the staple's legs.

Tools needed:

Tin SnipsTin Snips
Needle File SetNeedle File Set
Flat-Nose PliersFlat-Nose Pliers
7

Drill the pivot

Clamp the halves together, punch the centre of the rear ear and drill through both.

Tools needed:

Center PunchCenter Punch
Hand DrillHand Drill
Bench ViseBench Vise
8

Rivet the pivot

Rivet the flat ends together (Doniger used an eyelet; ours: a steel rivet). Close it firmly: the friction of the flat ends must hold the halves wherever you swing them.

Materials for this step:

Steel RivetsSteel Rivets1 piece

Tools needed:

Riveting HammerRiveting Hammer
AnvilAnvil
9

Anneal and cut the blade blank

Soften a piece of spring steel strip about 0.4 mm thick (ours), as in the connected spring-steel blueprint. Cut a blank as wide as the gap between the shoulders.

Materials for this step:

Spring Steel StripSpring Steel Strip1 piece

Tools needed:

ForgeForge
Forge TongsForge Tongs
Hardwood AshHardwood Ash
Tin SnipsTin Snips
Welding GlovesWelding Gloves
10

Cut the centre slot

Cut a slot (18) in the exact middle of the blank that fits closely over the staple. Drill its ends and file out between them.

Tools needed:

Center PunchCenter Punch
Hand DrillHand Drill
Needle File SetNeedle File Set
Bench ViseBench Vise
11

Shape both points

Cut each end of the blank to a slanting point, as in Fig. 1, and grind a cutting bevel at both ends.

Tools needed:

Tin SnipsTin Snips
GrindstoneGrindstone
Metal FileMetal File
12

Harden and temper the blade

Harden the blade in oil as in the connected spring-steel blueprint. Temper it to the knife colour given in the connected heat-treatment blueprint, not to spring blue.

Tools needed:

ForgeForge
Forge TongsForge Tongs
Rapeseed OilRapeseed Oil
Welding GlovesWelding Gloves
13

Hone both edges

Hone both ends keen on the sharpening stone.

Tools needed:

Sharpening StoneSharpening Stone
14

Fit and lock the blade

Swing the halves open. Lay the blade flat on the wall, its slot over the staple and its edges between the shoulders. Swing the locking half shut: the tongue enters the staple and the channel grips the blade. No tools needed.
15

Reverse or change the blade

Swing the locking half up, lift the blade off the staple and turn it end for end, or fit a new one. The spare end sits protected inside the handle.
16

What the patent says, and what is ours

The patent fixes the parts and how they lock: hinged shell halves, flat riveted pivot ends that hold by friction, a wall with shoulders and a pressed-out staple, a slotted double-ended blade, a springy channel with tongue and cut-outs. It gives no sizes, no metals and no blade making. All sizes, the mild steel, the rivet and the spring steel blade are our choices. Doniger's better-known X-Acto knives hold the blade in a round collet instead.

Materials

3

Tools Required

21

This blueprint makes

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Craft Knife

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