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Knurled Worm Gear for an Adjustable Spanner, Thread Cut to the Rack
The worm of an adjustable spanner is a short screw on a pin: its thread engages the rack on the movable jaw, so turning it with the thumb opens or closes the jaw, and its rim is knurled for grip (Haist, US 2,112,840, 1938). This one is turned from mild steel, its thread cut on the lathe to the pitch of the jaw's rack. Method and sizes are ours.
The picture: Haist's patent drawing.
Advanced
Half a day
Instructions
1
1
Measure the rack
Measure the rack
Measure the pitch of the teeth on the movable jaw's rack with the pitch gauge, and the height of the opening the worm sits in.
Tools needed:
Thread Pitch Gauge
Digital Caliper 6-Inch2
2
Turn and bore
Turn and bore
Chuck the mild steel bar, face it, turn it to the worm's outside diameter, and centre-drill and drill it through for the pin.
Materials for this step:
Mild Steel Bar1 pieceTools needed:
Metal Lathe
Lathe Chuck 3-Jaw
Lathe Cutting Tool
Center Drill Set
Drill Bit Set
Cutting OilDigital Caliper 6-Inch
Safety Glasses3
3
Cut the thread
Cut the thread
Set the lathe's gearing to the rack's pitch and single-point cut the thread along the worm's length, testing against the rack until it runs smoothly.
Tools needed:
Metal LatheLathe Cutting ToolCutting OilThread Pitch Gauge4
4
Knurl the rim
Knurl the rim
Run the knurling tool lightly over the thread crests to roughen them for the thumb, without closing the thread.
Tools needed:
Metal Lathe
Knurling ToolCutting Oil5
5
Part off and fit
Part off and fit
Part the worm off a little short of the opening's height, file off the burrs, and check it turns freely on its pin in the opening.
Tools needed:
Parting Tool
File SetDigital Caliper 6-InchMaterials
1- 1 piecePlaceholder
Tools Required
12- Placeholder
- Placeholder
- Placeholder
- Placeholder
- Placeholder
- Placeholder
- Placeholder
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