THREADING IN WOOD Using a Turning Jig

THE SCREW

Screw a. A cylindrical rod incised with one or more helical

or advancing spiral threads, as a lead screw or worm screw.

b. helical form of the inclined plane, a simple machine for elevating object

c. – f. definitions in the colloquial form (need not be listed here)

HISTORY, THE BEGINNING?

Thought to be invented about 400BC by Archytas of Tarentum

One of the first applications of the screw principle was in presses for the extraction of oils from olives and juice from grapes. The oil presses in Pompeii were worked by the screw principle.

HISTORY

Berson's French Lathe, built in 1569

HISTORY

The construction of the screw thread depended upon the eye and skill of the craftsman. Advances on this occurred in the eighteenth century. Antoine Thiout, around 1750, introduced the innovation of equipping a lathe with a screw drive allowing the tool carriage to be moved longitudinally semi-automatically. Screws with fine pitches are essential in a wide variety of instruments - such as micrometers. To construct such a thread a lathe was essential. Jesse Ramsden in 1770 made the first satisfactory screw-cutting lathe.

HISTORY

Thread-Cutting Machine using a "Master Screw.“ Circa 1770

THREADING JIG

Thread-Cutting using “Master Screw” cutting Jig

MASTER SCREWS

Selection of master screws

THREAD FORMS

There are several common thread forms: American Standard - 60˚ thread angle Metric - 60˚ thread angle British Standard Whitworth - 55˚ thread angle ACME - 29 ˚ thread angle used in lead screws of

machine tools

THE CUTTER

There are a line of commercial cutters available 60˚ angle

Home made “Fly Cutter”. Constructed from an Allan wrench

MAKING A “FLY CUTTER””

Grinding a fly cutter Grind the cutter to a 60˚ point. Rake angle about -10˚ Clearance angle about 15˚ or greater

THE MATH

Calculating the depth to cut.

Formula: 𝐷𝐷𝐷𝐷𝐷 = 𝐷𝑃𝐷𝑃𝐷 = 1𝑡𝑡𝑡

∗ 0.64033

PLANNING

Determine the size of the tenon and mortise Male side:

Diameter of outside minus thread cut depth x 2 = core diameter (red)

Female side: core diameter of male side (red)

SETTING UP

Setting up the Cut

RUNNING THE CUT

The cutting operation

FINISHED PRODUCT