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What are knife, pippin and auriform files?

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Image of the edge of a knife file Knife, pippin and auriform files are machinist’s files characterised by a thin ‘knife’ edge.
Image of a keyhole which has tight internal angles and is therefore best deburred by a knife or pippin file The extremely acute angle of this ‘blade’ makes these files very versatile tools. They can be used to smooth and deburr tighter internal corners than three square files.

What are the characteristics of knife, pippin and auriform files?

Diagram of a wedge-shaped cross section

Cross section

Knife files have a wedge-shaped cross section.

A kitchen knife which lends its name to knife files They are easily identified, because they look like knives!
Wonkee Donkee jokes about eating your dinner with a knife file
Diagram of a pippin file cross section Pippin files have similar cross sections to knife files, but the face opposite the knife edge is rounded and double cut.
Image of some apple seeds, which lend their name to the pippin file thanks to their shape Due to the shape of their cross section, these files are also known as apple seed files.
Image of a V-shaped groove being created by a knife file Knife and pippin files can be used to create narrow v-shaped grooves and slots.
Image of a key with notches that have been cut by a pippin file Pippin files can also be used to create the rounded notches in a key that allow it to open a lock.

For more information, see: How to clone a key with a pippin file

Diagram of an auriform cross section Auriform files are almost identical to pippin files, but one of their straight faces is rounded.
Image of an ear, which the auriform file is named after The word ‘auriform’ means ear-shaped, which is where the file got its name.
Filing a concave surface with a half round file Thanks to its wide, curved face, auriform files can also be used to file concave surfaces.
Image of a knife file showing cut and outline

Profile

Knife, pippin and auriform files all taper in both width and thickness.

Diagram showing the type of cut on each surface on a knife file

Cut

Knife files are double cut on both faces, single cut on the ‘knife’ edge and safe on the remaining side (back).

Image of a pippin file showing cut and outline Pippin and auriform files are double cut on all faces except for their ‘knife’ edge, which is single cut.
A screw with damaged thread that will have to be repaired with a knife file The single cut knife blade on any of these files can be used to clean out and repair damaged screw threads.
An indication of the range of lengths in which knife files are usually available

Length

Knife files are usually available in lengths from 100mm (4 inches) to 300mm (12 inches).

An indication of the range of lengths in which pippin files are usually available Pippin files are produced in fewer sizes, ranging from 150mm (6 inches) to 200mm (8 inches).
An indication of the range of lengths in which auriform files are usually available Auriform files are usually 133m (51/4 inches) long.
American and Swiss flags, illustrating that this type of file is made in either American or Swiss pattern

Swiss or American?

Knife files can be either Swiss or American pattern.

Flag of Switzerland - home of the Swiss pattern file invented by F. L. Grobet in the 19th Century Pippin and auriform files are Swiss pattern files.

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