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What is a rasp’s coarseness?

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Image of machine stitched rasp teeth of a medium coarseness The term ‘coarseness’ refers to how rough or smooth the face of a rasp is. This is based on the size of the teeth and the distance between them.
Image to show that there are three different ways to measure the coarseness of a rasp The coarseness of a rasp can be measured in three different ways.

American pattern system

The American flag, representing American pattern files Some rasps will be listed as coarse, bastard, second cut, smooth or dead smooth in a similar way to files.

Teeth per row

Image to show how the measurement of teeth per row works when describing rasp coarseness Other rasps may be described as having a certain number of teeth per row. This refers to the number of times the triangular punch has been hit during each diagonal pass across the face of the tool.
Image to show a rasps with different numbers of teeth per row The higher the number of teeth per row, the finer the rasp will be.
Wonkee Donkee warns the DIYer that rasp teeth are measured per row, not per inch

Grades

Image to show the difference between grade 1 and grade 15 on rasps Rasps can also be measured in grades, from 1-15, with 1 being the coarsest and 15 being the finest. Grade 1 has a small number of large teeth on each row, whereas grade 15 has a lot of very small teeth.
Image to show that the majority of grade 1 rasps are used for industrial purposes Grade 1 is so coarse that it tends to only be produced for industrial use!
Image of a DIYer smoothing down a piece of wood with a rasp

Whichever system is being used, all you need to do is choose a grade, cut or number of teeth per row that will be fine enough for the finish you would like.

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