How often do I need to "lap" my Coticule?

Many synthetic hones tend to glaze rapidly with abraded metal debris, sticking to the surface. Regular cleaning is required, to reclaim the full performance of the hone. Coticules, however, do not glaze. They are non-porous and therefor metal particles have no recesses to stick on to.

Another reason for lapping whetstones, is to reinstate a trued flatness. Yet it is not necessary to be persnickety about such flatness. For the honing of straight razors, that need perfect edges, because no razor can bluff its way through a shave, tests did not reveal any advantage for a mathematical flatness over a trueness "at first sight".  For chisels, gouges, and other tools that have a way of wearing a transverse hollowing into a hone (as opposed to longitudinal hollowing caused by sharpening razors and knives, lapping needs to be done at slightly higher frequency. The wear rate of a Coticule depends on its purpose: sharpening chisels being one of the more eroding tasks and sharpening razors the least eroding. If you adhere to a few habits to keep your hone flat within good reason, depending on its purpose of use, it may stay serviceable during its entire lifetime, or only rarely demand lapping. These habits are:

1. While raising slurry, spend extra time on the far ends, notably the corners of the hone. Secondly, concentrate on the "high" spots. They can be identified because you'll feel less resistance rubbing over them. At the lower spots, the rubbing stone will suck itself to the hone.

2. If possible don't use the hone in the same direction during the regular slurry stage of honing. Once you arrive at the "refining" stages, do keep the stone oriented in the same direction. (You don't want slight variations introduced in you honing at that point)

Should the Coticule arrive at a state where the out-of-trueness affects the quality of the resulting edge, it is time to lap.

There are several viable options:

1. Lapping with a dedicated lapping plate and abrasive powder, usually carborundum.

2. Lapping with a diamond hone in the 100-400 grit range.
Rub the lapping hone and the Coticule together under a slow running tap.

3. Lapping with sandpaper (in between 100 and 400 grit) on a known flat surface.
This can be done dry or wet. For dry use, spray-glue the sandpaper to a flat surface, and rub with the Coticule over it. Brush the sandpaper clean regularly.
For wet use, stick moistened sandpaper to a slick surface and work under a slow running tap.

To control for flatness, draw a pencil grind on the surface of the Coticule and check if you can remove the entire grid with just a few lapping strokes.

Last update on 2010-08-15 by Bart Torfs.

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