Sharpening edged tools involves two processes: grinding and honing. Grinding is done in the workshop with a machine sandstone, bench grinder or file. Honing is done with a stone, of which various types are available. Honing of most tools is done in the workshop, but tools used for cutting herbaceous growth, such as scythes and grasshooks, need honing in the field.
Cutting edges
The sketches opposite show various cutting edges in cross-section. An obtuse edge is often assumed to be blunt, and a fine edge to be sharp. In fact an obtuse edge can, and should be sharp, and a fine edge can, and should not, be blunt. (Note that ‘obtuse’ should not be taken in the strict geometrical sense, but merely as a contrast with ‘acute’.) Of the examples sketched, only bluntness is always undesirable.
An acute edge will cut soft material, such as grass and other herbaceous growth, extremely well. It is particularly effective when drawn across the material like a knife, as when scything. However, it is a very fragile edge. If used percussively, like an axe, it is liable to fold over or crumple. It also drives deep without splitting the material, and is thus easily wedged in a wooden stem.
An obtuse edge is not particularly effective with a knife action, though it will still cut a finger open, but it is very suitable for axes and some types of billhook. It is a durable edge, with the mass of material behind it lending strength at the moment of impact. An obtuse edge often runs onto convex cheeks, so that wood is forced apart vigorously without keeping a large area of metal pressing onto the wood cleft, and so binding.
A hollow-cheeked or concave blade has in exaggeration many of the properties of a fine edge. It usually arises as a side effect of dressing with a grinding wheel, and is not often seen in conservation tools.
Convex cheeks may arise unintentionally as a result of lazy sharpening. A lot of metal has to be removed to sharpen a blunt fine edge. The temptation is to improve the edge but with less grinding by making a more obtuse edge.
This is not always a bad idea. A reasonable strategy is to be slightly lazy on most occasions, doing enough to keep the edge sharp, and then removing the developing shoulder occasionally with a grinding wheel or coarse file. The important thing is not to let it get out of hand, particularly if no grinding wheel is available.
Equally importantly, avoid overenthusiastic acute grinding on edges which are supposed to be obtuse and/or convex-cheeked.
New tools are often supplied without proper edges. This is deliberate, as sharp edges are both dangerous and liable to damage in transit. It is for such tools that a grinding wheel is most needed, and it may be worth hiring one as necessary if many new tools need dressing. Thereafter, hand-held stones are quite adequate for normal sharpening, if proper care is taken when the tools are in use.
Responsibility for sharpening
You should have a definite policy about who is to sharpen tools. It is tempting to regard sharpening as a lot of hard work, and enlist as many helpers as you can to get the job done. However, proper sharpening requires time, skill and good workshop facilities. Incorrect sharpening by an untrained person can wreck an edge in a few moments, and restoration can take hours of hard work.
Ideally, after a day’s work in the field, one or two trained people should give the tools a quick ‘brush-up’ sharpening before storing, putting aside any which need further sharpening or grinding. Once slightly blunt, tools get blunter much more quickly, and sharpening becomes a difficult and time consuming job. Then in addition train a few enthusiastic volunteers to make an effective team, who can organise special sessions to undertake tool sharpening and other repairs.
