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How to Sharpen Tools - Introduction.

A right-handed person wrote the following instructions.

New awl blades, knives and edge finishers always require sharpening and polishing before use.

New leatherworking knives are usually supplied factory sharpened.
They will cut well enough and should have a correct bevel angle but may have a rough edge and an un-polished finish.
Do not accept this level of finish, spend some time making them SHARP and POLISHED to improve the quality and safety of your work.
Do the work yourself, if you send the tools away they will come back factory sharpened again and with a lot of the metal missing!
Sharpen your knives frequently, remembering that stropping IS sharpening.

A blunt tool is a dangerous tool.
If you have to use excessive pressure to make a cut you increase the risk of losing control of the blade.

A short Glossary.

A normal bevelA chisel bevel
Fig.1 - A symmetrical edge and a chisel edge.

The Bevel

Most of the sharp edges used in leatherworking take two basic forms, the symmetrical 'V' and the bisected 'V' also known as a chisel edge.
The angle of the 'V' is the bevel.
See Fig.1.

A second, sharper angle at the very edge of the blade is known as the micro-bevel. This holds the sharp edge. Chisel edges may not have a micro-bevel.

The Edge

Having perfected the bevel, polish out the scratches with progressively finer hones until the edge is truly sharp and the bead has been removed.
The edge is pulled away from the hone during this process. Once again check for dull parts of the edge glinting when inspected under a strong light source.

Clamping or jigging systems

These systems utilise clamps and blocks that ensure a consistent blade angle during sharpening.
The process is slower because setting up is required, but they are fool proof and encourage very sharp edges.
The jigs come with a set number of angles that may not match the bevel of your tool.

Steels

Steels do not sharpen by removing metal, they merely align the microscopic nicks of the edge and stop them dragging - this is called 'straightening'.
They are designed for use on large kitchen knives and are not suitable for use on leatherworking tools.

Silicon carbide papers (wet or dry)

A piece of wet or dry sandpaper glued to a wooden block is an inexpensive alternative to a stone.
When placed on plate glass it is ideal for sharpening bevel edges, especially the flat side.

Strops

Strops are used for polishing sharpened edges and removing the bead or burred lip from an edge.
A strop can be home-made by gluing a piece of vegetable tanned leather flesh side out to a piece of wood and then working a polishing compound into it (Silicon Carbide or Aluminium Oxide for instance).
Automotive fine grade valve grinding paste is good for this.
A piece of fine (600 grit) wet or dry carbide paper glued flat to the other side of the wood is useful for the polishing of chisel bevelled blades such as paring knives.

V sharpeners

These have a pair of steel or ceramic rods or wheels set in a wooden or plastic base so that they form a 'V'.
The knife is held perpendicular at the bottom of the V and stroked against the sides of the V.
They are a very quick way of sharpening edges during use, as they do not leave a burr.

STONES

Bench stones

These are usually rectangular (typically 50mm x 200mm) and will remove steel from a blade to form an edge.
Stones can be graded by grit numbers; the higher the number, the finer the stone.
Arkansas stones made literally of stone, water stones from Japan, ceramic and even diamond.
Ceramic and diamond stones aren't lubricated at all.
A bench stone will put as good an edge as is possible on a knife as long as the person using it has the skill and practice to maintain a consistent angle throughout.
My personal preference among the bench stones is for the diamond-covered models such as those from DMT. Diamond stones cut faster than the other types and require no lubrication.
Two stones, one coarse and one fine, will get the job done.

Arkansas stones

These require oiling during use to prevent fouling. They are hard, black and fall in the fine and extra fine categories of stones.
Originally quarried natural stone, they are now usually re-constituted grits.

Ceramic stones

Ceramic stones are made from aluminium oxide (alumina) or silicon carbide in a ceramic bond.

Diamond stones

Diamond stones do not require lubrication, but swarf removal is sometimes necessary with a pencil eraser. They come in all grit sizes.

India stones

Usually made of compressed carbide materials, they require oiling during use to prevent fouling.

Whetstones or Water stones

Before each use fully submerge the whetstone in water and wait until no bubbles no longer escape from the stone. This may take up to 20 minutes.
Use droplets of water during sharpening to cool the blade.
Water stones cut more quickly than oilstones but do not last as long. Usually formed from reconstituted aluminium oxides.
 

A short guide to tool sharpening.

A blunt edgeA normal bevel
Fig.2 - A blunt edge and a symmetrical edge
with micro-bevel.

Sharpening involves three distinct activities - Grinding, Honing and Stropping.

First the blunted bevel must be ground to the correct angles, then honing and polishing with finer abrasives perfects the micro-bevel edge.
See Fig.2.
A steeper bevel
Fig.3 - A new bevel at a steeper angle.
Finally, stropping removes the burr left by honing. After multiple stroppings and honings the bevel angle will be altered and the edge will not be as good.
See Fig.3.

It is essential to re-grind the bevel to the correct angle.
See Fig.4.
A re-ground bevel
Fig.4 - A re-ground bevel.
It is important to maintain a constant angle during grinding. The same applies when honing; a rounded edge will not cut well.
Keeping a straight edge is a matter of practise and not rushing the job. Items such as clothes pegs or paper clips can be clipped over the spine of the blade to act as angle guides against the sharpening stone.
The flat side of a chisel bevel should be flat. A curved edge will never be sharp and will impair the function of the tool.
The edge is generally pushed towards the grinding surface during this process. Use appropriate lubricants during grinding.
Once correctly ground the edge will have a 'bead' or burr of metal along it that can be turned from side to side with a hone or strop.
This bead can be felt by gently pushing a fingernail across the blade from the spine towards the edge. It is sometimes visibly shiny and bright when held under a good light for inspection.

SHARPENING EDGE SHAVES.

Blunt edge shaves leave furry, ridged edges that are difficult to rub and burnish.

Standard edge shaves

Polish the underside of a flat shave with a fine polishing stone.
This will cause a burr along the inside of the cutting slot that can be carefully removed using a piece of fine emery paper folded in two and pulled through the groove.
The cutting groove of an edge tool can also be sharpened using strong twine with a mixture of cutting oil and grinding paste applied.
Draw the twine through the groove, working away from the tool. It is important to maintain the correct profile of the cutting slot and not to enlarge it.

Hollow or Bevel edge shaves

The back edges of these are concave and require the use of specially shaped stones or folded wet and dry emery sheets. The grooves can be sharpened using twine as above.

KNIFE BLADES.

A blunt knife requires excessive force in use, causing poor results and nasty accidents.
Knife sharpening is an acquired skill and requires fairly good close-up eyesight, most people can master it with care and experience.
If you think a brand new factory-ground craft blade is sharp, try working it properly with a stone and strop, you may be amazed at the improvement.

It is usually best to maintain the original angles and relative sizes of any bevelled edges on your tools.
They have been designed for a reason, especially on paring or splitting blades that have only one bevelled edge.
With this in mind it is also important to maintain flat, even surfaces on your stones. With the tip pointing away from the body a right-handed person should start with the right side of blade. A left-handed person should start with the left side of the blade.

During sharpening prepare your stone's surface with oil or water if required to prevent scoring and overheating.
Lay the bevelled edge of the blade across the stone and tilt the blade experimentally until you feel that the bevel is perfectly flat on the stone.
For most leatherworking blades this will be an angle of between 10 and 20 degrees.
Draw the blade back and forth along the stone - maintaining the correct bevel angle at all times - until a burr is observed along the sharp edge or any nicks have been ground out.


Turn the blade over and do the same with the other side. The resulting burr will come off during stropping, which is the final process.
Try to use long, even and straight back and forth strokes, the angle of the bevel will be easier to control if you avoid circular or diagonal motions.

When placing fingers over the blade to steady it, stay on the part being sharpened and always stay within the confines of the edges of the stone.
If your fingers overhang the stone there will be a tendency to tip the blade.

HINT; use the strop to periodically hone the blade and keep it at its best.

Paring Knives and other chisel bevel edges.

It is usually best to maintain the original angles and relative sizes of any bevelled edges on your tools.
They have been designed for a reason, especially on paring or splitting blades that have only one bevelled edge.
The flat side of a chisel bevel should be flat. The flat edge can be ground against fine grade emery cloth on top of a flat glass surface.This gives a good polished finish relatively quickly.
A curved edge will never be sharp and will impair the function of the tool.

Using the strop.

The strop should be used regularly to maintain sharp cutting edges.

Stropping is the most frequent way of returning an edge to sharpness. It is often done before a cut.
A good strop can be made by gluing a piece of vegetable tanned cowhide - flesh side uppermost - to a flat wooden stick with a handle carved at one end. Please see our tutorial for further details.
Hold the strop with the handle towards you and the stropping area pointing away.
Taking care to get the proper bevel angle lay the blade on the strop with the sharp edge facing you and draw it away to the far end.
Without lifting the blade from the strop surface, tip the blade over and draw it towards you again. In this way the sharp edge cannot cut you and the small burr will be taken off.
If you are using a strop with carborundum paste keep it well oiled and loaded with grit. Carefully clean blades with a cloth after stropping or you may mark your leather.

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