Sharp, Very Sharp & Frighteningly Sharp……
(when the hair jumps off your arm in fright at the approach of the sharp blade)
Jim Davey Feb 2014
Whether it be hand tools or power, we can’t do good woodwork without sharp tools. Sharp tools will give a better finish, require less effort, whether it be pushing a plane or chopping a joint with a chisel. Producing more precise joints resulting in more accurate woodwork. (also: less risk of slips and accidents which means – less blood in the workshop).
There is little difference between high and low quality tools if both are dull. So money spent on quality tools is wasted if they are not kept sharp. As the old saying goes: “You only cry once when buying quality tools”.
Bevel Side, of Blade: Side which is Ground and Honed. (Not called Front of Blade)
Face, of blade: Flat Side (sometimes called the Back – incorrectly in my opinion)
Bevel can be a single flat face or several faces including hollow grind and honed facets
Grinding Angle: Angle at which Bevel Side is Ground. Either Hollow Grind or Flat Grind - hollow grind is pictured.
Honing Angle: Angle at which the Bevel side is honed. Angle at the very point of the blade.
Can be 2-5o greater than Grinding Angle or in case of “heel-toe” honing, same as Grinding Angle.
Hone or Secondary Bevel: Sometimes a third angle is added to save time. Honing may be at 5o greater than Grinding, then a Micro Bevel Hone on finer Stone at 1-2o extra
Back Bevel: 1-5o Honed on the Face side of Blade. Not for Chisels, only Plane Irons. Used in two situations: when Face is too difficult to flatten and polish. Also when greater approach angle is required in a bench plane, as in York Pitch, for hard to plane, difficult grain woods.
Included Angle: Honing angle + Back Bevel angle = Included Angle
Approach Angle: In Planes, angle of blade relative to the wood. 45o for Bench plane, 22o + Honing angle for Standard Block Plane, (maybe 47o), 12o + Honing angle for Low Angle Block Plane, (maybe 37o).
Most tools for woodworkers are ready to use – right out of the box, except for Planes and Chisels which require honing prior to use, even premium planes such as Lie Nielsen require some work.
A Plane is only as good as the Blade in it.
The 4 “R’s”
- Ready – to Prepare a new Blade
- Refresh – a quick hone to refresh the edge
- Regrind – when the hone area gets too big and takes too long
- Restore – overhaul of an old abused, neglected or damaged Blade
Equipment for Sharpening
- Hollow Grind with 2880rpm 8”/200mm Bench Grinder – 6”/150 is too small as it will create too much hollow, especially when it wears, and reduce strength at the Tip. This is a “normal speed” grinder and there is a risk of burning the steel.
- Hollow Grind with 1440rpm 8”/200mm “slow speed” Bench Grinder – the slower speed reduces the risk of burning the steel.
- Hollow Grind with 10”/250mm water-cooled slow grinder. The blade holder is cumbersome when used with woodworking blades. The water cooling will eliminate the risk of burning but the grinding is slow and the wheels are slow to dress (clean and true).
- Flat Grind with “high speed” grinding wheels or abrasive discs – risk of burning the metal. The rotary action will pull and twist the Blade and produce a Tip which is not square
- Flat Grind with “slow speed” water-cooled grinding wheels. No risk of burning but usually slow.
- Hollow Grind with a Hand Cranked Grinder. Less risk of burning than “high speed” Grinders but it can still happen. Relatively quick grinding.
Whatever is used, the wheel should be kept clean and true.
- Oilstones. Aluminium Oxide, Silicon Carbide, natural stones such as Arkansas
- Waterstones. Either natural, man-made, Japanese, American.
- Diamond Plates. Monocrystaline or Polycrystaline. Depending on quality, some are flatter than others.
- Abrasive Paper glued to glass or other flat surface. Silicon Carbide “wet and dry” glued with thin spray contact adhesive.
- Abrasive particles, carborundum or diamond, loose on a flat surface. This will not produce a flat face as the particles will cut more at the edges than the middle.
- For more info on Equipment, see extra notes on p.5
What is sharp? Perfect intersection (meeting) of two polished surfaces. The finer the polish – the sharper the edge. This Sharp is different to a Butcher’s Knife which has very fine serrations which slice the meat.
There is no “wrong” way to sharpen, just better ways. Better in that they may be quicker, less wasteful, easier – different methods suit different people and different applications.
To create a sharp edge or to refresh a dull edge, we must move metal – hardened steel. Remove the metal around the damaged area to expose a new, fresh cutting edge. This extraneous metal is removed by “cutting” on an abrasive surface. For chisels and plane irons, it works better if the abrasive surface is flat.
There are many choices of abrasive medium:
- a block of natural abrasive (such as Arkansas stones)
- a block of bonded abrasive in a man-made block (such as Norton stones)
- or can be loose abrasive particles (such as silicon carbide or diamond) on a flat surface (such as granite, cast iron or even MDF).
The choices are wide and various but whatever we choose, the process of sharpening - of moving the metal - is the same. We start with a coarse grit and go down through the grit sizes or up through the numbers. Whatever we do to one face – we must do to the other, so if we aim to finish at #1000 (Japanese) then it must be both faces. If we want a finer edge then #6000 or even #8000 must be done on both faces. For an extremely sharp edge – use extremely fine cutting compound such as chromium oxide which has a particle size of 0.5 micron (very, very fine). Why do we go that fine? The finer the edge – the finer the surface finish of the wood and the easier it is to use the tool.
Essentials for Sharp Tools:
- The Abrasive Surfaces must be Flat.
- Use the entire surface with an even pressure.
- Do to the other side what has been done to the first side.
#1 - FLATTEN THE STONE: Before any Sharpening – make sure the Medium is flat. Slight Convex or Hump is OK but Concaved or Dished Stones must NOT be used.
§ Grey Oil Stones (Silicon Carbide) are extremely difficult to flatten.
§ Brown Oil Stones (Aluminium Oxide) are softer and easier to flatten with Silicon Carbide paper (wet ‘n dry) glued to a flat surface, or use an old Diamond Plate – do not use a new diamond plate as it will cause premature wear of the plate. Use Kero as a wash to remove sludge and rubbish.
§ Arkansas Stones and soft Oil Stones same as Brown Oil Stones.
§ Waterstones can be flattened using Silicon Carbide paper glued to glass using water as a wash. About 120# for Medium Grit Stones and 180-240# for Fine Stones. Stones usually need flattening because of dishing in the middle, either flatten the entire surface or, quickly flatten the ends and use these flat surfaces for the backs of small chisels, then flatten again. This will save flattening time and also save some stone – the high spots are being used to good purpose rather than being washed down the sink. Another method is to rub similar-gritted stones together under a dripping tap – 3 stones or surfaces are needed to produce a flat surface. Some sharpeners find this produces a fresher surface than when using Wet ‘n Dry, one answer would be to give the stone a few rubs with another stone after flattening on the Wet ‘n Dry. A third method uses the Dressing Stone sold by Waterstone Suppliers, After Flattening, abrade a small chamfer on the edges by passing a couple of times at 45o on the Wet ‘n Dry. This will reduce crumbling of the edge.
§ Note: even though abrasive paper glued to glass is flat when the paper is new but it usually wears in the middle and thus dishes and then puts a hump in the Face of the Blade.
#2 - USE THE ENTIRE SURFACE – EVEN PRESSURE
To lessen the chance of hollowing the stone:
§ Keep the Blade flat on the Stone.
§ Use an even pressure on the Stone – same for forward and back strokes - firm but not too hard – let the Stone do the work.
§ Use the entire surface of the Stone – use a pattern which moves across the Stone as well as going over the ends.
#3 - HONE BOTH SIDES TO THE SAME LEVEL
If the bevel is honed superfine on 6000# but the Face is only 1000#, the resultant edge won’t be much better than 1000#. So the Face must be polished to 6000# if the bevel is finished to that level of polish.
When breaking in a new blade or restoring on old blade, rather than spend a lot of time polishing to 6000# for a super edge, a utility edge can be reach in a short time by abrading on coarse then medium 1000# on both sides. Each time the edge is refreshed, go a bit finer until the required level of polish is achieved. This way the blade can be used in utility situations earlier if it goes through full polish to a super edge.
Flatten and Polish the Face
Very important for Chisels. Need a flat Face for accurate work.
Plane Irons only need a few mm of flat, polished area so that the underside of the Back Iron can contact perfectly. So if the Face of the blade is hollow – leave it, no need to polish that hollow out. It will gradually work out as the Tip is ground back and the Face is honed over the years.
A hump can also be removed by using a Saw Doctor’s Pecking Hammer on the bevel side of the blade to remove the hump, may even create a hollow. Or use a Die Grinder (Dremel) to carefully remove some of the excess metal.
A flat surface is required for flattening the Face. Start with coarse grit and gradually work finer. Working at an angle, say 45 degrees, the coarse grit will create lines, work from the other side of the stone to remove those lines and create a new set of lines. Alternate from side to side until all imperfections are removed and the entire surface is lined. Then go on to a finer grit and repeat until the lines from the previous grit are removed.
Tip: Finishing each grit at 90 degrees will produce a set of lines across the blade which makes it easy to see when they are eliminated during the following grit. Work through the grits until the desired level of polish is achieved.
A very fine edge is required for accurate work but not so necessary for utility work.
Tip: Save time by half finishing the blade – maybe only go to medium stone, use it, resharpen, use, and go a bit finer each time it is sharpened. After a while the blade will have a fine edge and the task will not have been so arduous.
Back bevels on Plane Blades have advantages:
- It takes too long to flatten the Face of an old blade with rust pitting or one with a convex, humped blade from honing on a dished stone. An easy shortcut is to create a very small back bevel on the Face. 1-2mm is all that is required. 1-5o back-angle. 1o won’t affect normal planing, 5o is advantageous for hard or cranky wood.
- To increase the approach angle when planing difficult grains. Some of the old English and Scottish planes such as Norris and Spiers were available in 45o, 50o or 55o angles. The HNT Gordon Plane (Aus.) has an approach angle of 60o .
For 1o, place a thin strip, such as a steel rule, along one edge of the stone to raise the tool up. When polishing 50mm from the strip – 1mm will give 1o, 5mm will give 5o etc.. Note: Don’t use your favourite steel rule as the graduations will wear – use an old worn rule or a thin strip of plastic.
For Block Planes with 22o bed angle – anything from 5-10o on the back then hone front to give desired included angle. Only 5o for Low angle block planes which are usually 12o bed angle.
Grinding angles – 5o less than honing angle
Honing angles - 30o is a good all round angle
25o for parring
25-30o for block planes
30o for chisels and plane irons
35o for heavy chisels and planing cranky or very hard wood
40o for very heavy mortise chisels
Micro Bevels – 1 or 2o higher than Honing angle.
Grinding is done to save honing time. A small area at the Tip only needs to be honed. The larger the area, the longer it takes to hone so honing the entire Bevel area is time wasted. Grinding removes metal quickly so grind most of the Bevel and just hone the very tip – 1/2mm is all the honing needed.
Rough grind flat or hollow.
Hollow grind on a stone no smaller than 200mm – any smaller makes the hollow too deep and reduces strength at the tip. Some sharpeners prefer flat grinding for this reason. Flat grind by machine or by hand on a coarse stone. Manufacturers recommend that Japanese chisels should not be hollow ground.
If machine grinding without coolant, hold the tool with a finger or thumb up near the edge so the temperature can be monitored. Let cool when uncomfortably hot. Do not dunk in water, best to let air-cool, micro cracks can form if dunked in water.
Grey wheels (Aluminium oxide) - for Mild Steel or Cast Iron,
White, Red, Blue (Aluminium oxide) - for tool steel, (high carbon steel, high speed steel)
Green wheels - for Tungsten carbide.
For Chisel and Plane Iron Tool Steels: 38A80-H8VBE is ideal, but any from 60 – 120 Grit is OK
A is for Al. Oxide,
80 is the grit,
H is the Grade (hardness of Grit),
8 denotes Grain spacing,
V means Vitrified Bond,
BE denotes a modification to the basic bond. A80 is important as well as H8V, the rest is flexible.
Wheels should be kept true and dressed using a diamond or carborundum dresser – dull wheels rub more than cut which will burn the steel and lose hardness. During grinding, the steel should never be allowed to blue, straw colour is the limit before loosing hardness.
One grind will be good for many hones. Each honing will deepen the area being honed until the honing takes too long, then regrind leaving a tiny amount to hone. No need to go all the way to the tip unless a chip is being ground out, just go 1/16th from the tip.
Grey Stones – silicon carbide (hardest of all) – difficult to maintain flat
Brown Stones – aluminium oxide – less difficult to maintain flat
Arkansas Stones – coarse, medium white and hard black – easier to maintain flat
India – Norton trade name for aluminium oxide
Wachita/Washita – Another trade name - Norton
Waterstones – usually Japanese but some made in USA. Some are natural (very expensive), some man-made. Easy to maintain flat.
Diamond Plates – monocrystalline and polycrystalline. The better ones are usually monocrystalline. The better ones are flat but must be used “all over” to continue to be flat otherwise they may dish in the middle like any other stone.
Note that Japanese grit numbers differ from US numbers which differ slightly from English/European. They do wear out, the cheaper ones very quickly and are false economy.
Silicon carbide powder or paste on a flat surface such as glass, granite etc
Diamond powder or paste on MDF
Polishing compound such as Chromium oxide, Rouge, “Autosol” on leather, wood, MDF etc. for that final mirror finish.
Note that leather strops produce a slight rounding at the sharp edge; which may be excellent for carving tools because it helps the tool come out of the cut, but this curve will increase the honing angle which is not wanted for Plane Irons and Chisels.
Lubricants (Wash) – not really a lubricant but more as a Wash to remove the excess filings and rubbish so that the pores of the stone don’t clog. It is important to use something and not to sharpen dry .
Oilstone: Light Oil, Kerosene or a mix of the two. Don’t use heavy oil (Engine oil) or Neetsfoot Oil as they will clog the Stone.
Arkansas, Wachita or India: Light Oil, Kero or Water.
Diamond: Water or Kero.
Waterstone: Water only.
“Scarey” Sharp System
Uses “Wet and Dry” paper (silicone carbide) on a flat surface, such as glass. As with all sharpening – go through coarse, medium to fine with paper grades of #120, #240 to #600 and finer if required. The flat surface doesn’t have to be glass; it can be anything which is flat. Make sure to use the entire paper surface otherwise the surface will hollow in the middle and the resultant blade will have a hump.
Care of the Stone
Look after your stones and they will look after you.
Grey (Silicon Carbide) stones are difficult to flatten – better to “use” the corners and ends rather than try to flatten out any hollow in the middle.
Brown Al. oxide stones are easier to flatten but still difficult. Use an old diamond plate and Kero as a wash.
Waterstones are probably the easiest to maintain because they are the softest. The coarser the grit – the softer the stone. (It may actually be softer but it seems that it is easier to form a hollow in the middle).
Waterstones can be flattened using paper glued to glass. #120-220 grit. (Use spray glue rather than double sided tape as the tape can compress resulting in a surface which is not flat). Then use water to wash away the mess. Some sharpeners rely on the water to adhere the paper to glass but the paper can lift at the corners so the surface is not flat and the result is not flat.
Store Waterstones in water to avoid distortion. (If they do dry – don’t flatten when dry, soak for 30 min.s then check for flatness – they can reform back to flat state when wet). Not absolutely necessary to store the finer grits like #6000 in water all the time but should do for #1000.
The use of a guide takes the guesswork out of the angles and creates accurate precise edges. The absolute minimum of steel is removed to recreate that fine edge, thus saving time at each sharpen and also saving steel, so time and money is saved. Good steel is expensive, smart sharpening will extend the life of the tool.
After honing, a few sweeps on the back to remove any remaining burr and finish the job.
Free-hand Hone of Bevel
Is OK for those that have practised for years but for most of us it is easier to use a guide. The old thick blades are the easiest to hone freehand using heel-toe method. Freehand tends to wear the centre of the stone because the user is reluctant to go over the edge so concentrates on the centre.
1. Place the Blade on the Stone with Toe and Heel of Bevel both in contact. Don’t change the angle – hone Toe and Heel together. This will ensure the contact angle stays constant. When the honed facets get larger and close to meeting, then it is time to regrind. This method is really easy on very thick Irons – 3/16”/5mm.
- Place the Blade on the Stone same as above but this time raise it a little to increase the angle then hone. Recheck the angle often to maintain the correct honing angle.
Straight – general purpose
Rounded corners – smoothing
Light Crown – smoothing
Heavy Crown – scrubbing
The oil from Oil Stones is enough but if using water as a wash, extra precautions should be used.
Inox, CRC Longlife, Lanotec, Tallow, are all good – G15 seems to be best. It doesn’t stay wet but leaves a thin, heavy, protective film. WD40, RP7 or CRC may disperse a little water but have very little rust prevention qualities. Take extra care with cast iron as it is much more susceptible to rust than steel, especially if the surface is sanded or ground.
Old, oil-clogged stones can be cleaned with Thinners.
Sharpen often, don’t leave it too long – the edge will take much longer to restore.
Enjoy your tools and keep them sharp,