Copyright JWPopp 10/2006. REV: 05/2007. May not be reproduced for profit, nor without credit to the author.
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The "Scary Sharp" Honing Method
(From a forum contribution of mine)
SiC Paper, Float Glass, Honing, Stropping Alternates, Angles, and Secondary Bevel
It seems that this gets into discussion several times a year. Gonna post this soon as a web page. Not encyclopedic, but defensible as a method. Lots of folks practice this and many may have more sophisticated ideas. This isn't intended as an invitation to an opinion brouhaha. Hopefully, it will help newbies and perhaps confirm a useful idea or two for older hands. (That doesn't mean you can't criticize what I've suggested - it just means be nice when you do it....)This addresses chisels, but with but minor modifications, this same system serves to flatten and square hand planes, and to sharpen their blades. See Jeff Gorman's outstanding articles with instructions regarding fettling and use of hand planes. (I'll be posting one even more comprehensive one o' these days...)It takes lots of words to say how it works, but bear in mind that the whole idea is to practice a very fast, accurate, consistent and effective method, and at reasonable cost. Who wants to spend forever sharpening, or to sharpen poorly?
It's my firmly held opinion that dull tools are dangerous. If it's a cutting tool, then it's safest when it's sharpest. A sharp cutting tool requires less force and invites fewer accidents. (Of course, if you're terminally clumsy, then a different line of work might be advisable.)
Why Scary Sharp?
There are many old-timers who fuss that the old ways were always good and there's no point in progress. Uhhh - this old-timer understands that:
- stones become quickly out-of-flat and are difficult and messy to restore;
- stones need to be replaced;
- float glass is inherently flat;
- scary-sharp doesn't wear the glass;
- scary-sharp uses cheap and replaceable abrasives;
- use of a honing guide ensures accuracy and absolute repeatability and conserves time, energy, and steel.
1.) SiC PAPER
Just for reference, Amazon sells good SiC (silicon carbide wet or dry) paper for $12 per 50 - about $0.24 per sheet. The link is as usual overly long, so I'll just suggest that you go to Amazon and search on "wet or dry sandpaper" - it'll come right up. Sure beats $1/sheet at the hdwe store.
I suggest ordering about 3:1 of coarser versus finer grits. My own experience is that through 2500 is *really* a fine edge - one which will degrade quickly in heavy service. (I also infrequently use 5000 and 9000 - - that is, about 5 micron and 0.5 micron.) There's a lesson - somewhere between 600 and 1500 is a good place to hone for everyday work, except for the super-fine light paring blades. (Finer honing is definitely perceptible in hand working, but soon lost under striking conditions in hard material. Personally I nearly always go to 2500 because it's fast and easy, and is always better so long as I ain't a-beatin' on 'em.) It's not efficient to skip grits, as it just takes that much more work on the next finer to remove past scratch marks. I find that 5-10 fast strokes for each grit gets there in about less than 10 seconds per grit, including changes.
A little experience will let you set your own working standard. Nothing is sacred, and there's no point in huffin' argument. This is a good method, and you can extend it to whatever level of refinement best suits your particular working style.
Heavy removal for flattening or nick removal will require 120-220 grits, and will consume them quickly. (I will use as coarse as 60 or 80 for the purpose, but would suggest gaining a little experience with less aggressive grits before making more work for yourself with the deep scratches inherent to use of very coarse grits. Stated otherwise - " if the scratch is deeper than the nick, then you're going backwards.") Once surfaces are correct at those grits, then refining through finer grits is very fast, and consumes much less paper.Routine: 120 then 220 to shape and flatten Then: 400, 600, 800, 1000, 1200, 1500, 2000, 2500 Then maybe 5000, 9000, and finish with green stick and palm-slap (see below.)Point of Order: With a good, fast system, edge maintenance becomes simple. I personally prefer to use a top-quality honing guide such as the Veritas MK2 to ensure simple and speedy matching of honing angles. My chisels are top quality, and I foundnd that I spent about 30-50% of cutting time in resharpening. (Not 30-50% of the time in the shop but 30-50% of the time the chisels were actually cutting.) Planes ditto. This faster method reduces time and makes it less of a chore to tune 'em when they need it! If honing is fast and easy, then likelihood of keeping edges tuned up rises dramatically - for most of us, anyway.
CAUTION: The much-vaunted Klingspor self-adhesive roll SiC paper is useless for this, as its backside layer of adhesive is uncontrolled with huge variations in thickness. Avoid it. Wetted SiC will self-adhere if you don't work it too hard. Trick - soak it in your preferred cutting fluid for an hour or two before use so the back can pick up enough liquid to form a capillary bond with the glass.
2.) FLOAT GLASS
There's nothing exotic about float glass, although it's an important part of the method. Something over 90% of all the flat glass produced in the U.S. is "float glass", produced by the float method in which glass rolled "close to flat" at plastic temperature is introduced to a furnace containing a bath of molten tin. The tin's surface is naturally dead flat and hot enough to melt the glass to liquid; the molten glass floats on top and tends to layer out at perfect and uniform thickness - flat both sides. Many glass shops don't even know that's what they stock (honest!) - sometimes it takes a little asking to be sure that's what's being sold every day, but the stuff's as common as dirt and certainly affordable.
1/2" is ideal, just because it has the strength to withstand a little knocking about. Be sure to have the edges and corners fully radiused - that is, they need to be sanded (at the glass shop) in the usual everyday manner so as to minimize the potential for chipping when accidentally struck with the tool you're sharpening. Note that glass is flexible - too thin and insufficient support can yield bizarre sharpened edge shapes.
Tempering isn't a good idea, as it involves heating the glass to plastic temp and rolling it again, which tends to introduce surface irregularities which destroy the float's inherent flatness.
Bottom line: Just get a hunk of 1/2" standard annealed glass with the edges sanded as though for shelving or tabletop. (Homework: get 'em to confirm that it really is float glass.) I attach the little clear self-adhesive buttons every 3" or a sheet of Home Depot's self-adhesive cork so I can easily set the glass down and get it back up again.
I use 12x12 for nearly everything, although I do also have 12x18 and 12x30 to fettle longer plane bodies.
WD40 is a good cutting fluid, but it's stinky and not good to breathe for long periods. An open door, etc., is a good idea. (I have given myself emphysema over these many years by generally ignoring such minor safeguards. Live hard, learn hard.) Water works extremely well, but is harder to manage from the standpoint of not ruining whatever is under the glass. With water, a hand held hair dryer or heat gun can be used to heat both top and tool so as to promote full evaporation.
I don't much care for the idea of using a saw table, etc., as the mounting surface for paper, because
Personally, I'd sooner replace a hunk of glass than the saw table. I do use my ground saw extensions ( with plastic sheet and 2 layers of newspaper) as the base for the cushioned glass. Be sure to remove the lot as soon as you're done so as to reveal and correct any unforseen leakage thru the plastic.
- that ground surface isn't as good as it may appear to be
- the process necessarily releases some grit which can (will!) erode the mount surface.
I regularly mirror-polish 3 base surfaces plus the sharpened bevel. The cutting edge is affected by:
Flattening the underside and edges should be a one-time event, save for repair of inadvertant damage. (If edges aren't also polished, then the corners are always suspect and frequently flaky.) I flatten and polish just those three at least through 1500 grit, then polish them with green (chromium oxide) rouge on a cloth wheel. Once that's done, the polishing wheel never again strikes the bottom of the chisel until/unless damage is being repaired, as I want for that surface to remain as flat as possible.
- the underside,
- the two vertical sides
- the sharpening bevel at the line where all 4 come together as the cutting edge.About the underside surface:
It takes a terrific amount of work to get the entire underside flattened and polished (more below) - too much to bear repeating in response to unthinking actions. I try to avoid doing anything that might upset all that work!
Since every operation affects the edge, I always perform secondary operations first, and end finally at the secondary bevel in this order:
- Edges: Grind, hone, polish
- Underside: Grind, hone, polish
- Primary bevel: Grind
- Secondary bevel: Grind, hone, polish
Obviously, a well-kept tool will require only step #4 to remain in tune, the #3 and #4 as the secondary widens.
There are those who love the tools that are polished 6 ways from Sunday. They are undeniably pretty, but the only surfaces that actually benefit from polishing are those that form the cutting edge. Side bevels and other chisel body parts are extremely smooth in the hand at 400-600 grit, and I personally see no point in going further with them for any reason other than braggin' rights.
I'd never strop the underside after sharpening. No matter how fine, underside stropping must inevitably cause an unwanted back bevel (because the strop isn't a rigid, hard surface) that will interfere with the tool's operation.A secondary bevel is placed in addition to the sharpening bevel on the blade's topside, with benefits as below.
A back bevel is an accident on the underside of the blade and is likely to ruin the blade's usefulness. Back bevels must be worked out by grinding away the sharpened edge until the exposed back is again flat.
Once the 3 adjacent surfaces are done, then the sharpened bevel may be addressed. Although it may be honed somewhat haphazardly by feel (the macho old-fashioned way I did it for 40 years before scary sharp arose), the only good way to ensure efficiency and accuracy of honing (& re-honing) is to use a good sharpening jig, such as Veritas'. Run through all of the intended grits. Don't worry about underside burr - it gets progressively finer with each grit.
When all the intended grits have been applied, turn the blade underside-down on 2500 or 5000 paper, hold it dead flat, and pull it backwards an inch or two to (almost) polish off the final burr. Be especially careful not to lift the handle, as that will create a back bevel and destroy all of your careful work.
At that point, I run the bevel ONLY across the green polishing wheel - never the underside - and I'm careful to keep the wheel's contact line up in the bevel and away from the actual edge. Fiber distortion in the wheel will provide adequate contact along the edge. It's still likely that a microscope could reveal an infinitesimal burr, which can be removed by the ancient and time-honored palm-slap method. (Balance and ease-of-motion will come quickly, but don't get cocky and speed up too soon lest you slice yourself silly.) Just hold the tool so that the underside will strike the palm of the opposite hand when the tool body is rotated slightly downward, and the sharpened bevel will strike the back of the hand on the return up-stroke. Up/down, up/down, slap/slap ... with the holding hand imparting just a bit of complementary rotation .
Additional description: This slap-slap-slap etc. action is performed repeatedly as the chisel rotates in about a 90deg arc up and down. Hands are held at the same level, perhaps waist high. The struck or target hand is held flat, horizontal, and palm up. The striking hand holds the tool underside down at about its midsection, and rapidly (after you learn how) rotates the chisel over its length so that the sharpened edge first strikes the palm and then the back of the struck hand. Rotate the struck hand slightly and in alternating direction so that each strike allows the sharpened edge to slide off. This tiny bit of skin-stropping really will remove any remaining burr, and provide a finer stropping than any leather-and-compound method. I can strike a pace of about 4 slaps per second if not distracted, and will slap myself - er - I mean it - for about 30-60 seconds. (Get back in your cage - it's the blade I'm talking about...)
The various chisel types are assigned increasingly steeper angles in anticipation of more and more vigorous work. A 35 degree angle will virtually always work, but a 20 or 25 will makes paring much easier. (Paring chisels are never struck, and amount to little more than "knives with long handles.") You will undoubtedly develop your own preferences. My regimen is:(Although a steeper angle will always work, I find that my own hands are particularly sensitive to nuance as the blade moves, and I genuinely prefer the variability in feel with varying angles. Not everyone agrees. There's no point in adding work you don't care about - find your own preferences and stick to your guns.)
Paring: 15-20 degrees, + 3 to 5 degree secondary Bevel Sided bench: 25 degrees, +3 to 5 degree secondary Firmer or Registered: 30 degrees, secondary optional Mortising: 35-40 degrees, secondary optional (Skew chisels are inherently designed for hand work, and I thus choose to sharpen mine as for paring.)
5.) SECONDARY BEVEL:
The Secondary Bevel (or microbevel) allows for quicker interim honing, as only a tiny area is worked at one time. It saves time, in that the primary bevel may be ground (honed) coarsely and therefore faster, with only the secondary refined through extra fine grits. It might grow to 1/8" wide (pretty big), but is most useful at around 1/16"to 3/32" Lee Grindinger convinced this old skeptic to try them, for which I'll be forever grateful. At work, they don't mean hooey (other than honing speed) when the chisel's right-side-up, but when the chisel is turned upside down for delicate hand paring or trimming, the secondary bevel imparts a tremendous added degree of sensitivity and depth control. Such an edge blurs the distinction between traditional carving gouges and bench chisels, as should be the case.
If you have but one set of chisels, then a 30-35 degree grind with a 3-5 degree secondary bevel may provide about optimum performance for you.
The secondary bevel should show as a polished line no more than 1/16" to 3/32" wide. When subsequent honings make it over about 1/8" wide, then it's time to re-hone the entire bevel until the secondary is sufficiently narrowed.
Why do it? Honing speed. Honing speed. Honing speed.
6.) GRINDING METHOD:
There are as many approaches as practitioners. Once upon a time, I took great pride in being able to freehand grind a single hollow across the width of a blade - any blade. Straight. Square. On a grinder. Not easy. Me Tarzan. Heap big expert 50 years. Of course, the angle was close to something possibly useful, but its control was nonrepetitive. There's no question in my mind that precise repetition of grinding and honing angles pays dividends in "no surprises" performance if the chisels are much used. Besides, ya tend to use up an awful lot of perfectly good steel in teaching yourself the one-line-grind technique ...
There is rational (and true) argument that a flat bevel is stronger than one hollow-ground. It's unlikely that you'll ever actually turn a hollow-ground edge, but flat-grinding at the correct angle may solve that problem, should it occur. I flat-grind as a preferential matter of course because the engineer in me can't stand the thought of having one micropeapod less than absolute available strength whether I need it or not. So who's anal-retentive?
There's no point in polishing the entire bevel surface. I'll leave it fairly rough at 120 - 220, and use the finer grits on the secondary bevel only. That approach makes it fast to "grind" the entire bevel at coarse grit, and equally fast to hone the tiny secondary.For planes, the leading edge of the chipbreaker should also be polished so as to minimize friction against the shaving's movement. Don't believe it? Try it!Point of Understanding:
I view machine grinding as an emergency operation used in case of an "Oh, woe" accident and serious nicking of the blade. Once angles are established, I anticipate "grinding" solely with coarse paper.
Finally, though this method is a relatively quick way to develop extremely fine edges, it's not instantaneous, and losing an edge to accident or abuse remains painful. In my own practice, chisels receiving this degree of attention are not carried around the house in a metal tray for weekend projects, nor do they perform any rough-in work. They're protected as well as is practicable with rubber floor mats in the work area, and restraints on the benchtop. (I keep a set of beaters plus an all-steel rough-in set for the bull work.) NO ONE gets to borrow my planes!
Storage can be an issue. Some folks like wall-hung racks, but in my neck of the woods, any fine steel left hangin' around will rust in a heartbeat. I prefer a closed cabinet or drawers into which I can toss a mothball to minimize/prevent oxidation. Hard Paste Wax (Johnson's is one) is an automatic and generously used part of the care-and-feeding routine. So are dividers to keep the edges separated from one another -- duh. I'm not partial to oils, as they attract dust and have the potential to soak into the sacred workpiece.
8.) BACK FLATTENING:
Almost fergot ta mention flat back philosophy, which may or may not meet with agreement. For what it's worth:
Some say to flatten only the end 2 or so inches of a chisel's underside. I disagree, from the standpoint that on the occasion of needing to actually follow a guide block to maintain a specific angle, any back only partially flat is going to rock and therefore will not yield the desired cut plane.
Rather, I flatten the entire length (only has to be done once), but with extra firm pressure at the business end to impart an imperceptible taper. As a result, the entire back is made planar, but only the last 1/2"-3" are actually polished and free of scratch marks.
If the underside has any cup (seen often enough from overly aggressive grinding by the manufacturer), I only flatten until all of the cupped area is showing perhaps 50% contact. Also there must be an area extending back 1/2" or so from the edge that's entirely flat and polished. The approach ensures that the cutting edge is sharp and straight and that the entire length of the chisel's back will follow a guide, but doesn't require excessive removal of material at the time of initial fettling.
As length is gradually eroded from honing, the cupped or non-polished area may require a bit of additional flattening, but will require less effort than it would had the work been accomplished at first pass.
I Hope some of this interminable rattling-on was useful for you, and wish you good luck!