CliveE: Chisels and planes need to be extremely sharp in order to work properly. They are both sharpened in the same way (but for a plane you'll need to turn the blade at an angle if it is wider than your oilstone so that the whole width is sharpened each pass.)
The business end of chisel blades usually have two angles - a ground angle of 25deg finished off with a honed angle of 30deg at the very tip. If a blade has been abused and has chunks missing it will first have to be reground on a grinding wheel before any attempt is made to hone it. If you don't have your own grinder then a tool shop may be able to do this for you. Another alternative is to use a small electric grinding machine or a drill attachment which can usually also hone the blade by swapping the grinding stone for a honing one. (Some can also make a rough attempt to sharpen a limited range of twist drill bits.) Note: it is very important to keep the blade cool. It's rather easy to overheat the steel thus ruining the temper.
Chisels should be re-honed before every job. Final honing is best done by hand, using a honing guide and a fine grade oilstone (or water or diamond whetstone) before every job. Decent honing guides are available for less than a tenner and have wide wheels which do not damage the stone. Oil the oilstone. Insert the chisel into the guide, set for a 30deg angle. Pull the blade over the stone several times until a burr is raised on the top side. Remove the chisel from the guide, turn it over and lay it flat on the stone. Rub it from side to side until the burr has gone. Finally, protect yourself and your chisels by keeping them in a soft leather tool roll (costs less than a fiver!).
Personally, I prefer silicon carbide wet and dry paper for sharpening chisels. Find something really flat, a 6" square of plate glass is ideal but an off-cut from a kitchen worktop works surprisingly well too. Clamp the chisel in the honing guide and start working it on fairly coarse (say 180 grit) paper. If there are bad chips or nicks in the edge which means you need take a lot of metal off consider starting with something even coarser. Work through finer and finer grades of abrasive until it is as sharp as you need (at least 600 grit). I sometimes go as fine as 1200. The most important thing is to make sure that you lap (flatten) the back of the chisel with as much care as you hone the bevel (front edge). If the back is not flat and finely polished you wont get or keep a decent edge.
I've got the Stanley sharpening guide which is used in conjunction with an oilstone to sharpen chisels and plane blades. I find it reasonably easy and I'm not particularly well endowed with practical ability.
First you must restore the primary bevel which if I recall correctly tends to be about 20 degrees. First use the coarse side of the stone and grind until you have a perfect bevel, then turn the chisel over and lightly remove the burr. Then repeat the process with the fine side of the stone, just removing enough material to get a fine finish. Once the primary bevel is OK you grind a secondary edge at 30 degrees. Use only the fine side of the stone. Remove the burr.
The result is a chisel which is plenty sharp enough for me. Fanatics will insist that back and bevel need to be mirror polished but they obviously need sharper tools than I do. [Note: Piers is using a two-sided "combination" oilstone here].
Get a good school metalwork or Engineers handbook and learn first of all about the required angles for cutting, clearing swarf etc and methodology employed to sharpen metal cutting tools. I've seen some absolute abortions produced by otherwise quite intelligent people when they decide to "sharpen" a drill etc. Somehow it never seems to occur to them to look at a new drill before ending up with something like a needle point and wondering why it won't cut anymore.
Dormer and Osborne both do very good little booklets on angles, speeds, feeds etc for drills, mills etc. although they do not always agree with each other. I suggest getting one of those and including the details [of the books] in the FAQ. [Editor's note 2002, see Dormer Tools site under Regrinding menu for online data].
By Tony Williams
All cutting blades need a backing-off (or clearance), lathes, drills, etc.
Take a drill bit, hold it at a fixed angle to the grindstone, and rotate it. It will produce a nice conical pointy bit, and a nice cutting edge..... BUT, at that instant the metal behind the cutting edge is parallel to it, [ ] there is no clearance. Try to use that drill and it will just rub and overheat. The backing-off behind the cutting edges has to be carefully put in as a separate grinding operation.
A fine backing-off (A is small) produces a drill that cuts clean holes, with minimum chatter, but with a tendency to overheat if pushed too hard. It needs patience to use.
A coarse backing-off gets a drill that cuts fast, but with a tendency to grab and chatter... oversize rough holes.
You have to judge what to do according to the material being drilled... for example, brass grabs and snags, so anything less than minimum backing-off is lethal. Indeed, it is even quite useful for brass to slightly blunt the cutting edge with a slip-stone.
In the larger drill sizes it is quite handy to have a varying backing-off.... almost nil near the point, so that it remains steady, increasing near the edges.
I was taught to back off the drill by first setting the cutting edge, then sweeping the edge up the wheel whilst turning it about 30 degrees. Easy to do but very hard to narrate...
By Rick Hughes
Backing off ... hmm difficult to explain.
If you took a drill and held it at angle X to a rotating grindstone, and then keeping the angle the same turned the drill. You would have a lovely spear point on the drill but it would not cut anything ... it might burn through wood.
What you need is that the leading edge of the cutting face of the bit higher than the trailing edge, that way the leading edge cuts into the material, and the part of the drill immediately behind it is not in contact with the material, allowing swarf to come away and avoiding friction.
There are jigs that change the angle of the drill as you rotate them, which is the professional way to do it. Unfortunately not many people have these.
Most fitters will do this by eye, first rotate to get a smooth clean face all round at the correct angle, then one face at a time line up the cutting edge to just be touching the grindstone, then rotate, altering the angle of the drill to grind away a clearance. Only needs a degree or so on hand drill sizes.
As to the angle - like the drill point angle itself this depends on the material you are going through and the thickness of it. i.e. if you were to drill soft thin sheet, you need a flat drill bit angle with little clearance - otherwise it will corkscrew into the work when it breaks the other side. For thicker and harder material, points can be more acute and also more clearance.
By Charles (Joe) Stahelin
Unless sharpening techniques have changed since 1941 when I deserted an engineering apprenticeship for other things I think the business of drill sharpening is something that can only be learned by demonstration combined with explanation. There is a bit of turn and swing involved rather than just grinding a simple angled face. I have tried to do it in recent years but I have lost the 'touch' and get less than perfect results.
By Dave Plowman
I agree, Charles. I've never been able to make a satisfactory job of it, and I guess few will. One of those 10 quid add-on-to-your-drill-thingies is well worth it for the larger sizes, but even they need *some* practice.
By Elron Hoover (aka "Dave")
I agree, 'tis a bugger to get right, but the results are worth it once you do.... I always had good results on those large, slow, water bath grinding wheels; the fast bench grinders are ok but you have to go for the finest grade of wheel.
I'd be interested to know the kind of angles you'd expect to find on set of HSS jobber twist drills.
By Andy Wade
The angles I was taught for O-level metalwork many years ago are:
- point angle 118deg. (59deg. between drill axis and cutting edge)
- clearance (behind cutting edge) 12deg.
Rake angle is predetermined by the flutes and can't be changed. Freehand grinding is quite easy to learn - practice on the larger sizes first so you can see what you're doing. It's very important to make sure that the two cutting edges are equal in length, otherwise oversized holes will be drilled.
In fact I was told some years ago that if you wanted drills sharpened in a 'good' engineering works, you were asked by the toolmaker (sharpener?) how many thou oversize you wanted the hole to be!
Would it not be much easier to direct interested parties to the Dormer Handbook or, with their permission, lift the section on drill the sharpening part? [Roger quoted the angles in the news posting but they are not reproduced here for reasons of copyright] The Dormer book also has illustrations. And in all honesty I have to say that despite all this guidance I rarely get a good result. Drill sharpening is a knack which some of us may never learn.
By Elron Hoover (aka "Dave")
Yep,,, that's the way to do it...after a few, or many, attempts at it, it finally comes right,,, and you wonder what all the fuss was about. :)
To which Dave Plowman replied:
True. And all those 1 in long drills are very useful for tight spaces. ;-)
My sharpening experience would be in the field of wood-working tools (chisels, plane blades etc.) as well as domestic knives , scissors, hedge clippers etc.
The first tool I learned to sharpen was a scythe. (We used to use them to clear thistles from meadow fields) This was done dry with what we called a sharpening stone . (A carborundum stone about 12" long , oval in section and tapering to each end. Posh ones had a wooden handle). The scythe was sharpened by alternate strokes to each side of the blade and could be got alarmingly sharp. A similar tool and method was/is commonly used to sharpen domestic knives though I've known people to use a sandstone window sill or threshold stone. The sharpening stone was quite coarse so presumably left the edge a bit ragged (microscopically speaking). I presume this suited the slicing type cut used with scythes, sickles , knives etc., a point validly made by Donald [see below].
Axes and hatchets were also touched up with a sharpening stone. A file or rasp would have been used to remove any nicks , and establish the basic angles.
Regarding wet systems there basically two. One is oil based and the other is water based. Stones designed for use in the oil based systems are just that, designed and made to be used with oil. This is why they are known as oil stones! Years ago when hand tools were more in use in workshops all the old timers had their own favourite oil stones and recipes for lubricants. All claimed almost miraculous properties for their own favourites and some made a big thing about secrecy regarding their own lubricant recipe. There would be mention of paraffin oil, engine oil cut with paraffin oil, neat's-foot oil (a light yellow oil obtained from the feet and shinbones of cattle, used chiefly to dress leather) with some type of thinner, cutting oil obtained from machine shops etc. etc. Every protagonist was convinced that he and he alone had the "right " system. It was a sure way of brightening up the tea break if the apprentice asked for advice !
Water stones are similarly designed and manufactured to be used with water. (While I have known people like carpet fitters to sharpen their "Stanley" blades with a small slip stone and a bit of spit I always put this down to convenience and the desire not to soil the carpet with oil.)
The structure of the two stones is fundamentally different to allow for the differing fluids being used.
Japanese water stones are relatively soft so that in their usage they wear easily and are constantly exposing fresh grit. They are soaked fully in water prior to use and the surface is further flooded with water before sharpening commences and kept flooded. In use, being so soft, they wear rapidly, and this wear means that a fresh cutting surface is constantly being exposed while the copious amounts of water wash the old particles away. This makes them very fast cutting.
Man made oil stones differ in that they are designed to allow the oil lay more on the surface thus keeping the microscopic particles being ground off in suspension, and the stone free cutting. Water alone used on these stones would be too thin and run off the surface. They should be cleaned after use and stored in a box to ward off dust etc. They really only become clogged up if abused.
(There is now a belief that the fluid only slows down the sharpening process and that India type stones can be effectively used dry, but only if they have been used dry from new. If oil has once been used then it will be necessary to continue using it, I have never tried this myself.)
Relative newcomers to this market are Diamond stones (used either dry or with water depending on which manufacturer's advice you take). Very effective and quick but also quite expensive.
Ceramic stones, which are used dry are another newcomer. Reports I've read place them between Oil stones and Diamond based products as regards effectiveness. They would also fall between these two in their price.
Japanese water stones are currently my favourites for chisels and plane blades and kitchen knives.
"Scary Sharp" is a much touted American system of using waterproof wet and dry automotive paper. Starting with a coarse grade of paper, fixed to a very flat surface ( a piece of plate glass is ideal, and I have found the paper will adhere simply via suction after wetting the glass and conditioning the paper in a container of water for a short time). You can go as fine as you want with the paper grades depending on the application. It is very effective.
Easily available machine based systems would be the ubiquitous bench grinder and the various water wheel devices such as Tormek. The bench grinders are not too expensive but really need to be used with care as their high speed means they can "Blue" a blade frighteningly fast. (Blueing occurs when the blade is allowed to overheat and thus have its temper drawn. The only cure is grinding back beyond the blued section, which will not hold an edge effectively, and starting anew.) The water wheel systems use a grinding stone which runs in a water bath. They revolve quite slowly and obviously run no risk of over heating the tool edge. Some such as the Tormek can have various accessories affixed them to facilitate differing sharpening operations. Regrettably price raises its ugly head here as they can be quite dear. I have a Tormek which I use no where near as much as I thought I might, only using it when a blade needs its primary bevel renewed. Between times the secondary bevel is formed with a Japanese water stone.
With regard to sharpening chisels, plane blades etc., the objective is to get two perfectly flat surfaces meeting at the required angle. The first step would be to flatten the back of the blade and progressively polish it by going through the grades of stones available, or wet and dry silicon carbide paper if following "Scary Sharp" methods. Only when this is achieved can one start on the other side. A primary bevel of 25 to 30 degrees should be established and then a secondary bevel of about 2 1/2 degrees more can be formed. This secondary bevel can be re-established easily many times before the primary bevel would need re done. There are many proprietary aids to this process, each having there own strengths and weaknesses. This is a very brief description. The appended web site addresses or a good book such as Jim Kingshott's "Sharpening, The complete Guide" published by the Guild of Master Craftsmen should satisfy those needing a more in depth approach.
If asked, my advice for a neophyte would be a double sided ("combination" - two grit grades) India stone as a starter. It will do all the average user will require, if a little slowly. If more is desired then a double sided Japanese water stone, with the addition of a very fine stone later, if the ultimate edge is wanted, will serve admirably.
Never ever use oil on an 'oilstone'.
This stops the pores of the stone from becoming clogged with a congealed amalgam of crushed stone, metal swarf and dried out oil. It will keep the stone in tip-top condition and will remain 'sharp' for it's entire life!
(If you have a clogged stone, soak it over night in a strong hot solution of CLOTHES BIOLOGICAL washing detergent. You might have to repeat this a couple of times. Then never use oil on it again!)
This is contentious suggestion, especially to craftsmen with years of experience in oiling an oilstone. But please try it. It really does make a vast difference - I have used both methods and will never use oil again!
ALL oils will eventually dry out, dragging in the crushed stone & swarf into the stones pores. Thin oils could be worse in as much as they are more volatile and will dry out quicker.
If you use detergent/water solution as a lubricant all you need to do is a quick rinse in water and then put it away. They can dry out completely and no special needs to keep it 'wetted' with oil!
I have several carborundum stones which were my dads and have seen well over 50 years of service. Each one cuts metal as good as the day they were made. (Do you remember the delightful way a new stone 'bites' the metal - my 50 year old stone is like a new one every time!)
I use the same solutions on my 'India' stones that I use as a hone for chisels. It even keeps the slip stones 'clean' that I use for polishing small surfaces.
Place about quarter of a sheet of wet and dry on a very flat & clean surface and wet it with soapy water and sharpen the chisel or knife as if it were a proper stone! Use 240 grade to shape a very blunt/worn/damaged edge then sharpen with 400 grade. (scalpels can be honed with 600~800 grade). It is pointless to use finer grade than 800 because it in theory the edge of the blade is more perfectly formed, it will not 'cut' as well as an edge that has very slight imperfections. (The imperfections act like the teeth on a saw)
I always have a sheet of 400 grade in my desk draw with a small block of Formica covered ply. If I need to sharpen my pen knives, I use them with a goodly dollop of spit - instant sharpener!