|Sharpening - Overview|
|Microbevels front and back.|
|Use a jig.|
|Copyright (c) 2002-14, Brent Beach|
Sharpening involves two steps -- grinding and honing. Grinding -- except when necessary to correct edge defects -- shapes the tool by removing metal back from the edge. Honing removes metal right at the edge.
While grinding does not directly affect the cutting edge, correct grinding is crucial to the sharpening process. Honing using fine abrasives, removes only limited amounts of metal, but leaves a very smooth finish. Honing cannot remove enough metal to correct errors created by faulty grinding techniques. If you can't grind, you can't sharpen. Once you master grinding, honing is a breeze. You can find lots more about grinding here.
That leaves us with honing. Honing prepares the cutting edge by smoothing both faces at the edge and creating the desired angle between those faces. Honing involves only two factors - the abrasives used and the honing angle. Since you can easily use the best abrasives and the correct honing angle, you might as well. Anything else produces an inferior edge (and is probably more work).
You will have questions - the FAQ has the answers.
I have sharpened lots of plane irons and I am pretty comfortable with the jig and the abrasives on glass. I can sharpen any of the standard steels used in plane blades. All it takes me is a couple of minutes. In spite of all my experience, I cannot get a better edge than you can, if you use the same abrasives and jigs. I may sharpen a blade in 2 minutes where it will take you 3, but I cannot do it better than you. Watch the videos, try it a couple of times. You can get a great edge too.
This page is often the landing spot for search engines, so I want to make a couple of points right away to counter popular misconceptions.
Read on, the explanation of these and other facts about sharpening is in these pages.
Most new irons will have a 25 degree primary bevel and will be ready for honing. Any new iron that comes with a 30 degree primary bevel must be ground back to 25 degrees. Most blades that have already been sharpened by any other method will require grinding before honing.
Sheet abrasives are fine for honing -- removing small amounts of metal at the cutting edge. I don't use them for grinding, the removal of much larger amounts of metal away from the edge.
For grinding straight (rather than curved) edges, I use a coarse Silicon Carbide bench stone.
Before switching to bench stones, I was using a 1" belt sander. I still use it when grinding radiused irons and some badly nicked or pitted blades.
I almost never use a grinder, but here are a couple of tips on setting the tool rest angle when using a grinding wheel.
During honing we use a series of very fine abrasives working on the edge itself, to produce two very smooth planes (we hone both the front and back of a plane blade) which meet along a line of near zero radius. This level of accuracy is only possible with a jig.
To summarize, honing is done at the edge with only the finest abrasives. It is a mistake to use a coarse abrasive on the edge - it would nick the edge and shatter the underlying metal. It is a mistake to use a fine abrasive away from the edge - fine abrasives work too slowly and remove too little metal to be of any use except right at the edge.
The finest quality edge can only be achieved by using the finest and most uniform abrasive. Modern industrial abrasives are finer and more uniform in particle size than any naturally occurring abrasive. They are also harder and sharper. The FAQ includes a general discussion of abrasives.
For a given type of manufactured abrasive, quality depends on the uniformity of grit size, quality of the binder and quality of the backing. The very best modern abrasives are available in sheets from 3M. 3M calls them Micro-finishing abrasives.
Aside from abrasive quality the only other factor is flatness. Sheet abrasives attached to glass -- get the PSA (Pressure Sensitive Adhesive) form of the sheets -- are always flat. Bench stones and lapping plates require regular flattening -- are almost always out of flat. (A slightly out of flat bench stone is not a problem when grinding - as long as you grind up to, but not through, the edge.)
Aside from grit uniformity and hardness, the quality of sheet abrasives depends on the backing and the binder. 3M micro-finishing abrasives use high strength polyester film which do not degrade when soaked with a cutting fluid, as some paper or cloth backed abrasives do.
About the same time I switched from oil stones to sheet abrasives for honing, I developed a shop-made wooden jig that allowed me to consistently hone microbevels on both the front and back of a plane blade. By using consistent front and back bevels, I was able to design a plane blade test platform in which each test blade began with exactly the same bevels. This means that any variation in edge durability must arise from differences between the blades, not from blade preparation.
Using sheet abrasives on glass, with this simple jig, you too can achieve high quality edges consistently and quickly.
To get the best edges, you must build a jig and hone front and back bevels with each abrasive.
But I need a larger range of motion than the jig allows!
But my chisel is too short to use in the jig!
This page discusses a slanted jig design that you can custom fit to your requirements.
I developed my jig for use with sheet abrasives on glass. If you prefer to use bench stones (oil stones, water stones) you can still use the honing jig if you build this simple benchstone holder.
The bevel angle is determined by the distance from the front of the jig to the edge, what I call the blade extension. To calculate the extension for a particular bevel angle, you need to know the exact jig dimensions and the thickness of the blade. This page contains an extension calculator for any jig and blade dimensions.
This pages shows what you can expect to see - using actual size scans rather than 200X images - when you grind then hone a plane blade. The plane iron used is a New Old Stock Stanley blade.
The key to success is getting feedback from the bevels you are putting on the iron. Knowing what to look for is important. Find it in the pictures on this page.
Some people recommend stropping -- honing on leather or even wood, with or without a stropping compound -- after honing. If you use the system outlined in these pages, stopping is unnecessary and wrong. This page shows you why.
Stropping after honing on 3M abrasives is like slapping latex paint on your just finished arts and crafts table. The paint hides the errors if you built the table poorly, but hides the craftsmanship if you built the table well.
I use 3M Microfinishing abrasives. They provide superior grit uniformity and cutting ability at reasonable cost.
Natural abrasives cannot match the hardness and uniformity of these abrasives.
These abrasives can easily handle the hardest tool steels (M2, D2, CPM).
Sharply radiused edges - like scrub or moulding planes, turning or carving chisels - usually require other techniques.
In addition to explaining the parts of my sharpening system, I also discuss a number of other techniques that I do not use. A lot of common knowledge related to sharpening and plane irons is just wrong. Many sellers of replacement plane irons do not appear to understand how planes work. They make extravagant claims about the qualities of their products in comparison to other products. I suspect they have never done any rigorous testing of their products. The Jig Faq exposes some of these false claims. (It may be a good general rule that the more a company advertises the worse their product. The blade with the best results in my testing is made by Academy Saw Works. I have never found any advertising from this company.)
If you want to know the detailed reasoning behind microbevels, continue on.
If you want to know about wire edges (burrs formed at the edge during grinding or honing), continue on.
If you are wondering why your bevel up plane is not working any more, continue on.
There is lots more here. In fact, most of the pages in this web site lurk behind this link.
I have been reading the book Evolution of Useful Things, by Henry Petroski. Petroski has written many books about design of everyday items. This particular book discusses paper clips, safety pins, and other simple tools. He has written an entire book about The Pencil.
His point is that each new design arose because someone decided that current designs had limitations. An inventor found a way around some of those limitations, producing a more useful design.
You, readers of these pages, must have seen or experienced many limitations or inadequacies of the design of my jig.
For example, if you look through the Shop made honing jigs you will see jig designs that work with odd shaped chisels - see those by Tom Culver.
Another example, the range of motion of the jig. The original jig was small and the tool was held square to the face. This meant the range of motion was small. Honing is easier and produces a better result if the range of motion is larger. The solution was what I call the slanted jig.
What is the next stage in the evolution of the jig? It will depend on the perceived shortcomings. So, before I can evolve the design of the jig, I need to know the perceived shortcomings of the jig.
What prevents the jig from being more useful?
What do you see as shortcomings of the various jigs?
Send me an email with a design deficiency of these jigs and I will add that deficiency to the list here. Who know? Perhaps a new more useful design will result.
|You can email me here.||
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If you have any ideas on how to manage translations and versions of web pages, that would be helpful as well.
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