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| Other questions |
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| Finest abrasives. | ||
| Microbevels front and back. | ||
| Use a jig. | ||
| Copyright (c) 2002-15, Brent Beach |
Now, that actually involves some work. People, always looking to make themselves more efficient, hope that they can reduce the effort in this step by using Marble, of some kind.
Marble - the naturally occurring mineral - is unsuitable. It is too soft and almost certainly not flat. As you hone on a non-flat surface you will cut the abrasive paper.
Marble - the tiles found in building supply stores - can be anything. Given the variety of tile types that get named marble, it is impossible to guess whether any given piece is suitable or not.
Granite - the kind used in countertops and in headstones - can be flat. It is however heavy and may not have the same friction qualities as glass. It is crucial that when you rest the jig on a slip, moving the jig back and forth brings the slips along with it. That does work on glass. It does not work on plexiglass. It may not work on granite or marble.
If you have some tiles (or some other surface) around you want to try, you will need to make three tests:
To take all the guesswork out of the surface on which you stick your honing abrasive, buy new plate glass from a glass store.
In the fall of 2005, an Oldtools list member mentioned that he has been waxing the blade as well! Now, generally I sort of avoided the blade when applying wax to the sole, thinking that getting wax into the workings of the plane was probably a mistake - just a tidiness issue.
The person posting mentioned that he planed a wax block (beeswax and carnauba), getting a few flakes on the blade.
It seems to me that waxing a blade, or using any technique that reduces the friction between the blade and the wood, will lower the temperature at the edge. Temperature is a major factor in blade wear -- the only factor for a given type of wood. This has to be a good idea.
I would like to perform a controlled series of experiments comparing waxed and unwaxed blades. If you have any ideas on how to wax the blade, or how to control for waxed versus unwaxed blades, let me know!
A pixel is a point in a computer graphic image. All the images I get on the QX3 are rectangular arrays of pixels.
I use a free Graphics program called Irfanview when working with the QX3 images. I position the mouse cursor over a point of interest and click the left mouse button. Irfanview displays the coordinates of the pixel at the left of the top window bar. Better yet, if I click at one point and drag to another then it displays the size of the rectangle on the top line as well. The dimensions of the rectangle can often be used as an approximation of the number of pixels between the points.
To measure the width of a wear bevel, I get the pixel locations of a number of points along the edge, then of a number of points at the other side of the wear bevel, then calculate the difference in width measured in pixels.
To convert pixels into inches, I use an image of a ruler, like the image on the right. The two lines represent 32nds of an inch. I count the pixels from the left side of the left line to the left side of the right line, using Irfanview, to be about 410, or 410*32 = 13120 pixels to the inch.
Each pixel on the screen represents 1/13120 = 0.00007622 inches.
A micron is a millionth of a meter. A meter is 39.37 inches. A micron is therefore 0.00003937 inches.
Each pixel is about 2 microns wide.
In 2007 I switched from the QX3 to an inspection microscope combined with a digital camera. Both the microscope and the camera have zoom lenses, so the magnification range is quite wide - from about 10X to about 850X and everything in between. This flexibility means that I am now never sure exactly what the magnification is - both zooms are only approximate.
For one pair of settings, measuring the marks on a ruler gives me a conversion factor of 54,400 pixels per inch. The other way, each pixel represents 0.0000184 inches or about half a micron. Since the camera was at about 15.3x and the microscope also at 15x, the combination is around 230x. Measuring on the screen, 1/32" was about 7 3/8" for a magnification of 236x.
Testing on this site, and similar testing done elsewhere, makes use of jigs to ensure exact bevel angles. Any testing procedure that does not make use of jigs is not reproducible.
Almost all tests here also use microbevels on the front and back of the blade. Any testing procedure that does not produce known geometry on both the front and back of the blade is not reproducible.
My tests almost always use 3M microfinishing abrasives made with Silicon Carbide and Chrome Oxide to hone the edge. These abrasives are very finely graded to the known micron standard. Many abrasives (all natural abrasives, most water-stones) are not accurately graded.
If you use a jig, hone front and back, use finely graded abrasives, then you will be able to reproduce these results even if you do not check each edge after each microbevel using a QX3 (as I often do when testing a plane blade).
In testing blades with the same geometry but honed with different final abrasives, I found that a finer final abrasive produces a more durable edge.
Metallography tells us that the subsurface deformation left by the coarser abrasives can be 3 times the depth of the deepest scratch.
The most deformed layer - the shear band layer - wears quickly, leaving us with a dull tool. The deformed layer below that wears more slowly, but more quickly than the undeformed metal.
By the time we reach the undeformed metal, we have a dull shape. Pushing this dull edge through the wood results in more friction, more heat, and faster wear of the good metal.
When we use microbevels, the final edge has no deformed metal, no shear band layer which would wear quickly. We removed the deformed metals while creating the microbevels. The edge is undeformed metal with the durability characteristics we expect of the steel.
Metallography and the revelation of the deformed layers resulting from abrasion with coarse abrasives explains why microbevels work to achieve longer useful edge life.
While I am certain that you should not touch up a blade sharpened as described in these pages, I also admit that many very qualified woodworkers do touch up their blades during use.
Finding out why this works for them, and finding out whether it works better for them than starting with a sharp blade (ok, a blade sharpened as described in these pages) seem to require that I have access to such a craftsperson and I am able to examine her tools after sharpening, after use and before touchup, and after touch up.
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