A close look at the back of the blade - a blade which Clifton advertises as being usable without honing - convinced me to use my standard back bevel honing procedure. I believe that Clifton uses a high-speed grinding technique to prepare these irons. I don't believe you can properly prepare a plane iron with any high speed grinding process.

People who flatten the back of the iron have a considerable challenge ahead of them. I have moved a small rant on this type of deceptive advertising out of the stream of the text.

• Region 3

  The second microbevel on the back of the iron, created using 3M 5u micro abrasive. Again, I angled the plane iron to the direction of motion during honing to make this part of the iron easy to see, producing scratches that go up to the right.

  Normally I would put a third microbevel on the back, using 3M 0.5u micro abrasive. There are problems seeing the scratches left by this abrasive using this microscope. It is especially difficult since the resulting 0.5u bevel looks a lot like the back wear bevel.
  
  

• Region 2

  The first microbevel on the back of the iron, created using 3M 15u micro abrasive. These scratches are almost straight along the blade.
  
  

• Region 1

  The original back. I put that black mark on to simplify locating the same part of the iron for each picture. This was only marginally helpful.

• Before use, the 5u scratches go right to the edge. This honed back bevel is about 0.006" wide. These back bevels have removed all evidence of the scratches present on the delivered plane iron. The total time spent doing this was probably no more than 30 seconds in the 3 or 4 minute sharpening process.
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
• Already after 50 passes, the wood has worn away enough metal that the 5u scratches are no longer visible, over almost the entire wear bevel. The wear bevel is about 0.0047" wide.

  Notice that there is no wear evident beyond this point. That is, the shaving is not rubbing the back hard enough to wear down the metal once the shaving has moved 0.0047" up the back face of the plane iron. This makes it clear that the second iron, the cap iron or chip breaker, does not in fact break the chip unless it is within 5 one-thousandths of an inch of the edge.
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  

• After 100 passes, the wear bevel is not noticeably wider. It looks a bit different to me, but the difference is small.
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
• After 150 the wear bevel appears little changed. The texture has changed a little, the width hardly at all.
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
• After 200 passes, we begin to see a slight difference in the appearance of the wear bevel, right at the edge. Having noticed this very small wear bevel - 0.0002" - in this last picture, looking at the others it is faintly visible even in the 50 pass image.

  To distinguish this very narrow bevel from the rest of the back wear bevel, I will call this the back high wear bevel.

During the test, shavings average between 0.0015 and 0.002" thick. So, this back high wear bevel is as little as 1/10 of the thickness of the shavings! The full back wear bevel is about 0.0047" wide, or 2 to 3 times the shaving thickness.

So, the blade is wearing differently right at the edge on the upward facing blade surface, just as it is wearing differently right at the edge on the downward facing surface. What is causing this extra wear? For a given piece of wood, blade wear is affected only by heat. Areas of increased wear must have been subjected to higher heats. Higher heat means higher friction, which in turn means higher forces involved.

As the plane moves through the wood, the wood fibres collide with the front of the blade. The unbroken fibre collides first with the iron right at the edge. Because the blade is at a 45 degree angle to these fibres, only the part of the shaving right at the edge makes actual contact. The wood fibres are rigid, driving into the blade face and being forced upwards. At some point with the end of this fibre near the top of this front high wear bevel the fibre snaps down somewhere in front of the edge. The force of the shaving against the blade is greatly reduced, with the friction and heat generated being reduced accordingly. This part of the shaving is now lying flat on the front of the blade and sliding along with much less force against the blade. Then the blade reaches the fracture point of the fibre and once again an unbroken shaving collides with the blade and is forced upward. The width of this high wear bevel appears to be the amount the shaving must rise before it breaks.

If this high wear bevel has been subjected to greater heat, has the quality of the steel at the edge been affected? Should we hone back past this wear bevel in the next sharpening operation? Interesting but difficult questions.

• The black line is the 25 degree primary bevel.
• The red line represents the 15u first microbevels, 29 degrees on the front, 2.4 degrees on the back. All the metal between the red and black lines is removed during the first creation of the 15u microbevels. It is clear that most of the metal removal is taking place in this step. [Remember that the 15u bevel on the lower face is only 0.02" wide, and thus this diagram is like a 2000X magnification.]
• The blue line represents the 5u second microbevels, 31 degrees on the front, 3.6 degrees on the back.
• The green line is a guess at the shape of the wear bevels. The upper wear bevel have a short section at a much steeper angle, followed by a long section at almost the angle of the 5u bevel. On the lower side, a fairly wide bevel at a more or less constant angle. I believe this angle is almost parallel to the work surface.

Amazingly, in spite of the relatively small amount of metal worn off during the formation of the wear bevels, we would have to hone away almost the entire original 15u microbevel.

While this is possible, it is probably faster to do the majority of the metal removal with the coarser 15u abrasive.

We have renewed the entire 15u microbevel, but the amount of metal removed this time is somewhat less than on the initial sharpening. Having done the 15u microbevel, the amount of metal we remove in doing the 5u microbevel is the same as in the initial sharpening.

Notice that the new 15u microbevel is not much wider than the original.

Using both 15u and 5u abrasive means we must remove more metal than we would with Plan I, but we are doing it with a much faster abrasive.

This is the plan described in my sharpening pages.

This drawing shows what happens if you redo the first microbevel until you hit the edge (the upper red line), then redo the 5u microbevel (the upper blue line).

In fact you do remove the back high wear bevel (when using the 5u abrasive), but leave some of the back wear bevel (green line on back above top blue line).

Using a microbevel, even when not using back bevels, appears to do a pretty good job of preparing the edge (assuming you go right to the edge with the 15u abrasive). This is not a bad sharpening strategy.

Wear Bevel Shape - Checking the Drawings

These drawings are just that - guesses at the shape of the front and back wear bevels. Is there any way to test those estimates?

It is possible that by taking pictures of exactly the same spot with the blade at different angles, some combination of the resulting images could be used to generate a 3D composite, but that is beyond my skills.

It seemed to me that it should be possible to determine the shape of the wear bevel by taking slices off the top of the wear bevel and measuring the width after each slice. I thought I could slice by simply honing the blade at a slightly different angle. To make it clear that the honed bevels produced during this test are special, I will call them slice bevels.

I started with this used blade - exactly as shown after 200 passes. I used 5u abrasive on a slip just a little thicker than the 0.06" slip. I honed each side of the blade a few times (from 3 at the start to 10 later on) then took a picture of the slice bevel at a particular part of the front and back of the blade. I did this 13 times, until the new slice bevel reached the edge on the front side (the slice bevel had not yet reached the edge on the back side - I may do some more work on the back).

Each new slice bevel corresponds to a slice of the wear bevel (and part of the old honed bevels) at an angle slightly greater than the blue lines in this diagram.

The number crunching - determining the width of the new honed surface and its placement in the existing known geometry, then calculation of the implied wear bevel geometry, is all that remains to be done to see if this will indeed determine the wear bevel shapes.

1. A dark scratch in the primary bevel. This is one of two points I used to make sure all pictures showed exactly the same part of the blade.
2. A pair of lines that are not quite parallel were the second feature used to ensure all pictures were of the same part of the blade.
3. The new slice bevel. This slice bevel is at an angle just slightly larger than the original 5u bevel that used to reach the edge.
4. The wear bevel, between the slice bevel and the edge.
5. The old 15u bevel, created as the first step in the original sharpening.
6. This is the problem area. It has scratches from the slicing operation, some scratches from the original 5u honing, and perhaps even some scratches from the original 15u honing.
7. A line scratched into the bevel which I hoped would help me locate the same part of the blade each time. Such marks can help, but not when this close to the edge - this mark was removed during the slicing.

This technique, slicing, will probably never be accurate enough to provide good wear bevel shape estimates.

Here the two bevels produced by the initial sharpening are a total of 272 pixels wide (but only about 232 pixels wide in the above image). The bevel width varies across the blade because the edge was not square to the sides in the blade as delivered (very few are, this is not a particular problem with the Clifton iron). This shows how important it is to find exactly the same part of the blade for each step in the resharpening process.

This picture highlights the last microbevel - the 5u bevel. The scratches do not all end a uniform distance from the edge.

To determine fairly precisely the shape of the wear bevel, it will be necessary to be able to narrow these boundary regions.

A dull blade has a wear bevel on the back of the iron (whether used bevel up or bevel down). This back wear bevel can be easily removed using back bevels. This back wear bevel cannot be removed by later flattening of the back. It can be removed without back bevels by protracted grinding/honing from the front. The flat back fetish is discussed in the FAQ.

By going to all the work to flatten the back so carefully, Lee Valley actually does a disservice to its customers. Lee Valley leads their customers to believe that they have no responsibility for the back of the iron in the future. To assume that Lee Valley has done all their work for them. The woodworker would then be resistant to any argument that they need to prepare the back during each sharpening session. People would be better off if Lee Valley abandoned back flattening and added something about back bevels to their literature. However, since super flat is the chrome bumper of the plane iron business, I see little chance of this happening. [It is possible that Lee Valley understands they may be misleading some customers. The technical discussion of their blades now (Dec 2009) contains the sentence: "You will also still need to hone the intersecting bevel." I have no idea what that means, but it might refer to the back wear bevel. The phrase appears no where else on their site according to google.]

Check out my jig page for a simple jig you can make in your shop, along with a sharpening set up using sheet abrasives, that reliably produces excellent edges, for all types of irons.

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