sharp/dull blade drawing How Plane Irons Wear small map
Finest abrasives.
Microbevels front and back.
Use a jig.
Copyright (c) 2002-15, Brent Beach



This page illustrates what happens to a plane iron as it wears during use.

Just to illustrate the various parts of the worn blade, below is an image of the front bevel of a Clifton blade after 200 passes on a 4 foot Douglas-fir board. I have done a large number of plane iron tests on boards take from the same part of a large Douglas-fir tree that blew down 4 years ago on our property. The wear shown on this blade is an accurate comparison of the durability of this blade with other blades I have tested.

The picture was taken with a QX3 microscope at the 200X setting. This image corresponds to 0.03" of the blade at the edge, and represents a length of about 0.025" along the edge.

Clifton ships this blade with a 25 degree bevel (region 1). I added two microbevels during preparation of the blade (regions 3 and 2). Using the blade added the wear bevel (region 4). This first image is of a sharpened blade after 200 passes along a 4' Douglas-fir board. I wanted to show the wear bevel right away, in context of the honing bevels.

Worn Blade

The 4 regions are:

  • Region 4

    This very narrow region is the wear bevel - it is about 0.0006" wide. What scratches you can see are created by the wood scraping/wearing away metal from the bottom side of the blade. This is the downward facing side of a bevel down iron, so this wear bevel was worn away during contact with the douglas-fir board.

  • Region 3

    The second microbevel, at 31 degrees, created using 3M 5u (5 micron) micro abrasive paper. I hold the blade at an angle to the direction of motion during honing, at different angles for different grits, to make the various microbevels more evident. Honing at this angle has almost removed all of the deep scratches from the next microbevel - if you look closely you can see some ghostly lines heading up to the left in this microbevel.

  • Region 2

    The first microbevel, at 29 degrees, created using 3M 15u (15 micron) micro abrasive paper. The scratches in this region actually go up to the left, but are not apparent because of the position of the light source.

  • Region 1

    The 25 degree primary bevel. The original grinding marks show two different patterns. The main pattern a slight slope up to the right, a second pattern upward to the left on top. The second pattern appears to be a coarser grit. Why would they finish with a coarser grit?


Blade front wear over a test

wear during test The following picture shows 5 images of the edge of the same blade as in the above picture - after 0, 50, 100, 150, and 200 passes of the test. In all cases the edge is on the right side of the picture. I have aligned the edges so help with the comparison of wear after each series of passes.

  • The first image, shows the front bevels before use. My normal practice is to hone three microbevels after the primary, using 15u (15 micron), 5u and 0.5u 3M micro abrasive paper. I omitted the 0.5u microbevel for this series of pictures because the 0.5u scratches are not visible with this microscope. Here the 5u scratches are visible right to the edge, so any change at the edge is clearly visible.

  • The wear bevel shows up after 50 passes as a change in the texture of the scratches at the edge. It is 0.0002" wide.

  • After 100 passes, the wear bevel is clearly visible. It is now 0.0035" wide.

  • After 150 passes, the wear bevel is 0.00057" wide.

  • After 200 passes the wear bevel is 0.0007" wide. This blade was still performing fairly well. While this blade is not much more durable than other high carbon steel blades I have tested, it was still quite usable with this level of wear. A typical Stanley iron from the "laminated blade" era - 1890 to 1935 - wears at about the same rate, but is not as usable when this worn. The extreme thickness of this iron - 0.130" where the Stanley irons are around 0.080" - seems to make an important difference in plane performance, over the entire range of blade sharpness. I am quite amazed by the performance of this blade.

    The bad news is that this blade is too thick to fit in most Stanley planes without modification of the plane mouth. There was no frog setting for which the blade did not collide with the front of the mouth on any of the Stanley planes in which I tried it. For this test I used a Record plane with a very wide mouth. The combination of an ordinary plane and a very good [thick] blade was excellent. It makes me wonder how a transitional would work with this blade.

The Rest of the Story - The Back of the Blade

This test was designed to look at the geometry of dull blades in more detail. This means looking at the upper surface of the blade as well as the lower surface. This section looks at the upper surface in detail.

I thought about leaving the back of this blade flat for this test [more closely simulating how most people prepare their irons], or even using conventional techniques to flatten the back.

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.

original blade back
Here is the back of the blade after sharpening and before use. Again, there are 3 regions corresponding to three bevel angles.

  • 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.

sharpened blade back

Wear on the Back during the test

wear bevels This composite of 5 pictures shows the back wear bevel as it changed during the test.
  • 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.

high wear bevel High Wear Bevel

This very narrow back "high wear bevel" shows up as the darker area right at the edge in this digital enlargement of the last image above - after 200 passes. The high wear bevel is the slightly darker region at the edge. It is about 0.0002" wide. The next region is the regular back wear bevel, followed by the remnants of the 5u microbevel.

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.

Sharpening a Worn Blade

The above images show the extent of the wear bevels on the front and back surfaces, but not their shape. In this section, I use a drawing of the profile (side view) of a worn edge to illustrate what happens when we re-sharpen a dull blade.

Knowing the angles of the various microbevels (which we know exactly from the geometry of the jig and the iron extension) and their widths, we can draw an exact profile of the sharp blade.

To that we add an estimate of the profile of the wear bevels. It is only an estimate because while we know the width of the wear bevels, and the exact location of the worn edge relative to the various microbevels, we cannot say what the shape of the wear bevel is between those two locations.

Drawing of a Dull Blade

In this drawing, representing the Clifton iron with the main bevel angle of 25 degrees, with the two microbevels on each side, as well as the wear bevels. [This drawing is based on the sizes of the microbevels as photographed during this testing session.]
  • 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.
dull blade
Sharpening Plan I - renew just the 5 micron microbevels

What if we just use the 5u paper to renew the previous 5u microbevels? The inner blue lines show the resulting microbevels on the front and back of the iron. [The blue lines should go even farther than they do, but drawing the longer lines was a problem.] These lines are drawn from the worn edge at the second microbevel angles on the front and back.

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.

sharpening plan 1
Sharpening Plan II - renew both the 15 and 5 micron microbevels

This diagram shows the profile after honing the worn blade with the 15u paper at the standard first microbevel angle. The inner red lines show the resulting profile, assuming we just remove the wear bevels.

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.

sharpening plane 2
Sharpening Plan if you Don't use Back Bevels

People who do not use back bevels have a slightly different problem. The back wear bevels are the same, but they lie in the plane of the back face of the iron, not along back microbevels.

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.

sharpening no back bevels

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.

worn blade drawing


The pictures I took of the blade during this slicing process are not sharp enough to allow accurate estimation of the sizes of the various slices.

This is a typical image I have to work with - an image of the front bevels after 3 very light honings (slices), with 7 numbered areas.
  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.

It must be possible to estimate the width of the slice bevel with some precision if there is any chance of determining the wear bevel shape using slices. To do that, some method of shrinking the width of area 6 - the area which shows scratches from up to 3 sources - must be devised. Area 6 is too wide in this series of pictures to continue the analysis.

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

blade image
A before use picture of a slightly different part of the blade further illustrates the problem of estimating the intersection of two microbevels through examination of the two sets of scratches.

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.

last microbevel
This is the same part of the blade (compare the heavy scratches in the primary bevel), but with the lighting moved to emphasize the scratches in the 15u bevel. Notice again that the boundary between the 15u scratches and the 5u scratches is quite a wide area.

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

wear bevel shape


I find it extremely annoying when manufacturers claim that their blades can be used right out of the box. Other instances of manufacturers making this claim are mentioned in these pages. Clifton is not the only manufacture to make this claim. Their blade is not much worse than most others. It is however just as clearly not usable right out of the box.

I don't understand what manufacturers think they are gaining by making such a claim. Experienced woodworkers know it is bullshit, but some may actually try the blade before sharpening. The poor results will leave them a little cynical about the maker's honesty.

Inexperienced woodworkers may try the blade, find it doesn't work, and assume it is their fault. How many have put the plane down and not picked it up again? How many have looked at the resulting surface and gone out and bought a planer?

I really wish that plane iron manufacturers would say on all their blade packaging that unless you know how or are willing to learn how to sharpen plane irons, there is little point in buying the blade. [Hock Tools - to their credit - makes no such claims for their blades and does discuss sharpening on their packaging.]

Update (Sep 09): Some manufacturers have started spending some time lapping their blades before they sell them. Some of these blades are in fact now usable right out of the box. Lee Valley uses a lapping machine to produce better surfaces than most woodworkers will get in later sharpening. Lee Valley spends quite a bit of time flattening the back of their plane irons. All this effort is useful only during the first uses of the plane, up until the first time the user sharpens the blade.

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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