The ruler trick

[Rob Luter]

I've been learning to sharpen for several years, and thought I was pretty good at it. I recently spent a few hours in my shop escaping the summer heat, and decided to get everything all sharpened up in anticipation of the next project. While I've always flattened and lapped the backs of my plane irons, this time I decided to employ David Charlesworth's "ruler trick" to assure the back of the iron near the cutting edge was as flat and smooth as possible. The results were nothing short of amazing. I thought I was getting sharp before, but I'm getting a whole different class of results now. My planes have never cut smoother. It was a simple change that made a big difference. Maybe I'm late to the party, but better late than never.

[Robin Frierson]

What is the ruler trick?

[Phil Mueller]

Robin, it's a technique David shares on his sharpening video. Downloads and DVDs are available through Lie Nielson. You essentially wet a fine stone, and "stick" a metal ruler along one long end of the stone. Place the plane iron back side down on the ruler perpendicular to the stone and run the back of the cutting edge (a few mm of it) back and forth over the opposite edge of the stone. Creating essentially a very slight up bevel to the back of the iron close to the cutting edge.

[Rob Luter]

What is the ruler trick?

What Phil said. It takes much or the work out of flattening the iron at the cutting edge as you only are dressing the 1/4 inch or so at the edge. The amount of back bevel is all but impossible to measure. Google "The Ruler Trick" and you'll get all sorts of results, how to videos, etc.

[Robert Engel]

Its an innovation, but keep a couple things in mind.

1. I view it as a permanent alteration to the blade.
2. Difficult to do on a cambered iron.

[Mike Holbrook]

Most of my plane blades are hollow ground and cambered. I am wondering if any one who uses these methods also uses the ruler trick? It seems like the method would involve moving the blade in an arch across the stone, much like is necessary to make the camber in the first place.

[Megan Fitzpatrick]

Here's a link to David Charlesworth's article on the subject, for those interested: http://www.popularwoodworking.com/techniques/the_ruler_trick

[Robert Engel]

Most of my plane blades are hollow ground and cambered. I am wondering if any one who uses these methods also uses the ruler trick? It seems like the method would involve moving the blade in an arch across the stone, much like is necessary to make the camber in the first place.I've wondered about this, too. Never tried it probably never will. :)

I think there's a certain amount of hype associated with this. Seems to me just a way achieve an edge quicker. I can't really see that much difference in performance and there is no perceptible difference in sharpness or blade life to me.

Can anyone tell me if there IS any advantage to a back bevel performance-wise?

[lowell holmes]

I've wondered about this, too. Never tried it probably never will. :)



Can anyone tell me if there IS any advantage to a back bevel performance-wise?

YES, there is! My apron plane was a disappointment until I read and did the ruler trick.

[Patrick Chase]

What Phil said. It takes much or the work out of flattening the iron at the cutting edge as you only are dressing the 1/4 inch or so at the edge. The amount of back bevel is all but impossible to measure. Google "The Ruler Trick" and you'll get all sorts of results, how to videos, etc.

You shouldn't be working anything like 1/4" with the ruler trick.

David's recommended configuration corresponds to about 1/2 degree of back-bevel, so if you work 1/4" back from the edge you'll have relieved the edge by 0.25*tan(0.5) = 2 mils. That doesn't sound like much, but it's way more than you need.

In my experience working back by 1 mm (~1/3 mil or 9 microns of relief) is enough to work through routine scratches and get a clean edge, assuming the back is reasonably well prepared to begin with.

[Patrick Chase]

Its an innovation, but keep a couple things in mind.

1. I view it as a permanent alteration to the blade.
2. Difficult to do on a cambered iron.

Neither of these is remotely true.

It's only permanent if you bungle it by working too far back from the edge (for example the "1/4 inch" suggestion). If you keep it within reason it amounts to ~10 microns of relief, and that will come out very easily in any subsequent flattening, without any significant impact on overall blade thickness. I've removed more "ruler trick bevels" than I can count.

To ruler-trick a cambered blade you simply pivot the blade over the ruler as you work. At any given position the section of the camber parallel to the ruler is the part being worked (assuming a flat back, if the back is "twisted" then there will be a rotational offset). I was able to do it on my first try once I'd worked out the physical principle.

For some reason the "ruler trick" is utterly mired in disinformation and bad advice. It blows my mind that something so simple could become so confused.

[Jim Koepke]

... It blows my mind that something so simple could become so confused.

Alas, as a member of the flat bevel society, it is very clear that keeping things simple is always subject to confusion and ridicule.

jtk

[Jim Koepke]

You shouldn't be working anything like 1/4" with the ruler trick.

(edit)



The way I understand the ruler trick it would be very difficult to produce it over a 1/4" depth.

jtk

[Patrick Chase]

The way I understand the ruler trick it would be very difficult to produce it over a 1/4" depth.

jtk

As I said above that corresponds to a couple mils of relief at the tip, so not that difficult if you use a medium stone (which you are absolutely not supposed to do).

[Robin Frierson]

I have been down the road of the back bevel and prefer not to use it. Each time I did the back bevel it got wider and wider. So I would increase the bevel and before long I had a 5 deg back bevel, combined with my 5 deg front secondary bevel, I was at 35 degrees. Which is ok for some woods. I probably made my back bevel too wide..but how do you only fit 10 micron of blade on the stone and maintain that. Perhaps if I had seen the video I may have had better results. I still have blades I need to regrind to get rid of those back bevels.

Once I do the work of mirroring the back then it just takes a minute to remove the wire edge and polish the back edge each time. I no longer use stones for the back, prefering 24inches of micron graded sandpaper on a granite plate. But whatever works...we all have different techniques for getting it done.

[Patrick Chase]

I have been down the road of the back bevel and prefer not to use it. Each time I did the back bevel it got wider and wider. So I would increase the bevel and before long I had a 5 deg back bevel, combined with my 5 deg front secondary bevel, I was at 35 degrees. Which is ok for some woods. I probably made my back bevel too wide..but how do you only fit 10 micron of blade on the stone and maintain that. Perhaps if I had seen the video I may have had better results. I still have blades I need to regrind to get rid of those back bevels.

I agree that what you describe is bad, but it's impossible to produce a result like that with the ruler trick, so it's irrelevant to this thread.

The entire point of using a ruler is that it limits the back-bevel angle to about half a degree. I personally use shim stock to limit it to about 1/4 deg, but you can get into other trouble at that point if your back isn't very flat to begin with, so that probably isn't for everybody.

There are many, many, many ways to ruin blades through poor technique (even while flattening them!). The fact that somebody did so once while applying a back bevel says nothing about the advisibility of back bevels as a whole.

[Warren Mickley]

I watched two recent Charlesworth sharpening videos this morning, one for a chisel and one for a plane iron. Both were from December 2015.

For the chisel, he doesn't use the ruler technique. He spends about six seconds abrading the back.

For the plane iron, he spends seven seconds positioning the ruler. And he also spends a few seconds removing the ruler and wiping it down at the end. The actual flattening is done in about 12 seconds. The entire sequence from picking up the ruler to wiping the iron off takes about 30 seconds.

I don't see how this method can save any time in the long run. We typically get many thousands of sharpening from an iron we have prepared but once. If the purpose, as suggested in the 2008 article referenced above, is to help beginners, I can see some value.

[david charlesworth]

Megan, thanks very much for posting the article.

Robin,

I can only conclude that you were working the "back bevel" on a stone which was far too coarse.

I have blades that have been sharpened regularly, this way for 20 years and more. The "back bevel" never gets more than about 1.5 mm or 1/16" wide. It is important to use a fine stone only for this work, something like 8,000 or 10,000 grit waterstones.

The reasons why the method may produce a sharper more consistent result are as follows;
What are the chances of the stone and the back of the blade being perfectly flat?
What therefore is the probability of correctly honing away the wire edge?
The small lift, 2/3 of one degree ensures the edge touches the polishing stone. (No stropping required, the wire edge just floats away on the stone, sponge cloth or towel.)

There is absolutely no problem with RT and modest cambers, like the ones I use on my jack and smoothing plane. (Because the lift angle is so small?)

When I learned something about wear bevels on the back of a plane blade, I realized that the RT removes metal in just this area! So I now do more work on the back (with the ruler) than the article suggests. (Maybe twice as much).

Best wishes,
David Charlesworth

[Patrick Chase]

I watched two recent Charlesworth sharpening videos this morning, one for a chisel and one for a plane iron. Both were from December 2015.

For the chisel, he doesn't use the ruler technique. He spends about six seconds abrading the back.

For the plane iron, he spends seven seconds positioning the ruler. And he also spends a few seconds removing the ruler and wiping it down at the end. The actual flattening is done in about 12 seconds. The entire sequence from picking up the ruler to wiping the iron off takes about 30 seconds.

I don't see how this method can save any time in the long run. We typically get many thousands of sharpening from an iron we have prepared but once. If the purpose, as suggested in the 2008 article referenced above, is to help beginners, I can see some value.

The key question there is whether he's getting (or even trying for) equivalent results for the chisel and the plane blade.

Also, the fact that planes are used with clearance leads to a very different wear pattern (the so-called "wear bevel") than with chisels, which are more often used flat. For a chisel you basically only work the back to remove the burr from sharpening the bevel, whereas with BU planes in particular you also have to deal with any wear bevel that was left behind after you worked the edge (for a BD plane the wear bevel is on the face, not the back).

The orientation of the wear bevel is such that it's a lot longer than it is "deep". You can therefore either remove a fair amount edge to get rid of it all, or refresh a small back-bevel by a couple microns (which leads to an interesting length-vs-thickness tradeoff in blade life). IMO the ruler trick is useful for managing that wear bevel, esp in low-angle BU planes where the resulting loss of clearance can be a real issue.

[Patrick Chase]

Can anyone tell me if there IS any advantage to a back bevel performance-wise?

I'll take a stab at this. It depends on the plane and your situation.

For BU planes I think that it gives you a hugely important knob to manage wear bevel formation on the blade back. It's a lot easier to correct a wear bevel by refreshing a ruler-tricked back bevel than it is to do so by either grinding the face far enough back to remove the wear bevel, or flattening the entire back (and thinning the entire blade) enough to remove it.

For other planes the tradeoff is more subtle. Essentially it allows you to work most of the blade back using only medium-grit stones, and then use your polisher to create a teeny tiny bevel with just enough relief to get past the scratches left by the medium stones. That in turn may speed up your flattening process quite a lot. Medium stones typically leave ~5 micron scratches, so about 10 microns of relief (a 1 mm back bevel at 0.5 deg) is sufficient.

[Rob Luter]

You shouldn't be working anything like 1/4" with the ruler trick....

Perhaps my eyes are out of calibration :o It might be closer to .090". When I just was flattening the backs of my irons (sans ruler) I always focused on the 1/4" nearest the edge. No sense working harder than necessary.

I will say that the metal scale I am using is very thin. It's much thinner than my Starrett scales. I didn't want to chance my good scales getting scratched by my sharpening media. Also, I work with a 3" wide sharpening block. If I get motivated I'll measure everything up and trig out the bevel angle...or not.

[Jim Koepke]

As I said above that corresponds to a couple mils of relief at the tip, so not that difficult if you use a medium stone (which you are absolutely not supposed to do).

If one were to produce 1/4" of "ruler trick" back bevel, how would it be possible to properly set the chip breaker?

Most of the time I sharpen my blades before the wear bevel on the back becomes large enough to not be removed by honing the bevel.

Then again, I am not one who normally uses secondary or tertiary bevels.

A flat bevel strategy also means my blades do not have to be taken to the grinder as often. Some of my most often used blades haven't been to the powered sharpening set up since they were acquired.

jtk

[david charlesworth]

If I had need of a time and motion man, Warren could have the job.

I am grateful to him for pointing out that the RT is not suitable for cabinetmaking chisels. Just blades of all types.

"Quite quick" was a term I used on the You Tube chisel sharpening video, but I am more interested in words like sharp, effective and repeatable.

David

[Normand Leblanc]

Jim,
I typically use a 3° backbevel for BD planes and my chipbreaker is adapted to that angle. I have no problem at all with this set-up.

Normand

[Jim Koepke]

There are many, many, many ways to ruin blades through poor technique (even while flattening them!).

This is why my recommendation to people beginning their journey into sharpness always start by keeping it as simple as possible.

When something isn't working, it is easier to troubleshoot if one is only looking at one thing instead of trying to determine if it is the back bevel, the front bevel, the secondary bevel, the tertiary bevel, the cambering or even something else at fault.

Once it is possible to repeatedly sharpen a blade then trying other enhancements is fine. If a person can not get a blade sharp to start, adding all the other tricks isn't likely to be the corrective measure to make it right.

jtk

[Rob Luter]

If one were to produce 1/4" of "ruler trick" back bevel, how would it be possible to properly set the chip breaker? jtk

On my planes, the chipbreaker doesn't know the difference. The bevel that I created is all but imperceptible beyond the fact it's a mirror finish in close proximity to the cutting edge. I set my chipbreakers at between .040 and .060 on my smoothers.

[Jim Koepke]

On my planes, the chipbreaker doesn't know the difference. The bevel that I created is all but imperceptible beyond the fact it's a mirror finish in close proximity to the cutting edge. I set my chipbreakers at between .040 and .060 on my smoothers.

1/32" = 0.03125"

I have been setting mine closer than that even before I knew about the effect of a close set chip breaker on controlling tear out.

Now most of my planes are set at less than 0.015". The plane I use for scrub work is back a bit further.

jtk

[Robin Frierson]

Well thanks for your response David, may I ask do you grind out the back Bevel from time to time. I no longer sharpen with stones but use a granite machinist surface plate with sandpaper. If you're using only a fraction of a degree, it seems to me the bevel would widen every time you sharpen..

I always work with a light with a built in magnifier and use other magnifiers on top of that so I'm able to keep a good eye on the edge and also feel it with my fingernail. Working on the granite plate I think I deal with a much flatter surface than any stone. Its been over 10 years since I messed with the back bevels. We also were using them to get higher angle of attack by going with the 5° back bevels for performance sake, not speed of sharpening..

[Rob Luter]

1/32" = 0.03125"

I have been setting mine closer than that even before I knew about the effect of a close set chip breaker on controlling tear out.

Now most of my planes are set at less than 0.015". The plane I use for scrub work is back a bit further.

jtk

Thanks Jim. Mechanical Engineer for 35 years. I've got the decimal thing all figured out. I don't set my chip breakers that close. Maybe I should. For now, if I encounter gnarly grain or have issues with tear out I use a bevel up smoother with a high angle blade (and no chip breaker). When it get's really ugly I just use a #80 scraper.

I have a LN 4 1/2 with a particularly well fitting chip breaker. I'll set it up nice and close tonight and see how it works. That may be another (of many) things I've yet to learn.

[david charlesworth]

Robin,

No, I never grind out the back bevel, There is no need.
The polish gets minutely wider but the blade is shortened by the work on the bevel surface.

The key to this technique is 8,000 grit stone or finer. (It also works with 6,000 but not quite so well.

Best wishes,
David

[Patrick Chase]

If one were to produce 1/4" of "ruler trick" back bevel, how would it be possible to properly set the chip breaker?

Easily. A properly configured (read: one with a flat, undercut leading edge) cap iron interfaces with the blade back along a line. The only thing that matters is that both the leading edge of the cap iron and the corresponding line along the blade are parallel where they mate such that they do indeed form an unbroken line. If you apply a back bevel uniformly then it doesn't matter how far back it extends, within reason. The only thing you can't do is apply any sort of curvature.

[Patrick Chase]

Perhaps my eyes are out of calibration :o It might be closer to .090". When I just was flattening the backs of my irons (sans ruler) I always focused on the 1/4" nearest the edge. No sense working harder than necessary.

I will say that the metal scale I am using is very thin. It's much thinner than my Starrett scales. I didn't want to chance my good scales getting scratched by my sharpening media. Also, I work with a 3" wide sharpening block. If I get motivated I'll measure everything up and trig out the bevel angle...or not.

Makes sense. I use plastic shim stock for the same reason - it's better for the blade and for my scales. It also gives me better control over the back bevel angle since I have a wider selection of shims than I do of scales.

[Patrick Chase]

1/32" = 0.03125"

I have been setting mine closer than that even before I knew about the effect of a close set chip breaker on controlling tear out.

Now most of my planes are set at less than 0.015". The plane I use for scrub work is back a bit further.

jtk

I set my chipbreakers very close, sometimes as close as 4-6 mils (evaluated under very high magnification). At that point they're well into the ruler trick bevel, but it isn't an issue for the reason I gave in a previous post: Adding a uniform bevel doesn't impact cap iron mating.

If you straddle the bevel or if it isn't uniform then that's different, though even then it depends on angle. My ruler-trick bevels are about 1/4 deg, so the resulting gap even if I straddle the bevel a teeny bit is on the order of a micron or two, in other words not enough to trap even a single wood fiber.

I frankly think that the whole "ruler trick hurts cap-iron interface" thing tends to be hugely overblown by people who've never tried it or bothered to think very deeply about it.

[Patrick Chase]

When I learned something about wear bevels on the back of a plane blade, I realized that the RT removes metal in just this area! So I now do more work on the back (with the ruler) than the article suggests. (Maybe twice as much).

Interesting that we both brought this up within 7 min of each other (and no, I hadn't seen your 9:53 post when I submitted mine at 10 :-).

I don't think you need to increase the amount of work that much, though. The micrographs I've seen show that the wear bevel is quite shallow, and you will remove some of it when you hone the face. In my experience the residual is easily controlled with "normal" ruler-trick handling, though YMMV.

FWIW I'm on a diamond-paste-on-steel-plates kick for blade back maintenance right now. I get absolutely gorgeous bevels (smooth, clean boundary to blade back, uniform thickness with no "roundovers" at the corners) with 1 um (#10000 or so) or 0.5 um (#20000) pastes. The plates have to be dead flat though.

[Simon MacGowen]

but I am more interested in words like sharp, effective and repeatable.

David


Agreed. 99.9% (exagg.) of the amateur woodworkers don't mind spending a minute or two or three more to get the results they want. If someone, as a hobbyist, can't afford to put that extra time to get the desired result, woodworking -- especially hand-tool woodworking -- isn't right for them! Power tools get things done much faster, for that matter.

Still can't understand why all the fuss about the RT. Either do it or don't it. It is such a simple concept and simple act that if it works for you, keep doing it . . . and if it doesn't, move on.

Simon

[Robert Engel]

Patrick, I get it about BU planes. I will start employing this.

Another question then: Can you simulate a high angle frog by an highly accentuated back bevel?

[Jim Koepke]

Rob,

I will send you a PM on what you will find if you Google > setting a cap iron <.

jtk

[Allen Jordan]

I've done the ruler trick for a while, but now I'm starting to switch away from it. It's difficult to keep a wide plane blade truly flat when doing the ruler back bevel, and it forces you to move the chipbreaker further back which reduces its effectiveness.

[Patrick Chase]

Patrick, I get it about BU planes. I will start employing this.

Another question then: Can you simulate a high angle frog by an highly accentuated back bevel?

In a BU plane the back bevel is facing down, so it doesn't do anything to the cutting angle. If you want to simulate a high-angle frog just hone a high secondary bevel onto your blade. For example many people use blades with 50 deg secondary bevels to get to 62 deg effective pitch in BU planes with 12 deg beds.

In a BD plane the back bevel faces up, so it can indeed be used to increase the cutting angle and thereby simulate a high-angle frog to a degree. I say "to a degree" because at some point it does interfere with the cap iron interface. The leading edge of the cap iron is usually undercut by a couple deg - fine for the 0.5 deg back-bevel in the "ruler trick", but not OK if you're trying to add several degrees to the cutting angle. You can increase the undercut a bit, but you'll run into other engagement problems before long by doing so. The bottom line is that if you use high back bevels to implement high cutting angles then you'll eventually be forced to set the cap iron behind the start of the bevel, and that will cost you the ability to use the "cap iron effect" to mitigate tearout.

[Tom M King]

Never have. Never will. I turn the stones up on edge, and use the side of the stone for the backs. This of course, is after any flattening that was needed was done. I don't remember ever going below 6,000 grit to hit the backs. The sides of the stones are flattened (cleaned up) when they need it. This gives me more sharpenings between flattenings, since I can look at using the whole stone for the bevel, and the sides dedicated to the backs.

My sharpening system has evolved over 43 years. I now do full, flat bevel only with Waterstones. I doubt I've had to regrind more than a couple of bevels in a year or more, since doing this simple system. I do use more than the fairly typical two or three stone system though, but it ends up taking less time overall. Bevels stay the same for years with no chasing of new angles created by micro-bevels taking over a full bevel.

Video coming. Lights came today.

[Patrick Chase]

I've done the ruler trick for a while, but now I'm starting to switch away from it. It's difficult to keep a wide plane blade truly flat when doing the ruler back bevel, and it forces you to move the chipbreaker further back which reduces its effectiveness.

Why do you think you have to move the chipbreaker further back? (hint: You do not)

[Allen Jordan]

Why do you think you have to move the chipbreaker further back? (hint: You do not)

You know, maybe I'll give it a try. I always througt setting the chipbreaker edge on the back bevel made by the ruler trick would make for uneven contact, but I guess there is an undercutting grind on most chipbreakers that would allow it to register on a small slope without much issue. I'll experiment the next time I sharpen, thanks for the tip.

[Patrick Chase]

You know, maybe I'll give it a try. I always through setting the chipbreaker edge on the back bevel made by the ruler trick would make for uneven contact, but I guess there is an undercutting grind on most chipbreakers that would allow it to register on a small slope without much issue. I'll experiment the next time I sharpen, thanks for the tip.

The key is that the back bevel has to be small. David's recommended configuration corresponds to ~0.5 deg, I use about half that. At those sorts of values the undercut on the cap iron will accomodate the bevel.

One word of warning: The bevel should run straight across. If you put more pressure on the corners than the center and end up curving the back of the blade in the bevel region then that creates at least the potential for an interface issue (though at the angles we're discussing here it's a matter of microns and you'll probably get away with it anyway).

[Rob Luter]

Rob,

I will send you a PM on what you will find if you Google > setting a cap iron <.

jtk

Got it. Thanks.

After taking a look at my planes last night and actually measuring the edge to chip breaker clearance, I find I average about .025". I don't generally have issues with tearout, but I may do some tweaking and see how close to the edge I can sneak up. One problem I have is my chip breakers are original to my Sweetheart era planes. They're not as perfect as they could be. Some tuning is in order I guess.

One poster wondered how the ruler trick impacted bevel up planes. I used this approach on my three 60 1/2 block planes with great success. They work better than ever. Note that I'm not adding a back bevel per se, the slight angle imparted by the ruler just localizes the flattening of the back of the blade near the cutting edge. The cutting angle isn't really changed, and these still slice through end grain with little effort.