The ruler trick

[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 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.