Ruler trick example

[Stewie Simpson]

It should be pointed out that not all manufactured plane irons and chisels are uniformly flat along the full length of their backs. As a result there are occasions where some lifting is required to insure that that the forward 1/2 to 1 inch is in direct contact with the surface of the stone. That's a primary reason why its deemed good practice when working these backs, to apply some downward pressure with your forward fingers close too the cutting edge. Whether 1 chooses to use the Ruler Trick or not, what's has come out of this discussion are the real benefits in keeping the top surface of your honing stones within a tight tolerance of flatness. That in itself has some relevance to Derek's inquiry within another post, as to why you would bother keeping your stones flat. Out of flat stones may be seen as acceptable for working the bevel side of your plane iron and chisels, but that's clearly not the case when working the backs.

[Normand Leblanc]

Even so, if my blade is as horrid as it may seem, it still does a pretty good job of cutting (slicing?) wood in a manner suitable for a smoothing plane.

jtk

That's the more important. If my blade is cutting properly who cares what technique I used.

Interestingly, every time I've seen an old stone it was dished quite a bit. I have to presume that the woodworker of that time did managed to get his work done.

Normand

[Patrick Chase]

I actually think that more of the curvature seen in the image is due to the cheapness of my camera and its lens than the geometry of the blade.

I accounted for that when I analyzed Stewie's picture.

His camera does have a fair bit of barrel distortion (the fancy technical name for "fisheye effect"), and that accounts for the "bulging" along the top and bottom edges, for example. That's why I only remarked on the dubbing, because there's no way that lens distortion caused the reflections to suddenly "bend" just behind the edge. Barrel distortion is easy to spot and correct once you understand the underlying physics.

[Patrick Chase]

FWIW here's an example of a blade that can't be back-beveled, from a low-angle shave. I worked it to 1 um, but didn't lap out the slight hollow in the middle as it has no functional impact (it's actually beneficial inasmuch as it eases flattening). The rest of it is flat to within 1/5000", but has visible striations even in the polished parts. Note that I chose the lighting geometry to accentuate those. If I'd rotated the blade 90 deg or focussed on the reflections instead of the blade itself then they'd be undetectable.

Back-beveling would have allowed me to fully polish the part behind the edge with a reasonable amount of effort, but the shave has so little clearance that doing so would be counterproductive.

IMG_1168.jpg

[Patrick Chase]

Whether 1 chooses to use the Ruler Trick or not, what's has come out of this discussion are the real benefits in keeping the top surface of your honing stones within a tight tolerance of flatness.

100% agreed. The profile of the iron needs to be a straight line where it meets the cap iron. It doesn't matter whether it's flat, back-beveled, dubbed, etc along the lengthwise axis though, provided that it isn't "tilted" by more than the cap iron's undercut angle.

[Stewie Simpson]

FWIW here's an example of a blade that can't be back-beveled, from a low-angle shave. I worked it to 1 um, but didn't lap out the slight hollow in the middle as it has no functional impact (it's actually beneficial inasmuch as it eases flattening).

Patrick; apologies for asking this question, but why would you bother working to 1 um when you leaving the most critical area of the blades contact untouched with a slight hollow. I would have considered it a higher imperative to work that hollow out with a coarser grit before moving on to 1um, or at the very least reached a stage where you had a clearly defined flat surface that encroached the full width of the cutting edge.

Stewie;

[Graham Haydon]

Jim, cheap camera or not the back of your Iron looks fine. All I'm looking for is to be able to remove a burr quickly, yours looks free from a burr. Since looking at all the different options that others find success with I've just gone back to what I was doing before. Fine India, raise a burr, remove a burr light strop and back to work. My cap iron fits, I can plane, pare and chop with no issue. There is nothing wrong with any approach shown here but lots of the ruler, micro, diamond approaches feel like something from a science/engineering lab.

[Patrick Chase]

Patrick; apologies for asking this question, but why would you bother working to 1 um when you leaving the most critical area of the blades contact untouched with a slight hollow. I would have considered it a higher imperative to work that hollow out with a coarser grit before moving on to 1um, or at the very least reached a stage where you had a clearly defined flat surface that encroached the full width of the cutting edge.

Stewie;

I think you're misinterpreting the photo.

The part of the back adjacent to the edge is polished all the way across, as evidenced by its high reflectivity. The change in lightness across the edge is simply reflections of lighter and darker objects (my finger on the left, the top corner of the camera and another finger in the center, etc). If I had focussed on the reflections instead of on the iron then the part along the edge would pass for a mirror.

The hollow is the "hazy", less-reflective part in the center of the iron's back, far away from all 4 edges. Given that this blade is for a low-angle (bevel-up) shave, that hollow is literally hanging out in space. It's as unimportant as it could possibly be.

[Stewie Simpson]

Thanks Patrick.

[Kees Heiden]

Personally I am moving more into the "good enough camp". Maybe it is the kind of wood I am working on at the moment (mostly cherry).

I find that getting rid of the wire edge, cleanly, is the most important thing about working the face side. Whether it is truelly polished, or has a few scratches, seems to be rather unimportant in the grand scheme of things. At least for me. My guess is that most people who have trouble getting an edge sharp, have some wire edge remaining. Working the bevel and the face, back and forth, on a fine(ish) stone, then stropping on a leather strop with autosol, is working fine for me. The face of a planeblade needs to be flat from side to side for me, so the capiron sits tight all the way across. But I don't mind a bit of convexity lengthwise.

In a similar vein, I don't mind anymore when a chisel back is a bit convex. I have one or two chisels with flat or slightly hollow backs and use these when I really want it for jigged paring.

[Pat Barry]

I actually think that more of the curvature seen in the image is due to the cheapness of my camera and its lens than the geometry of the blade.

Even so, if my blade is as horrid as it may seem, it still does a pretty good job of cutting (slicing?) wood in a manner suitable for a smoothing plane.

jtk

No doubt a camera can create distortion but you could put the edge up next to a known straightedge to verify the camber. To your second point though, I put it in the category of whatever floats your boat. Everyone eventually settles on what seems to be a comprise of sorts that works for them. I suspect everyone has room to improve though.

[Warren Mickley]

I think the "ruler trick" would be a big time waster for a serious worker. It takes a lot more time to position the ruler, flatten and remove the ruler. As I mentioned here in July, in recent sharpening videos David Charlesworth spent six seconds on the back of a chisel, and 30 seconds for the plane iron when starting with picking up the ruler.

For a hobbyist or a collector who was expecting to prepare a new plane or plane iron every few months, the "trick" would be worthwhile.

I don't remember doing any jigged paring.

[george wilson]

Another one of those GREAT threads where you can argue how many angels can dance on the ruler tricked micro bevel!!!

You all need to stop PREPARING TO WORK (It is an easy trap to fall into !),and get some wood out and start making something.

Of course,talking about work is cheaper on lumber cost than actually USING IT!!! And,if your shop is not heated,it is more comfortable!!!

[Kees Heiden]

Of course, you shouldn't forget, most of us are sitting at work behind the computer. During lunch hour of course (or maybe a tiny little bit beyond that) and are just discussing what fancies us. No harm done....

[Prashun Patel]

Statler and Waldorf,

What is a bigger waste of time? Geeking out about the ruler trick, or throwing peanuts at the geeking out of the ruler trick?