Smoke, Mirrors & Glint: Plane Iron Sharpening For The Bamboo Rod Maker

The vast majority of bamboo rod builders are faced with the continual task of sharpening a plane iron. Some, however, are not engaged in this task, namely makers who use hand or powered mills. But, for those of us who hand plane, understanding the unique obstacles we face is critical to planing success. 

Let’s begin by examining how planing bamboo on metal forms is different from planing a piece of wood. When planing bamboo, only a very small amount of the iron is touching the bamboo strip. This is because the bamboo strip is quite thin. So, while the center of the iron is maintaining contact with the bamboo strip, the right and left sides of the iron are hovering over the metal planing forms and contacting nothing. As the bamboo strip is planed down to the forms, the iron will eventually touch the forms on the right and left. One might assume that the iron that touches the metal forms becomes less sharp than the portion of the iron in contact with the bamboo, but this is usually not the case. The section of the iron touching the bamboo will dull quicker. Bamboo is rough on irons and can cause them to dull relatively quickly. So, when planing bamboo we see that only a very small portion of the iron edge is used, and as such, the edge will dull differently at different locations. Although it may be difficult to see, in the above photo, there is a shininess or "glint" in the center portion of the iron. This is the result of light shining off of the duller radius that forms from wear. The far left and right of the iron do not reveal as much glint and therefore remain sharper.

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Another interesting difference when planing bamboo is that a bamboo strip will often have different levels of moisture and differences of “grain” along the strip. Prior to planing bamboo, heat can be introduced into the bamboo numerous times. One may flame the bamboo culm, usually for aesthetic purposes. Thereafter, makers often heat and press nodes. Then makers use heat at various points along the bamboo to straighten the strips. And last, makers will often heat treat the bamboo strips, even if previously flamed. We see that heat actually changes the physical properties of the bamboo strips. But more importantly, we see that more heat may have been introduced at various points along the bamboo strip than at other points. Thus, when planing an entire strip of bamboo, the maker is using the iron to make consistent long cuts, along the bamboo strip with inconsistent moisture levels and with inconsistent physical properties at various points. So, while one portion of the bamboo may be planing nicely, another portion, often at or around the nodes where additional heat is used, may be more difficult to plane. This can result in chips or lifted pieces of bamboo. Compare and contrast this to planing a piece of wood with a relatively consistent moisture content throughout. And on top of this, the ambient humidity in one's shop, which may change throughout the year, can impact the moisture in bamboo.

To combat this issue, some will introduce moisture back into the bamboo strip when planing. Although this solves the moisture issue and makes planing easier, I've found that it can reintroduce a host of problems. Moisture can reintroduce bends in the bamboo strips, and nodes can mysteriously pop out. As such, my personal preference is to focus on planing and sharpening techniques rather than reintroducing moisture.  

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So, how does all of this relate to iron sharpening? Well, first a bit about “sharp.” Books have been written on sharpening, and those may be worth reading. But understanding what is or what is not sharp is not an overly complex concept. In its basic form, two “planes” (here the bottom of the iron and the operative bevel) meet at a point, which forms an edge. A duller edge has a more significant radius. When sharpening an iron, the goal is to reduce the radius. Of course, without any amplification, our human eyes can only see so small, and it is difficult to see such a radius. But there are clues. Our eyes can usually determine if an iron needs sharpening. If you take an iron and tilt it in various directions, and you can see glint at any point along the edge, the iron needs sharpening. A properly sharpened iron will not have any visible glint along the edge.

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Glint, however, will not tell you the sharpness of a given edge. Rather, it will only tell you if the edge needs sharpening. And herein lies one of the sharpening mysteries. Some believe that a better result will ensue with an edge that is sharpened with a 30,000 grit wet stone vs. a 3,000 grit wet stone. However, the finer the radius at the edge, the more fragile it is and the sooner it will break down and show glint. In my experience, polishing to about 3,000 or 4,000 grit (or their equivalent) is usually sufficient for bamboo rod making. (I’ve even had consistent luck at 1,000 grit or its equivalent.)

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That being said, I've polished with an agate stone, which is on par with a 10,000 grit wet stone. Although I’ve found no material difference in performance initially, the edge did breakdown much earlier, which impeded my planing results much more quickly. And I have not even discussed block plane nor iron preference. The reason for this is that the plane, the iron and the sharpening system is secondary to a nice, consistent, glint free edge, regardless of the way it is achieved and maintained.

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On to my current system… I prefer a vintage Stanley block plane, originally made in my home state of Connecticut, along with a replacement Hock A2 Cryo iron. I’ve found the vintage Stanley’s micro iron adjustments to be unparalleled. While there are many ways to get from point A to Z, for my own needs I find Arkansas stones to be perfect for my bamboo planing work. I do like to establish the initial bevel with diamond stones. I can be assured that I have the desired angle consistently imparted in the iron. But thereafter, I'm not concerned with removing a lot of metal when sharpening. Rather, my focus is to touch up the edge often and to maintain a consistent polished finish along the bevel, and my Arkansas stones do a great job at these tasks. Arkansas stones are not graded by grit level, but rather by hardness. The harder the stone, the more dense the stone. I typically use three stones in soft (coarse), hard (fine) and black (extra-fine). Rarely do Arkansas stones require lapping to remain flat. But if and when they do, a diamond stone with mineral oil can do the trick.

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My stones, along with a leather strop and some sharpening tools, sit in a sharping holder jig that i made from scrap wood. (The leather strop is typically used to make sure the burr is removed on the previously flattened back of the iron.) The stones are glued to wood, which I stained, and pockets in my jig are lined with adhesive cork to prevent sliding when sharpening. My sharpening angle jig is screwed into a block of wood with rubber feet in front of my stones. With this positioning, I can easily set the desired sharpening angle and immediately bring it to my stones.  There is a "lip" on my sharpening holder jig that is secured in the vice of a workbench directly to the left of my planing bench, making access simple and preventing my jig from moving while sharpening.

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Unlike wet stones that need to be soaked in water, which can also cause block plane and iron rust, I use mineral oil as a honing liquid on my Arkansas stones. Not only does it keep the metal pieces from nesting in the stone, it keeps all metal surfaces well protected with oil lubrication. Further, unlike wet stones that require frequent lapping to avoid “cupping,” Arkansas stones maintain their flatness for a much longer period of time. 

There is no perfect system, and there are many different types of stones and systems available.  However, the block plane, iron and sharpening system is useless if the maker does not maintain a glint-free edge at the appropriate sharpness. And, I’ve found the best way to keep glint removed from iron edges is to maintain a simple process, free of unnecessary obstacles. 

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