Tuesday, December 22, 2015

Compare and Contrast

Wood has grain, comprised of fibers which are adhered to one another and which are bonded to one another with lignin. Grain bonds are stronger in certain directions than others. When you work with solid wood you must design around this fundamental fact of grain, in regards to the effect of grain pattern aesthetically, in terms of the grain arrangement and how it associates to the wood's seasonal movement, and in terms of how the wood is most ideally worked given that it has grain.

Planing against the grain is normally best avoided, however often it simply cannot be avoided. It is in fact more often the case than otherwise that the plane user is confronted with sticks of wood in which the grain slope or direction is not consistent throughout the stick to be worked. This unpleasant fact, and the aggravations that can result when plane meets material, can result in aggravation at the very least.

One means of dealing with the issue, if you want to use a plane on difficult material, is to manipulate the chip breaker. The following video, which has been circulating for many years now, gives a clear description of how the sub blade can affect planing performance:



An informative video, and an analysis of an archaic tool - a plane blade - made possible by a large precision milling machine and sophisticated video equipment I might add. I find it fascinating to see the plastic deformation of the shaving flowing over the edge and chip breaker face. Mesmerizing, at least to me.

Metal also has grain, in at least a couple of distinct senses. One is the grain that is inherent to the polycrystalline nature of metal. Between these crystals are the grain boundaries. When a metal solidifies from a molten state, these grain crystals grow, and the longer the metal takes to cool the larger these grain crystals grow. Top blacksmiths in Japan make study of the grain structures of their tools with high power microscopes to check the grain configuration, a practice which likely originated with the late great Usui Kengo. The appearance and form of the grain crystals is a clear tell-tale as to whether a given step in the fabrication was executed perfectly or not. For further reading, check out the-warren.org.

Grain is present in metals which are formed/finished by rolling, like sheet metal:

During the fabrication process, most of the time, the sheet of metal will go through a line grain machine prior to forming, hardware, and finish. Line grain can also be known as Satin Finishing, Metal Brush Finishing, and Time Saver Finishing. Line grain is a uniform linear sanded finish that is used to remove and minimize scratches, blemishes, material defects, and mill scale.

From: http://www.vista-industrial.com/blog/material-grain-direction/

Thus, like wood, metal can be anisotropic. Grain size and orientation in both materials affects mechanical properties and surface appearance.

If a sheet metal worker or industrial designer ignores the grain issue, then problems arise. If the metal is bent parallel to the direction of the grain, then cracks can occur in the grain of the bend, especially with thicker materials. The line grain must run perpendicular to the bend:


From: http://www.shedworks.eu/hints.html

Grain in sheet metal also has other outcomes practically speaking - solar collectors, for example, which use metal as a reflective surface, need to have that metal sheet correctly aligned for proper performance. The run of metal grain scatters the light, but only in one direction, and this affects optical quality.

A third obvious example of grain in metal would be wrought iron, which has fibrous inclusions present:


From: https://en.wikipedia.org/wiki/Wrought_iron

The black lines in the above picture are fibrous inclusions, also known as stringers. They are filaments of slag characteristic of wrought iron.

When you partially cut and then bend a wrought iron bar, the grainy filaments will be obvious:


Now, I don't state the above points to suggest that metal and wood are exactly equivalent, but only to state a point or two of some similarity between the two materials. This information may be news to those who only have familiarity with one of those materials.

There are other intriguing similarities to wood as well which become apparent when working metal. Just like with wood, there is an option to grind or an option to cut shavings when removing material from stock.

Take a look at this video showing what happens when chips are taken from steel, and note the effect of certain types of coatings on the cut:



I know that video was likely not the rock and roll highlight of your day, but I hope it was enlightening at least.

Similarities would seem to abound between the scenes depicted in the above two videos. For one thing, both metal and wood can tear out, leaving a poor surface, with the wrong cutting set up. The plastic flow of material off of the cutter is very similar when you get close on in there to look. Wood resins can build up on the edge of a wood cutter as well, heating and dulling the edge and creating similar outcomes to what you see with metal. I wonder why tooling coatings haven't been put into play with woodworking to much extent, at least with router bits? Certainly they might be of help when working abrasive materials like teak. Now, in saying that, I do omit to mention the very recent utilization of diamond coatings on tooling that we're starting to see on shaper and planer knives.

A lot of people who work wood seem to have an allergy to metal, or are afraid of it - who knows? - and indeed many would characterize wood as 'warm' and metal as 'cold', that sort of thing. But when you look at cutting those materials closely, when making shavings or chips is the goal, there sure are a lot of similarities in terms of how those chips are taken from each material.

Both metal and wood can have tensions built up within as a result of the processes by which they are formed, and these tensions can manifest in the material moving after being cut. Metal has an advantage in that in certain cases the stresses can be normalized by a reheating process. With wood, you have to choose your tree carefully to minimize problems with growth stresses.

I find it interesting how two materials which can seem very different in a number of obvious ways otherwise can in fact display quite similar properties when we look closely enough.

Hope you found the above of interest. All for today.

Thanks for visiting the Carpentry Way.

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