{"id":539,"date":"2015-02-03T18:01:41","date_gmt":"2015-02-04T01:01:41","guid":{"rendered":"http:\/\/www.meanderinglines.com\/?p=539"},"modified":"2015-02-03T18:01:41","modified_gmt":"2015-02-04T01:01:41","slug":"sharpening_knives_chisel","status":"publish","type":"post","link":"https:\/\/meanderinglines.com\/?p=539","title":{"rendered":"A Sharp Blade"},"content":{"rendered":"

I was visiting Seattle one spring, to escape the inevitable mud and snow of Bozeman and remember what green things looked like, when I walked into a small shop that sold Japanese saws. There was nothing on display, just boxes stacked in the back of the room and a counter with an older Japanese gentleman standing behind it.\u00a0 I had heard he had a particular type of Japanese saw that I was looking for and inquired about it.<\/p>\n

\u201cYes, I\u2019ve got one\u201d, raising an eyebrow, \u201cbut it is not the best, you want to see the best.\u201d<\/p>\n

\u201cSure, I\u2019ll look at it, but show me the one I asked for too.\u201d<\/p>\n

He reaches under the counter and pulls out an menagerie of blades, handles and some wood to demonstrate on.<\/p>\n

He examined me as he handed me the saw I had asked him about, \u201cyou know how to use it properly?\u201d<\/p>\n

I took the saw and the piece of wood and started to cut.<\/p>\n

\u201cNo, like this\u201d and he took another saw to demonstrate a better stroke along with an explanation of the intricacies of the method.\u00a0 He was very accomplished.<\/p>\n

It was a rainy, I didn\u2019t have anything pressing, so I spent the next 45 minutes looking at and discussing the different saws he had; uninterrupted since no other customers had come in.\u00a0 I ended up buying a couple of the saws he that had demonstrated were the best and was getting ready to go.<\/p>\n

\u201cYou use chisels?\u201d he probed<\/p>\n

\u201cYes.\u201d<\/p>\n

\u201cAre they sharp?\u201d<\/p>\n

\u201cSharp enough, do you sell chisels too?\u201d<\/p>\n

\u201cNo, \u2026 You know how to sharpen them?\u201d<\/p>\n

\u201cI do OK.\u201d<\/p>\n

\u201cDraw what you think is sharp\u201d, as he slid a piece of paper and a pen across the counter.<\/p>\n

I made marks similar the the drawing in Figure 1a.<\/p>\n

\u201cThat\u2019s not sharp\u201d, he then drew the a drawing like Figure 2a.\u00a0 \u201cThat is sharp\u201d, while looking at me crossing his arms across his chest.<\/p>\n

I took the bait. \u201cwhat I drew is sharper than that.\u201d<\/p>\n

\u201cReally?\u201d, then he proceeded to lay out his case.\u00a0 It was a good case too.\"SomethingSharp\"<\/a><\/p>\n

He started by pointing out that when sharpening a blade to a fine edge, as in Figure 1a, there comes a point when the metal is so thin it has no structural support.\u00a0 In other words at the finest point where 2 planes of a piece of metal converge it is at places only 1 grain of metal thick and it is not consistent since even when using a very fine grit abrasive the grit of the abrasive is larger than the metal grains.\u00a0 The product of this process, if looked at under extreme magnification would look like the drawing in Figure 1b, and the edge so thin it would be fragile.\u00a0 While it would cut, or actually saw, and appear sharp it would dull quickly as some of the edge brakes off and other portions bend over.\u00a0 If fact when we use a sharpening steel to sharpen a blade, we actually aren\u2019t sharpening it, but realigning the metal at the edge. With this process it doesn\u2019t take very long before the blade is dull beyond the point of recovery.<\/p>\n

\"Polishing<\/a>

Polishing the back of a blade<\/p><\/div>\n

In reality what we want to produce when sharpening a blade is not 2 planes converging, but 2 planes coming very close to converging then being joined by a 3rd plane that is the minimum thickness to keep the 2 planes from converging while remaining to maintain the stability of the metal\u2019s lattice structure.\u00a0 This is best illustrated by the drawing in Figure 2a and the benefits and stability are illustrated by the drawing in Figure 2b.\u00a0 When you are able to achieve this configuration on a blade, it will cut smooth and remain sharp.<\/p>\n

\"Evidence<\/a>

Evidence that the back is flat<\/p><\/div>\n

Great theory, but how do you get there?\u00a0 Well, he showed me and I\u2019ll describe it as best I can, using a single bevel plane blade as an example.\u00a0 This process works on bi-bevel blades such as knives too, but requires some adjustments in technique.<\/p>\n

Start by polishing the back side of the plane blade first to insure that it is flat.\u00a0 This is done by laying it back side down on a stone and working it until it has an even patina of abrasion from edge to edge.\u00a0 Next you will work the bevel, to do this you will need a guide to maintain a perfect angle while sharpening, I don\u2019t believe anyone is able to hold it freehand precisely enough to meet the goal of creating a precision edge.\u00a0 Repeat this process, backside then front, until you are at the finest grit stone you will be sharpening with.\u00a0 While working with the last grit on the bevel polish it until you raise a burr all along the back side of the blade, then take the blade while holding it with the point resting on the stone and drag it smoothly about 1 inch, you just made your 3rd plane.\u00a0 Next, polish the bevel on the stone counting the strokes, checking for the burr to be raised again after each stroke.\u00a0 Once you get a burr again, hold the blade with the point on the stone and duplicate the drag you did previously.\u00a0 Now polish the blade one more time counting the strokes, but with 2 to 4 less strokes and you have a sharp blade that will maintain its edge.<\/p>\n

\"Draw<\/a>

Draw the blade back 1 inch<\/p><\/div>\n

A few details to be aware of:<\/p>\n