paulsellers.com https://paulsellers.com/2014/10/on-fractured-cutting-edges-to-edge-tools-part-ii/

25 October2014

On Fractured Cutting Edges To Edge Tools Part II

With one high end chisel sharpened to as near perfection as PS could gain, I pressed the chisel into pine wood forparing cross-grain and, moving across from one side to the other in swathes 1 wide, cleared an area 1/8 deep 3across from front to back and 4 long.

I then pared with the grain over the same area and then chopped 6 times hard onto the chisel edge with the samenumber of blows and equal force each time. The steel is new and specially formulated.

One of the hardest things for a chisel edge is scraping it on end along the surface of rough grain. Students do it all

the time at first, until I explain how much damage they do to their chisel edges. So, I then scraped the chisels testedacross the surface of the same grain as shown and applying much pressure. I did the same to all the makersincluding an unnamed maker from the late 1800s. The end results was surprising. Once treated so harshly, the highend chisels fared more poorly than I expected. Instead of boring photograph showing results we tested the damageby seeing how high the chisels had to be elevated on the surface of the wood before the edge bit the wood sufficientto start a cut.

In my tests all of the chisels bit the surface after sharpening at about the same angle of presentation.

The above measurement show the chisel elevated to 2mm before the bite was effective.

After the pressure and hammer tests the low end Aldi chisel and the old chisels continued to cut without furtherelevation. The high end chisels that fractured much more had to be elevated by 12mm to even start the cuts. Thiseffectively meant that the surface fracture on the edge was so cratered, compensation had to be made to make thechisel effective. The old chisel, having undergone the same treatment, needed elevating only 2mm. This chiselcontinued working for hours afterwards and I was cutting and paring oak shoulders across end grain and paring thefaces of tenons the whole time for demoing to students.

I took an angled shaving with one of the chisels I had run through the test, a reputable maker sold by high enddealers in the UK and USA. This had faired quite poorly in the tests and this is what we got.

I then took the Aldi chisel that had gone through exactly the same treatment and pared the same surface and it gaveme a clean surface.

Therein was my deciding factor. It wasnt based on cost but work. The Aldi chisel proved to be the better chisel.Others looked more prestigious and looked nice on the benchtop. Its all about choice then.

This then does tell us that the relief on the underside of all plane irons bar none was a development based onpractical application and not because science itself contributed much if anything at all. A man at his bench saw that achisel needed elevating to the work to make it work and lifted the chisel slightly higher. When the chisel was too highhe took it to a stone and honed it. Now some salesman from a distant office and of unknown background or perhapsa magazine says hone to 25.000 grit on glass covered with abrasive paper and we jump through all of legalistichoops. The scary-sharp method is just OK to get those first sharp chisel and plane edges when starting out inwoodworking, but its wow factor leaves a few big questions because its far from an economic or practical solution togood sharpening practice. At first glance it look feasible, logical, practical. Its not. Abrasive films are extremelyexpensive long term and well worth the money for some applications, but for sharpening edge tools for woodworkingin general I think it is obsessive at best. Its all become quite silly. I would say the same too for steel makes and soon.

My research shows that fracture takes place the very second the chisel touches the wood; so much so the beveledge top fracture and the flat face bottom or under-fracture fractures equally and at the same time. Most people dontknow this.

Immediately after sharpening, chisels with dead flat faces must in some measure be elevated to engage the wood.

The less the edge fracture the less the incline needed. Within a few seconds of use, depending on the wood and thework type, the chisel elevation increases to effect a similar cut. Its at this point then, when the rate of edge fracturediminishes dramatically, that we are given a practical working edge to chop, pare and plane with. The angle betweenthe two faces forming the edge may well now be altered, increased as it were by fracture wear to around 40-degreesas both faces fracture along the edge equally.

Because edge fracture occurs immediately, we should be aware when we sharpen that its the diminished return thatgives us the strength we actually need for real work not temporary or prissy work. After a few minutes of use, newlymade chisels by a major UK maker of chisels left me with a chisel that I could not cut myself with. But, that said andestablished, they are still sharp enough for 95% of general woodworking tasks surrounding furniture making. If youindeed doubt anything I am saying. Run the same experiments. Use any plane for a few minutes on a pine boardwith or without knots and remove the blade. Feel the edge and tell me the truth, as you (carefully) pull the fingersperpendicular to the edge, do your fingertips glide over the edge or does the edge catch ready to cut. Do the sametrial with your chisels and you then see how the wood and the work affects the router plane cutter.

I made a facsimile from styrofoam to show an enlarged approximation view of what happens at the cutting edges ofedge tools.

This post may seem to ramble between chisels and router cutters and bluntness, dullness, motives and so on, but forme they are apart of the same issue. Our world is all the more fractured into tiny bytes where media projects tinyinformational pockets into our lives and there is really no conclusive result because everything is negotiable in aworld of no absolutes. I cant separate the cutters from routers from chisels and planes because of the variousrealities uniting them. Two flat faces set at an angle creates a sharp edge. The most practical angle for this to beused and restored and at optimal strength is 30-degrees. Knives and axes, chisels and planes all have angle around30-degrees. This may vary with shearing-cut actions as on scissors and guillotines, but generally 30-degrees isaccepted universally and this is because the material dictates.

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