Thread: chisel theory

Sorry John, but I don't understand the question you are asking.

When using a chisel, it is usually registered off its flat back, and the honing angle is a compromise between the material being cut, the chisel steel, and edge life.
Softwoods usually respond well to a 20 degree edge, but using the same chisel in a hardwood will usually result in a folded cutting edge within minutes.

Typically with a chisel you want the lowest honing angle that works in the material being cut.

thanks Ian
It's about the angle of the whole tool not the sharpness . It's an obvious skill so probably no-one thinks twice about the steepness of the chisel-handle : it really is "theory" to measure it.

Chisel angles also depend on the application.

Paring chisels can have a lower angle (about 20 degrees) because they're only ever pushed by hand, chisels that are struck need a higher angle (25-30 degrees) to take the impact.

John, you're overthinking it.

chisels are used at two basic angles
vertical when chopping a mortise -- for the moment let's not deal with the direction the bevel faces for a particular task

parallel with the surface when paring to a line.

occasionally, a chisel will be used riding on its bevel,

if you are just hogging off material the angle of attack is what works

it's about control, angles other than 90 degrees and 0 degrees, relative to the chisel's back are very difficult to control.

yes , all true . But my thing is not about the skill , it's about the theory because there's another problem I'm interested in. So it needs overthinking . A elanjacobs says : "take the impact" ; that's the stuff I'm on about. ( skulls , swords , fractures and non-woodworking problems).

Extra details on what exactly you're trying to work out might help people give you the info you want.

If you're talking about edge durability, the steel itself will change the angle; Japanese chisels generally need a higher angle than western chisels because the steel is much harder and, therefore, more brittle than most normal tool steels

John
are you talking about Toorale Man?

If yes, perhaps a chisel is not a good analogue.
A bladed weapon needs both keenness and toughness -- attributes that while similar to what is required of a chisel are subtly different.

With a chisel you take care to select a steel that can be sharpened to the degree required to cut wood fibers and you also take care to protect the edge from abuse -- with a bladed weapon the edge is designed to absorb abuse and still function.

Ian
I'm still doing Toorale man. ".. It was originally thought to have sustained metal damage when first uncovered, but the subsequently dating caused re-evaluation. . It is now generally accepted that a boomerang could be sharp enough... I have the privilege of having access to two of the world’s leading experts on tool use and consider their advice on the impact of boomerangs on bone as well-informed. " _Branch Manager, Life and Geosciences | Australian Museum Research Institute,

This detail is about the resistance to a low cutting-angle ( off vertical) . Mulga blades have 30 to 60 degree tip as sharp as a spade dragged across cement , a Museum expert tells me. They are bi-convex like an egg with the small end pointed so the clearance angle is added to the "bulge" convex and to 30-60 degrees . Cutting angle is then around 45 to 15degrees off vertical for a hand driven edge. The resistance compared to normal hand-chisel must be enormous.

You say "absorb abuse" : if an edge is abused then function is hardly possible , resistance increases yet again.

John
a chisel needs to be sharp
a bladed weapon tough, if it were not it would become useless after a few strikes. This is what I mean by "absorb abuse".


I remain troubled by dating dominance surrounding Toorale Man.
If the injuries are consistent with a metal (steel?) bladed weapon, then to my mind the investigation should be focused on completely eliminating the possibility taht there was a metal bladed weapon travelling along the Darling that long ago.

My recollection of contact between Australian aborigines and other cultures and the song lines that criss-crossed the country does not rule out a metal bladed weapon making its way into western NSW well before Captain Cook.

Well if mulga could absorb / reject abuse it would be as hard / tough / brittle as metal . I've pushed a sharp mulga split-end and a chisel into softwood - the mulga cut less and rounded the edge. The academics eliminate metal by using the word "impossible" , end of argument . Let's assume that mulga is nearly metal. So then I'd like someone to state that any hand chisel at 45 to 15 degrees off vertical gets more resistance . Elanjacobs #4 post is useful for quoting.