Thread: How do you know how sharp something is

You can shave hair with a chisel or a plane blade when they have slightly lost their edge particularly on a wide plane blade when you have been planing narrow edges.

I check my blades when the cutting is OK but not quite 100%. A close inspection of the blade in the right light at the right angle usually reveals a shiny white line on the very edge. A hone with a 6000 water stone usually brings it back to a good edge again.

- Wood Borer

Arron

Good question. Yes, after you have shaved all the hair from your arms you have only your legs to turn to, and I don't think I want to go there.

Wood Borer is absolutely spot on when he described what to do when you sharpen the blade, how you see the sharpness. But below is how you experience it.

The best test of a truly sharp blade, either a freshly sharpened plane blade or chisel blade, is to see if you can cut pine end grain. If you think that is easy, just try it! Soft wood tends to be crushed before it is cut, and only a sharp edge will cut the wood fibres before they bend.

For the same reason pine is one of the hardest woods to chop handcut dovetails into. The ends just crumble and crack. To cut clean edges in pine you have to slice the ends. And only a truly sharp edge will do this.

One alternative to pine is Western Red Cedar. Same story.

Regards from Perth

Derek

If you happen to cut yourself & don't even know you are cut till you see the blood, the tool is probably sharp.

It all depends on what you call sharp, sharp enough to your average builder would be useless to a fine cabinet maker.

Many years ago, as an apprentice I almost cut my thumb off with a chisel I had just sharpened. (I was doing the wrong thing and I knew it, it's the one and only time I've needed stitches). The doctor that stitched me up congratulated me on the cut, said he couldn't have cut it any cleaner with a scalpel.

Mick

Mmm ....

I wonder how scalpels are sharpened?

Regards from Perth

Derek

Nowadays they use disposable blade scalpels (or in a lot of cases, disposable scalpels) a bit like an exacto knife. Need you ask really, in this day & age isn't almost everything disposable?

Mick

Mick

Sadly so.

Still, I wonder how they are sharpened to such a high degree when manufactured. Anything to learn from this?

Derek

Hmm, never gave it a thought, guess it's the same process that gives us razor blades, craft knives etc. Hmm disposable tip chisels and planes? (Oh actually the planes have already been done, laminated bodies with disposable cartridge knives or even TCT knives, made in Switzerland or Austria from memory. ).

Mick

Good fish hooks these days are usually sold as 'chemically sharpened' rather then 'mechanically sharpened'. Always wondered how they do that.

Arron

I dont think you would find too many surgeons usung scalpels these days,mostly Laser, bloodless.
If it cuts hair on your arm with only the slightest pressur its sharp.keep fingers away!!

Hi all,

I believe scalpels, lancets & most medical sharps are extremely sharp because they are electropolished/silicone coated. They are first cut to a sharp, low angle point then electropolished for smoothness. They are then given a silicone coating that virtually eliminates friction also. Scalpel blades I would think would be single use as to assure there sharpnes.

Cheers

Woodchuck

Perhaps something to bear in mind if a scalpel is used on a piece of wood that later needs to be polished.

I will keep them away from my shed.

- Wood Borer

When I was a boy, my 'master woodworking' neighbour said that after honing (spell?) a chisel or plane blade, you would lightly run it down your thumb nail to see how small a sliver you could peel off.

I suppose once you got down to skin, you'd use other fingers ... hmmm ... I can't remember how often I sharpened my tools as a boy ... by hey! ... that was nearly 30 years ago. Opps ... I just remembered, a few months back, I honed some chisels and used the same method ... just checked, the thumb's nail is smooth! I wonder how quickly thumb or finger nails grow? Luckily I've not had to sharpen lots of blades at the same time!


Burn

If you want to read about some truly amazing blades, try here.
They are sharpened down to a few atoms (sort of).

http://www.popularmechanics.com/scie...003/10/knives/

Ben.