The GREAT sharpening debate

[Kalimna]

And have you been fortunate enough to start passing on your knowledge/experience to someone younger? My eldest son has just passed 2 1/2 years, and already knows how to hold a square to an edge and look at it critically Well, he copied me once, not sure he'd do it again! Last night he wanted a piece of wood to cut with his Bosch toy jigsaw, and was a bit disappointed when it didnt work.... A very sweet moment to take to nightshift with me...
The fondness goes both ways indeed, whether you are the small child, or the big child

But your grandfathers' method of assessing sharpness is as good a rule of thumb as any and tells you in an instant what you need to know.

Adam

 

[Dodge]

And have you been fortunate enough to start passing on your knowledge/experience to someone younger?

Adam

Yes, as some of you will already know my lad is quite regularly in my workshop with me where he has his own bench and tools

All his own work and he is only 11!

 

[bugbear]

........ We do not have to do woodwork to confirm sharpness,

Yes you do. "Sharpness" means nothing out of context.

Sharpness is easily defined by the radius of the meeting between two planes - perfectly meaningful

Perhaps you mean "applicable" or "neccessary".

For example, a presentation sword might be well be beautifully sharp, even though it will never be used.

BugBear

 

[Jacob]

Jacob - Sharpness itself could very easily be deifned without any reference to intended use as the granularity/continuousness (?sp?) of an edge, itself defined as the interface between 2 planes. Context is quite unimportant, for instance micro scalpels used in eye surgery are exquisitely sharp (considerably more so than the edge tools used against wood) but utterly useless for woodwork!. Now, useful/efficient sharpness is perhaps a different matter.

Adam

Interesting but wrong.
'Sharp' or 'not sharp' is defined entirely by context.

A sharp axe might be too blunt for paring wood. A sharp chisel might be too blunt for eye surgery. A sharp micro scalpel might be too blunt for, er, I dunno, brain surgery?

Then taking them in reverse order - a thing can be too sharp for the purpose, i.e. with an edge too fragile, etc etc.

If you defined sharpness as ".....the interface between 2 planes...." etc then all woodwork tools would be blunt (except Brent Beech's presumably).

 

[Dangermouse]

And have you been fortunate enough to start passing on your knowledge/experience to someone younger?

Adam

Yes, as some of you will already know my lad is quite regularly in my workshop with me where he has his own bench and tools

All his own work and he is only 11!

Wonderful to see young people coming on in the hobby and what a craftsman he is!! A lovely box indeed, well done that ( young) man !

 

[243SS]

Jacob - Sharpness itself could very easily be deifned without any reference to intended use as the granularity/continuousness (?sp?) of an edge, itself defined as the interface between 2 planes. Context is quite unimportant, for instance micro scalpels used in eye surgery are exquisitely sharp (considerably more so than the edge tools used against wood) but utterly useless for woodwork!. Now, useful/efficient sharpness is perhaps a different matter.

Adam

Interesting but wrong.
'Sharp' or 'not sharp' is defined entirely by context.

A sharp axe might be too blunt for paring wood. A sharp chisel might be too blunt for eye surgery. A sharp micro scalpel might be too blunt for, er, I dunno, brain surgery?

Then taking them in reverse order - a thing can be too sharp for the purpose, i.e. with an edge too fragile, etc etc.

If you defined sharpness as ".....the interface between 2 planes...." etc then all woodwork tools would be blunt (except Brent Beech's presumably).

'Splitting hairs' here (how sharp for that?)...you're both correct. Sharpness within the remit of cutting wood for cabinet/joinery work etc is what should be under consideration.

 

[Dave D]

For me the most useful section of Brent Beach's website concerns BU planes.
He shows that it is particularly important to get rid of the wear on the back of the blade.
It does not matter how you do it but if the back wear is not removed the plane will not perform at its best.
He also points out that it is possible to get a good wire edge when sharpening the bevel while still not having removed all of the wear on the back, so just relying on the first appearance of a wire edge
is not proof that wear has been removed on the back as well as the bevel of the blade.
Before I understood this I was getting random occurrences of poor performance after sharpening a variety of BU planes.
I now realise that I was simply not removing enough metal to make sure that both the bevel and the back of the blade had all wear removed.
For chapter and verse please look at Brent's site. It is a bit disorganised but he has certainly done his homework.
I am now getting consistently better results than before I read it.

 

[bugbear]

Jacob - Sharpness itself could very easily be deifned without any reference to intended use as the granularity/continuousness (?sp?) of an edge, itself defined as the interface between 2 planes. Context is quite unimportant, for instance micro scalpels used in eye surgery are exquisitely sharp (considerably more so than the edge tools used against wood) but utterly useless for woodwork!. Now, useful/efficient sharpness is perhaps a different matter.

Adam

Interesting but wrong.
'Sharp' or 'not sharp' is defined entirely by context.

A sharp axe might be too blunt for paring wood. A sharp chisel might be too blunt for eye surgery. A sharp micro scalpel might be too blunt for, er, I dunno, brain surgery?

Then taking them in reverse order - a thing can be too sharp for the purpose, i.e. with an edge too fragile, etc etc.

If you defined sharpness as ".....the interface between 2 planes...." etc then all woodwork tools would be blunt (except Brent Beech's presumably).

This lparticular debate can be easily resolved.

Kalimna has clearly (and very conventionally) defined "sharpness".

Jacob appears to be defining "sharp enough", which he unhelpfully shortens to "sharp".

Two different things.

There's enough points of division on this topic without making needless ones.

BugBear

 

[Jacob]

If you are sharpening anything, then 'sharp enough' for the intended use, is what you want. So if it's my draw-knife, then personally I don't want to waste my time sharpening up to an eye surgery standard.
Sharp enough for the intended use is verified by using it, not by looking at it through a microscope and then looking at your navel.
Amazing that this has to be pointed out! No wonder these discussions go on and on so boringly.

PS and in any case, there is absolutely no way of knowing, by microscope and navel gazing, whether or not an edge is sharp enough, unless it has been put through an appropriate the test at some point.

Or 'the proof of the pudding is in the eating' etc. etc.

 

[woodbrains]

Hello,

A few more observations. Firstly, the author is sharpening woodworking tools with readily available abrasives and the usual woodworking methods and bevel angles. This automatically contextualises the issue. There is no possible way these tools will not be suitable for woodworking. And since the author sharpens the edges with very fine abrasives, it could never be true to say that the tools were less suitable for woodwork, than tools sharpened with coarser abrasives, nor could it be proved. Field testing the tools here would prove nothing.

How do we know what sharp enough means? If I sharpen my smoothing planes easily to super sharp for finishing, why would I not sharpen all my tools this way? I use 2 stones, one medium for removing the wear bevel and a polishing stone to hone the edge sharp. I cannot do less well than super sharp, for a tool that (not me) someone might say is needlessly sharp for a certain job. What am I to do- get the edge to super sharp and then dull it a bit on the concrete floor, because the job doesn't need that level of sharpness. That would take more effort than leaving it sharpest. This is ludicrous. But, if getting the thing super sharp means the edge lasts longer, and not just because it was sharper to begin with but that the edge was less damaged getting it sharper and thus less prone to frictional dulling, then I say only super sharp is sharp enough.

There is some confusion with sharpness and durability with some people here. There is no reason why an axe should not be sharpened to a fine level of abrasive. The included angle for an axe would be greater than a plane, giving it more durability for it's job, it would also be tempered to a lesser degree to remove some brittleness, but it can certaily be as sharp. How many American loggers shave their arm hairs with their axes, at the tree felling competitions they have over there. Using a dull axe is exhausting, sharper less so. Eye scalpels would have a much lower included angle, which would make them unsuitable for most woodworking tasks (poor durabilty) but they are not necessarily sharper. The abrasives used to sharpen these are no different than we might find.

If you don't think drawknives should be as sharp as a plane, then you do not know what they are for.

Mike.

 

[Dodge]

Could all participants in this thread please look at the other thread I have just started

calling-all-sharpeners-panic-not-t67804.html

Your Skills are needed :-k :-k

 

[Jacob]

……… Field testing the tools here would prove nothing.

It might show that he is spending too long sharpening

…… What am I to do- get the edge to super sharp and then dull it a bit on the concrete floor, because the job doesn't need that level of sharpness.

Don't be silly

That would take more effort than leaving it sharpest. This is ludicrous.

yes it is

But, if getting the thing super sharp means the edge lasts longer, and not just because it was sharper to begin with but that the edge was less damaged getting it sharper and thus less prone to frictional dulling, then I say only super sharp is sharp enough.

It's a question of diminishing returns. There come a point in sharpening where the effort put in is not worth the outcome on the job

………If you don't think drawknives should be as sharp as a plane, then you do not know what they are for.

Should draw knives be as sharp as micro scalpels?

 

[ivan]

I was under the impression that it was the Japanese chap who showed that a cap iron must be set very close or it doesn't work. My grandfather, a cabinet maker, insisted on "a hair's breadth" for difficult grain. A 55deg bed and a close cap iron reproduce the cutting geometry of a scraper plane, but with the advantage of a tight mouth. It's my belief that bevel up planes are thought to cut difficult timber as well as bevel down, because most cap irons are set too far from the edge to make any difference (ie more than 5-8 thou). Of course none of this is of importance if the timber is easy planing.

Standard Record/Stanley blades can vibrate whilst cutting (you can see it with a clock gauge) - the 2 piece cap iron was supposed to correct this. An infill plane blade will be nearly 30 times stiffer, cuts quietly and if of similar material will thus stay sharp longer.

 

[Kalimna]

Mike - good points, but just for interests' sake eye scalpels tend to be made from glass shards mounted onto a handle extension, which are fractured rather than ground, so it is unlikely that there will be many cutting edges that are sharper.
And on a similar note, most (if not all) disposable metal scalpel blades such as are produced by Swann Morton, initialy for use in surgery but now co-opted for marking out woodwork and other crafts, are not ground either but laser cut. And if we are talking abrasive particle grain size then it is unlikely much will be found smaller than a photon

Cheers,
Adam

 

[Peter T]

Laser sharpening of scalpel blades sounds interesting!

How does that work?

 

[RogerS]

There's nothing that a sharp blade can do that a piece of 80 grit cannot irrevocably destroy.

 

[Jacob]

Paul Sellers at it again. I agree with (almost) everything he says!
Strop are cheap and last forever. I've had the same bit of leather glued to a board since about 1966 (I estimate). I've still got the other half of the original piece, which I kept in case I needed a replacement. It keeps turning up when I'm looking for things, still untouched but looking a bit dusty after nearly 50 years of kicking about in the workshop.

I had a go with Sellers' recommended EZE-LAP diamond plates and they work fine but somehow I prefer the oil stones, in spite of their smaller size and hollowed out surfaces. One thing which has certainly made them more useful is a diamond 3m Diapad to freshen up the surface every now and then. No doubt there are plenty of alternative methods - I just happened to have Diapads from another job. The main thing is it has to be a bit flexible to go into the dips. Otherwise you'd have to flatten the stone which is otherwise unnecessary, a waste of time and a waste of stone.

 

[bugbear]

Some of what Sellers says sound most unlike Jacob's interesting innovations...

The use of a sequence of grits (like all practical sharpeners)

In my book, it’s best to use three abrasive plates that stay flat, cut fast and last long.

And a very traditional approach to strops...

Strops are simply the most effective way of discharging fine abrasive to the bevel of any edge tool.

BugBear

 

[Jacob]

Some of what Sellers says sound most unlike Jacob's interesting innovations...

The use of a sequence of grits (like all practical sharpeners)

In my book, it’s best to use three abrasive plates that stay flat, cut fast and last long.

And a very traditional approach to strops...

Strops are simply the most effective way of discharging fine abrasive to the bevel of any edge tool.

BugBear

Er - you obviously haven't been paying attention. What are you trying to say, if anything?

 

[woodbrains]

Mike - good points, but just for interests' sake eye scalpels tend to be made from glass shards mounted onto a handle extension, which are fractured rather than ground, so it is unlikely that there will be many cutting edges that are sharper.
And on a similar note, most (if not all) disposable metal scalpel blades such as are produced by Swann Morton, initialy for use in surgery but now co-opted for marking out woodwork and other crafts, are not ground either but laser cut. And if we are talking abrasive particle grain size then it is unlikely much will be found smaller than a photon

Cheers,
Adam

Hello,

I take your point on eye scalpels, obviously not sharpened as we know it. Laser sharpening of steel blades is more likely a production expedient, rather than a means of getting something sharper than trad methods, though, since I regularly sharpen a Japanese marking knife at least as sharp as Swann Morten scalpel blades. The point is, I do not fuss. The method I use is very, very quick, so I would save no time sharpening 'not as sharp' and I would not be taking any chances, with the edge not being sharp enough. I like consistency.

I know you are only funning me over photons, but I don't think their size has much to do with the coarseness or fineness of the resultant edge as compared to abrasive grit size. If the whim takes me, I might look into how it is done, but I would guess it has more to do with the frequency of the light, as with impulse or induction hardening. Possibly the 2 things are done simultaneously, too.

Mike.