Never by hand

[Jacob]

.....
So, Jacob and everyone, are my diagrams helpful?

I've done that first diagram myself but they still didn't get it! As you say, if the edge is the same (30º or whatever) it'll cut the same, whatever goes on with the bevel (within reason - some hollow ground edges can be a bit fragile IMHO).

And richarnold still hasn't said what is wrong with a convex bevel other than that it doesn't fit his sharpening regime. NB we are not talking about 'rounded over' bevels.

 

[Paul Chapman]

if the edge is the same (30º or whatever) it'll cut the same, whatever goes on with the bevel

So why do you keep banging on about it, year after year, after year...... :?

Cheers :wink:

Paul

 

[Jacob]

if the edge is the same (30º or whatever) it'll cut the same, whatever goes on with the bevel

So why do you keep banging on about it, year after year, after year...... :?

Cheers :wink:

Paul

Because it makes for easy sharpening and I'm just trying to spread the good news for other lazy pippers like me.

 

[Oryxdesign]

Amount of material you need to remove?

http://flic.kr/p/dQ8s6u

 

[Jacob]

Amount of material you need to remove?

http://flic.kr/p/dQ8s6u

No. You have already removed a large amount from the 2 bevel example so you aren't comparing like with like. In fact the amount of metal removed would be the same, if you were preserving the same shape of bevel (whatever it is) and advancing the same distance up the face/flat side.

 

[Oryxdesign]

But if I'd removed less I'd have less to remove. You don't hone the primary

 

[bobbybirds]

I wish someone could explain to me what is wrong with the convex bevel. It obviously worries people but nobody can explain why. There's no logical objection to it, and it works in practice. What is the problem?

I don't think anyone has an issue with the convex bevel being sharp and effective at cutting as much as being told they need to change the systems they have already learned and use that work very well for them, and I include myself in that camp, BUT, I am serious that I am going to throw aside my pride that tells me I already have figured it all out and I don't need to listen to anyone (sounds like someone else??? Haha!) and truly give the convex bevel method a fair an honest go and try and use it exclusively for this season, which for me means I am lucky if I have a shop to use from April/May until Sept/Oct before old man winter turns it sub-zero (I am talking as much as -50 degrees C sub-zero). I really want to be fair in my assessment and I will...

 

[woodbrains]

Ok, strictly in the interest of peace and goodwill to all readers, let's have a little try at explaining.

I suspect that in some of these discussions, we are not all talking about the same things, so let's try some pictures and work out what Jacob means by a rounded bevel and why some people might think it's a bad thing. When I first read about rounded bevels on here, I think I got the wrong end of the stick, but I now think I might understand what is meant.

Have a look at my first diagram. It's a cross section of a chisel. The black line is the short of sharpening you might get with a jig - it's ground at 25° and then honed at 30°, so you get two angles where flat surfaces intersect, at X and Y.

I've then superimposed an orange line, showing what I think a rounded bevel is. The difference is that the sharp intersections at X and Y have been rubbed away below the places where they would have been.

Taking away that extra bit of metal - which was never going to cut anything - is the 'rounding'. I really can't see anything wrong with it.
Down at the tip, the cutting edge is much the same, even if we're measuring the angle of a tangent to the curve instead of the angle of a flat surface. It's still sharp.



So why the apparent objections?

But if you look closely at the diagram, a tangent drawn from the tip of the rounded bevel is nothing like the angle of the flat secondary bevel; it is FAR less acute, which is why rounded bevels are no good. To have a tangent to an arc which approximates that 30 deg secondary bevel, the arc has to be backed off a great deal more than is shown in this diagram. This requires lots more time removing lots more metal. If the stone you use is too coarse, then this would appear to mitigate the problem, but then you do not have as sharp an edge as you would want. When a fine enough stone is used, the rounding method takes too long, compared to a similarly fine stone used to produce a small secondary bevel. This has all been said before, but people choose to ignore the explaination, to keep the myth that rounding over is better. The truth is, it just circumvents the task of freehand honing a flat bevel (either single or double bevels) because it is not so easy to do this (although not insurmountable, obviously). Those who decry the use of honing guides only have a point if the freehand method they use acheives the same end. If I want a flat bevel and can't do it freehand, then I might choose to use a jig to achieve it; I would not abandon my aims and do something else entirely then persuade myself they are the same thing. They are not.

Mike.

 

[Jacob]

......
But if you look closely at the diagram, a tangent drawn from the tip of the rounded bevel is nothing like the angle of the flat secondary bevel; it is FAR less acute, which is why rounded bevels are no good. ....

Well it's not that neatly drawn. An edge formed by a tangent at 30º to the flat is going to be exactly the same as a single flat bevel edge at 30º, and the red line would combine with the black asymptotically (if that's the right term).
I'm beginning to see why there is so much confusion!

 

[woodbrains]

......
But if you look closely at the diagram, a tangent drawn from the tip of the rounded bevel is nothing like the angle of the flat secondary bevel; it is FAR less acute, which is why rounded bevels are no good. ....

Well it's not that neatly drawn. An edge formed by a tangent at 30º to the flat is going to be exactly the same as a single flat bevel edge at 30º, and the red line would combine with the black asymptotically (if that's the right term).
I'm beginning to see why there is so much confusion!

No it wouldn't, it would depend entirely on the radius of the circle the arc was taken from. To have a tangent to the arc giving a 30 deg angle at the same point as a 30 deg triangle, the radius of the circle would have to be infinitely large, i.e. the arc would be a straight line. As soon as the arc becomes part of a smaller radiused circle, this angle must increase. Hence the arc must be backed off a great deal to enable the arc to be taken from a bigger (flatter) circle. You really just should learn how to hone with a flat and have done with it.

Mike.

 

[Dangermouse]

This is getting very very very monotonous, boring and verging on stupid. At the end of the day it doesn't matter what or how or when you sharpen a blade. If it cuts the wood to the satisfaction of the woodworker. :evil:

 

[Jacob]

This is getting very very very monotonous, boring and verging on stupid. At the end of the day it doesn't matter what or how or when you sharpen a blade. If it cuts the wood to the satisfaction of the woodworker. :evil:

I agree but I'm just interested in why some people don't get it. I've got the answer - some people (e.g. Woodbrains above) just get confused by the geometry.
I'll stop here I promise!

 

[woodbrains]

Hello,

Top drawing shows the arc must have a higher tangential angle to cut through the same points a flat bevel describes.
Middle drawing, the same arc, but with a tangential angle of 30deg is impossible to achieve.
Bottom drawing, increase the arc's radius to achieve 30deg tangent. Does anyone really back the arc off by so much, or do they cheat and bias it a bit to the front to get a 'sharp' edge quicker? Disaster, because the angle will become bigger than 30deg. Once it gets into the higher 30's a bevel down plane will function badly, as there is insufficient relief angle behind the blade
As you can see, some arcs are impossible to attain a tangent at the same angle as the bevel. An arc that is too tight can have a tangential angle so high that a bevel down plane will not function. (How do we know we havn't done this in reality, there is no meaningful way to measure this. Another disadvantage of honing an arc) Increase the radius and the arc has to be backed off by quite a margin to attain the required tangential angle. Increase the radius further and the arc is so close to a straight line, you may as well just shoot for honing flat and finish with the pretence that an arc has any benefit whatsoever. I understand the geometry quite well, thank you.

Incidentally, to back off the arc in the bottom drawing, the blade would be as low as 9 deg to the surface of the stone. Sore thumbs, meethinks.

Mike.

 

[Sheffield Tony]

Coming back to the original point - using honing guides - this geometry makes a guide seem good sense for the inexperienced (or uncoordinated !). If you raise your hand inadvertently, a stroke or two removes enough metal from the thin edge of the blade to raise the cutting angle. But if you drop your hand a tad, you can take many strokes without making any significant difference to the edge - you are just rounding the unimportant part of the bevel. So if you are wont to flap about a bit whilst honing, it is far more likely to result in a steep, rounded over cutting edge than a thin fragile one. One of my planes (a #4), when I acquired it, had a rounded edge like that and simply would not cut however adjusted.

 

[Tom K]

Why try to quantify a non event? Jacobs answer to his freehand sharpening dubbing over problem Ta dah drop your wrist at the end of each stroke. End result edge at 30 ish degrees, sharp and easily repeatable ish. Precise? No. Measurable? No. Provide an improved cutting edge? No.

 

[Dodge]

Hi folks,

I believe this topic has probably reached the point that we must all agree that everyone has their own way of sharpening and the ability to decide what is their own favoured method of sharpening.

What works for one person may not work for another - now lets get on with using our tools and get posting some of your completed projects and WIPs

Rog