Sharpening angle, how to define?

[Bosun]

Good afternoon,

 

For example, many experts quote the sharpening angle for a knife as 15 to 20 degrees. Would this be the angle of the blade to the stone, or the included angle?

 

Included angle - 15 to 20 degrees or 30 to 40 degrees, any offfers.

 

For plane irons and chisels it's easy as they are one sided, but what about knives, axes, etc.

 

Bosun

[Woodworks]

I used to follow guides for sharpening angles but with practice you can make your own choices. The finer the angle the sharper it will feel but this edge is fragile and will dull quickly. Vise versa if you sharpen at a coarse angle (say 40 degrees) it will not feel very sharp to start with but will hold this dull edge much longer. If you are using these knifes for light use I would suggest 12.5/15 degrees per side ie 25-30 degrees total if for hard materials I would look at a coarser angle. When I have new tools or knifes I will start off at fine angle if this edge dulls or chips quickly I will then adjust the angle until it suitable for the task I use it for.

Sorry if this is a bit long winded and I hope it makes sense. In all honesty I have never looked at the angle of knifes any differently to any other cutting edge. Top quality blades (I am thinking of Japanese chisels but some knifes are the same) Have a very hard but brittle steel for the cutting edge but this would chip easily but to avoid this it is laminated to a softer steel to give it support. I will have a measure of angle on some tools and knifes this afternoon.

 

Interesting topic

Edited February 7, 2013 by Woodworks

[muttley9050]

Good answer from woodworks. I sharpen everything freehand. Have several knives sharpened at different angles, pocket knife about 25 degrees down to detail carving about 10-12 degrees. All my planes I roll the hone and then put a micro bevel on rolled edge at about 25deg. Not strictly correct but was taught to me buy an old chippy and it works well and is quick, no need to be super accurate.

If you struggle with the angle, cut an offcut to desired angle and place next to your stone and use as a visual reference. With practice you can get super edges on your tools.

James

 

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[Bosun]

Thanks guys,

 

It's just not been clear whether the angles given were the sharpening angle, or the included angle. I guess, at the end of the day, it depends on what works best for you.

 

Bosun

[Woodworks]

Had a measure of my various chisels and knifes and all are between 25-27 degrees. This is the included angle so the sharpening angle is between 12.5-13.5 degrees to achieve the same on a knife.

[canoehead]

it took me ages, actually, make that years, to figure this out. it wasn't until i started making knives that it finally made sense.

 

essentially sharpening is about 3 things; the intended use of the blade (wether its an axe, saw, knife, plane, or chisel the same thing applies) which is the action of the cut (sawing, chopping, hewing, pairing/slicing);

the density/hardness of the material to be cut vs the hardness of your tools cutting edge;

and the angle of entry of the blade.

these inter-dependant things govern the angle you need to sharpen your tool at.

 

the angles quoted are the angle from the outside face of the blade that you sharpen to the centre of the blade.

 

different blades will cut differently, for different uses, and its hard to achieve an all round tool that works well in all situations. which is why, for instance, you may find it hard to make feather sticks for fire lighting with a hunting type knife, however sharp it is, because the shape of the leading edge of the blade is wrong. this is how we all end up with a shed load of tools. flat and hollow ground blades allow you to pair things more easily than convex ground which allows you to chop more easily.

 

although the exact angle you use to sharpen isnt entirely critical, it can fall well within a range (generally 12.5 -30 degrees), the consistency of maintaining the same angle is more important, honing guides help, but theres a point where you will have to go freestyle, because not everything fits in a honing guide, axes and knives esp.

 

its a thing where you have to spend an amount of time to get it to run right. if you use a mechanical sharpener, like a grinder you need to be really careful you dont heat the edge of the blade, or you will remove the temper from it and it will require you to grind out the whole area you've cooked or you will keep chipping the edge. tomak water wheels are a way to go, but its not so difficult to sharpen by hand.

 

the angle plane blades are set in the body of the plane determines to an extent the angle the blade needs to be sharpened at (generally 25 degrees) you can get away with putting a micro bevel on a blade, but only for so long before the micro bevel is too large and begins to hinder the process of cutting. they are a good way of avoiding having to sharpen the entire face of the cutting part of the blade, but you can only do that for so long before you have to completely re-grind the face. the same with chisels.

 

25 degrees will give you a finer point of entry which allows you to pair things, and 30 degrees will give you a better chopping edge.

 

too fine an angle of entry is counter productive for chopping blades as it causes them to stick, yet conversely, to pair something, the finer the angle the finer you can shave things.

 

the key to successfully sharpen double bevelled blades is to try and remember to count how many times you run it over the sharpening stone per face, and make sure its an even amount each side.

 

hope it helps

 

rick

[Bosun]

Hello Rick,

 

Many thanks for that comprehensive reply.

 

I'm also experimenting with different sharpening profiles. One thing I have found, is that a flat grind on a hand axe works better for me than a convex one, as many experts seem to prefer. While the convex grind may be a little stronger, I've found that it tends to glance off more easily if the angle of the cut is small. I guess that's why the one sided grind on a Side Axe is prefered for slicing.

 

Bosun

[morten]

For example, many experts quote the sharpening angle for a knife as 15 to 20 degrees. Would this be the angle of the blade to the stone, or the included angle?

 

Included angle - 15 to 20 degrees or 30 to 40 degrees, any offfers.

 

Included angle: 30 - 40 degrees.

 

I can highly recommend this book: [ame=http://www.amazon.co.uk/Complete-Guide-Sharpening-Leonard-Lee/dp/1561581259]The Complete Guide to Sharpening: Leonard Lee: 0094115581257: Amazon.com: Books[/ame]

 

It explains everything you need to know about sharpening knives, tools, saws, axes etc, and explains (more than) what you need to know about metallurgy.

Edited March 1, 2013 by morten
amazon UK

[canoehead]

morten, i like your link. had a look inside the book thankyou amazon, wish i had twelve quid.

 

bosun, gransfors bruks forest axe, and small forest axe. they do exactly what they say on the tin. limbing soft or hardwood and general working, you can do all kinds of craft/carpentry work with them. phenomenal. i didnt understand why until i bought them. they're flat ground and very fine at the leading edge. the steel is very high quality (i imagine a high carbon content), and they are made to an exceptional standard. easy to keep very sharp, and they maintain their edge. they never get so out of shape i can't maintain their razor sharpness with only a diamond router cutter sharpening card i carry in my pocket.

 

rick

[Cracker]

I'm a bit obsessed with sharpening. All I can say is it's something that comes with experience. I use water stones, finishing with 8000 grain, then strop on leather and check the edge with a microscope .