Questions about thinning...

Ok, so this is probably a really stoopid noob question but you guys must be used to them by now, so here goes.

This is my experience/understanding of sharpening so far and please do SHOUT if I've got anything wrong (I don't think it applies to wide bevel knives):

1. When you get a new knife, it usually comes with a very small, barely visible, primary bevel (the cutting edge) on it.
2. With each sharpening session, that primary bevel will become wider as you're taking more steel away from the edge.
3. The width of the bevel is also a function of the angle you sharpen at: the more acute the angle, the wider the bevel becomes.
4. Most people say that you should thin behind the edge every time you sharpen in order to maintain cutting performance.
5. Thinning behind the edge here means removing steel where the primary bevel meets the rest of the blade, i.e. the shoulder bit.
6. Thinning behind the edge blends in the primary bevel with the rest of the blade so, after thinning, there is no longer a visible primary bevel and you're back to step 1.

Am I right in thinking this is what you should aim for to maintain your knives? So the idea is to keep as small a primary bevel on the knife as possible?

Thanks!

Not a stupid question at all. To be honest what you said is pretty spot on. in most cases it is a good thing to have a small primary bevel although you can usually still see it even after thinning if you move the knife around in the light a bit.

The purpose of thinning behind the edge is to maintain the geometry of the knife, allowing it to glide through food and stop it wedging in food. Sometimes knives still need thinning OOTB, a good test to see if your knife needs thinning is to push it straight down through a thick carrot, if it cuts clean it's fine, if it splits apart it needs thinning.

Having a small primary then a Thinning/ secondary/ relief bevel also allows the knife to hold angles it wouldn't normally be able to hold. An extreme example: if you thinned at 3-5 degrees all the way to a bur then cut a tiny 15 deg primary bevel it would move through food like crazy but hold the angle a bit better due to the higher primary angle.

what you should aim for is a knife that cuts through food nicely with as little wedging as possible but also being able to hold its edge fairly well. this means you have to thin it. How often you thin and how much is really up to you as long as it's not wedging and the edge is holding your doing fine.

Thanks, Geo! You always give good advice

So, when thinning, do you always try and raise a burr at your thinning angle then cut in a primary bevel at a higher angle? I've never tried to raise a burr when thinning before.

Another good question. Many feel that you must raise a burr when thinning. However not always so. Your thinning bevel say 3-5 % close to the stone takes steel off the shoulders and sets you for your final bevel. When you raise the spine for FB you should aim for an even burr heel to tip. It will come quickly at this higher angle, you can hear it being cut in. Flip the blade over and burr will go to the other side. As long as you have the even burr all along your edges are meeting. Then burr removal taking care not to undo your work.

Mangelwurzel said:

So, when thinning, do you always try and raise a burr at your thinning angle .

Click to expand...

Definitly not , sorry for the confusion I was just giving that as an extreme example. If you did that everytime you may grind away any convex bevels behind the edge. You should start with a low angle of 3-5 degrees and keep stoping and looking at what your doing until that bevel gets close to the edge, then raise the spine slowly until you get to the edge and raise a burr. That would create a convex bevel behind the edge to aid with food release. If your right handed convex the RHS.

How much you thin is up to you. If you don't like how the knife cuts and it's wedging, thin until it cuts better. If your happy about how the knifes cutting and just want to maintain geometry just thin a little bit each sharpening session.

Before starting a large thinning operation verify for steering. If it steers you should correct that, see post nr. 109

http://www.kitchenknifeforums.com/showthread.php/5656-Asymmetry-–-The-REAL-DEAL/page11

Once steering corrected, thin evenly on both sides, and verify again.

Another approach to sharpening and thinning is the "zen" approach. If the knife is too thick, lower the angle and grind away. Since the human hand cannot maintain a perfect angle all the time, the knife ends up with a convex edge with not visible bevel. Convex is OK, no stress with having precise bevels and what not. Micro-bevel if you need a more robust edge. The end result may remind you of a Japanese sword and make you feel like a samurai.