Flattening; Yes or No. Why?

[samuraistuart]

For my touch, the final apexing of the edge needs to be done on a stone that is as flat as I can get it. Preferably on stones that don't dish much, like hard ceramics and the EEF DiaSharp plate. But for simply establishing the overall edge bevel when starting the session(the "meat" of the edge, not the very apex), I don't really care if the stone has a slight dish to it. I do try to work on the far edges when I feel the dish setting in, like Murray Carter does.

[Mojogyuto]

Flattening is key

[Chefcallari]

I’m viewing from the lens of I’m spending money on a proper sharpening medium to keep my knives sharp. The material lost is simply collateral damage ensuring my knives are in working order. I don’t worry about wasting tire tread by driving my car, the car moving is more important. Over time, I don’t think I’ve lost much, my stones are still usably large and have decades left. If they do wear away, they’ll simply get replaced. If I buy a stone and don’t flatten it, I’ll be left with my money spent on a lesser, loaded and warped stone producing lesser edges and cutting slower that’ll keep getting worse over the years I have it. The edge is more important than the stone to me.

On my non-chamfered stones, I’ve experienced zero problems at the sides, with a sharp corner it’s easier to sharpen serrated edges. Chamfering provides more negative than positive in my eyes. If the whole surface is flat, there is no edge to worry about. I can see high spots at the edge being problematic if a stone isn’t flat; however, that isn’t an issue with my flattening habits.

+1,000,000,000

Lol but i do champfer my edges

Fact .. You have to keep a stone flat. Period. Lol
You want to sharpen a knife you have to remove steel.. Reducing the life of the knife... Whats worse... Having a knife that keeps its original height and length but is dull as a spoon.. Or loosing a couple mm over the life of the knife and having a light saber lol

I feel like when guys see stone coming off when they flatten they have the same visual response as when they bleed.... when you cut yourself It LOOKS like like alot of blood ... But its really very little. Same with stone slurry and even swarf... Its microns of material being used.

Lol suck it up and flatten

[Peter Nowlan]

Personally, I don’t care what Murray Carter does in regards to flattening. They come flat so keep them flat. Now I have changed my stance a little with flattening. There was a time that every pencil mark had to disappear, every 3 Knives. Nowadays I don’t draw a grid, every few knives I do some gentle flattening, I can tell when it’s flat as there is no friction between the stone and the Lapping plate but there is absolutely no visible dishing.

[ChefKnivesToGo]

Michael, flatten your stones!

Angle control is the biggest part of getting a crisp edge and flattening eliminates one of the most common variables that changes the angle. Then you can focus your attention on maintaining a consistent angel as you move the blade back and forth on the stone. I flatten each stone every few knives. A little more frequent on the low grits and a little less on the high grits. If you do it regularly it only takes a half minute or so to get them flat.

[ken123]

Flattening is a critical task. You could compare it to flushing a toilet - a good thing to do

There is a question of degree. Do you flatten to within a couple ten thousandths of an inch? Personally I don't. That extreme of fineness goes after a few strokes of sharpening. Some do. Do some just not care? - yes. I don't recommend this approach.

Mark mentions angle control. Here's a good trick I recommend usually in some of my long phone conversations:

Get an overhead light shining on your workstation area (Daylight LED or halogen). LOOK at the reflection of the light coming off the knife. When you sharpen strive to KEEP the reflection coming off in a constant position. If it is moving around, you have sloppy angle control. Practice, Practice.

---
Ken

[lsboogy]

Here's a quick mathematical explanation - radius is a circle is h/2 X w(squared)/ h - h is height (or dish on a stone) and w is the light of the stone. A 0.003" dish on a stone will give you an angular inaccuracy of about 1.3 degrees over the length of your stone - we sharpen with tighter control than that - at least I do. I like Ken's trick too. Sharpening on a mildly dished stone (0.003" is the thickness of a sheet of paper) will result in a rounded edge - most stones I see have much more dish than that.

[Jeff B]

Well I think the answer to this question is pretty definitive.

[lsboogy]

Oops - my bad - it's 0.12 degrees for 3 thousandths on a 6 inch stone. But a stone dished 20 thou (pretty shallow dish) is about a degree flattening is a good thing. I dropped $150 bucks on a pair of new 1K (1K and 1200 grit stones) - my 5K and 8K stones are 20 years old and still plenty thick. I would guess if you sharpen a set of 6 knives once a month (heavy use - much more than I need to do) you might wear out 350 bucks worth of stones in 30 years - $1 a month - pretty cheap

[mlb1988]

Interesting... I am loving the answers on here lol.