Is it sharp yet?

[sam_acw]

I've followed the sharpening threads on this forum and have built up my own budget sharpening kit.
The trouble I've got is this - How do i tell when a knife is sharp?
I know that shaving hair is often used as a test, but to be fair this isn't something I actually need a knife to do.
The knives will all cut hard wood ok - is the level of effort required to cut it a function of it's sharpness?
I've only gone as far as 400 grit paper so far as this was the finest I've got to hand.
Any help is much appreciated!!!

 

[British Red]

sam,

My test of a "working edge" on a knife (or axe) is to hld a piece of paper vertically by one corner and draw the blade across the paper. It should slice neatly through it without tearing. If it will do this, its sharp enough for most things.

I you can't get hold of some finer paper and would like some, PM me your address and I'll put some in the post to you

Red

 

[Mantic]

Very helpful of British Red but just to let you know, Homebase sell an assorted pack of wet and dry for £1.99 (240, 400 and 600 grade paper - I think you get one of each but 2 of the 400). Cheap as chips.

The pack isn't proprietary so I guess you could get it at Focus, et al.

Oh and just as a reminder, it's a good idea to test the sharpness of your knife, axe, etc before you start sharpening it - that way you can compare before and after

 

[JonnyP]

How do i tell when a knife is sharp?
I know that shaving hair is often used as a testQUOTE]
Trying to shave hairs on your arm is as you say only a test, you only do it to see if the blade is razor sharp, if it is not then it won't cut the hairs. You maybe do not need to get a blade this sharp, but the sharper the blade, the less of a chance you have of having an accident as less effort is needed. Obviously it goes without saying, be careful pulling a blade on your arm................Jon

 

[torjusg]

If it is easy to take off small shaves off your thumbnail, it is sharp. If you have to put any weigth or much force into the job it is not yet sharp enough.

Torjus Gaaren

 

[laurens ch]

I think 400 grit is a bit course, I’d take british red on his offer if i was you.

 

[Andy]

I tend to start with 800 and work up to 2500 and remove the burr with 2micron I've put a link to a good source of wet&dry paper in teh £5 sharpening thread

I tend to go one frther then slicing a piece of paper while holding it up. I tend to slice it whilst it's free falling

 

[torjusg]

I am not suggesting that you use paper from that exact type of book, but I would assume the paper British Red is talking is quite similar to what most bibles are made of.

Torjus Gaaren

 

[Andy]

the paper for roll ups is handy slicing test

a really polished edge (good for push cuts used in woodwork) will slice tesco value loo roll but you don't rally need to go that far. taking shavings from a pop bottle is quite a good test

 

[Bjorn Victor]

If it shaves hair just as well on my left arm as on my right arm, I know I have a razor sharp knife with a clean centered edge without an (invisible to the naked eye) micro-bur on one side.
That is where I stop sharpening.

Bjorn

 

[Hoodoo]

I think sharpness is something you get a feel for over time and it really depends on the type of knife and what you are cutting. Take a mild steel kitchen knife for instance. You can get it sharp, cut with it for awhile, and gradually you will feel the edge slip away. Slicing tomatoes is often a good test. You can use a smooth steel on it several times or more, depending on what you cut with it, to "straighten" the edge and you will be good to go. But eventually, you will need to run a stone or a sharpening steel over it. This will expose fresh carbides which contribute to the "sharpness" of the knife. Fresh carbides give the knife a "serrated" edge at the micro level, and improve the ability of a knife to slice through soft to medium hard material.

In contrast, a good woodcarving knife is usually sharpened for push cutting rather than slciing, although for green wood, you can do a lot of slicing cuts. But generally, you would want a highly polished edge and you can consider it sharp when it will slice wood effortlessley. One common test of a woodcarving knife is to slice across the end grain of a hardwood board. If you can peel off a thin shaving, you are usually good to go.

Keep in mind that sometimes the knife will feel sharp and even shave hair but can dull quickly. If it does, the knife was not truly sharp because you still had a burr edge. I've often seen a knife with a burr edge shave hair on one side of the edge but not the other. That's a good sign you need to work more on the burr.

 

[OldJimbo]

I've often seen a knife with a burr edge shave hair on one side of the edge but not the other.

It's great that Both Bjorn and you pointed this out. That's one that got me for a while! Naturally a quick stropping straightens the burr and all appears good - for a very short time. A few slices through a newspaper will rip off the burr, but then a bit more polishing may be needed.

 

[sam_acw]

Thanks for the advice; I've found some 1600 grit and that's improved things.
The scandi grind and opinel knives hev come up pretty sharp but I've got one folder which tends to slide off of cuts. I thik this is due to the blade grind though and not the sharpening.