How can you tell a knife is sharp?

[dougk]

I was using one of my better knives yesterday and not please with the sharpness.  However, the knife had just been cleaned and sharpened by the maker.  How can I tell if the knife is sharp?

Thanks
Doug

[savageT]

dougk,
I like to view the sharpened edge with a strong overhead light.  Look for any portion of the edge that shows a shinny appearance that would indicate a "flat spot".
If you have ever used a chef's steel (that's the sharpening tool that looks like a round file about 12 inches long w/ handle), it can bring back a slightly dulled edge quickly.  Lay the knife's edge on the top surface of the steel, about a 10 degree angle, starting at the tip of the steel and draw it down towards your body.  Now do it again on the back side of the steel.  With some practice, you can shave the hair on the back of your hand.
Jim

[savageT]

dougk,
I like to view the sharpened edge with a strong overhead light.  Look for any portion of the edge that shows a shinny appearance that would indicate a "flat spot".
If you have ever used a chef's steel (that's the sharpening tool that looks like a round file about 12 inches long w/ handle), it can bring back a slightly dulled edge quickly.  Lay the knife's edge on the top surface of the steel, about a 10 degree angle, starting at the tip of the steel and draw it down towards your body.  Now do it again on the back side of the steel.  With some practice, you can shave the hair on the back of your hand.
Jim

[Graybeard]

My test is that if I cut myself while using it the knife is dull but if I cut myself while checking it out it is sharp. At least that's the way it seems to always work out for me. When I have a knife really sharp I always seem to manage to cut myself with it while checking it out. It then cuts thru stuff so easily little effort is required. But when a knife is dull you must use more effort to make cuts and then you're more likely to cut yourself in use.

You can also try the hair shaving trick or paper cutting trick. Dull knives do neither.

[Daveinthebush]

I use a Lansky diamond hone and cutting oil.  When I can fillet a piece of paper it is sharp enough.  A little dull up here does one no good.

[dougk]

I did do the paper cut and it worked great.  In the future I will used the bright light test.  Also, I did not cut myself when field dressing the deer.

Thanks,
Doug

[Daveinthebush]

I would advise you to use latex gloves.  I somehow nicked a finger this spring and by the time I got to a doctor that knew what to do, it had started to turn black, swelled 2X's its size and was running down the arm.

I had an IV stint in my arm and had to do 1,000 cc of something that I had to report to the hospital for, for five days.  The bill was.....$2,000+.

Could have been form a bear, shrimping or something called seal skin.

[ShadowMover]

I like the paper cutting trick. You hold a piece of printer paper so it's edge is up, and starting with the edge of the blade near the handle pull the blade through and down the paper so all parts of the blade cut through the paper. If you have a dull spot the blade will slide on the paper, until you get past it and then it will start cutting again. If you look where the 'sliding' started, you can see the flat spot as a shiny line. Just like you mentioned.

I use the Lansky tool too, and it works great.  One other trick when using the Lansky stones, is to coat the blade edge with a black felt tip pen and let it dry. When you start sharpening with the stones you can see where the metal is grinding and how far the work is progressing. It keeps you from working on the spots that are already 'there'.
I knife guy once told me cutting thin slices of styrofoam was another good test of a sharp blade. I haven't tried it yet. Has anyone else heard of this?

[Graybeard]

Yup it takes a really sharp knife to cut styrofoam without tearing it. A very thin blade helps also.

[victorcharlie]

I've always tested by shaving hair.  If it won't shave, it ain't sharp.

[Joel]

When I'm putting an edge on a knife, I like the hair shaving and the styrofoam method.  Also I've probably nicked myself with just about every knife I've ever made.  Like that...shows the knife is ready :?   You can drag it accross your thumbnail also....if it drags its sharp, if it slids its dull.  A lot also depends on blade/ edge geometry.  A knife with a fairly thick blade,sharpened to a blunt angle, say around 25 Degrees(50 inclusive) or more will skin okay and chop, but won't shave wood or slice really well.  A thinner blade/edge will slice well and whittle, but might actually be too sharp for skinning(unless you know what you're doing) and would  dull quickly if you chopped anything reasonably hard with it(wood).  The edge bends fairly easily.  You didn't say what sort of knife it is, or if you've any idea what the angle is on the blade. If you sharpen it at the original angle and it's not satisfactory,i.e. it still dulls quickly, then you would need to change the blade angle so it's suitable for whatever you use the knife for.

[Will52100]

I use the fingernail test along with shaving a little arm hair and my favorite is to slice news paper.  If the blade will slice the newspaper with no catches or tears it's sharp.  I don't use it much anymore but when first starting out I used a 20x radio shack microscope to inspect edges, it makes for some interesting viewing.

[HoppyLV]

The "Razor Edge Company"  makes a little inexpensive synthetic tool used for scoring blade edges. I have used it with good results. You may want to check it out.   They advertize in the most the knife rags.  Most of you have seen ther ad where the lumberjack in a beanie is shaving of half his beard with an ax.  Although I not a big fan of their sharpening systems, I recomend their book for beginers or anyone learning about establishing a good edge.  They also sell a perty nifty compact folding steel (mirror polished) that works good.

I too do the paper test, and my left arm is always bald...

[HoppyLV]

I too use the paper and fingernail test.  More importantly, I like a edge to pop hair with no effort and with out drawing the blade.  My left arm is always bald.

The "Razor Edge Company"  makes an inexpensive tool that is used to score a edge.  It's a little synthetic rod used for testing.  You may want to check it out.  Although I am not a big fan of their sharpening systems, I recomend their book (The Razors Edge) to anyone who does not understand  about different types of edges.  They advertize in most of the knife rags.  Their ad has a lumberjack looking dude shaving off half of his beard with a long handle ax.

They also make a nifty little folding pocket steel (that is mirror polished) that I have used for years.  It works...

[DeviousApe]

I use a piece of boot sole leather, from my leather scrap box.

I slowly pull the knife's edge along the leather watching how it cuts and feeling any change in the resistance to the cutting.

I can judge the sharpness and check for dull spots this way.

[kyote]

all good ideas.I must have all the sharpening thingies made.I believe.I find to check the whole blade I use a piece of paper (copier)and run the length of the blade through the papaer very slowly and carfully listening and feeling for some different noise are feel of the blade hesitate going through the slice then I look at the area under my optivisors with a strong over head light to try and see the imperfection in the blade and use a very fine stone in that area to bring it together with the rest of the blade.after all is done I stroth it with leather.

[Don Fischer]

I have a "Track" made years ago in Whitefish, Mont. The thing will take an edge you wouldn't believe and also don't need! Knives that shave hair and cut paper and foam are to sharp and dull to quickly in use. It's not so much dull as it is the edge rolls over. Thats when you use the steel to re-straighten the edge.

Trick I was taught by the owners of "Track". Use 400 grit wet/dry paper and a leather strop to finish. The edge get's polished then and actually feels dull but is sharp as hell. Also, don't push the blade into the sharpening medimum, pull it. According to "Track", by dragging the blade and taking the feather edge off with leather, the angles stay truer. Does it work? Hell, I don't know but my knives are sharp!

By the way, a knife works best and stays sharpest longest when used as a splitting tool rather than a slicing tool. When sharpened to slice, the edge is to thin and dulls easier. As big a pain as the old "Bucks" were, they were tuffer edges only because of the beveled edge. Kind of like cutting with a chisel!

Hollow ground edges get razor sharp but flat ground edges last longer and get damn near as sharp.

[S.S.]

I was reading about the Crusades once and a neat part of it came to mind
when I saw this question. A question came up about the quality and sharpness of a Sarisan Sword and the Quality and sharpness of an english Sword. The Englishman promptly swung his sword and cut the thigh bone of whatever animal had been roasted for dinner in two. I assume it was a cow because of the No pork diet of Muslims. The Sarisan casually walked over and removed the silk scarf from around the waist of one of the dancers at the feast. He held out his sword edge up and dropped the scarf over it. The scarf hit the ground in two pieces. His only statement was
" Your arm is strong, My sword is sharp"

[Patriot_1776]

You guys kill me.  First-off, if you want it "sharp enough to shave hair," you gotta use the right tools.  Here's what I came up with:







 :-D  :lol:    :-D  :lol:  

-Patriot

[curdog]

was that made to cut hair??? lol

[TNrifleman]

For me, the blade must cleanly and easily shave hair off my arm. A good Norton India oll stone and WD40 will put a good edge on a blade  when used by skilled hands.

[joshco84]

i use the hair method at three different spots on the blade (back, middle and point/front) i like for it to cut the hair effortlessly (not pushing hard).  we always take three or four to the garage with us so if one goes dull we can just grab another, and then sharpen them all later that night.  we usually do two deer at a time, and if we gut, skin and bone meat, it will take two knives a piece ( two for me and my grandpa)