Help with sharpening

[SVanderkolff]

Over the years I have figured out how to make a knife sharp but never hair popping , cuts before it touches sharp. This is one area of my craft I would very much like to improve upon. I purchased a set of the Norton water stones, 220, 1000, 4000 and 8000 grit but can't seem to get the knives truly sharp. One of the problems I am having is finding a simple test to ensure that the whole length of the blade is uniformly sharp.
Any help greatfully appreciated.
Thanks
Steve

[chiger]

Hey Stephen,

A really good magnifying glass is the best way, short of a microscope of course. A close visual inspection with good light will usually reveal any flaws. If you've missed any places it will look like a white spot. But then I suspect you know that. I don't know anything about Norton stones, but you've got the right ideal about stone being the only way to go for a superior edge. The harder the stone you can afford or find the better.

I will say that the kind of edge that makes you bleed before you know you're cut is as much about angle as edge. Really sharp trades durability for cutting ease. If you are sure that your edges are of a consistent hone and you are not getting a wire (rolled) edge then angle is the next thing to look at. Around 15 degrees per side will produce a fairly sharp edge of moderate durability. The further down you lay the angle the greater the cutting ease. It's about reducing the drag behind the cutting (contact) edge. A finely honed edge helps compensate for some of that lost durability and further reduces drag.

I've found that a truly sharp blade is about patience. By the time I get to ultra fine stones, I'm resolved to spending a long time just letting the weight of the knife and the stone do the work. I concentrate on keeping the angle uniform from end to end and not adding pressure that might wire the edge.

Oh, I do have one tip for quickly telling if you have a rolled (wire) edge. You can lay the blade on your thumb nail (or a piece of wood if you're a chicken like me) at the same angle as the hone angle and pull it backwards away from the edge. If it is rolled it will pull up a little curl like a furniture scrape. It just saves a little time going to the magnifying glass is all.

I doubt I've told you anything you don't already know, but these are a couple of the things I've found to be important over the years. And it's the number one question I and I suspect most knife makers get asked. So much so that I was actually compelled to write an article about it. Which about 5 people probably read.

Oh, well. Hope I helped. If not maybe some of the master blade smiths on the forum here will chime in.

chiger,

[AcridSaint]

Hi Steve - I don't use stones or anything to put an edge on my knives, but I'll tell you what I do and maybe you can use some parts of it.

I put a wire edge on my knives in one of two ways - either with the slack portion of the belt between the idler and the wheel/platen or just on the wheel. I grind edge down on slow speed and make one or two passes then check the knife and change sides. Once I get a uniform wire along the entire edge of the blade (it usually takes me several tries), then I flip it over, put a wire on the other side and get off the grinder. I think this is easier to get on the wheel, but you get a slightly sturdier edge if you do it on the slack belt. I generally use a 220 or 400 grit belt for this.

Next I go to a hard buffing wheel with green rouge on it and knock the wire off. You can use a cardboard wheel too, but I think the hard wheel works better. I picked that up from the S.R. Johnson video I think. From here you can stop or move on to a wheel with white rouge and even go to a strop. Generally when I stop at green rouge the knife is sharp enough to make my arm bare in one pass.

I learned this method from Alan Folts and I'm still not very good at it. I can make a sharp knife, but it usually takes me 15 minutes or so to get it where I'm happy and sometimes I'm not steady enough and get a little wave somewhere that should be worked out. The price of power tools I suppose.

[Greg obach]

well... you got all the right stones to do it... it just takes time as was said...

do it in strong sunlight... if you can see the edge ..then its not sharp..... loupes are good to help
- i start with my bad side .... and thoroughly work the edge in the course stone..... i used to have a tendency to give a couple swipes on course and run right to the finest... hah.. not good at all... put the required time for each stone

if the high grit stones are too soft ... you can pull the blade backwards accross it.. don't dig in

try with a bunch of practice blades.... try using plain carbon knives, they sharpen quick... and you'll find your technique very quickly if your serious and sit down with it..

then lastly put some green compound on a piece of flat hard wood... and strop it backwards.... and try not to roll the blade while doing it...
-- some use other fine compounds at that stage

at this point.... becareful if you test on your arm.... may need a skin graft...


Greg

[SVanderkolff]

Thanks Guys
How do you test the edge? I know shaving hair on the arm looks really gool but I figure there should be a more scientific test.
Also , How do you know when to move from one grit yto another?

Thanks for all the help.
Steve

[Andrew Garrett]

Steve,

One pass on a belt grinder with 320 or 400 grit is worth 50 passes on a stone..., and you only have to maintain that perfect angle a few times instead of hundreds. I have a leather scrap taped to the side of my platen as an angle guide 22* off center, 44* total edge bevel angle).

I use a dry belt but might try some lube on it in the future (experimenting).

When the wire comes up, I use paper charged with green wrapped around my finger to polish and strop.

A quick 'leg strop' on tight denim (one or two in each direction) and my knives are scary sharp. Then whole process takes 5-10 minutes from an edge that's 1/16' thick. I know the stones are tried and true, but hey..., I can't argue with results.

I test my knives by trying to cut slivers of paper as thin as they are thick. If it's a really sharp one, I do this with newspapers. If the whole edge passes the test, the blade gets shipped.

[chiger]

Good question Stephen.

A close visual inspection with a good magnifying glass is really the best way for both of your questions. Just like sanding the blade, move on when the hone marks from the previous step are gone. That's why the magnifying glass. As the hone gets finer it gets really hard to see.

There is a scientific method for testing used by some high production service knife makers, like chiefs knives. It involves a test bed that applies a certain poundage of force, 8 Lbs I think, a stack of 10, 1/2" balsa wood squares or something. They measure how many it will cut repeatedly before the edge degrades. I'm not going there! But I'll bet you can find the standard on line if you just gotta. ;~)

Try it on arm hair to see if it is that hair popper you wanted. That's test one. Then on thin skinned tomatoes, rope, a branch of your wife's wisteria and whatever else you can think of. Look at the cuts. They should be crisp with no fraying or tearing at all. Once you are satisfied with the way it cuts, just repeat that edge geometry every time.

Once you've put that edge on one of your custom knives, if it is a hair popper like you said you were looking for and it passes the mechanically enhanced visual inspection....call it good.

Like Greg said, practice on one of those old kitchen knives everyone has stuck in the back of a drawer somewhere. Test the cutting ability of that edge. Confidence in the edge geometry you're using is the most important thing. Cutting ease and edge durability is all about edge geometry. After you've learned it that first time it's simple to duplicate.

chiger,

[Bob Hatfield]

Steve;
sharping a knife used to be one item that I was never satisfied with until I came across the methold of using slack belts to grind a convex edge on the blade.
I use a 2X48 D-5010 belt sander that Texas Knives sell. It is mounted horizontal with a light off to the upper left side. this light allows me to see the wire edge as it is being made on the blade. In fact it stands out like a sore thumb for a good reference guide.
After the knife is completed, I start with a 120 grit belt and make equal passes on each side until I get my wire edge. I then progress to a 220 grit, 320 grit, 400 grit, 600, 800 grit , 1000 or 1200 grit. Then polish with a worn crocus belt loaded with Jackson 51 white.
Most of the passes will envolve the 120 grit until you get the wire edge. From there it is only about 2-3 passes per side per higher grit. The blades come out hair popping sharp and will cut newspaper without tearing the paper. Texas knives also sells the belts you will need. The 120 grit will last about 10 blades, but the other grits will last for 25-30 blades or more on the supper fine grits.
I use very light pressure to avoid over heating and you must watch the tip in order to avoid taking off too much metal. Very light pressure there. Get those old kitchen knives out and practice and you will be sold. I have has several customers tell me that my knives are the sharpest they have bought compared to other knives. I found out about this convex grinding on this site, but I forgot which knife maker posted it in order to give him the credit he deserves for passing it on to us.
One reason I love this site. We have some of the best knife-sheath makers around and they are more then willing to help other newer makers get going without making the mistakes they made though trial and error.

Bob Hatfield

[Don Cowles]

Steve, A.G. Russell uses the plastic/styrofoam peanuts used for dunnage in shipping packages. So do I. If you can make a nearly transparent slice from one of those, the blade is indeed sharp. Saves the hair on your arm, too.