Coarse apexed vs. Fine apexed edge

So I came across this blog done by Todd Simpson which has EXCELLENT photography of knife edges. I asked Todd and he did not mind if I post some photographs here, so here they are!


 

Following the bevel set on the Chosera 1k, the razor was honed on Shapton glass stones; 2k, 4k, 8k and 16k. At each step in the progression, SEM imaging was performed.

The side-view images, at 5000x magnification are shown below. As expected, scratch depth and width decrease with each step. Although the Shapton 2k is rated 7.35μm grit and the 16k is rated 0.92 μm, the observed scratch depth is much shallower, less than one tenth the grit size.

CHO_1K_P
Chosera 1k
Shap2k_P
Shapton Glass 2k
SH4k_5kx
Shapton Glass 4k
Shap8k_P
Shapton Glass 8k
Shap16k_P
Shapton Glass 16k

The above side-view images provide little insight into the edge geometry or keenness. Edge view images, taken at an inclined angle to provide perspective, allow direct assessment of the apex width. The edge width (or width of the apex) decreases with increasing hone grit rating.

edge-on view images after Chosera 1k
edge-on view image after Chosera 1k, showing an apex width in the range of 0.7 microns.
Shap2k_E
Edge-on view images after Shapton 2k, showing an apex width in the range of 0.4 microns.
Shap4k_E
Edge-on view images after Shapton 4k, showing an apex width in the range of 0.3 microns.
Shap8k_E
Edge-on view images after Shapton 8k, showing a apex width in the range of 0.15 microns.
Shap16k_E
Edge-on view images after Shapton16k, showing an apex width in the range of 0.1 microns.

Cross-section images for the progression are shown below.

CHO_1K_X_measured
Cross-sectioned edge-on view images after the Chosera 1k. Sharpness: 1.4 microns width at 3 microns from the edge.
Shap2k_x
Cross-sectioned edge-on view images after the Shapton 2k. Sharpness: 1.2 microns width at 3 microns from the edge.
Shap4k_X
Cross-sectioned edge-on view images after the Shapton 4k. Sharpness: 1.05 microns width at 3 microns from the edge.

No significant change in the bevel angle or width at 3 microns occurs after the 4k level. No measurable difference is observed between the 4k and 16k level, other than a reduction in the apex width, observed in the edge-on views (above).

Shap16k_X
Cross-sectioned edge-on view images after the Shapton 16k. Sharpness 1.05 microns width at 3 microns from the edge.

The convexity near the apex is removed by the 4k level, and the measured geometry is unchanged with higher grits beyond the 4k. This result indicates that the bevel set is completed at the 4k level, not the 1k level as commonly believed. Beyond the 4k level, the bevel polish is refined and the edge width is reduced from about 0.3 microns to about 0.1 microns.

Sharpness is achieved during the bevel setting stage up to 4k grit. Beyond the 4k grit, Keenness improves, but Sharpness is not improved further.

 


 

What this teaches me is explained very well by knife guru, Cliff Stamp (see Cliff’s forum here):
” A low grit finish will generate a much thicker apex than a high grit edge which is one reason why a low grit apex will be stronger (resist lateral deformation) more than a high grit edge at the same micro-bevel angle. However the main issue is the type of cutting which is why I started with “If they are slicing soft materials (cardboard, ropes, foods, etc.) …” . In this case the apex will typically not be under high loads to deform it, it will dull mainly from slow abrasion. To combat that, use a low grit edge to make an irregular surface which will take a lot of abrasion before it is worn smooth and stops cutting and use a low angle apex to both enhance the roughness and maximize the amount of wear required. Because the loads are small the angle you can use can be very low and there is no real risk of deformation.

However if they are push cutting hard materials this type of finish won’t work because the apex will come under heavy loads to try to deform it and if you use a low angle and finish the apex with a low grit finish it is very likely to collapse almost immediately. For example that finish in the above which easily slices though ~2000 piece of 1/2″ hemp will fail dramatically in less than 10 cuts if you try to push cut because the forces will be so high that the apex will just deform and can crack right off. In order to make the apex perform well under cutting that type of material you have to raise the polish and then increase the angle to prevent it from deforming. Now of course continuing to increase the angle past the point it stops deforming doesn’t help. It is just that this point will be a lot higher in push cutting a hard material vs slicing a soft one.”

In other words, a coarse edge will have higher edge retention at very low angles when cutting soft material. I believe it will even have higher edge retention at the same angles as a polished edge, although a polished edge may excel in some push cutting tasks.

Straight Razor Honing Progression

How sharp does a straight razor need to be to shave your face and throat area with? SHARP =) We make sure it can pass the HHT (Hanging Hair Test) before returning it to our customers. Also, in experience we have found that finishing a straight razor on the .125 CBN pasted strop  will yield a smooth and yet very close shave. Check out this grit progression below… note that the higher we go up in grits, the more light, and the less we can actually see the edge.

Damaged edge before honing:

 

800 Grit Chosera Water Stones

2000 Grit Chosera Waterstones (note: reversed direction to see scratch pattern)

5000 Grit Chosera Waterstones

10k Grit Chosera Waterstones

Note: I increased the angle 1 degree per side to make sure to hit the very edge. This is seen in the pics.

Final Stropped bladed (.125 CBN kangaroo strop)

Steeling your knife – explained

Again, this information is given by Chad Ward, a knife sharpening expert. This information will also be explained to you in person upon completion of your knives.

 Why Edges Wear


The ability of a knife to hold an edge is affected by several factors. Many are properties of the steel, others are job-specific.

Wear resistance – the ability to resist abrasion – comes primarily from the amount, type and distribution of carbides in the steel.

Strength is resistance to low-impulse deformation. In other words, bending. Strength is directly related to the hardness of the steel.

Toughness is resistance to high-impulse deformation – impacts, chipping and cracking.

As a general rule, strength and toughness are inversely related. A hard, unbendable steel can be brittle. It will not withstand chopping through bone as well as a tough, slightly softer steel. A tough steel might roll its edge if it encounters significant lateral stress or is forced through very hard materials – stresses that a strong steel would easily resist. The most extreme examples of both would be the extremely hard, yet shatter-prone ceramic knives from Kyocera compared to very tough, soft stainless Chinese cleavers.

Edge holding is a function of wear resistance, strength, toughness and the tasks the knife is used for. Toughness is required to resist chipping when you are cutting through materials where you might encounter bone or other hard bits and pieces. Strength is required to resist rolling and impaction if, for example, someone in your kitchen (despite repeated warnings) uses a glass cutting board. Wear resistance becomes important for edge holding when you’re cutting through abrasive materials.

So the way your knife holds an edge depends on the steel and what you use the knife for.

The most common culprits that put wear resistance, strength and toughness to the test are:

Wear. Duh. As a knife blade encounters abrasive materials, the edge wears away. Unless you cut only soft foods, your edge will always wear somewhat, though the most wear in the kitchen will come from sharpening your knives. Significant wear could take years.

Indenting and rolling. As pressure is put on the edge of the blade (and remember, the edge’s job is to concentrate tremendous amounts of pressure), the edge can indent, impact or roll over to one side or the other. The harder the steel, the less likely it will be to indent or roll. This is actually fairly common in the kitchen, which is why you need to steel frequently (more on this below).

Chipping. The edge can chip or crack under impact, especially when encountering hard materials like bone. Micro-chipping can be an important factor in edge degradation, although kitchen knives are fairly tough.

Corrosion. The wet, acidic environment of the kitchen can give knives a real beating. Micro-rusting and the attack of acidic foods can lead to edge loss at the very apex of the edge in short order.

Technique. As chef Thomas Haslinger points out, “Having sharpened my own knives and other chefs’ knives, I can say that an often overlooked factor in cutting edge performance is how each individual holds and uses his knives. A person that ‘feels’ the cut will always have a knife that outperforms an individual who just cuts and slams the edge into the cutting board”

 

Steeling your Knife


Steeling regularly is the most critical maintenance you can perform on your knife. Whenever you use your knife, especially soft kitchen knives, the edge can turn out a bit. Turn the knife with the edge pointing to the ceiling under strong light. You shouldn’t be able to see it. The edge itself should be invisible. If, however, you see glints of light, those are spots where the edge has rolled. The edge is still reasonably sharp, it’s just not pointing straight down anymore. The steel realigns the edge of the knife, forcing the rolled spots back into line, making it usable again.

We will get into the various types of steels in just a moment, but be aware that the grooved steels that come with knife sets do in fact remove metal. A grooved steel acts as a file when used with a heavy hand, knocking microscopic chips out of your edge. At the very least, it is much coarser than the fine abrasive you used to achieve your edge. Steeling heavily with a grooved steel is taking several steps backward. A grooved steel should be used with caution and a very light touch.

The standard image we all have of steeling a knife involves a chef with his knife in one hand and steel in the other, blade flashing and ringing. If you’re particularly adept at this type of swordsmanship, have at it. It impresses the tourists.

A more effective method is to stand the steel straight up and down with the handle up and the tip resting on a folded towel to keep it from slipping. Why? Geometry.

Place the knife edge against the steel with the blade perpendicular to the steel – 90 degrees, right? Rotate your wrist so that you reduce the angle by half – 45 degrees. Reduce that by half – 22.5 degrees, and you are exactly where you need to be to steel your knife (if you have a 20 degree edge). You generally want to steel at a very slightly steeper angle than the edge bevel itself.

You can also use the Paper Airplane Trick to make a guide to prop against your steel so you know you are hitting the proper angle.


When you’re steeling, lock your wrist and stroke the knife from heel to tip by unhinging at the shoulder – it’s your pivot point – and slowly dropping your forearm. The key is to maintain a consistent angle all the way through the stroke. By locking your wrist and elbow, you will keep your angle stable from top to bottom. Go slowly and follow all the way through the tip. You don’t have to press very hard to realign the edge. Steeling requires barely more pressure than the weight of the knife itself.

Alternate from side to side, keeping the same alignment and angle on both sides. It really only takes four or five strokes per side to get your knife ready for more work.

When should you steel? Every time you use your knife. Oddly enough, steeling before you use the knife is much more effective than steeling afterward. A steeled edge can be very sharp, but it is not as durable as a freshly honed edge. If you don’t use a steeled edge right away it can actually relax back into its blunted state. The same is true of a blunted edge. If you really degrade the edge of your knife in a heavy cutting session, let it sit overnight before sharpening. It will be in much better shape than it was the day before.

You should also steel before sharpening so any rolled or impacted edges are pushed back into alignment. That way you don’t cut off the rolled edge and lose more metal than you really need to. You also can steel after sharpening to add a final bit of polish (especially on a medium to medium fine edge) and tooth alignment. A steel actually “smears” the edge, teasing out a little more thinness. You’ll have a keener edge, but it will be weaker than the freshly sharpened edge.

Restoring Factory Blade Geometry

So you have some kitchen knives you want to send off and get sharpened… Well this article should interest you! Before you have your knives sharpened by someone local or even online, see if you can determine the amount of attention they will pay each of your blades. Here at Razor Edge Knives, we work on each blade as if it were our own!

Most knife sharpening companies will charge for blade repair… at Razor Edge Knives, we include it as a complimentary service when you send in 10 knives or more. What do we mean by blade repair? Well, typically it is a chipped tip or a large nick taken out of the edge… but many times the blade has not been sharpened properly in the past and the “heel” of the edge gets worn and the “return” goes out past the edge (click here for a knife diagram explaining the different parts of a knife). If you have less knives, it’s only $3/blade to fix.

This poses a problem for your larger kitchen knives (you know, the ones you typically “chop” things with). The reason is because as you try to use the “heel” of your edge to cut all the way through something, let’s say a tomatoe, it won’t cut all the way through because there is actually a gap between your edge and the cutting board (see above photo). Here are some pictures to show what a finished blade looks like when we are done

   

   

You can be rest assured that by sending us your blades, they will be well taken care of and extra time and effort will go into your blades if they need it – even at a monetary loss to us. The testimonials and reviews back up this claim. When you want to talk to the person who actually will be sharpening and handling your blade (I.e. Josh, the owner) all you have to do is pick up the phone and call! Thanks for checking us out.

Here is one more example… do your larger knives look like this?

General Knife Maintenance Tips

Everyone should at least know some basics on maintaining their knives… whether its their kitchen knives or hunting knives, the rules are the same. The first point is HUGE, don’t miss it. If you are cutting on a class cutting board or plate, this will destroy your edge… do yourself a favor and go buy a wooden, bamboo, or plastic cutting board and a good steel.

“- Use wooden or composite plastic cutting boards only. Glass, ceramic, marble and steel will cause the edge to roll or chip. Bad. Don’t do it.

- Don’t drop your knives in the sink. Not only is it a hazard to the person washing dishes, but you can also blunt the tip or edge.

- Don’t put your knives in the dishwasher. The heat may damage wooden handles and the edges may bang against other cutlery or plates.

- Keep your knives clean and dry. Sanitize if necessary.

- Do not store your knives loose in a drawer. Use a block, magnetic strip, slotted hanger or edge guards. The magnetic strip is not recommended if you have children or inquisitive pets.

- Finally, your knife is not a can opener, a screwdriver, a pry bar, box cutter or hammer.”

Information from Chad Ward

Polished Vs. Toothy Edge?

Below is an article by a sharpening expert, Joe Talmadge. In my own findings, a highly polished edge is not only not needed very much, in most cases it actually hinders the cutting ability of the blade. High polish is for push cutting (i.e. “pushing” through a cut vs. “slicing” through a cut) such as straight razor shaving or wood carving. It has very limited uses. In most other situations, you will want and use a toothier edge.

” Many treatises on sharpening tend to focus on getting a polished, razor-like edge. This is partially the fault of the tests we use to see how good our sharpening skills are. Shaving hair off your arm, or cutting a thin slice out of a hanging piece of newpaper, both favor a razor polished edge. An edge ground with a coarser grit won’t feel as sharp, but will outperform the razor polished edge on slicing type cuts, sometimes significantly. If most of your work involves slicing cuts (cutting rope, etc.) you should strongly consider backing off to the coarser stones, or even a file. This may be one of the most important decisions you make — probably more important than finding the perfect sharpening system!

Recently, Mike Swaim (a contributor to rec.knives) has been running and documenting a number of knife tests. Mike’s tests indicate that for certain uses, a coarse-ground blade will significantly outperform a razor polished blade. In fact, a razor polished blade which does extremely poor in Mike’s tests will sometimes perform with the very best knives when re-sharpened using a coarser grind. Mike’s coarse grind was done on a file, so it is very coarse, but he’s since begun favoring very coarse stones over files.

The tests seem to indicate that you should think carefully about your grit strategy. If you know you have one particular usage that you do often, it’s worth a few minutes of your time to test out whether or not a dull-feeling 300-grit sharpened knife will outperform your razor-edged 1200-grit sharpened knife. The 300-grit knife may not shave hair well, but if you need it to cut rope, it may be just the ticket!

If you ever hear the suggestion that your knife may be “too sharp”, moving to a coarser grit is what is being suggested. A “too sharp” — or more accurately, “too finely polished” — edge may shave hair well, but not do your particular job well. Even with a coarse grit, your knife needs to be sharp, in the sense that the edge bevels need to meet consistently.”

By Joe Talmadge