How can I design a custom ergonomic knife handle?

Steel_Magnet77 said:
Anything bushcraft. Skinning, chopping, carving, etc...
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If all having the same priority, this will be the best handle, IMO.

i-3JrBPBQ-X2.jpg
 
ferider said:
If all having the same priority, this will be the best handle, IMO.

i-3JrBPBQ-X2.jpg
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I agree and often say that the Kephart is probably the best knife design. If I had to pick one, it's Right Up there ....
 
I need to get my hands on a Kephart...😂 I like the simplicity. The biggest things I see that I would do differently would be a larger finger stop and an angled handle (to keep the wrist straighter while cutting which prevents cumulative wrist and hand injury). That's just my opinion.😇 I will post an update on my findings soon...
 
ferider said:
If all having the same priority, this will be the best handle, IMO.
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Yup…equally sub optimal for everything. 😁
Said with mix of humor and seriousness. I agree that if you really put equal weight on everything, you end up with a very basic shape. You end up relying on the conformance of the human hand. A handle that doesn’t so much shine as comfortable, but isn’t unacceptably uncomfortable in any situation.

Just a tiny bit of weighting bias, and you get a very different design.

When one takes into account the materials, manufacturing methods available, method of design and economics of the time, there is no reason to place the Kephart knife on a modern pedestal. No more than you would place any other piece of equipment designed in the 1900s on a pedestal now.
 
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I realize that a knife handle has variations due to use but also agree that there are some basic shapes to stay near when "designing" a knife handle.

Here is an observance from a fellow who has used tools for 70+ years and has 200-years-old tools in his shop.:
Screwdrivers were invented in the Middle Ages. The handle was more-or-less a simple lathe-turned spindle with a rounded butt.

in the 1800's, they made a few slight changes, like making them octagonal or adding grooves along the sides, and in the early 1900's using modern materials like plastic and rubber coatings ... but the shape really did not change.

In the 20th century people and manufacturers tried to invent the "perfect screwdriver handle". They made them round like a ball and said it was more ergonomic. They made them ratchet and said they were more efficient. They made them T-shaped and said it was more powerful. Despite all that, go to a big hardware store and nearly every screwdriver handle is pretty much the same as they were in the 15th century. Why??? because it is the shape that works. Those "special" shapes still exist, but 99.9% of screwdrivers made today are still in the original shape.

About the only re-invention that worked out was making the shanks replaceable and interchangeable as done by Xcelite. Even their "improvement" of making the injection molded handles from Butyl Plastic seemed good ... until the handles aged for about 20 years and started to smell of butyric acid - AKA vomit smell.

(Humidity, heat, and time make a chemical change to the butyl plastic and release butyric acid. The change also makes a white mold looking fuzz form on the plastic. Storing in a cool dry location with good air flow deters this. Unfortunately, a toolbox is the opposite of a good location. Cleaning well with denatured alcohol and 0000steel wool, drying well, and rubbing down with WD-40 can help restore the handles to a less-smelly and good-looking condition.)
 
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comparing knife handles to screwdriver handles is kind of an apples and oranges type thing, imo
 
I'll give you guys an update. So essentially, after reading many scientific articles on this subject, I found a simple formula that seems practical for my purpose. An important note is that what Kong and Lowe found is based on COMFORT, not greatest grip strength, ie. they surveyed a selected group of healthy individuals on comfort by giving different diameter cylinders to hold. They turned the graph to a percentage ratio; then they created a formula for the most comfortable size. So the circular diameter of the handle that will provide the greatest comfort to the user is: user's hand length X (.618/pi). Supposedly. Experimentation wise I was going to manufacture a cylinder with my optimal diameter and chop two parallel, flat faces on each side to the width of my middle finger joint (see pic below). (The middle finger joint is the largest, then index, ring, and pinky.) Then take off all the hard edges. That's for general experimentation. The next step would be to grind out my favorite handle profile and have the largest diameter be the one the study says is the most comfortable. I have no idea if it will make a difference or not. I will say that the diameter seems large, but I am very willing to give it a shot. Remember my goal is to be able to make a knife for someone and be sure of the comfort and ergonomics of its handle. As of right now I would ask their hand length (HL) and palm width. Pretty much I am just finding a sketch box to fit the standardized handle shape in. That 2D box will slightly change for each buyer.

That is my main reference article.
https://www.sciencedirect.com/science/article/pii/S0169814104002148

This BLADE article is a good general informer that compliments what I found.
https://blademag.com/knifemaking/knife-handle-ergonomics-101-getting-a-grip-on-the-basics

This is the picture I referenced (you might have to paste in a web browser):
file:///home/chronos/u-57fb6d924ffd73638934ce43a5958400a60eba2f/MyFiles/Camera/Finger.jpg
 
I now realize that I should probably make the handle width the length of the index finger joint because it is at the pivot point...
 
Steel_Magnet77 said:
I'll give you guys an update. So essentially, after reading many scientific articles on this subject, I found a simple formula that seems practical for my purpose. An important note is that what Kong and Lowe found is based on COMFORT, not greatest grip strength, ie. they surveyed a selected group of healthy individuals on comfort by giving different diameter cylinders to hold. They turned the graph to a percentage ratio; then they created a formula for the most comfortable size. So the circular diameter of the handle that will provide the greatest comfort to the user is: user's hand length X (.618/pi). Supposedly. Experimentation wise I was going to manufacture a cylinder with my optimal diameter and chop two parallel, flat faces on each side to the width of my middle finger joint (see pic below). (The middle finger joint is the largest, then index, ring, and pinky.) Then take off all the hard edges. That's for general experimentation. The next step would be to grind out my favorite handle profile and have the largest diameter be the one the study says is the most comfortable. I have no idea if it will make a difference or not. I will say that the diameter seems large, but I am very willing to give it a shot. Remember my goal is to be able to make a knife for someone and be sure of the comfort and ergonomics of its handle. As of right now I would ask their hand length (HL) and palm width. Pretty much I am just finding a sketch box to fit the standardized handle shape in. That 2D box will slightly change for each buyer.

That is my main reference article.
https://www.sciencedirect.com/science/article/pii/S0169814104002148

This BLADE article is a good general informer that compliments what I found.
https://blademag.com/knifemaking/knife-handle-ergonomics-101-getting-a-grip-on-the-basics

This is the picture I referenced (you might have to paste in a web browser):
file:///home/chronos/u-57fb6d924ffd73638934ce43a5958400a60eba2f/MyFiles/Camera/Finger.jpg
Click to expand...

I am quoting the author of the Blade article, I think his name was Mr Price.

"There is no agreement on the shape of the perfect handle, so you are left with my opinion"

I like That.
 
Steel_Magnet77 said:
I'll give you guys an update. So essentially, after reading many scientific articles on this subject, I found a simple formula that seems practical for my purpose. An important note is that what Kong and Lowe found is based on COMFORT, not greatest grip strength, ie. they surveyed a selected group of healthy individuals on comfort by giving different diameter cylinders to hold. They turned the graph to a percentage ratio; then they created a formula for the most comfortable size. So the circular diameter of the handle that will provide the greatest comfort to the user is: user's hand length X (.618/pi). Supposedly. Experimentation wise I was going to manufacture a cylinder with my optimal diameter and chop two parallel, flat faces on each side to the width of my middle finger joint (see pic below). (The middle finger joint is the largest, then index, ring, and pinky.) Then take off all the hard edges. That's for general experimentation. The next step would be to grind out my favorite handle profile and have the largest diameter be the one the study says is the most comfortable. I have no idea if it will make a difference or not. I will say that the diameter seems large, but I am very willing to give it a shot. Remember my goal is to be able to make a knife for someone and be sure of the comfort and ergonomics of its handle. As of right now I would ask their hand length (HL) and palm width. Pretty much I am just finding a sketch box to fit the standardized handle shape in. That 2D box will slightly change for each buyer.

That is my main reference article.
https://www.sciencedirect.com/science/article/pii/S0169814104002148

This BLADE article is a good general informer that compliments what I found.
https://blademag.com/knifemaking/knife-handle-ergonomics-101-getting-a-grip-on-the-basics

This is the picture I referenced (you might have to paste in a web browser):
file:///home/chronos/u-57fb6d924ffd73638934ce43a5958400a60eba2f/MyFiles/Camera/Finger.jpg
Click to expand...
I tried the formula for my hand length and came up with 1.28 inches. That would be a super girthy handle!!!

There is defiantly a limit to handle width when it comes to handle height. A short handle height feels a little odd with a wide handle from my experience. If I want a girthy handle I also need to add a little more handle height to the pattern to get a ratio that works.
 
Seedy Lot said:
I tried the formula for my hand length and came up with 1.28 inches. That would be a super girthy handle!!!

There is defiantly a limit to handle width when it comes to handle height. A short handle height feels a little odd with a wide handle from my experience. If I want a girthy handle I also need to add a little more handle height to the pattern to get a ratio that works.
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The blade author showed a 1.0" diameter as being not enough for maximum hand strength.

Maybe maximum hand strength isn't the same as required dexterity....

I agree with You, he wanted very (too)large handles according to his measurements.

And that's coming from someone who likes very large handles....haha
 
Crag the Brewer said:
The blade author showed a 1.0" diameter as being not enough for maximum hand strength.

Maybe maximum hand strength isn't the same as required dexterity....

I agree with You, he wanted very (too)large handles according to his measurements.

And that's coming from someone who likes very large handles....haha
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And maybe maximum hand strength is not something we need to be overly concerned with when talking about knife handles.
 
Not meaning to rain on your parade SM77 but…as a (now retired) orthopedic surgeon, the article you cited has basically no relevance to knife handle size. Manipulating cylindrical grips on a machine is nothing like using a knife. Maximum grip strength not relevant either. In fact, grip strength (especially in twisting motions), is maximized with your wrist in about 25 degrees of extension…which would only be relevant in a knife in a “maximal vertical stab downward” and somewhat less in a chopping motion.

FWIW, the radial (thumb) side of the hand is basically designed for “precision grip” while the Ulnar (pinkie) side is for power grip.
A little “hook” at the end of the handle allows your 5th finger to lock in and participate a bit more strongly when you need a tighter grip.
A “pinch area” near the handle front will facilitate precision - like in a chef knife.

So, basically, as the knife makers here have said….it depends on what the knife will be used for. There is NO perfect knife handle shape for all tasks…and that’s not even considering the differences in hand shapes, sizes and grip strength - for instance women have typically 50% less grip strength than men…

SO, there IS science involved in using your hands….but it is much more art in this particular instance

Bill
 
Since you listed multiple tasks you are looking to accomplish with one handle I would add that I would rather have a Delica to make shavings and curls for fire than a beefy bushcraft knife to butcher an animal.

Decade ago I had to butcher a big black bear deep in the mountains of Montana so we could carry it to the distant vehicle, at the time I had a trusty SBT bushcraft knife. After a while of butchering I realized I was getting arm fatigue from the weight of the knife but also because if the unwieldy thicker handle and handle design, and thicknesses of stock.

I am a fairly active outdoors knife user and the knife I carry and use the most is 0.700 inches wide at the center. Yes at times I would like a wider handle but I get by. If I am taking multiple knives into the woods I will also have a larger one with a wider comfortable handle but still much slimmer than the formula's ideal. I find a well contoured 0.900 handle to be pretty popular with a larger hard use knife.
 
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