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Basic Blade Geometry.

Discussion in 'Knives' started by JonSidneyB, Jan 25, 2014.

  1. JonSidneyB
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    Post in progress. (By the time it is done I have a bad feeling it is going to be very very long when finished, I will need to edit it a lot later too) (Yep, it is in dire need of proof reading)

    Some recommendations I have seen to specific questions made me feel the need to post this. I realize that knives are not used day to day as much as they were in the past and I think quite a bit of knowledge that may have at one time been commonplace is lost now days.

    I know I know, this post is in that hard to follow stream of consciousness manner that I frequently use. I am doing a bit of a brain dump for now and drawing some really bad pictures. I will come back and try and edit it to make it easier to read and add many more examples and explanations of knife function.

    This is a very simplistic review of blade geometry (actually understanding blade geometry is not complicated at all but there is a lot to cover). This is not about different types of grinds. I want to eventually cover 12 different blade shapes but I am going to start with just a handful at first.

    Belly can create more aggressive slicing than a straight edge using draw and push cuts in some materials especially materials that have some elastic qualities and a bit of thickness.

    Belly varies with some examples causing a loss in versatility to gain additional cutting ability. The amount of belly a knife has can change more than just cutting ability, some of them negative. An extreme example of belly could be a trailing point skinner.

    The reason why belly can enhance cutting ability is if you draw the edge into something more edge steel is involved in the cutting then a straight blade would provide.

    I am going to take a big jump to a comparison between a Sheepfoot blade vs a knife with a small amount of belly. In this case the belly is not there to enhance cutting as it is to prevent snagging.

    This is a more mundane example and there are far better examples in the industrial and practical world but this one is easy to understand and I will build from here. We know steak knives are usually dull but that is because a very small portion of the blade keeps contact the plate but that is not what I am going to try an illustrate.

    Lets cut a steak with a Sheepfoot and then with a knife with a small amount of belly and a steak knife.

    steak.jpeg

    Steaks are usually cut with a sawing motion, The Sheepfoot blade does fine on the draw part of the cut, what happens when you do the push portion of the cut? I bet you can see a problem right away. You cannot do a sawing motion with a Sheepfoot blade if the tip is engaged. That thing is going to get hung up on the push.

    steaknife.jpeg

    Lets make some observations here. Notice the part of the blade that is making the most contact with the steak has all the belly. Belly on any other portion of the blade really does not contribute much. Next it will not snag, it will be cutting on both the draw and push portion of the movement. I don't know why I picked food as the examples so far, I am making this up as I go along. The same principles apply in untold numbers of situations. "Just get a Wharncliffe" is not always a good answer but there are times where a Sheepsfoot blade is the best answer.

    Lets look at a few belly's now.

    bark.jpg Mikro_Canadian_II_154CM_Black_Canvas_Micarta.jpg MDP_Amazon_Bloodwood.jpg barkMT_Green_Canvassized.jpg

    In the first photo the upper picture is a trailing point. On this specific knife a large portion of the cutting edge is curved some examples the entire blade is curved. If you were to measure the length of the blade then measure the length of the edge you will notice that it has more cutting edge than blade length. As you cut with this knife more metal will be involved in the cut than a straight edged knives. We still want straight edge knives for many jobs but this knife will slice easier into animal tissue, and many things with an elastic quality and some depth. These types of knives are very aggressive cutters that lets you get a large portion of the knife into the act. It also has some drawbacks.

    The second photo has a lot of belly in the forward portion of the blade and a bit of width to the blade. The straight part of the blade would be used for things like notching and cutting motions you would use as if you were sharpening a pencil. It is a rather aggressive cutter on the forward portion of the blade. It is a form of a drop point of course. I will get to the width of this blade a bit later.

    The third photo has another drop point, you will notice that is has belly but not near as much as the previous mentioned knives.

    Of course the last photo is a knife with no belly at all, this knife does not need a belly for the jobs it does and would be worse if it had one.

    Lets cut a piece of linoleum (we could be cutting a lot of different things) using a draw cut.

    linolium.jpeg

    When doing this kind of a cut with a coping blade the angle will probably be less than 45degrees. The blade has a lot of stiffness up front, the cut is happening at an angle making the effective blade contact area greater than the depth but the material is stiffer than something like a deer hide. You are not using the entire blade for this. The tip digs in easily and with a guide a straight line is easy to cut.

    linolium2.jpeg

    Wait! We have a problem, no tip contact. Hmmmm, the other knife had tip contact. I will just rotate the blade some. Oh no.....the leverage is now working against me when I try to make the draw cut. This knife is not the right one for the job. This would be fine if I was cutting a steak but this is a straight single pass on a tough piece of linoleum.

    cut.jpeg

    What to do what to do?

    I will use a dagger. Ummm, that won't work. How about a Bowie, hummmm, nope. That trailing point knife wont work and the Sheepfoot will not cut on the push that well and will get hung up.

    Wait, I have an idea.

    nocut.jpeg

    It works...wooo hoooo. Oh, that is what a drop point is for. It gave up some belly real estate to lower the point.


    Have you ever worked with a knife where you put some part of your hand on the spine and pushed? I have, many many times. Not recently but working on many things when I was younger it was quite common.

    Since I was on a wood theme earlier I will continue down that path but this type of cutting more often dealt with wood.

    When you cut a fresh hand tossed pizza out of the oven you know a sawing motion is not the best way to do it. A roller or a straight down push with a long knife works better. You place the long knife over the Pizza, put your off hand on the spine of the blade and push straight down. You don't drag cheese and topping off that way.

    "Hey, bring me a long knife for the Pizza"

    If you bring me a Black Bear by Loveless I will cry. I wanted a long knife with a dull spine.



    Big-Bear-2.jpg

    You want me to put my hand on that spine and push straight down? No way am I don't that.

    If you want to to be able to cut a someone throat from behind and not have to shift my grip...well this knife is fine for that. This is a fighting knife that can do some utility functions but it is not a utility knife and is less versatile and unsuited for many jobs.

    I ain't going to do any fitting on the split rail fence with this knife either. No way no how. If you told me it was a weapon....I will go along with that.

    If put a swedge on a knife it can lose some of it's utility.

    Blade geometry is also why muti-bladed knives were so common in the past.

    (This post has a long long long way to go before being finished.)
     
    Last edited by JonSidneyB, Jan 26, 2014
  2. JonSidneyB
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    This is going to end up being a really really really long post.

    (a continuation of the previous post that is not close to being finished yet)
     
    Last edited by JonSidneyB, Jan 26, 2014
  3. JonSidneyB
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    Handles:

    "Oh this handle feels comfortable" Ack!! but the OP might be doing cuts that does not let him hold the knife like that.

    "You need to make that knife handle grippier" NOOOOOOOOOOOOOOO please don't, not this knife. It won't work as good.

    (This will be a work in progress later)
     
    Last edited by JonSidneyB, Jan 26, 2014
  4. JonSidneyB
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    History:

    Things might not be as you expect.

    (This will be a work in progress)
     
  5. Kripto

    Kripto Evil Sid

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    What a great post! I'm interested in blade design decisions on classic knives.. Like what are the blades on a Stockman intended for, and why would you carry a filet knife.. (Unless you're cooking in the outback) ;)
     
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  6. J_C
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    I've also found that a sheepsfoot blade works really well for the "edge up" cutting method you described when explaining the use of a drop point.
     
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  7. CSM-101
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    I've been wondering the same thing after this post in the "Knives that withstand the test of time" thread. Why were those blades picked? Were they
    the most popular blades of the time or the shapes needed for tasks common for the times? I need to know!
     
  8. JonSidneyB
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    Knives used to be based on activity and what was going to happen rather than what might happen.

    You would see many knives based on occupation, others for various activities, while others for the daily things people did in a non-prepackaged world.

    There was not a collectors market or cool factor back then. The world was more blue collar and even the white collar people had a more blue collar home life.

    These things were around when there were no cars, no electric can opener, no gas powered lawn mower. You carried what was useful to you and didn't carry what was not.
     
  9. JonSidneyB
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    Another thing to consider was it the other person was also using another knife. The other knife can affect blade choices on the multi bladed knife. Even as late as the 60-80's in very rural areas these knives were used heavily but for smaller tasks.

    When working harvest we used fixed blades but the muti blade utility knife when along for the ride for the other little tasks that might come up that the fixed blades were not suitable for. When inspecting a fence line other tools were carried but the little folder was carried for the little things that come up that the other tools were not appropriate for. When working cattle you carried a stockman even if there were other larger knives around because there were always little things it could do better.

    The Sheepfoot blade was not named because of the shape. It was named this because it was used to trim sheep hooves. The also worked to repair horse hooves when a proper hoof knife was not available in the field. There are similar enough to to coping blade to stand in for one.

    It was not about preference but about what tools they could carry with them to match what the expected to be doing.

    It also got beat into me that you don't use some of the highly portable tools when you were near the shop, the barn, or at home (some were fine to use however) You had better tool and you saved wear and tear on the pocket tools so they would be their for field work.
     
    Last edited by JonSidneyB, Jan 26, 2014
  10. Fabregas485
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    Thanks Jon, I never really gave the shape of a knife a thought.
     
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  11. JonSidneyB
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    I think it is just the reality of knives being less a part of daily life. If you work with them all the time you find some things work better than others for different things. You also find a favorite that is great for one job but really stinks at what you are doing at the moment.

    :)
     
    Last edited by JonSidneyB, Jan 26, 2014
  12. Fabregas485
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    Very well put. I find a large SAK blade does well for most jobs I have thrown at it, but I have had to give up on a few odd jobs due to the knife blades shape (and possibly lack of lock).
     
  13. Xiii
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    great post Jon very informative. Should answer lots of peoples queries.
    Xiii
     
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  14. Jimmer2109

    Jimmer2109 Loaded Pockets

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    Wow, what a great thread idea. I literally read the entire thing lol. I'll take this info as my "learn a new thing everyday" thing.
     
  15. JonSidneyB
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    Thanks for the comments guys. I will try and finish it as time allows.
     
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  16. dmattaponi

    dmattaponi Loaded Pockets

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    Artist or not;) , I think those were some great examples you gave. Clear and understandable. Looking forward to your updates.
     
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  17. flatblackcapo

    flatblackcapo EDC Junkie!!!!!

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  18. MJGEGB

    MJGEGB Loaded Pockets

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    I would use the Green River Buffalo Skinner as an example of a trailing point knife, it's more obvious than the sharp finger pattern, which I actually consider a clip point, I could be wrong wouldn't be the first time and won't be the last.

    A good topic without a doubt, I tend to lean to drop points because I find them versatile but I really need to give more blade shapes a try.
     
  19. JonSidneyB
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    A drop point is very versatile. It gives up a little belly over a straight spine and even more to a swept point blade so it loses a little bit of slicing power but is capable of things the other two are not as good at. There are things a swept point is horrible at but that is the price of it's enhanced slicing ability.

    A drop point is very versatile.
     
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  20. JonSidneyB
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    A knife can be both a trialing point and a clip. If the point is higher than the material behind it it is trailing.
     
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