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Big Bowie question
- Thread starter Augustus
- Start date
Guilty as charged!
I did find out from a place that sold them that the other Bowie that they have up for auction - the Canute Battle Dagger from Last Legends - really is a retired piece by them.
Everything happens tonight!
Not sure I can handle the excitement!
Thanks for the help.
Augustus
Cliff Stamp
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Kumdo :
The problem with this can be be understood by the simple mechanics of how wood splits when cut, Leonard Lee when into this in detail on his book on sharpening. Look at the development of the axe geometry for how this was put into practice.
To be quite clear, hollow grinds are found on high performance chopping blades - but not as the primary grinds. They serve as relief grinds to the primary profile which is optimally convex to insure grain splitting with minimal wedging.
A primary grind done as shown on the MMHW bodies such as the following :
http://www.plan-a.org/mmhw/dw.htm
Will both reduce penetration (mainly due to the shallow nature of the grind) and induce wedging due to the way it compacts the wood instead of splitting it. As the curvature expands out over the cut, it will compress down on the wood reducing the split and thus raising the binding effect.
They are ~1/3 of the blade height, very shallow grinds except when compared to the cheapest machetes.
-Cliff
The problem with this can be be understood by the simple mechanics of how wood splits when cut, Leonard Lee when into this in detail on his book on sharpening. Look at the development of the axe geometry for how this was put into practice.
To be quite clear, hollow grinds are found on high performance chopping blades - but not as the primary grinds. They serve as relief grinds to the primary profile which is optimally convex to insure grain splitting with minimal wedging.
A primary grind done as shown on the MMHW bodies such as the following :
http://www.plan-a.org/mmhw/dw.htm
Will both reduce penetration (mainly due to the shallow nature of the grind) and induce wedging due to the way it compacts the wood instead of splitting it. As the curvature expands out over the cut, it will compress down on the wood reducing the split and thus raising the binding effect.
They are ~1/3 of the blade height, very shallow grinds except when compared to the cheapest machetes.
-Cliff
- Joined
- Mar 7, 2000
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- 1,048
First of all, "shallow" normally refers depth, not length. When talking about hollow grinds, the depth of the grind usually indicates... well how deep it is. But since we are talking about circular cuts in steel the deeper the cut, the longer it will be as well. So you are right- these grinds are fairly shallow in length.
Regardless, there is a problem with how you try to understand how a knife chops. The grind doesn't split the material; the edge does. A convex edge functions the same way that a convex grind does- it splits the material. Now if you look at the cross section of a MMHW bowie, you'll can draw an imaginary line that continues from the edge and continues PAST the top of the grind. In other words, binding can't occur because it the material sails to either side of the blade. Since there is no steel for the material to drag on (like in a flat ground knife), chopping is more effective in hollow grind knives, so long as the edge facilitates the actual splitting and the tops of the grinds don't impede the movement of either side of the material.
Regardless, there is a problem with how you try to understand how a knife chops. The grind doesn't split the material; the edge does. A convex edge functions the same way that a convex grind does- it splits the material. Now if you look at the cross section of a MMHW bowie, you'll can draw an imaginary line that continues from the edge and continues PAST the top of the grind. In other words, binding can't occur because it the material sails to either side of the blade. Since there is no steel for the material to drag on (like in a flat ground knife), chopping is more effective in hollow grind knives, so long as the edge facilitates the actual splitting and the tops of the grinds don't impede the movement of either side of the material.
Cliff Stamp
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Kumdo :
While the secondary edge grind on knives will induce some splitting action, because the edges are very thin (0.025 to 050" usually) compared to the knife thickness at maximum penetration (about 0.188 to 0.25 usually), the main splitting effect comes from the wedging action of the primary grind. This is nothing on a hollow grind, even worse, depending on the exact nature of the curvature, it can actually act to increase binding by compacting the material directly down at the top of the arc.
[MMHW bowie]
This is true for any knife with a secondary edge profile, as they are always more obtuse than the primary grind. Hence your conclusion :
Directly contradicts your next statement :
As most flat ground knives also have secondary edge bevels. So do machetes for example, which are known to bind horribly on thick woods.
The problem with your arguement is that is fails to take into account the fact that wood is elastic. While the edge of the knife will distort thw wood to some degree it will quickly rebound to almost the full extent it was distorted, unless it is distorted very far and the resilence is exceeded. This is why on soft woods fully convex profiles are used on axes as anything else wedges too badly.
Now on hardwood axes, the secondary edge is also convex, and the primary hollow as on the bowies being discussed here, but there are a number of significant differences which make the behavior of the two tremendously different. Note as well that this profile is again only used on hardwoods, it isn't functional on soft woods as the penetration is too deep. Same reason why splitting mauls don't have hollow grinds.
First of all the edge bevel on the axe is massively wider and therefore thicker. A quality qood working axe will have an edge bevel as wide as the primary grind on the above hollow ground bowies. Since the edge is now significant in thickness compared to the body of the blade it can actually induce a significant amount of wedging.
Secondly the blade above the hollow relief grind is not flat stock, but also continues in a convex grind to also reduce wedging. Ideally the entire primary convex grind is a smooth continuation of the edge curvature.
Finally, the hollow grinds on axes as relief grinds, not the common way they are done on knives which is to have the curvature at the top of the arc almost perpendicular to the blade face. This is critical to avoid the direct compaction of the wood as noted in the above.
Note as well that as noted, all wood binds to different degrees. I could for example use the PAB from strider (hollow ground) to chop on seasoned hardwoods with little difficulty. On such woods the penetration is shallow and the wood not very elastic, so wedging is minimal. However trying the blade out on various fresh woods, mainly soft to medium density (pine, birch, oak, fir), the binding would be so bad the knife had to be hammered out at times.
-Cliff
While the secondary edge grind on knives will induce some splitting action, because the edges are very thin (0.025 to 050" usually) compared to the knife thickness at maximum penetration (about 0.188 to 0.25 usually), the main splitting effect comes from the wedging action of the primary grind. This is nothing on a hollow grind, even worse, depending on the exact nature of the curvature, it can actually act to increase binding by compacting the material directly down at the top of the arc.
[MMHW bowie]
This is true for any knife with a secondary edge profile, as they are always more obtuse than the primary grind. Hence your conclusion :
Directly contradicts your next statement :
As most flat ground knives also have secondary edge bevels. So do machetes for example, which are known to bind horribly on thick woods.
The problem with your arguement is that is fails to take into account the fact that wood is elastic. While the edge of the knife will distort thw wood to some degree it will quickly rebound to almost the full extent it was distorted, unless it is distorted very far and the resilence is exceeded. This is why on soft woods fully convex profiles are used on axes as anything else wedges too badly.
Now on hardwood axes, the secondary edge is also convex, and the primary hollow as on the bowies being discussed here, but there are a number of significant differences which make the behavior of the two tremendously different. Note as well that this profile is again only used on hardwoods, it isn't functional on soft woods as the penetration is too deep. Same reason why splitting mauls don't have hollow grinds.
First of all the edge bevel on the axe is massively wider and therefore thicker. A quality qood working axe will have an edge bevel as wide as the primary grind on the above hollow ground bowies. Since the edge is now significant in thickness compared to the body of the blade it can actually induce a significant amount of wedging.
Secondly the blade above the hollow relief grind is not flat stock, but also continues in a convex grind to also reduce wedging. Ideally the entire primary convex grind is a smooth continuation of the edge curvature.
Finally, the hollow grinds on axes as relief grinds, not the common way they are done on knives which is to have the curvature at the top of the arc almost perpendicular to the blade face. This is critical to avoid the direct compaction of the wood as noted in the above.
Note as well that as noted, all wood binds to different degrees. I could for example use the PAB from strider (hollow ground) to chop on seasoned hardwoods with little difficulty. On such woods the penetration is shallow and the wood not very elastic, so wedging is minimal. However trying the blade out on various fresh woods, mainly soft to medium density (pine, birch, oak, fir), the binding would be so bad the knife had to be hammered out at times.
-Cliff
- Joined
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Cliff-- I've used my White River bowie pretty extensively on a wide variety of woods, and have had no binding problems. I read what you have written about hollow grinds on choppers before I purchased the White River bowie, and almost didn't purchase the knife as a result. However, I've been very happy with the knife's performance so far. The only time I've experienced binding is when trying to cut carboard. In terms of chopping ability, I'd have to rate the bowie slightly below say an 18" AK from HI, but I think this has more to do with the weight distribution of the two blades. The khukuri puts a lot more weight towards the tip. I'm not trying to start an argument here, just trying to make sense of my own observations in terms of what you have said.
--Josh
--Josh
Cliff Stamp
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As noted in the above the extent of binding depends on other factors besides the geometry of the knife. The skill and power of the user play a great part as well as the nature of the wood, density and elasticity.
At times I have used machetes to chop with and had no problems with binding, this doesn't mean the profile isn't inherently flawed in that respect, it was a simple matter of the wood not having enough wedging ability.
However for those that have problems with binding, due to skill, power or just heavily wedging woods, flat stock machetes, and hollow ground blades (of the above style) are horrible choices.
There are also lots of other reasons to avoid blades ground in that style as well. The edge durability for example is low in extreme situations. Damage that exceeds the edge bevel can easily cause gross failure. This is impossible with flat or convex grinds.
Lateral impacts to the blade are also focused on the edge with hollow grinds of that type. Flat blades will absorb much of the impact on the primary grinds, and convex blades are even better at handling such loads.
-Cliff
At times I have used machetes to chop with and had no problems with binding, this doesn't mean the profile isn't inherently flawed in that respect, it was a simple matter of the wood not having enough wedging ability.
However for those that have problems with binding, due to skill, power or just heavily wedging woods, flat stock machetes, and hollow ground blades (of the above style) are horrible choices.
There are also lots of other reasons to avoid blades ground in that style as well. The edge durability for example is low in extreme situations. Damage that exceeds the edge bevel can easily cause gross failure. This is impossible with flat or convex grinds.
Lateral impacts to the blade are also focused on the edge with hollow grinds of that type. Flat blades will absorb much of the impact on the primary grinds, and convex blades are even better at handling such loads.
-Cliff
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- 1,048
Okay this last part about hollow grinds being weaker is totally misleading, maybe even flat out wrong. There are so many other variables that are involved with strength issues, that the point is moot. I can think of only 2 makers that put their knives under "extreme conditions" during shows, and both were hollow grind knives. One maker hacked apart steel table legs (Strider) and the other cut apart one of those big oil drums (MMHW). I don't think I need to go into all the elements that make a knife strong, but I know a few very well respected makers who would take issue with your comments on grind strength.
The original discussion about chopping boils down to this: Cliff says that the wedge created by the grind is what effectively splits the material. With this argument, hollow grinds impede chopping because the back of the grinds wedge into the material. I think that, since the edge is doing the splitting, any material on the sides of the knife is going to create resistance, and thus impede chopping.
Cliff talks about flexibility of the material being an issue; the material doesn't move in straight lines to either side of the blade. With my opinion of the nature of chopping, this would make hollow grinds work better; because the material has more distance to travel laterally to make contact with the blade. Because of the nature of the edge angle, by the time the material passes by the start of the grind, it generally is fairly far from the blade.
I have in front of me a Mineral Mountain camp bowie in flat grind. Ted has been offering flat grind blades for about 6 months now. It will not chop as well as its brother in hollow grind (and it certainly will not slice as well). Period.
Several years ago I started noticing that the MMHW I owned seemed to perform better than other (flat grind) knives I owned, but it wasn't until Ted started flat grinding that it was possible to actually test grind VS grind. This is because there are SO many other variables involved with performance (edge, geometry, thickness, steel, etc.
As far as I'm concerned, all of the "scientific" style analysis in this thread is a waste of time; Cliff is much better at it than me, but it is fuzzy logic at best- for both of us. Semantic masturbation. In this matter, Truth is based only on experience and real world feedback, not pretend-scientific jaw-flapping. The thoughts I've expressed in regards to the explanation of how each grind works/doesn't work are speculation; speculation derived out of an effort to explain my and other users' experiences.
And I am SO out of my league with Cliff in this debate. I simply do not have the capability to argue with him, so this is going to be my last post here (unless I feel particularly masochistic
). As always, I look forward to reading what you have to say, Cliff, but my mind won't be changed unless my experience somehow changes. I hope other readers will consider the same method of "reason via experience".
Later!
The original discussion about chopping boils down to this: Cliff says that the wedge created by the grind is what effectively splits the material. With this argument, hollow grinds impede chopping because the back of the grinds wedge into the material. I think that, since the edge is doing the splitting, any material on the sides of the knife is going to create resistance, and thus impede chopping.
Cliff talks about flexibility of the material being an issue; the material doesn't move in straight lines to either side of the blade. With my opinion of the nature of chopping, this would make hollow grinds work better; because the material has more distance to travel laterally to make contact with the blade. Because of the nature of the edge angle, by the time the material passes by the start of the grind, it generally is fairly far from the blade.
I have in front of me a Mineral Mountain camp bowie in flat grind. Ted has been offering flat grind blades for about 6 months now. It will not chop as well as its brother in hollow grind (and it certainly will not slice as well). Period.
Several years ago I started noticing that the MMHW I owned seemed to perform better than other (flat grind) knives I owned, but it wasn't until Ted started flat grinding that it was possible to actually test grind VS grind. This is because there are SO many other variables involved with performance (edge, geometry, thickness, steel, etc.
As far as I'm concerned, all of the "scientific" style analysis in this thread is a waste of time; Cliff is much better at it than me, but it is fuzzy logic at best- for both of us. Semantic masturbation. In this matter, Truth is based only on experience and real world feedback, not pretend-scientific jaw-flapping. The thoughts I've expressed in regards to the explanation of how each grind works/doesn't work are speculation; speculation derived out of an effort to explain my and other users' experiences.
And I am SO out of my league with Cliff in this debate. I simply do not have the capability to argue with him, so this is going to be my last post here (unless I feel particularly masochistic
). As always, I look forward to reading what you have to say, Cliff, but my mind won't be changed unless my experience somehow changes. I hope other readers will consider the same method of "reason via experience".Later!
Cliff Stamp
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Kumdo :
This is trivially a matter of steel cross section. Simply extend your preposition to the edge geometry and note the conclusion you are supporting.
Impacts on concrete with a Strider WB :
http://www.physics.mun.ca/~sstamp/images/wb_tip_snapped.jpg
note the damage penetrating into the primary grind. Now with a flat ground bowie :
http://www.physics.mun.ca/~sstamp/images/rk_bowie_light_concrete_chop.jpg
The bowie had a more acute edge, and was longer and a much more powerful chopper. Of course the steels are different, 52100 is much tougher than ATS-34. But the basic point remains, the failure seen on the WB is due largely in part to the hollow grind.
The reason that the cases you cite failed to produce any damage was simply that it could not exceed the edge, which was the situation I described. Of course if the damage doesn't exceed the ability of the edge then the nature of the primary grind is of little consequence as it never comes into play anyway.
If it was ground to the same shallow depth as the hollow grind then obviously it will cut worse. Yes you can make a flat ground blade a poor chopper. Use a flat ground blade from someone like Ray Kirk and compare it to the hollow ground bowie you describe.
You don't need to look at large bowies either, take a look for example at the praise of the cutting ability of the high flat ground Spyderco knives as compared to the shallow hollow ground ones. Same relative performance due to the differnence in the depth of the grinds.
[of course these knives don't have the same critical dependance on wedging as chopping tools, but penetration or raw cutting ability issues are much the same]
Of course it is not the case that as Kumdo implies that the argument I made in the above is based simply on theory. I have used blades of all types described in the above. This year I have cut and stacked with use of an axe and various long blades, about 15 truckloads of wood, same for last year, and will possibly double this by the fall.
The underlying details are given for those who are interested in such things, and they were worked out to explain the difference in performance seen during use. Once understood, this allows prediction of knife performance and the selection of more optimal knives in the future. Which of course is the reason why theory is developed in general.
-Cliff
This is trivially a matter of steel cross section. Simply extend your preposition to the edge geometry and note the conclusion you are supporting.
Impacts on concrete with a Strider WB :
http://www.physics.mun.ca/~sstamp/images/wb_tip_snapped.jpg
note the damage penetrating into the primary grind. Now with a flat ground bowie :
http://www.physics.mun.ca/~sstamp/images/rk_bowie_light_concrete_chop.jpg
The bowie had a more acute edge, and was longer and a much more powerful chopper. Of course the steels are different, 52100 is much tougher than ATS-34. But the basic point remains, the failure seen on the WB is due largely in part to the hollow grind.
The reason that the cases you cite failed to produce any damage was simply that it could not exceed the edge, which was the situation I described. Of course if the damage doesn't exceed the ability of the edge then the nature of the primary grind is of little consequence as it never comes into play anyway.
If it was ground to the same shallow depth as the hollow grind then obviously it will cut worse. Yes you can make a flat ground blade a poor chopper. Use a flat ground blade from someone like Ray Kirk and compare it to the hollow ground bowie you describe.
You don't need to look at large bowies either, take a look for example at the praise of the cutting ability of the high flat ground Spyderco knives as compared to the shallow hollow ground ones. Same relative performance due to the differnence in the depth of the grinds.
[of course these knives don't have the same critical dependance on wedging as chopping tools, but penetration or raw cutting ability issues are much the same]
Of course it is not the case that as Kumdo implies that the argument I made in the above is based simply on theory. I have used blades of all types described in the above. This year I have cut and stacked with use of an axe and various long blades, about 15 truckloads of wood, same for last year, and will possibly double this by the fall.
The underlying details are given for those who are interested in such things, and they were worked out to explain the difference in performance seen during use. Once understood, this allows prediction of knife performance and the selection of more optimal knives in the future. Which of course is the reason why theory is developed in general.
-Cliff