- Joined
- Apr 8, 2012
- Messages
- 242
Response From a Gentleman Involved in timber sports for Years.
His Opinion, gained by years of chopping.
Good stuff,But I am sure some will disagree.
Moose
Good to hear from you the other day! I looked around a bit but found no sort-of literature on axe grinds but for my own notes and ideas...nothing ever published.
I could make a few points, however, from my experience in working tools and competition equipment. You can take from it what you may.
I think there are only three basic grinds:
1. Chisel- uniform width conforming to the radius of the edge of the axe. half inch, three quarter inch, one inch, etc.
2. Banana - asymmetric variation of chisel with wider chisel in the middle and narrower at the toe and heel. This can be called a full banana if the chisel measured at the center of the blade is closer to the eye of the axe than that measured at the toe or heel. Half banana if the chisel measured at the center of the axe is only slightly wider than the toe and heel.
3. Flat grind- the axe being a symmetrical wedge from the edge to about 3.5 to 4 inches back.
There are many little variations with different names but these are the basics. They are listed by their difficulty to produce and maintain....chisel being easiest to produce and maintain through subsequent sharpening...flat grind being the most difficult because if you get a little hump or irregularity in the flat surface it can really stick or if you make it too thin you will break it. Plus you always need a flat belt or grinder to reproduce it.
The thing that has always interested me about the grinds is the logic of how they cut:
In theory an axe has to do three things
1. cut fiber
2. displace wood, i.e. the chip
3. then release itself
The edge takes care of the cutting while the grind works on number two and three...displacement and release.
You can make an axe wicked sharp but it won't go in the wood or come out. Likewise you can make an axe for displacement or release that won't cut because it doesn't have an edge. Given that we can make a sharp edge how do you figure the #2 and #3 functions?
The elements that work on displacement and release are 1. force and 2. friction
We know that wide wedges create more displacement force but for the same reason require more energy to put it into the wood. Part of that extra energy is to overcome more friction. Narrow wedges cause less displacement force (necessary for blowing out the chip) but will go deeper with the same energy inputs. There needs to be a balance to get more penetration. Only if the chip wood is displaced can the edge cut deeper.
The first inch or so of the axe back from the edge creates the displacement force (and durability for a work axe). Racing axes run 14 degree angle for good pine...felling axes could start at 18 degrees and up to 28 degrees for a limbing axe. But the angle isn't the only thing...the length of the chisel plays a big role too. Take a pencil and draw an 18 degree angle on paper. At one inch from the apex it measures .3" gap, (distance between the lines) at 2 inches= .6" at 3 inches =.9" so that is how much volume of wood needs to be displaced at each interval of depth of penetration. So, if we stop the wedge shape at one inch from the edge (.3" displaced area) then relieve it somewhat with some hollowing out or change of wedge angle we can overcome some friction and displacement force to allow more penetration. Most good hardwood axes have a thick chisel wedge (18 degrees +) but narrow chisel (half inch or less) then hollowed out a bit. If the axe goes in deep enough the "bust" or swelling of the axe back closer to the eye will once again displace the chip with more force this time to blow out the chip.
Some would say that chopping wood is actually splitting wood because after you drive the axe in at the 45 degree angle (+ or -) and look at the effected fibers they have to split apart to allow the wood to bend out to compensate for the displacement. The wood "feathers" out by splitting into layers fine enough to bend out of the way. At some point those feathers break off as chips. Different thicknesses for different species.
The release part is a result of friction once the axe is driven all the way in and the pressure or spring action of the residual flaps of wood still in place and not chipped out of the cut. For this reason you don't want any convex surfaces. Though it has long been recommended by some to make a convex surface of the chisel just behind the edge these make very sticky and dishy axes that won't go in the wood very deep anyway. They make a strong axe though and work well for limbing...especially in winter. The "bust" (if you can get the axe in deep enough or at a shallow angle will open the residual fibers enough to spit the axe back out with a spring-like force.
I'll bet by now you are sorry you asked.
So, the different grinds do this in different ways. There is another dynamic in the radius of the axe edge...usually banana grinds have a smaller radius or a little more curve and so therefore you wind up delivering the heel a little more when chopping. This makes for a little more slicing action.
Much of this theory comes from racing axe design but can be useful to put into practice on a work axe. Unfortunately, we have to consider durability and abuse in work axes, Pulaski, etc....something that will hold up in the hands of a wood beater back on a trail somewhere with only a dull file for back-up.
His Opinion, gained by years of chopping.
Good stuff,But I am sure some will disagree.
Moose
Good to hear from you the other day! I looked around a bit but found no sort-of literature on axe grinds but for my own notes and ideas...nothing ever published.
I could make a few points, however, from my experience in working tools and competition equipment. You can take from it what you may.
I think there are only three basic grinds:
1. Chisel- uniform width conforming to the radius of the edge of the axe. half inch, three quarter inch, one inch, etc.
2. Banana - asymmetric variation of chisel with wider chisel in the middle and narrower at the toe and heel. This can be called a full banana if the chisel measured at the center of the blade is closer to the eye of the axe than that measured at the toe or heel. Half banana if the chisel measured at the center of the axe is only slightly wider than the toe and heel.
3. Flat grind- the axe being a symmetrical wedge from the edge to about 3.5 to 4 inches back.
There are many little variations with different names but these are the basics. They are listed by their difficulty to produce and maintain....chisel being easiest to produce and maintain through subsequent sharpening...flat grind being the most difficult because if you get a little hump or irregularity in the flat surface it can really stick or if you make it too thin you will break it. Plus you always need a flat belt or grinder to reproduce it.
The thing that has always interested me about the grinds is the logic of how they cut:
In theory an axe has to do three things
1. cut fiber
2. displace wood, i.e. the chip
3. then release itself
The edge takes care of the cutting while the grind works on number two and three...displacement and release.
You can make an axe wicked sharp but it won't go in the wood or come out. Likewise you can make an axe for displacement or release that won't cut because it doesn't have an edge. Given that we can make a sharp edge how do you figure the #2 and #3 functions?
The elements that work on displacement and release are 1. force and 2. friction
We know that wide wedges create more displacement force but for the same reason require more energy to put it into the wood. Part of that extra energy is to overcome more friction. Narrow wedges cause less displacement force (necessary for blowing out the chip) but will go deeper with the same energy inputs. There needs to be a balance to get more penetration. Only if the chip wood is displaced can the edge cut deeper.
The first inch or so of the axe back from the edge creates the displacement force (and durability for a work axe). Racing axes run 14 degree angle for good pine...felling axes could start at 18 degrees and up to 28 degrees for a limbing axe. But the angle isn't the only thing...the length of the chisel plays a big role too. Take a pencil and draw an 18 degree angle on paper. At one inch from the apex it measures .3" gap, (distance between the lines) at 2 inches= .6" at 3 inches =.9" so that is how much volume of wood needs to be displaced at each interval of depth of penetration. So, if we stop the wedge shape at one inch from the edge (.3" displaced area) then relieve it somewhat with some hollowing out or change of wedge angle we can overcome some friction and displacement force to allow more penetration. Most good hardwood axes have a thick chisel wedge (18 degrees +) but narrow chisel (half inch or less) then hollowed out a bit. If the axe goes in deep enough the "bust" or swelling of the axe back closer to the eye will once again displace the chip with more force this time to blow out the chip.
Some would say that chopping wood is actually splitting wood because after you drive the axe in at the 45 degree angle (+ or -) and look at the effected fibers they have to split apart to allow the wood to bend out to compensate for the displacement. The wood "feathers" out by splitting into layers fine enough to bend out of the way. At some point those feathers break off as chips. Different thicknesses for different species.
The release part is a result of friction once the axe is driven all the way in and the pressure or spring action of the residual flaps of wood still in place and not chipped out of the cut. For this reason you don't want any convex surfaces. Though it has long been recommended by some to make a convex surface of the chisel just behind the edge these make very sticky and dishy axes that won't go in the wood very deep anyway. They make a strong axe though and work well for limbing...especially in winter. The "bust" (if you can get the axe in deep enough or at a shallow angle will open the residual fibers enough to spit the axe back out with a spring-like force.
I'll bet by now you are sorry you asked.
So, the different grinds do this in different ways. There is another dynamic in the radius of the axe edge...usually banana grinds have a smaller radius or a little more curve and so therefore you wind up delivering the heel a little more when chopping. This makes for a little more slicing action.
Much of this theory comes from racing axe design but can be useful to put into practice on a work axe. Unfortunately, we have to consider durability and abuse in work axes, Pulaski, etc....something that will hold up in the hands of a wood beater back on a trail somewhere with only a dull file for back-up.
