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Rubber Band Test
- Thread starter CAL
- Start date
- Joined
- Nov 6, 1999
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- 2,639
Nineteen pieces? Wow. I had to write this twice thanks to Spark and his forum shut down today, but here is my best guess at the rubber band meets blade phenomenom:
I spent some time about a year ago conduction 'rubber-band test' experiments. The main conclusion I came to is the test does not really measure the sharpness of the edge.
Different knives with different shapes and edge geometry cut 3 X 1/4 inch rubber bands into different numbers of pieces. Smaller knives tended to make more pieces than larger knives. Sharper knives tend to cut more pieces than duller knives, but some really sharp knives conistantly made very few pieces.
I began marking the center point of the stretched band (between my thumb and forefingers) so that I could see the relative position of the cuts. I was surprised to find that the cuts made pieces of different length, from tiny to long, and these cuts were not evenly distributed around the center point. There might be many on one side and only two on the other. Reconstructing the rubber band showed many curious patterns. The same blade might cut a band in many different ways.
Although it would take a high speed camera and a sophisticated mechanical device to consistently hold, stretch, and release the rubber bands into the blade to confirm this, I think the rubber band phenomenon has more to due with the mechanical physics of the release of the rubber band than it has to do with the sharpness of the blade, although a dull blade will fail to cut at all, or produce only a few discreet pieces or nicks in longer pieces. Smaller sharp blades will make more cuts than larger sharp blades.
A clue comes from observations about the best way to 'shoot' a rubber band. Personal experience shows that a rubber band will travel the farthest if tensioned on only One arm of the stretched circle compared to stretching both arms 'equally'. The ideal equal tension state is probably very difficult to achieve because of variations in the thickness of the rubber band, and the difficulty of holding and releasing the rubber band in exactly the same way every time. These forces in different vectors along two sides of the direction of motion will tend to cancel each other out, decreasing the overall forward momentum (energy) of the moving rubber band. A rubber band shot from thumb and forefinger but tensioned mostly along only one side of the folded band will travel much farther and with more accuracy than a rubber band shot in the usual manner.
When the band is released from it's stretched (tensioned) position; the two sides of the spring will tend to return to their rest position. This energy is transformed into the energy moving the whole mass of the band forward. If the two sides are unequally tensioned, there will be movement much like waves in the moving band. After it reaches its rest point, the band will begin to fold into segments of different lengths that will overlap as the band approaches the blade. A sharp blade will then cut through the band Many times producing various lengths of cut pieces.
If the blade is very wide (approaches the diameter of the rubber band at rest), it will tend to cut the band in fewer pieces because there is less time for the traveling blade to fold. Try tensioning the rubber band on only one side before releasing into the blade and observe the results. Fewer pieces.
The rubber band test says more about the physics of 'shooting' a rubber band than it has to do with blade sharpness. Although a dull blade will tend to produce few cuts than a sharp one, a very sharp blade of the right dimensions may produce only a single cut. Much more is going on here than the cutting ability of the blade.
I would love to see a super slow motion film of this in action. The rubber band test is fun, astonishes people, and is mystifying, but not really all that hard to understand.
Paracelsus
I spent some time about a year ago conduction 'rubber-band test' experiments. The main conclusion I came to is the test does not really measure the sharpness of the edge.
Different knives with different shapes and edge geometry cut 3 X 1/4 inch rubber bands into different numbers of pieces. Smaller knives tended to make more pieces than larger knives. Sharper knives tend to cut more pieces than duller knives, but some really sharp knives conistantly made very few pieces.
I began marking the center point of the stretched band (between my thumb and forefingers) so that I could see the relative position of the cuts. I was surprised to find that the cuts made pieces of different length, from tiny to long, and these cuts were not evenly distributed around the center point. There might be many on one side and only two on the other. Reconstructing the rubber band showed many curious patterns. The same blade might cut a band in many different ways.
Although it would take a high speed camera and a sophisticated mechanical device to consistently hold, stretch, and release the rubber bands into the blade to confirm this, I think the rubber band phenomenon has more to due with the mechanical physics of the release of the rubber band than it has to do with the sharpness of the blade, although a dull blade will fail to cut at all, or produce only a few discreet pieces or nicks in longer pieces. Smaller sharp blades will make more cuts than larger sharp blades.
A clue comes from observations about the best way to 'shoot' a rubber band. Personal experience shows that a rubber band will travel the farthest if tensioned on only One arm of the stretched circle compared to stretching both arms 'equally'. The ideal equal tension state is probably very difficult to achieve because of variations in the thickness of the rubber band, and the difficulty of holding and releasing the rubber band in exactly the same way every time. These forces in different vectors along two sides of the direction of motion will tend to cancel each other out, decreasing the overall forward momentum (energy) of the moving rubber band. A rubber band shot from thumb and forefinger but tensioned mostly along only one side of the folded band will travel much farther and with more accuracy than a rubber band shot in the usual manner.
When the band is released from it's stretched (tensioned) position; the two sides of the spring will tend to return to their rest position. This energy is transformed into the energy moving the whole mass of the band forward. If the two sides are unequally tensioned, there will be movement much like waves in the moving band. After it reaches its rest point, the band will begin to fold into segments of different lengths that will overlap as the band approaches the blade. A sharp blade will then cut through the band Many times producing various lengths of cut pieces.
If the blade is very wide (approaches the diameter of the rubber band at rest), it will tend to cut the band in fewer pieces because there is less time for the traveling blade to fold. Try tensioning the rubber band on only one side before releasing into the blade and observe the results. Fewer pieces.
The rubber band test says more about the physics of 'shooting' a rubber band than it has to do with blade sharpness. Although a dull blade will tend to produce few cuts than a sharp one, a very sharp blade of the right dimensions may produce only a single cut. Much more is going on here than the cutting ability of the blade.
I would love to see a super slow motion film of this in action. The rubber band test is fun, astonishes people, and is mystifying, but not really all that hard to understand.
Paracelsus
- Joined
- Nov 6, 1999
- Messages
- 2,639
Ahhh shucks... I hate to have to move a thread BTTT by myself!
Come on people. Try this at home. Try it in the office. Amaze your friends, your boss, your spouse!
Simply put a rubber band around a blade with the edge facing you (be careful with folders), pull the rubber band back towards your face using the spine of the blade, and let go.
The rubber band will Probably be cut into several pieces.
Do it several times and post the results. My analysis is far from perfect and may be completely Wrong!
Any other guesses as to what is actually happening? Does a very high cut number correlate with edge sharpness?
Paracelsus
Come on people. Try this at home. Try it in the office. Amaze your friends, your boss, your spouse!
Simply put a rubber band around a blade with the edge facing you (be careful with folders), pull the rubber band back towards your face using the spine of the blade, and let go.
The rubber band will Probably be cut into several pieces.
Do it several times and post the results. My analysis is far from perfect and may be completely Wrong!
Any other guesses as to what is actually happening? Does a very high cut number correlate with edge sharpness?
Paracelsus
hey, para.
i just tried it with my bm42. pretty sharp blade, but not as sharp as i thought, i guess. only got one cut in the band -- now i have a super-handy rubber string.
guess i'll have to go home and sharpen up after work, because now it's determined that i have a dull blade, and dull blades make me do this: :barf:
peace.
aleX.
edited for spelling.
i just tried it with my bm42. pretty sharp blade, but not as sharp as i thought, i guess. only got one cut in the band -- now i have a super-handy rubber string.
guess i'll have to go home and sharpen up after work, because now it's determined that i have a dull blade, and dull blades make me do this: :barf:
peace.
aleX.
edited for spelling.
- Joined
- Jul 29, 2000
- Messages
- 555
I'm curious too. Just tried it with a sharp Delica and a small rubber band. Nothing happened until I decided to put the egded part of the blade to the rubber band. It obviously was cut.
More directions are needed.
More directions are needed.
- Joined
- Nov 6, 1999
- Messages
- 2,639
OK. Step by step intructions:
1. Hold knife in left hand at arms length with the blade towards your face.
2. Place rubber band around the spine of the blade and stretch the band towards your face by grasping the band between thumb and forefinger.
3. Pull back exactly the same as 'shooting' a rubber band across the room. Use enough force that the rubber band should fly at least ten feet.
4. Release the rubber band. It is best to do this while 'shooting' into nearby wall so that all of the pieces (different lengths) can be found.
No cuts means your knife is not sharp enough for this test.
A single cut Probably means your knife is not very sharp. This rarely if ever happened during my testing. You will have to take my word for it that my knives are SHARP (push cut optimized by polishing acute edges on a strop after finishing on ultrafine ceramic stones)
Many cuts means ...?
I have no idea what difference serrations may make. Interesting idea...
BTW, please be careful with locking folders. You may apply enough force with the band to close the blade on your hand.
Paracelsus
1. Hold knife in left hand at arms length with the blade towards your face.
2. Place rubber band around the spine of the blade and stretch the band towards your face by grasping the band between thumb and forefinger.
3. Pull back exactly the same as 'shooting' a rubber band across the room. Use enough force that the rubber band should fly at least ten feet.
4. Release the rubber band. It is best to do this while 'shooting' into nearby wall so that all of the pieces (different lengths) can be found.
No cuts means your knife is not sharp enough for this test.
A single cut Probably means your knife is not very sharp. This rarely if ever happened during my testing. You will have to take my word for it that my knives are SHARP (push cut optimized by polishing acute edges on a strop after finishing on ultrafine ceramic stones)
Many cuts means ...?
I have no idea what difference serrations may make. Interesting idea...
BTW, please be careful with locking folders. You may apply enough force with the band to close the blade on your hand.
Paracelsus
- Joined
- Nov 6, 1999
- Messages
- 2,639
I got the best results using 1/4 inch wide standard office bands. I did not try using the skinny 1/8 inch or smaller bands, but I am guessing that they may not allow enough tension or have enough mass to work well for this test. Use the heavier rubber bands.
If your knife is very sharp, you should get Many pieces. Nineteen would be extraordinary, but five to ten is fairly common.
Get 20-30 fresh unused bands, and give it a try...
If your knife is very sharp, you should get Many pieces. Nineteen would be extraordinary, but five to ten is fairly common.
Get 20-30 fresh unused bands, and give it a try...
- Joined
- Jul 29, 2000
- Messages
- 555
Ahh, I was using very thin rubber bands.
Tomorrow, I'll try it in my office...
Tomorrow, I'll try it in my office...
- Joined
- Nov 24, 1999
- Messages
- 4,981
I've done it a couple times and always get multiple cuts. I think it has to do with the physics of the rubber band as its being shot. An object in motion stays in motion, an object at rest stays at rest unless acted upon by an outside force yadda yadda yadda. You build up kinetic energy in the rubber band by stretching it. The energy draws both ends towards each other. The spine of the knife holds one end in place so the build up of energy acts completely on the end you release. The end you release is put into motion while the other end stays stationary.The slack in the middle crinkles up as the back end of the band snaps forward. Multiple folds of the rubber band hit the cutting edge and are severed. That explains why there tends to be more cuts on one side than the other. As the rubber band crinkles up, You get two stacks of folds side by side. One side makes more contact with the blade while the other side is pushed off to the side.
This could be a load of complete BS too, but think thats how it happens. Do I win anything ?
Doh, I just read your first post paracelsus. Looks like we agree.
Can I still win a prize
This could be a load of complete BS too, but think thats how it happens. Do I win anything ?
Doh, I just read your first post paracelsus. Looks like we agree.
Can I still win a prize
i decided to give it another shot, using a different knife (good thing i always carry more than one, or else i would've had to go home from the office to get one. ).
i tried with my oldschool bucklite, which is pretty sharp, and i got 12 pieces and some extra slits in the rest of the rubber band. how cool!
peace.
aleX.
). i tried with my oldschool bucklite, which is pretty sharp, and i got 12 pieces and some extra slits in the rest of the rubber band. how cool!
peace.
aleX.
- Joined
- Feb 21, 2001
- Messages
- 1,981
I gotta get some rubber bands and give this a good test. For at least 2 years of my life, shooting rubber bands was an almost daily experience. I was a paperboy, always had vast quantities of them, as did all the other boys at the "spot" where we picked up, and folded our papers prior to delivery. We usually went early to have time for good wars. As might be expected, we got to be pretty good shots. Modesty should prohibit this, but I was always a captain or first picked. Was considered one of, if not the best marksman in the group.
Now of course we were using the typical red bands seen with newspapers. Round, perhaps an inch and a quarter or half in diameter. The bands were approximately an eighth of an inch wide. For that size/type of band, I always believed -- tho perhaps wrongly -- that evening the stretch on the two sides maximized both distance and accuracy.
I could only find a few bands in my house. Most are old enough to be approaching the rotting status. As I expected, my first band, about 1/8" wide, and maybe 1 1/4" in diameter was tried first. I made the tension as even as I could on both sides. As I expected, the band flew on as if nothing was in the way. A single cut. Another band was stretched closer to the base of the blade, where it is wider. Because it wasn't very strong, didn't use as much tension as on the first. Nothing happened. Applied the lightest of pressure's as I began stretching it. Immediately parted at the single cut mark.
Tried a bit larger, heavier band. Wish I'd paid a bit more attention to original diameter. It too flew hard against the board at which I aimed it, as if nothing was in the way. I found only two pieces. It appears there could be another possibly, but I can't find it. My "range" was relatively short, and I aimed just a couple inches above the floor. No more pieces.
I don't profess to be the world's greatest sharpener of knife blades. The knife I used was a new Calypso Jr. Ltwt. I consider it to be the sharpest knife I have.
I simply have to go buy a couple boxes of bands and try them. I can't help but think that an evenly stretched band hitting a truly sharp edge should part instantly at the site where the blade and band meet, and the band should fly on unimpeded, tho no longer a band, technically. It seems realistic to me that bands stretched unevenly would hit the blade edge at significant angles, with a resulting vibration/flapping that brings the rubber into repeated contact with the edge.
I know how silly it is, but for most of my life, have considered myself an excellent rubber band shooter/expert. And, I lived awhile in Missouri. Guess I gotta be shown. I'll report back.
Now of course we were using the typical red bands seen with newspapers. Round, perhaps an inch and a quarter or half in diameter. The bands were approximately an eighth of an inch wide. For that size/type of band, I always believed -- tho perhaps wrongly -- that evening the stretch on the two sides maximized both distance and accuracy.
I could only find a few bands in my house. Most are old enough to be approaching the rotting status. As I expected, my first band, about 1/8" wide, and maybe 1 1/4" in diameter was tried first. I made the tension as even as I could on both sides. As I expected, the band flew on as if nothing was in the way. A single cut. Another band was stretched closer to the base of the blade, where it is wider. Because it wasn't very strong, didn't use as much tension as on the first. Nothing happened. Applied the lightest of pressure's as I began stretching it. Immediately parted at the single cut mark.
Tried a bit larger, heavier band. Wish I'd paid a bit more attention to original diameter. It too flew hard against the board at which I aimed it, as if nothing was in the way. I found only two pieces. It appears there could be another possibly, but I can't find it. My "range" was relatively short, and I aimed just a couple inches above the floor. No more pieces.
I don't profess to be the world's greatest sharpener of knife blades. The knife I used was a new Calypso Jr. Ltwt. I consider it to be the sharpest knife I have.
I simply have to go buy a couple boxes of bands and try them. I can't help but think that an evenly stretched band hitting a truly sharp edge should part instantly at the site where the blade and band meet, and the band should fly on unimpeded, tho no longer a band, technically. It seems realistic to me that bands stretched unevenly would hit the blade edge at significant angles, with a resulting vibration/flapping that brings the rubber into repeated contact with the edge.
I know how silly it is, but for most of my life, have considered myself an excellent rubber band shooter/expert. And, I lived awhile in Missouri. Guess I gotta be shown. I'll report back.
- Joined
- Mar 15, 2001
- Messages
- 2,450
You know, I was just sitting here thinking to myself, "now what am I going to do with all those rubber bands in my desk drawer?" Hmmm.
Very cool test, but here's the weird part. Two rubber bands of equal size (length and width), age, and my best job of stretching them equally. The first was tried on a NIB Sebenza blade. Result? Three pieces -- not stellar. Then the exact same test on my NIB Point Guard. It virtually exploded into pieces. Strange, huh? Ideas?
- Mark
Very cool test, but here's the weird part. Two rubber bands of equal size (length and width), age, and my best job of stretching them equally. The first was tried on a NIB Sebenza blade. Result? Three pieces -- not stellar. Then the exact same test on my NIB Point Guard. It virtually exploded into pieces. Strange, huh? Ideas?
- Mark
- Joined
- Nov 6, 1999
- Messages
- 2,639
Don't be distressed by only three pieces. Although the knife obviously has to be sharp to cut through enough rubber to make Lots of pieces, if there is no folding of the band at the time it contacts the edge, it will only be cut once. A single fold cut only once will produce only three pieces. Take a rubber band and start folding it and think about it. Though experiments are how Einstein discovered Relativity.
The rubber band test simple demonstrates Einsteins theory of the weird and wacky results of the bending and folding of the space-time continuum. It is physics in action!
I found most of my attempts produced three to five pieces. Sometimes a great number more. My most serious attempts with a 10 inch long and 1 1/2 inch wide flat ground blade of 1075 would often make one cut, but frequently only three, one long piece and two short ones.
That is why I think the dimensions of the blade and the testing band are important. A narrower blade will allow more distance (time) for the band to fold into complex configurations, allowing for more potential pieces.
If the band is only cut once, it could be because you released the band perfectly and the dimensions of the blade favored fewer cuts. On the other hand, a single cut might mean that your blade is not sharp enough to cut multiple times.
Not achieving a lots of pieces does not necessarily mean your edge is dull. But lots of pieces definitely means you have a sharp knife. Try it several times with a bunch of different knives.
I don't think the rubber band test really says very much unless your knife fails to cut at all. But it is a great trick that you perform for friends. Until someone makes of high speed movie of this phenomenom, I think it is going to remain somewhat mysterious.
Paracelsus
The rubber band test simple demonstrates Einsteins theory of the weird and wacky results of the bending and folding of the space-time continuum. It is physics in action!
I found most of my attempts produced three to five pieces. Sometimes a great number more. My most serious attempts with a 10 inch long and 1 1/2 inch wide flat ground blade of 1075 would often make one cut, but frequently only three, one long piece and two short ones.
That is why I think the dimensions of the blade and the testing band are important. A narrower blade will allow more distance (time) for the band to fold into complex configurations, allowing for more potential pieces.
If the band is only cut once, it could be because you released the band perfectly and the dimensions of the blade favored fewer cuts. On the other hand, a single cut might mean that your blade is not sharp enough to cut multiple times.
Not achieving a lots of pieces does not necessarily mean your edge is dull. But lots of pieces definitely means you have a sharp knife. Try it several times with a bunch of different knives.
I don't think the rubber band test really says very much unless your knife fails to cut at all. But it is a great trick that you perform for friends. Until someone makes of high speed movie of this phenomenom, I think it is going to remain somewhat mysterious.
Paracelsus
- Joined
- Oct 26, 2000
- Messages
- 6,104
I remember trying this when it was originally posted awhile back. Never got any consistent results, and never got more than 5 cuts, sometimes only one.
Thomas, this is like the toilet paper test.....don't let your boss (or anybody else) catch you, they'll think you're nuts
Thomas, this is like the toilet paper test.....don't let your boss (or anybody else) catch you, they'll think you're nuts
- Joined
- Jul 29, 2000
- Messages
- 555
My Delica was obviously not so sharp after all.
I got the best results with a CRKT Stiff Kiss (chisel ground), where the rubber band separated into three pieces of different lengths.
I also tried a Spyderco Endura newly purchased, not used in any way, and I got two pieces.
How are you guys getting 19 pieces...?
I got the best results with a CRKT Stiff Kiss (chisel ground), where the rubber band separated into three pieces of different lengths.
I also tried a Spyderco Endura newly purchased, not used in any way, and I got two pieces.
How are you guys getting 19 pieces...?