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Woodworking clamps, does force add up?
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I was watching a woodworking video about glue, and the guy was clamping two pieces of wood together using a total of 8 clamps. He argued that by doing so he would apply 8 times the maximum force of 150N (a property of the clamp), resulting in 1200N in total.
I think he's wrong. I think the force of 150 N is only working locally where the clamp is and will decline drastically radially from that spot. And so the clamping force on any given spot on the board will never exceed the max. force of the clamp.
Who's right?
forces classical-mechanics pressure everyday-life
edited Aug 24 at 10:18
Kyle Kanos
21.3k114690
asked Aug 21 at 14:58
Holli
1134
add a comment |Â
up vote
2
down vote
favorite
I was watching a woodworking video about glue, and the guy was clamping two pieces of wood together using a total of 8 clamps. He argued that by doing so he would apply 8 times the maximum force of 150N (a property of the clamp), resulting in 1200N in total.
I think he's wrong. I think the force of 150 N is only working locally where the clamp is and will decline drastically radially from that spot. And so the clamping force on any given spot on the board will never exceed the max. force of the clamp.
Who's right?
forces classical-mechanics pressure everyday-life
edited Aug 24 at 10:18
Kyle Kanos
21.3k114690
asked Aug 21 at 14:58
Holli
1134
I think the question is still confusing - the title asks whether pressure from the clamps adds up, but then the body of the question asks about forces, rather than pressure. It is virtually important to note the distinction.
– Time4Tea
Aug 22 at 1:07
Please do not make your post look like a revision table, instead just seamlessly integrate the new material into the post. There is an edit history button at the bottom of the post for those interested in seeing what changed.
– Kyle Kanos
Aug 24 at 10:19
add a comment |Â
up vote
2
down vote
favorite
up vote
2
down vote
favorite
I was watching a woodworking video about glue, and the guy was clamping two pieces of wood together using a total of 8 clamps. He argued that by doing so he would apply 8 times the maximum force of 150N (a property of the clamp), resulting in 1200N in total.
I think he's wrong. I think the force of 150 N is only working locally where the clamp is and will decline drastically radially from that spot. And so the clamping force on any given spot on the board will never exceed the max. force of the clamp.
Who's right?
forces classical-mechanics pressure everyday-life
edited Aug 24 at 10:18
Kyle Kanos
21.3k114690
asked Aug 21 at 14:58
Holli
1134
I was watching a woodworking video about glue, and the guy was clamping two pieces of wood together using a total of 8 clamps. He argued that by doing so he would apply 8 times the maximum force of 150N (a property of the clamp), resulting in 1200N in total.
I think he's wrong. I think the force of 150 N is only working locally where the clamp is and will decline drastically radially from that spot. And so the clamping force on any given spot on the board will never exceed the max. force of the clamp.
Who's right?
forces classical-mechanics pressure everyday-life
edited Aug 24 at 10:18
Kyle Kanos
21.3k114690
asked Aug 21 at 14:58
Holli
1134
edited Aug 24 at 10:18
Kyle Kanos
21.3k114690
edited Aug 24 at 10:18
Kyle Kanos
21.3k114690
edited Aug 24 at 10:18
Kyle Kanos
21.3k114690
21.3k114690
asked Aug 21 at 14:58
Holli
1134
asked Aug 21 at 14:58
Holli
1134
asked Aug 21 at 14:58
Holli
1134
1134
I think the question is still confusing - the title asks whether pressure from the clamps adds up, but then the body of the question asks about forces, rather than pressure. It is virtually important to note the distinction.
– Time4Tea
Aug 22 at 1:07
Please do not make your post look like a revision table, instead just seamlessly integrate the new material into the post. There is an edit history button at the bottom of the post for those interested in seeing what changed.
– Kyle Kanos
Aug 24 at 10:19
add a comment |Â
I think the question is still confusing - the title asks whether pressure from the clamps adds up, but then the body of the question asks about forces, rather than pressure. It is virtually important to note the distinction.
– Time4Tea
Aug 22 at 1:07
Please do not make your post look like a revision table, instead just seamlessly integrate the new material into the post. There is an edit history button at the bottom of the post for those interested in seeing what changed.
– Kyle Kanos
Aug 24 at 10:19
I think the question is still confusing - the title asks whether pressure from the clamps adds up, but then the body of the question asks about forces, rather than pressure. It is virtually important to note the distinction.
– Time4Tea
Aug 22 at 1:07
I think the question is still confusing - the title asks whether pressure from the clamps adds up, but then the body of the question asks about forces, rather than pressure. It is virtually important to note the distinction.
– Time4Tea
Aug 22 at 1:07
Please do not make your post look like a revision table, instead just seamlessly integrate the new material into the post. There is an edit history button at the bottom of the post for those interested in seeing what changed.
– Kyle Kanos
Aug 24 at 10:19
Please do not make your post look like a revision table, instead just seamlessly integrate the new material into the post. There is an edit history button at the bottom of the post for those interested in seeing what changed.
– Kyle Kanos
Aug 24 at 10:19
add a comment |Â
5 Answers
5
active
oldest
votes
up vote
1
down vote
accepted
You're both wrong.
Although I would say you are more right than the expert. When you apply a force to an object's surface, the stress (a.k.a pressure) on the object clearly can't be constant across the surface; it must have a maximum closest to the point of contact and then dissipate as distance from the point of contact increases.
A very simple model of the clamping pressure experienced by a piece of wood might look like this:
The units here aren't important (pressure is in unites of 1 clamp). What is important is that clamping stresses add up:
Here is an animation of what happens when seven identical clamps are taken from clamping at the center of a board to being equally spaced across it's length. Total clamp pressure is just the sum of the seven separate clamps. Some observations:
- Only when all the clamps are at same location do you get 7 times the pressure.
- The total pressure however is higher (above any one clamp) everywhere.
- The average pressure doesn't change, only the peak pressure. (note it does dip slightly as the end clamps reach the ends).
- The pressure is very uniform when enough clamps are used. This is probably of greater value to a woodworker than maximum clamping pressure.
answered Aug 21 at 22:21
cms
2,8272415
The question might be somewhat unclear, but the "expert" ist still right that the forces add up.
– Toffomat
Aug 24 at 11:10
add a comment |Â
up vote
2
down vote
If the area stays constant the pressure will increase as the total force increases when more clamps are used.
The wood is probably flexible and not perfectly flat so the force will only be exerted over a region close to a clamp where the two bits of wood are in contact.
answered Aug 21 at 15:22
Farcher
44.2k33388
I apologize for the confusing post title. The question is, is there any spot on the board where the force acting on that spot exceeds the max force of a single clamp.
– Holli
Aug 21 at 15:29
It's possible (and a known technique) to deliberately make the work piece just slightly bowed, and clamp in such a way that the flexibility of the work piece helps distribute the clamping force across the glue joint, rather than localizing the force near the clamp.
– The Photon
Aug 21 at 16:34
add a comment |Â
up vote
1
down vote
Forces add in that way, and the clamps would do the same. You can prove this to yourself by drawing a free body diagram for the forces that would act upon the beam. Applying Newton's laws would show that the force you lift with will have to exceed the total clamping force if you wish to move the clamped board.
Obviously, this is extremely oversimplified, and there are many situations where this doesn't really apply.
The stiffness of the board is extremely important. A stiff board will even out the load between the clamps better than a flexible one. A flexible board may be able to cheat the total force rules; because it has less internal forces that resist relative movement this means that just adding the total clamping force and comparing that to the total applied force is not enough to represent the situation. It is possible to apply the force to one location and have that undo the clamp and bend the board there, but because the board is very flexible, it doesn't transmit enough force to undo any of the other clamps. You can't reliably treat it as a single object to apply Newton's Laws to anymore, but instead have to consider how the board interacts with itself as well as the clamps.
Basically, the proximity to each clamp is important, and it will be more important the further you are from the point of the applied load.
For the case of clamping wood, if it's a thick piece of sturdy wood, with clamps evenly spaced, you can assume that the forces approximately add. If you require the clamps to hold a specific force for safety reasons, I would suggest doing some more detailed calculations for your material, and providing some extra allowance for errors.
answered Aug 21 at 18:00
JMac
7,92821732
add a comment |Â
up vote
1
down vote
And so the clamping force on any given spot on the board will never
exceed the max. force of the clamp.
This would, quite obviously, be the case, if we assumed that the clamps are evenly distributed around a circle.
Under these conditions, due to symmetry, any redistribution of the reaction force, which, in total, is equal to the total applied force, would not be possible, so the reaction force applied locally by each clamp would have to be $150$N and the pressure under all clamps would have to be the same.
If the clamps are not placed symmetrically, we can still state that no redistribution of the forces will occur by looking at one pair of clamps at a time and observing that, if that was not the case, the work (the two pieces of wood) would rotate, since two different reaction forces would create a net torque acting against two equal applied forces.
answered Aug 21 at 18:09
V.F.
7,1982621
add a comment |Â
up vote
0
down vote
He's right - the forces of the clamps will add up. You seem to be confusing force and pressure. The pressure from each clamp would reduce radially outwards from each clamping point, as you describe (although adding clamps will increase the average pressure acting across the entire length of the planks, thus increasing the force!).
answered Aug 21 at 15:06
Time4Tea
2,131929
But how can that be? Imagine two boards, 1m by 1m by 0.01m on top of one another. On the southeast corner I attach two 150N clamps. There are certainly no 300N acting on the nortwest corner.
– Holli
Aug 21 at 15:22
Now imagine springs between the boards, when I clamp it as described the strongest deflection would occur where the clamps sit, and decline the further you get away from them.
– Holli
Aug 21 at 15:27
1
@Holli The total contact force between the two boards is the sum of all the contact forces across the whole surface. Again, you seem to be confusing force and pressure. If the boards are very thin and flexible, then the region of the boards under one clamp may not be 'aware' of the pressure being applied by a second clamp (as it is not being transmitted well across the board). However, the total clamping force is still twice the force from a single clamp.
– Time4Tea
Aug 21 at 15:30
@Holli by adding a second clamp, you are doubling the average pressure that acts across the whole area of the board; therefore, the total force is doubling.
– Time4Tea
Aug 21 at 15:33
1
@Holli the case is a little different for very thin, flexible boards and very rigid boards. For very rigid boards, if you put a spring/meter in between, then it will measure the sum of all the clamps, because you are changing the nature of the contact so that all the contact load goes through it. For the very flexible ones, it would indeed only measure the force of a single clamp, because the stress is not being distributed effectively across the boards. I think you should clarify which case you are referring to in your question though.
– Time4Tea
Aug 21 at 15:46
 |Â
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5 Answers
5
active
oldest
votes
5 Answers
5
active
oldest
votes
active
oldest
votes
active
oldest
votes
up vote
1
down vote
accepted
You're both wrong.
Although I would say you are more right than the expert. When you apply a force to an object's surface, the stress (a.k.a pressure) on the object clearly can't be constant across the surface; it must have a maximum closest to the point of contact and then dissipate as distance from the point of contact increases.
A very simple model of the clamping pressure experienced by a piece of wood might look like this:
The units here aren't important (pressure is in unites of 1 clamp). What is important is that clamping stresses add up:
Here is an animation of what happens when seven identical clamps are taken from clamping at the center of a board to being equally spaced across it's length. Total clamp pressure is just the sum of the seven separate clamps. Some observations:
- Only when all the clamps are at same location do you get 7 times the pressure.
- The total pressure however is higher (above any one clamp) everywhere.
- The average pressure doesn't change, only the peak pressure. (note it does dip slightly as the end clamps reach the ends).
- The pressure is very uniform when enough clamps are used. This is probably of greater value to a woodworker than maximum clamping pressure.
answered Aug 21 at 22:21
cms
2,8272415
The question might be somewhat unclear, but the "expert" ist still right that the forces add up.
– Toffomat
Aug 24 at 11:10
add a comment |Â
up vote
1
down vote
accepted
You're both wrong.
Although I would say you are more right than the expert. When you apply a force to an object's surface, the stress (a.k.a pressure) on the object clearly can't be constant across the surface; it must have a maximum closest to the point of contact and then dissipate as distance from the point of contact increases.
A very simple model of the clamping pressure experienced by a piece of wood might look like this:
The units here aren't important (pressure is in unites of 1 clamp). What is important is that clamping stresses add up:
Here is an animation of what happens when seven identical clamps are taken from clamping at the center of a board to being equally spaced across it's length. Total clamp pressure is just the sum of the seven separate clamps. Some observations:
- Only when all the clamps are at same location do you get 7 times the pressure.
- The total pressure however is higher (above any one clamp) everywhere.
- The average pressure doesn't change, only the peak pressure. (note it does dip slightly as the end clamps reach the ends).
- The pressure is very uniform when enough clamps are used. This is probably of greater value to a woodworker than maximum clamping pressure.
answered Aug 21 at 22:21
cms
2,8272415
The question might be somewhat unclear, but the "expert" ist still right that the forces add up.
– Toffomat
Aug 24 at 11:10
add a comment |Â
up vote
1
down vote
accepted
up vote
1
down vote
accepted
You're both wrong.
Although I would say you are more right than the expert. When you apply a force to an object's surface, the stress (a.k.a pressure) on the object clearly can't be constant across the surface; it must have a maximum closest to the point of contact and then dissipate as distance from the point of contact increases.
A very simple model of the clamping pressure experienced by a piece of wood might look like this:
The units here aren't important (pressure is in unites of 1 clamp). What is important is that clamping stresses add up:
Here is an animation of what happens when seven identical clamps are taken from clamping at the center of a board to being equally spaced across it's length. Total clamp pressure is just the sum of the seven separate clamps. Some observations:
- Only when all the clamps are at same location do you get 7 times the pressure.
- The total pressure however is higher (above any one clamp) everywhere.
- The average pressure doesn't change, only the peak pressure. (note it does dip slightly as the end clamps reach the ends).
- The pressure is very uniform when enough clamps are used. This is probably of greater value to a woodworker than maximum clamping pressure.
answered Aug 21 at 22:21
cms
2,8272415
You're both wrong.
Although I would say you are more right than the expert. When you apply a force to an object's surface, the stress (a.k.a pressure) on the object clearly can't be constant across the surface; it must have a maximum closest to the point of contact and then dissipate as distance from the point of contact increases.
A very simple model of the clamping pressure experienced by a piece of wood might look like this:
The units here aren't important (pressure is in unites of 1 clamp). What is important is that clamping stresses add up:
Here is an animation of what happens when seven identical clamps are taken from clamping at the center of a board to being equally spaced across it's length. Total clamp pressure is just the sum of the seven separate clamps. Some observations:
- Only when all the clamps are at same location do you get 7 times the pressure.
- The total pressure however is higher (above any one clamp) everywhere.
- The average pressure doesn't change, only the peak pressure. (note it does dip slightly as the end clamps reach the ends).
- The pressure is very uniform when enough clamps are used. This is probably of greater value to a woodworker than maximum clamping pressure.
answered Aug 21 at 22:21
cms
2,8272415
answered Aug 21 at 22:21
cms
2,8272415
answered Aug 21 at 22:21
cms
2,8272415
answered Aug 21 at 22:21
cms
2,8272415
2,8272415
The question might be somewhat unclear, but the "expert" ist still right that the forces add up.
– Toffomat
Aug 24 at 11:10
add a comment |Â
The question might be somewhat unclear, but the "expert" ist still right that the forces add up.
– Toffomat
Aug 24 at 11:10
The question might be somewhat unclear, but the "expert" ist still right that the forces add up.
– Toffomat
Aug 24 at 11:10
The question might be somewhat unclear, but the "expert" ist still right that the forces add up.
– Toffomat
Aug 24 at 11:10
add a comment |Â
up vote
2
down vote
If the area stays constant the pressure will increase as the total force increases when more clamps are used.
The wood is probably flexible and not perfectly flat so the force will only be exerted over a region close to a clamp where the two bits of wood are in contact.
answered Aug 21 at 15:22
Farcher
44.2k33388
I apologize for the confusing post title. The question is, is there any spot on the board where the force acting on that spot exceeds the max force of a single clamp.
– Holli
Aug 21 at 15:29
It's possible (and a known technique) to deliberately make the work piece just slightly bowed, and clamp in such a way that the flexibility of the work piece helps distribute the clamping force across the glue joint, rather than localizing the force near the clamp.
– The Photon
Aug 21 at 16:34
add a comment |Â
up vote
2
down vote
If the area stays constant the pressure will increase as the total force increases when more clamps are used.
The wood is probably flexible and not perfectly flat so the force will only be exerted over a region close to a clamp where the two bits of wood are in contact.
answered Aug 21 at 15:22
Farcher
44.2k33388
I apologize for the confusing post title. The question is, is there any spot on the board where the force acting on that spot exceeds the max force of a single clamp.
– Holli
Aug 21 at 15:29
It's possible (and a known technique) to deliberately make the work piece just slightly bowed, and clamp in such a way that the flexibility of the work piece helps distribute the clamping force across the glue joint, rather than localizing the force near the clamp.
– The Photon
Aug 21 at 16:34
add a comment |Â
up vote
2
down vote
up vote
2
down vote
If the area stays constant the pressure will increase as the total force increases when more clamps are used.
The wood is probably flexible and not perfectly flat so the force will only be exerted over a region close to a clamp where the two bits of wood are in contact.
answered Aug 21 at 15:22
Farcher
44.2k33388
If the area stays constant the pressure will increase as the total force increases when more clamps are used.
The wood is probably flexible and not perfectly flat so the force will only be exerted over a region close to a clamp where the two bits of wood are in contact.
answered Aug 21 at 15:22
Farcher
44.2k33388
answered Aug 21 at 15:22
Farcher
44.2k33388
answered Aug 21 at 15:22
Farcher
44.2k33388
answered Aug 21 at 15:22
Farcher
44.2k33388
44.2k33388
I apologize for the confusing post title. The question is, is there any spot on the board where the force acting on that spot exceeds the max force of a single clamp.
– Holli
Aug 21 at 15:29
It's possible (and a known technique) to deliberately make the work piece just slightly bowed, and clamp in such a way that the flexibility of the work piece helps distribute the clamping force across the glue joint, rather than localizing the force near the clamp.
– The Photon
Aug 21 at 16:34
add a comment |Â
I apologize for the confusing post title. The question is, is there any spot on the board where the force acting on that spot exceeds the max force of a single clamp.
– Holli
Aug 21 at 15:29
It's possible (and a known technique) to deliberately make the work piece just slightly bowed, and clamp in such a way that the flexibility of the work piece helps distribute the clamping force across the glue joint, rather than localizing the force near the clamp.
– The Photon
Aug 21 at 16:34
I apologize for the confusing post title. The question is, is there any spot on the board where the force acting on that spot exceeds the max force of a single clamp.
– Holli
Aug 21 at 15:29
I apologize for the confusing post title. The question is, is there any spot on the board where the force acting on that spot exceeds the max force of a single clamp.
– Holli
Aug 21 at 15:29
It's possible (and a known technique) to deliberately make the work piece just slightly bowed, and clamp in such a way that the flexibility of the work piece helps distribute the clamping force across the glue joint, rather than localizing the force near the clamp.
– The Photon
Aug 21 at 16:34
It's possible (and a known technique) to deliberately make the work piece just slightly bowed, and clamp in such a way that the flexibility of the work piece helps distribute the clamping force across the glue joint, rather than localizing the force near the clamp.
– The Photon
Aug 21 at 16:34
add a comment |Â
up vote
1
down vote
Forces add in that way, and the clamps would do the same. You can prove this to yourself by drawing a free body diagram for the forces that would act upon the beam. Applying Newton's laws would show that the force you lift with will have to exceed the total clamping force if you wish to move the clamped board.
Obviously, this is extremely oversimplified, and there are many situations where this doesn't really apply.
The stiffness of the board is extremely important. A stiff board will even out the load between the clamps better than a flexible one. A flexible board may be able to cheat the total force rules; because it has less internal forces that resist relative movement this means that just adding the total clamping force and comparing that to the total applied force is not enough to represent the situation. It is possible to apply the force to one location and have that undo the clamp and bend the board there, but because the board is very flexible, it doesn't transmit enough force to undo any of the other clamps. You can't reliably treat it as a single object to apply Newton's Laws to anymore, but instead have to consider how the board interacts with itself as well as the clamps.
Basically, the proximity to each clamp is important, and it will be more important the further you are from the point of the applied load.
For the case of clamping wood, if it's a thick piece of sturdy wood, with clamps evenly spaced, you can assume that the forces approximately add. If you require the clamps to hold a specific force for safety reasons, I would suggest doing some more detailed calculations for your material, and providing some extra allowance for errors.
answered Aug 21 at 18:00
JMac
7,92821732
add a comment |Â
up vote
1
down vote
Forces add in that way, and the clamps would do the same. You can prove this to yourself by drawing a free body diagram for the forces that would act upon the beam. Applying Newton's laws would show that the force you lift with will have to exceed the total clamping force if you wish to move the clamped board.
Obviously, this is extremely oversimplified, and there are many situations where this doesn't really apply.
The stiffness of the board is extremely important. A stiff board will even out the load between the clamps better than a flexible one. A flexible board may be able to cheat the total force rules; because it has less internal forces that resist relative movement this means that just adding the total clamping force and comparing that to the total applied force is not enough to represent the situation. It is possible to apply the force to one location and have that undo the clamp and bend the board there, but because the board is very flexible, it doesn't transmit enough force to undo any of the other clamps. You can't reliably treat it as a single object to apply Newton's Laws to anymore, but instead have to consider how the board interacts with itself as well as the clamps.
Basically, the proximity to each clamp is important, and it will be more important the further you are from the point of the applied load.
For the case of clamping wood, if it's a thick piece of sturdy wood, with clamps evenly spaced, you can assume that the forces approximately add. If you require the clamps to hold a specific force for safety reasons, I would suggest doing some more detailed calculations for your material, and providing some extra allowance for errors.
answered Aug 21 at 18:00
JMac
7,92821732
add a comment |Â
up vote
1
down vote
up vote
1
down vote
Forces add in that way, and the clamps would do the same. You can prove this to yourself by drawing a free body diagram for the forces that would act upon the beam. Applying Newton's laws would show that the force you lift with will have to exceed the total clamping force if you wish to move the clamped board.
Obviously, this is extremely oversimplified, and there are many situations where this doesn't really apply.
The stiffness of the board is extremely important. A stiff board will even out the load between the clamps better than a flexible one. A flexible board may be able to cheat the total force rules; because it has less internal forces that resist relative movement this means that just adding the total clamping force and comparing that to the total applied force is not enough to represent the situation. It is possible to apply the force to one location and have that undo the clamp and bend the board there, but because the board is very flexible, it doesn't transmit enough force to undo any of the other clamps. You can't reliably treat it as a single object to apply Newton's Laws to anymore, but instead have to consider how the board interacts with itself as well as the clamps.
Basically, the proximity to each clamp is important, and it will be more important the further you are from the point of the applied load.
For the case of clamping wood, if it's a thick piece of sturdy wood, with clamps evenly spaced, you can assume that the forces approximately add. If you require the clamps to hold a specific force for safety reasons, I would suggest doing some more detailed calculations for your material, and providing some extra allowance for errors.
answered Aug 21 at 18:00
JMac
7,92821732
Forces add in that way, and the clamps would do the same. You can prove this to yourself by drawing a free body diagram for the forces that would act upon the beam. Applying Newton's laws would show that the force you lift with will have to exceed the total clamping force if you wish to move the clamped board.
Obviously, this is extremely oversimplified, and there are many situations where this doesn't really apply.
The stiffness of the board is extremely important. A stiff board will even out the load between the clamps better than a flexible one. A flexible board may be able to cheat the total force rules; because it has less internal forces that resist relative movement this means that just adding the total clamping force and comparing that to the total applied force is not enough to represent the situation. It is possible to apply the force to one location and have that undo the clamp and bend the board there, but because the board is very flexible, it doesn't transmit enough force to undo any of the other clamps. You can't reliably treat it as a single object to apply Newton's Laws to anymore, but instead have to consider how the board interacts with itself as well as the clamps.
Basically, the proximity to each clamp is important, and it will be more important the further you are from the point of the applied load.
For the case of clamping wood, if it's a thick piece of sturdy wood, with clamps evenly spaced, you can assume that the forces approximately add. If you require the clamps to hold a specific force for safety reasons, I would suggest doing some more detailed calculations for your material, and providing some extra allowance for errors.
answered Aug 21 at 18:00
JMac
7,92821732
answered Aug 21 at 18:00
JMac
7,92821732
answered Aug 21 at 18:00
JMac
7,92821732
answered Aug 21 at 18:00
JMac
7,92821732
7,92821732
add a comment |Â
add a comment |Â
up vote
1
down vote
And so the clamping force on any given spot on the board will never
exceed the max. force of the clamp.
This would, quite obviously, be the case, if we assumed that the clamps are evenly distributed around a circle.
Under these conditions, due to symmetry, any redistribution of the reaction force, which, in total, is equal to the total applied force, would not be possible, so the reaction force applied locally by each clamp would have to be $150$N and the pressure under all clamps would have to be the same.
If the clamps are not placed symmetrically, we can still state that no redistribution of the forces will occur by looking at one pair of clamps at a time and observing that, if that was not the case, the work (the two pieces of wood) would rotate, since two different reaction forces would create a net torque acting against two equal applied forces.
answered Aug 21 at 18:09
V.F.
7,1982621
add a comment |Â
up vote
1
down vote
And so the clamping force on any given spot on the board will never
exceed the max. force of the clamp.
This would, quite obviously, be the case, if we assumed that the clamps are evenly distributed around a circle.
Under these conditions, due to symmetry, any redistribution of the reaction force, which, in total, is equal to the total applied force, would not be possible, so the reaction force applied locally by each clamp would have to be $150$N and the pressure under all clamps would have to be the same.
If the clamps are not placed symmetrically, we can still state that no redistribution of the forces will occur by looking at one pair of clamps at a time and observing that, if that was not the case, the work (the two pieces of wood) would rotate, since two different reaction forces would create a net torque acting against two equal applied forces.
answered Aug 21 at 18:09
V.F.
7,1982621
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up vote
1
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up vote
1
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And so the clamping force on any given spot on the board will never
exceed the max. force of the clamp.
This would, quite obviously, be the case, if we assumed that the clamps are evenly distributed around a circle.
Under these conditions, due to symmetry, any redistribution of the reaction force, which, in total, is equal to the total applied force, would not be possible, so the reaction force applied locally by each clamp would have to be $150$N and the pressure under all clamps would have to be the same.
If the clamps are not placed symmetrically, we can still state that no redistribution of the forces will occur by looking at one pair of clamps at a time and observing that, if that was not the case, the work (the two pieces of wood) would rotate, since two different reaction forces would create a net torque acting against two equal applied forces.
answered Aug 21 at 18:09
V.F.
7,1982621
And so the clamping force on any given spot on the board will never
exceed the max. force of the clamp.
This would, quite obviously, be the case, if we assumed that the clamps are evenly distributed around a circle.
Under these conditions, due to symmetry, any redistribution of the reaction force, which, in total, is equal to the total applied force, would not be possible, so the reaction force applied locally by each clamp would have to be $150$N and the pressure under all clamps would have to be the same.
If the clamps are not placed symmetrically, we can still state that no redistribution of the forces will occur by looking at one pair of clamps at a time and observing that, if that was not the case, the work (the two pieces of wood) would rotate, since two different reaction forces would create a net torque acting against two equal applied forces.
answered Aug 21 at 18:09
V.F.
7,1982621
answered Aug 21 at 18:09
V.F.
7,1982621
answered Aug 21 at 18:09
V.F.
7,1982621
answered Aug 21 at 18:09
V.F.
7,1982621
7,1982621
add a comment |Â
add a comment |Â
up vote
0
down vote
He's right - the forces of the clamps will add up. You seem to be confusing force and pressure. The pressure from each clamp would reduce radially outwards from each clamping point, as you describe (although adding clamps will increase the average pressure acting across the entire length of the planks, thus increasing the force!).
answered Aug 21 at 15:06
Time4Tea
2,131929
But how can that be? Imagine two boards, 1m by 1m by 0.01m on top of one another. On the southeast corner I attach two 150N clamps. There are certainly no 300N acting on the nortwest corner.
– Holli
Aug 21 at 15:22
Now imagine springs between the boards, when I clamp it as described the strongest deflection would occur where the clamps sit, and decline the further you get away from them.
– Holli
Aug 21 at 15:27
1
@Holli The total contact force between the two boards is the sum of all the contact forces across the whole surface. Again, you seem to be confusing force and pressure. If the boards are very thin and flexible, then the region of the boards under one clamp may not be 'aware' of the pressure being applied by a second clamp (as it is not being transmitted well across the board). However, the total clamping force is still twice the force from a single clamp.
– Time4Tea
Aug 21 at 15:30
@Holli by adding a second clamp, you are doubling the average pressure that acts across the whole area of the board; therefore, the total force is doubling.
– Time4Tea
Aug 21 at 15:33
1
@Holli the case is a little different for very thin, flexible boards and very rigid boards. For very rigid boards, if you put a spring/meter in between, then it will measure the sum of all the clamps, because you are changing the nature of the contact so that all the contact load goes through it. For the very flexible ones, it would indeed only measure the force of a single clamp, because the stress is not being distributed effectively across the boards. I think you should clarify which case you are referring to in your question though.
– Time4Tea
Aug 21 at 15:46
 |Â
show 2 more comments
up vote
0
down vote
He's right - the forces of the clamps will add up. You seem to be confusing force and pressure. The pressure from each clamp would reduce radially outwards from each clamping point, as you describe (although adding clamps will increase the average pressure acting across the entire length of the planks, thus increasing the force!).
answered Aug 21 at 15:06
Time4Tea
2,131929
But how can that be? Imagine two boards, 1m by 1m by 0.01m on top of one another. On the southeast corner I attach two 150N clamps. There are certainly no 300N acting on the nortwest corner.
– Holli
Aug 21 at 15:22
Now imagine springs between the boards, when I clamp it as described the strongest deflection would occur where the clamps sit, and decline the further you get away from them.
– Holli
Aug 21 at 15:27
1
@Holli The total contact force between the two boards is the sum of all the contact forces across the whole surface. Again, you seem to be confusing force and pressure. If the boards are very thin and flexible, then the region of the boards under one clamp may not be 'aware' of the pressure being applied by a second clamp (as it is not being transmitted well across the board). However, the total clamping force is still twice the force from a single clamp.
– Time4Tea
Aug 21 at 15:30
@Holli by adding a second clamp, you are doubling the average pressure that acts across the whole area of the board; therefore, the total force is doubling.
– Time4Tea
Aug 21 at 15:33
1
@Holli the case is a little different for very thin, flexible boards and very rigid boards. For very rigid boards, if you put a spring/meter in between, then it will measure the sum of all the clamps, because you are changing the nature of the contact so that all the contact load goes through it. For the very flexible ones, it would indeed only measure the force of a single clamp, because the stress is not being distributed effectively across the boards. I think you should clarify which case you are referring to in your question though.
– Time4Tea
Aug 21 at 15:46
 |Â
show 2 more comments
up vote
0
down vote
up vote
0
down vote
He's right - the forces of the clamps will add up. You seem to be confusing force and pressure. The pressure from each clamp would reduce radially outwards from each clamping point, as you describe (although adding clamps will increase the average pressure acting across the entire length of the planks, thus increasing the force!).
answered Aug 21 at 15:06
Time4Tea
2,131929
He's right - the forces of the clamps will add up. You seem to be confusing force and pressure. The pressure from each clamp would reduce radially outwards from each clamping point, as you describe (although adding clamps will increase the average pressure acting across the entire length of the planks, thus increasing the force!).
answered Aug 21 at 15:06
Time4Tea
2,131929
edited Aug 21 at 15:20
answered Aug 21 at 15:06
Time4Tea
2,131929
answered Aug 21 at 15:06
Time4Tea
2,131929
answered Aug 21 at 15:06
Time4Tea
2,131929
2,131929
But how can that be? Imagine two boards, 1m by 1m by 0.01m on top of one another. On the southeast corner I attach two 150N clamps. There are certainly no 300N acting on the nortwest corner.
– Holli
Aug 21 at 15:22
Now imagine springs between the boards, when I clamp it as described the strongest deflection would occur where the clamps sit, and decline the further you get away from them.
– Holli
Aug 21 at 15:27
1
@Holli The total contact force between the two boards is the sum of all the contact forces across the whole surface. Again, you seem to be confusing force and pressure. If the boards are very thin and flexible, then the region of the boards under one clamp may not be 'aware' of the pressure being applied by a second clamp (as it is not being transmitted well across the board). However, the total clamping force is still twice the force from a single clamp.
– Time4Tea
Aug 21 at 15:30
@Holli by adding a second clamp, you are doubling the average pressure that acts across the whole area of the board; therefore, the total force is doubling.
– Time4Tea
Aug 21 at 15:33
1
@Holli the case is a little different for very thin, flexible boards and very rigid boards. For very rigid boards, if you put a spring/meter in between, then it will measure the sum of all the clamps, because you are changing the nature of the contact so that all the contact load goes through it. For the very flexible ones, it would indeed only measure the force of a single clamp, because the stress is not being distributed effectively across the boards. I think you should clarify which case you are referring to in your question though.
– Time4Tea
Aug 21 at 15:46
 |Â
show 2 more comments
But how can that be? Imagine two boards, 1m by 1m by 0.01m on top of one another. On the southeast corner I attach two 150N clamps. There are certainly no 300N acting on the nortwest corner.
– Holli
Aug 21 at 15:22
Now imagine springs between the boards, when I clamp it as described the strongest deflection would occur where the clamps sit, and decline the further you get away from them.
– Holli
Aug 21 at 15:27
1
@Holli The total contact force between the two boards is the sum of all the contact forces across the whole surface. Again, you seem to be confusing force and pressure. If the boards are very thin and flexible, then the region of the boards under one clamp may not be 'aware' of the pressure being applied by a second clamp (as it is not being transmitted well across the board). However, the total clamping force is still twice the force from a single clamp.
– Time4Tea
Aug 21 at 15:30
@Holli by adding a second clamp, you are doubling the average pressure that acts across the whole area of the board; therefore, the total force is doubling.
– Time4Tea
Aug 21 at 15:33
1
@Holli the case is a little different for very thin, flexible boards and very rigid boards. For very rigid boards, if you put a spring/meter in between, then it will measure the sum of all the clamps, because you are changing the nature of the contact so that all the contact load goes through it. For the very flexible ones, it would indeed only measure the force of a single clamp, because the stress is not being distributed effectively across the boards. I think you should clarify which case you are referring to in your question though.
– Time4Tea
Aug 21 at 15:46
But how can that be? Imagine two boards, 1m by 1m by 0.01m on top of one another. On the southeast corner I attach two 150N clamps. There are certainly no 300N acting on the nortwest corner.
– Holli
Aug 21 at 15:22
But how can that be? Imagine two boards, 1m by 1m by 0.01m on top of one another. On the southeast corner I attach two 150N clamps. There are certainly no 300N acting on the nortwest corner.
– Holli
Aug 21 at 15:22
Now imagine springs between the boards, when I clamp it as described the strongest deflection would occur where the clamps sit, and decline the further you get away from them.
– Holli
Aug 21 at 15:27
Now imagine springs between the boards, when I clamp it as described the strongest deflection would occur where the clamps sit, and decline the further you get away from them.
– Holli
Aug 21 at 15:27
1
1
@Holli The total contact force between the two boards is the sum of all the contact forces across the whole surface. Again, you seem to be confusing force and pressure. If the boards are very thin and flexible, then the region of the boards under one clamp may not be 'aware' of the pressure being applied by a second clamp (as it is not being transmitted well across the board). However, the total clamping force is still twice the force from a single clamp.
– Time4Tea
Aug 21 at 15:30
@Holli The total contact force between the two boards is the sum of all the contact forces across the whole surface. Again, you seem to be confusing force and pressure. If the boards are very thin and flexible, then the region of the boards under one clamp may not be 'aware' of the pressure being applied by a second clamp (as it is not being transmitted well across the board). However, the total clamping force is still twice the force from a single clamp.
– Time4Tea
Aug 21 at 15:30
@Holli by adding a second clamp, you are doubling the average pressure that acts across the whole area of the board; therefore, the total force is doubling.
– Time4Tea
Aug 21 at 15:33
@Holli by adding a second clamp, you are doubling the average pressure that acts across the whole area of the board; therefore, the total force is doubling.
– Time4Tea
Aug 21 at 15:33
1
1
@Holli the case is a little different for very thin, flexible boards and very rigid boards. For very rigid boards, if you put a spring/meter in between, then it will measure the sum of all the clamps, because you are changing the nature of the contact so that all the contact load goes through it. For the very flexible ones, it would indeed only measure the force of a single clamp, because the stress is not being distributed effectively across the boards. I think you should clarify which case you are referring to in your question though.
– Time4Tea
Aug 21 at 15:46
@Holli the case is a little different for very thin, flexible boards and very rigid boards. For very rigid boards, if you put a spring/meter in between, then it will measure the sum of all the clamps, because you are changing the nature of the contact so that all the contact load goes through it. For the very flexible ones, it would indeed only measure the force of a single clamp, because the stress is not being distributed effectively across the boards. I think you should clarify which case you are referring to in your question though.
– Time4Tea
Aug 21 at 15:46
 |Â
show 2 more comments
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I think the question is still confusing - the title asks whether pressure from the clamps adds up, but then the body of the question asks about forces, rather than pressure. It is virtually important to note the distinction.
– Time4Tea
Aug 22 at 1:07
Please do not make your post look like a revision table, instead just seamlessly integrate the new material into the post. There is an edit history button at the bottom of the post for those interested in seeing what changed.
– Kyle Kanos
Aug 24 at 10:19