Results 103 to 108 of 108
04-16-2012, 02:04 AM #103
It is the direction of the movement that counts:
The mains pull the frame inwards between 12 and 2 0’clock.
This causes the frame to move outwards between 2 and 3 o’clock.
The forces of the cross strings pull the frame back to the original width.
So there is no reason to support the frame against the inward forces.
The saying is: If the racquet head does not get shorter it does not get wider either.
The perfect system has an inside support at every position of a main string.
The racquet head will not get wider and the racquet will not “feel” anything.
The 3 point inside support with wide support is a good method of approach which is adjustable to the shape of the racquet.
If all the forces during stringing are inwards, then the inward supports are very well suited offcourse.
But, if you string cross-strings you can clearly see the frame moving outward (say you string bottum-up and arrive at the last 3-8 crosses)
The worst thing that you can do is prevent this with the outside support, because the pressure on the support goes up then which increases the chance on cracks.
It is much better to let the frame move outward a little and gradually pull it back cross string by cross string.
04-16-2012, 04:35 AM #104
the problem is, this movement does occur, even in your machines (which I have seen). So this pressure on the frame comes from somewhere (which is the tensioning off a string).
On one hand you say: you can't let the frame move during the stringing of the mains because <insert story about internal support>, but on the other hand you seem to be just fine letting the frame move a bit during the crosses
04-16-2012, 07:00 AM #105
The primary load and the secondary deflection.
The primary load is in the direction of the mains, so every movement that you can avoid is good.
The secondary movement is in the direction of the crosses, this is not caused by load in that direction but because of the movement in the direction of the mains.
So if there is no movement in the direction of the mains there will be none in the direction of the crosses either.
With every cross that is inserted the load on the frame goes down.
Second and major question is:
What is better for the frame when you enter the crosses even bottom up:
- Avoiding every movement, causing a "point load" with an outside support?
- Or to let the frame move outwards gradually over the hole length.
The important issue of this story is:
The bad thing for the frame is not the movement (or deflection), it is the bending stress in the racquet material.
Compared to the beam in the wall:
In the upper beam without support, there is a lot of movement in point A, but no bending stress at all between C and A.
- With the support in point A there is no movement in point A at all, but there is bending stress between C and A.
So the load on the beam is higher with the support in A then without!
04-16-2012, 03:35 PM #106
first off, will you please -for the love of god- stop posting that picture in every post you make... It's starting to get to me.
The problem with your simple beam is that this is clearly not the case with a badminton frame. Both sides are fixed and another problem is that both sides aren't fixed exactly (with all supports there is movement)
You say there's no movement with 3 internal supports, I disagree. Because you can't tighten the supports outwards (you can only lock them down) there's an inherent hysteresis when tension is applied.
You ask me which I think is better; letting the stress divide or pressing it back with a support.
I think an outward support does the job quite nicely, I also think that "letting the frame move" sounds like a very bad idea (a frame has its limits)
savenium liked this post
04-16-2012, 03:51 PM #107
the issue is the over simpifications.
the racket head resembles less of a beam, but instead an arch.
the static analysis of an arch is very different from a beam.
the beam analysis shown assumes one side anchored while the other side is free moving. it also assume a straight edge. a badminton racket top looks nothing like that.
an arch analysis however, holds more resemblance. the quadrant of the racket is curved, just like an arch, and there are inward forces acting on it, just like weight sitting on top of the arch. in a arch, both ends are anchored. in a way that is actually true for a badminton racket. the 12 oclock point is kinda anchored. the 3 oclock is anchored in a way by that it is the same structure as the bottom quadrant. looking at it like an arch, then it does make sense to support/anchor the 3 oclock position. the resulting structure then will be compressive force on the racket frame (along the direction of the frame) and thus will be as strong as a arch.
what is missing though, is that we are trying to apply uneven forces to the arch while we are tensioning the mains. which means there is a risk of "bulging" at the 2 oclock position due to uneven forces. this is the reason why side supports are applied at theoutside of the 2 oclock. once the forces (main strings) at that location is completed. then we don't need any support there anymore. but we still need 3 oclock support to complete the arch. thus we cannot remove the side supports.
04-17-2012, 01:11 AM #108first off, will you please -for the love of god- stop posting that picture in every post you make... It's starting to get to me.
the racket head resembles less of a beam, but instead an arch.
And the racquet will not brake because of deformation but because of stress in the material that is too high.
There 2 are more practical proves of that out of the stringing history:
* In the 70’s some stringing machine manufacturer thought that it was a good idea to avoid outward movement and added a cross bar between 3 and 9 o’clock to restrict that .
The idea disappeared quicker then it came because the racquets broke on the machine.
The bar caused huge bending stresses at 2 and 10 o’clock.
* When Prince came with the first Extender racquets, with the very wide head and narrow throat, the main strings ended at the throat and many stringers strung in one piece then still.
Because the head side was very wide the main strings caused a big outward movement.
On 6-point machines this meant a very high pressure on the outside supports at the head side.
Going bottom up, pushed even more pressure on the outside supports and the racquets cracked on the machine.
Prince advised not to use the outside supports at the head, or go top down so that pressure on the outside supports was decreased with every cross string that was entered.
On the direct supports these racquets could be strung without any problem bottom up and top down.
Last edited by stringtechno; 04-17-2012 at 01:22 AM.
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