Classic screw and nut(or sleeve?) system
Classic screw and nut(or sleeve?) system
(OP)
hi ,
I am a bit confused here and i would like your help here please. I have a classic screw and nut(or sleeve?) system and I have attached a pic of it for your reference. the torque is applied to the screw and causes the translation of the sleeve. I have derived the relation between the torque applied on screw and tensile force generated on the sleeve. Now I want to find the minimum value of tensile force on the sleeve required to overcome the frictional force generated due to the sliding of this sleeve in a cylinder. I just want to know how do I calculate the friction due to sliding of sleeve in the cylinder? Thanks. In the pic the thing in green is supposed to be the sleeve. sorry for the image I dont have a CAD software.
I am a bit confused here and i would like your help here please. I have a classic screw and nut(or sleeve?) system and I have attached a pic of it for your reference. the torque is applied to the screw and causes the translation of the sleeve. I have derived the relation between the torque applied on screw and tensile force generated on the sleeve. Now I want to find the minimum value of tensile force on the sleeve required to overcome the frictional force generated due to the sliding of this sleeve in a cylinder. I just want to know how do I calculate the friction due to sliding of sleeve in the cylinder? Thanks. In the pic the thing in green is supposed to be the sleeve. sorry for the image I dont have a CAD software.





RE: Classic screw and nut(or sleeve?) system
OK, so the compression in the sleeve will cause it to burst outwards, by poisson's law, and will then be constrained by whatever hole it is in, causing a pressure at the interface, and then the friction between the sleeve and the hole will resist any attempt to move the sleeve axially.
At this point I'm going to tip toe away, it seems to me there is either a plug and chug solution or the answer can be infinitely complex.
If the sleeve is rubber like and the hole is steel and the initial fit is tight, then poisson's ratio is 0.5, mu is 1, and life is relatively straightforward. If the initial fit is loose, the sleeve is steel, and the hole is concrete, then go and test it.
Cheers
Greg Locock
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RE: Classic screw and nut(or sleeve?) system
TTFN
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RE: Classic screw and nut(or sleeve?) system
When the tangential force F overcomes the frictional force between two surfaces then the surfaces begins to slide relative to each other.
The Co-efficient of Friction for power Screws is dependent on material of Screw & Sleeve (Collar)
See below Co-efficient of Friction values for various material combinations
http://www.roymech.co.uk/Useful_Tables/Tribology/c...
RE: Classic screw and nut(or sleeve?) system
RE: Classic screw and nut(or sleeve?) system
You have still completely failed to identify whether we are talking about soft sleeve/hard socket, or whatever.
Good luck, I'm inclined not to play 20 questions.
Cheers
Greg Locock
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RE: Classic screw and nut(or sleeve?) system
And here is why: provided that the screw rotates with constant velocity (i.e. equilibrium conditions), the couple you apply to the screw is balanced by a couple applied by the thread to the screw. Due to thread peculiar geometry, an axial force is generated and applied on the screw, which is balanced by an external load (in this case, friction).
Therefore the sleeve undergoes ONLY axial load: if the sleeve is externally threaded, it won't move.
Stefano
RE: Classic screw and nut(or sleeve?) system
RE: Classic screw and nut(or sleeve?) system
You need to know how much normal force there is between the sleeve and bore in order to know how much friction force, normal force * mu, is present.
Ted
RE: Classic screw and nut(or sleeve?) system
what sort of fit is there, between the sleeve and the hole ? (sliding ?? clearance ??)
how does twisting the screw translate the sleeve ? is the head of the screw captive (so that twisting the screw thread drives the sleeve) ?
presumably there is positive postioning of the sleeve ? something like a small spring (that's being compressed as the sleeve translates) and probably another one above the sleeve.
RE: Classic screw and nut(or sleeve?) system
RE: Classic screw and nut(or sleeve?) system
thanks for showing interest in the post, basically I started off the post by asking a question with basic configuration where the rotation of screw causes linear motion of the sleeve (this happens by blocking the sleeve to rotate by a flat surface on the outer suface).
In the second configuration I wanted to quicken the mechanism (I wanted the sleeve to move laterally from position A to position B faster, so I wanted to see if by threading on both sides of the sleeve can be better than just on one side), so removed the external flat surface and threaded on the outer surface of sleeve so it rotates as well as translates. I did the initial analytic analysis and it seems that if the thread pitch of sleeve inner surface is greater than the pitch on the outer surface , this can be achieved .
Can there be any other parameter other that pitch and friction coefficient that can effect this? thanks hydtools, engdoitbetter for your reply too
RE: Classic screw and nut(or sleeve?) system
RE: Classic screw and nut(or sleeve?) system
In the first case, increasing the pitch of the thread will increase the translation of the sleeve per screw revolution.
Ted
RE: Classic screw and nut(or sleeve?) system
draw a free body of the sleeve. the torque applied to the screw will be reacted by a couple onto the sleeve, which will apply a couple to the body around the sleeve. this should also show you the forces translating the sleeve.
to speed up movement of the sleeve, i'd suggest changing the pitch of the thread. this is what links the translation of the sleeve to the applied twist of the screw.
RE: Classic screw and nut(or sleeve?) system
if it helps, the sleeve has thread (groove or female) internally as well as externally ..the threads(males) are provided on the bore and screw.
RE: Classic screw and nut(or sleeve?) system
wouldn't it be simpler to thread whatever is restaining the screw to the body, so twisting the screw causes it to translate. then the sleeve is simply fixed to the screw.
RE: Classic screw and nut(or sleeve?) system
yes I agree that it is difficult to translate the sleeve with blocked rotation, thats the reason I taught of the second config. According to the design, the sleeve has to move for fixed number of rotation of screw and disengage the screw and bore(body) (by moving the sleeve). thats the reason I cannot think of fixing the sleeve. Thanks
RE: Classic screw and nut(or sleeve?) system
i think once you draw the free body diagram you'll see some of the difficulties in using a flat. what about using two tabs, slotted into the body ?
RE: Classic screw and nut(or sleeve?) system
RE: Classic screw and nut(or sleeve?) system
RE: Classic screw and nut(or sleeve?) system
RE: Classic screw and nut(or sleeve?) system
RE: Classic screw and nut(or sleeve?) system
RE: Classic screw and nut(or sleeve?) system
Ted
RE: Classic screw and nut(or sleeve?) system
RE: Classic screw and nut(or sleeve?) system
http://www.edmundoptics.com/mechanics/positioning-...
http://search.newport.com/?q=*&x2=sku&q2=T...
In the latter cases, the speed of the motion is strictly limited by the screw pitch and turning speed.
p.s. I agree that outside threading will not work; if anything it's more likely to jam in place, since there's insufficient torque on the sleeve to cause it to rotate, since the inner screw drag will cause it to want to rotate in the same direction as the screw, but it will actually need to rotate in the opposite direction
TTFN
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RE: Classic screw and nut(or sleeve?) system
RE: Classic screw and nut(or sleeve?) system
TTFN
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RE: Classic screw and nut(or sleeve?) system
RE: Classic screw and nut(or sleeve?) system
Second, If the sleeve does rotate due to the torque applied on the screw, there will be no relative motion (or a slower one) between the screw and the sleeve, so a slower (or no) axial movement.
RE: Classic screw and nut(or sleeve?) system
the pitch of the thread controls the displacement due to applied torque, coaser thread, more displacement per rotation.
you could thread the sleeve/body interface (what we've called an external thread) and it'll work If the screw is fixed to the sleeve, so that twisting the screw rotates the sleeve.
clear as mud ?
RE: Classic screw and nut(or sleeve?) system
Build a physical model and let us know how it performs.
Ted
RE: Classic screw and nut(or sleeve?) system
http://files.engineering.com/getfile.aspx?folder=9..."
Where did you get this "file" ?
I wasted 20 minutes reading this nonsense.
I can't believe that any credible kinematic analysis would allow the frame to rotate and in the end he/she gets an "amplification" directly dependent on the ratio of the screw rotation divided by the "fictitious" frame rotation. Fatally flawed and wrong conclusions.
Perhaps a PHD candidate??
Same guy probably can prove 0=1.
Bottom line
OP-- don't believe everything that's written especially when it is not published.
RE: Classic screw and nut(or sleeve?) system
Let the screw rotation be N1 and the sleeve rotation N2
The pitch of the internal and external threads are P1 and P2.
I get the translation to be
P1(N1-N2) which must be equal to -P2N2, the translation along the external thread.
Then you can write
P1(N1-N2)=-P2N2
In order to amplify the motion, N2 must be negative. For example, if the amplification= 2,
(N1-N2) = 2N1 , or
N2=-N1
and
2N1P1=P2N1
To satisfy this, the external pitch is
P2=2P1
If the amplification is 3,
then N2=-2N1 and
3P1N1=2P2N1
P2=1.5P1
Now, the trick is to get a small muscular little man to rotate the sleeve accordingly.
That is the problem with all this. I just doesn't work. Moreover, what has the external thread done for the system? Nothing.
Once the little guy has done the spinning, the amplification is accomplished.
RE: Classic screw and nut(or sleeve?) system
TTFN
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