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Offline JP

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Neat animations of complicated mechanisms
« on: 31/08/2010 09:17:44 »
Someone sent me this today.  I figured it might be appreciated here.  It's the first time I've actually understood how a sewing machine works!


http://mytechnologyworld9.blogspot.com/2010/08/complicated-mechanisms-explained-in.html


 

Offline peppercorn

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Neat animations of complicated mechanisms
« Reply #1 on: 31/08/2010 12:28:27 »
Nice set of animations there, JP.

Not sure I understand this one though:

-Steam engine Principle-
 

Offline LeeE

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Neat animations of complicated mechanisms
« Reply #2 on: 31/08/2010 18:09:48 »
Yes, nice animations, but I'm not sure about that 'steam engine' one either, and the 'Torpedo-Boat destroyer System' is rather badly named too (it actually shows how the shells and charges for battleship main armourment are stored separately, deep within the ship and protected by blast doors, and are only brought together immediately prior to firing).
 

Offline Geezer

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Neat animations of complicated mechanisms
« Reply #3 on: 31/08/2010 19:25:48 »
The steam engine one has me beat too  ???

I suppose the slides running in the dovetail slots might represent the valve motion for a two cylinder engine?
« Last Edit: 31/08/2010 23:45:05 by Geezer »
 

Offline imatfaal

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Neat animations of complicated mechanisms
« Reply #4 on: 01/09/2010 12:26:09 »
I must admit I still don't understand the sewing machine - the loop grabbed by the lower mechanism from the needle seems to go round both sides of the lower mechanism.  If it goes around both sides what holds the mechanism?
 

Offline LeeE

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Neat animations of complicated mechanisms
« Reply #5 on: 01/09/2010 16:04:34 »
Unless I'm much mistaken, the end of the 'rod' of the steam engine thingy is tracing out an ellipse.  And I still can't see how that relates to steam engines.

I think the lower mechanism in the sewing machine is actually mounted obliquely, and that's how it manages to pick up the thread from the needle on the far side of the thread from the lower feed and then swing it across the front to loop it.
 

Offline imatfaal

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Neat animations of complicated mechanisms
« Reply #6 on: 01/09/2010 17:02:59 »
Lee - you are right about the ellipse being traced.  This device is a Trammel of Archimedes   and is actually used in drafting and woodworking to describe an ellipse.  It's also used as a toy called a "nothing grinder" . Note the diagram on the rhs of the above wikipedia page.

I am still trying to get my head around the sewing machine!  This page of animations isn't an elaborate hoax is it?

Matthew
 

Offline neilep

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« Reply #7 on: 01/09/2010 17:31:42 »
I find the radial engine quite exciting !!



 

Offline Geezer

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Neat animations of complicated mechanisms
« Reply #8 on: 01/09/2010 18:16:24 »
Lee - you are right about the ellipse being traced.  This device is a Trammel of Archimedes   and is actually used in drafting and woodworking to describe an ellipse.  It's also used as a toy called a "nothing grinder" . Note the diagram on the rhs of the above wikipedia page.

I am still trying to get my head around the sewing machine!  This page of animations isn't an elaborate hoax is it?

Matthew

Yes, it's an ellipse and I believe the locus of the mid point between the pivots on the two sliders is a circle.

In the sewing machine the "shuttle" (the thing that holds the lower spool) is not permanently attached to the machine at all. What happens essentially is that the mechanism creates a big loop in the upper thread on the bottom side of the cloth, then it "throws" the shuttle with the lower thread bobbin through the loop. After that the threads are tightened up before the next stitch is begun.

On some sewing machines you wind the lower thread onto a thing that looks a lot like the shuttle in a weaving machine rather than the more typical bobbin arrangement. 
« Last Edit: 01/09/2010 18:53:43 by Geezer »
 

Offline imatfaal

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Neat animations of complicated mechanisms
« Reply #9 on: 02/09/2010 11:07:47 »
Yes, it's an ellipse and I believe the locus of the mid point between the pivots on the two sliders is a circle.

Yep agree with that as well - its a really cute device.  In a hand wavy way; I guess the centre of the locus must be at the cross over point, cos what ever shape the mid-point traces must be symmetrical on both axes, and it seems that at any point of the rotation you could imagine two isosceles triangles formed by the midpoint, the device centre, and each pivot point.  the distance device centre to midpoint thus remains constant (ie circle) and radius is equal to half the distance between the two pivots

Quote
In the sewing machine the "shuttle" (the thing that holds the lower spool) is not permanently attached to the machine at all. What happens essentially is that the mechanism creates a big loop in the upper thread on the bottom side of the cloth, then it "throws" the shuttle with the lower thread bobbin through the loop. After that the threads are tightened up before the next stitch is begun.

On some sewing machines you wind the lower thread onto a thing that looks a lot like the shuttle in a weaving machine rather than the more typical bobbin arrangement. 

That sounds possible - but two things make me think that other methods are used.  Firstly, that would create a real stitch which if you cut one loop would hold on the next, or next but one;  but machine sewing will run if you break  a stitch (OK subsequently discovered this is only old and bad commercial machines) making me think it is more complex than a real stitch  .   Secondly the mechanism for "throwing" doesnt tally with memories of my mums sewing machine - i thought it worked as loops through loops.  Will seek out or draw diagrams.
« Last Edit: 02/09/2010 11:38:40 by imatfaal »
 

Offline Geezer

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Neat animations of complicated mechanisms
« Reply #10 on: 02/09/2010 17:42:34 »
That sounds possible - but two things make me think that other methods are used.  Firstly, that would create a real stitch which if you cut one loop would hold on the next, or next but one;  but machine sewing will run if you break  a stitch (OK subsequently discovered this is only old and bad commercial machines) making me think it is more complex than a real stitch  .   Secondly the mechanism for "throwing" doesnt tally with memories of my mums sewing machine - i thought it worked as loops through loops.  Will seek out or draw diagrams.



This diagram shows how a sewing machine forms the stitches.
 
T is the top thread. B is the bottom tread. The green line is the material.

Obviously this is not showing how the loops are tightened up. Ideally, after the tightening, the top and bottom threads should meet half way through the material. If the tension is not set properly you will see loops either on the top or the bottom of the material.

Edit: I noticed the diagram is not quite right. The top thread only goes through the material at one point (where the needle passes through the material) for each stitch. The diagram makes it look as if it goes through twice, which would be impossible.
« Last Edit: 02/09/2010 17:48:06 by Geezer »
 

Offline Geezer

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Neat animations of complicated mechanisms
« Reply #11 on: 02/09/2010 18:16:53 »
Yep agree with that as well - its a really cute device.  In a hand wavy way; I guess the centre of the locus must be at the cross over point, cos what ever shape the mid-point traces must be symmetrical on both axes, and it seems that at any point of the rotation you could imagine two isosceles triangles formed by the midpoint, the device centre, and each pivot point.  the distance device centre to midpoint thus remains constant (ie circle) and radius is equal to half the distance between the two pivots.

The connector forms a right angle triangle with the two perpendicular slots. Sine of one of the angles always equals cosine of the other, so one slider has sinusoidal motion and the other has cosinusoidal motion. The result is a circle (or something like that!  ;D)
« Last Edit: 02/09/2010 18:19:50 by Geezer »
 

Offline imatfaal

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Neat animations of complicated mechanisms
« Reply #12 on: 03/09/2010 11:52:30 »
Sewing Machining - you are quite right about the end result of the "lock stitch" sewing machine - from examination of pictures of bobbin cases I think most designs have a free floating bobbin within a drum case.  with some beautiful engineering and nice smooth edges it is possible for the loop of thread to be threaded into the bobbin case (which is connected to body of machine) and looped around the actual bobbin  (which is not connected to body of machine).  I am still not certain as I haven't had a chance to examine a machine - and all the animations have a continuous loop of thread passing around an 'axled' bobbin.  the fact that a reasonable cheap mass-produced machine can do this many times a second with very delicate silk thread is just one of those every day miracles of engineering.
 

Offline Geezer

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« Reply #13 on: 03/09/2010 17:00:07 »
You got it. The bottom spool of thread sits in a carrier thingy (the shuttle). The entire shuttle passes through a loop formed in the top thread when the needle pushes through the material and starts to retract.

The really tricky bit is arranging for the shuttle to hook onto the little loop made in the top thread and expand it. If the timing and spacing between the needle and the shuttle is not just right, the hook misses the loop and the stitch is dropped.
« Last Edit: 03/09/2010 17:02:19 by Geezer »
 

Offline Geezer

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Neat animations of complicated mechanisms
« Reply #14 on: 03/09/2010 19:06:54 »
The Maltese Cross mechanism is also known as a Geneva Drive or Geneva Mechanism (not to be confused with The Geneva Man referred to in Hogan's Heroes).

You'll find exactly the same animation on the Wiki page http://en.wikipedia.org/wiki/Geneva_drive

If you want to make a Maltese cross, just poke him in the eye.
 

Offline Geezer

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Neat animations of complicated mechanisms
« Reply #15 on: 03/09/2010 19:14:40 »
Nice set of animations there, JP.

Not sure I understand this one though:

-Steam engine Principle-

I suppose what they were suggesting is that there is some similarity with the geometry in this (see link). It's reasonably clear what it's trying to do, but exactly how it does it is another matter! BTW, this is only one of many types of valve gear arrangements.

http://en.wikipedia.org/wiki/Walschaerts_valve_gear

I think the animation on Wiki leaves out a very important point re. thermodynamics. The valve gear is variable, so it is possible for the valves to allow the admission of steam for a limited part of the piston stroke. This allows the maximum amount of work to be extracted from the steam (the steam is allowed to expand as much as possible.)

Note that the engines in today's hybrid automobiles try to take advantage of the same effect.
« Last Edit: 04/09/2010 05:48:54 by Geezer »
 

Offline RD

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Neat animations of complicated mechanisms
« Reply #16 on: 11/09/2010 20:44:22 »
More "Neat animations of complicated mechanisms" ...

feature=channel  :D
 

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Neat animations of complicated mechanisms
« Reply #16 on: 11/09/2010 20:44:22 »

 

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