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Author Topic: Reinventing the Wheel  (Read 2696 times)

Offline Atomic-S

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Reinventing the Wheel
« on: 29/12/2006 05:17:54 »
What the world needs today is a furniture caster that works. I, Wondering why the new ones I installed on my bed went bad in a short time,  examined one, and discovered it is a poor example of engineering. The problems are the relations of its torque moments, and its poorly designed lubrication system. The typical furniture caster has a moment arm about the axis which lies in the swivel plate and also in the plane of the wheel, which is greater than the moment arm about the axis which runs at right angles to the swivel plate and through its center. That means that a side thrust applied to the wheel is more effective in putting strain about a non-rotating axis than about a rotating axis. This is not a problem under ideal conditions; however if the swivel bearing is at all sticky, the static friction is disproportionatly recognized by the non-rotating moment, so that applying more side thrust to the wheel simply increases the normal force inside the bearing, raising the static friction force, further jamming the mechanism.

2 things are needed: Change the ratios of gyrations by increasing the ratio of the swivel radius to that of the wheel radius. The swivel radius should be significantly larger, but in most casters is not.  This would require a better bearing, and on casters having a ball raceway, the diameter of the raceway would have to be increased some so as to remain over the wheel. The other thing needed is to install a seal over the swivel bearing, as for example a disk of felt, that would keep dirt out of it. Because casters run close to the floor, they are subject to all manner of dirt, grime, and lint; and oiling them only helps them pick up evne more of this. So seal them.

These changes are probably not seen on commonly available casters due to costs: manufacturers seem to want to manufacture the unit at the least possible cost. Too bad; some people might pay a bit more for a better unit.


 

Offline Heliotrope

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Re: Reinventing the Wheel
« Reply #1 on: 30/12/2006 00:51:32 »
I may be jumping the gun here but it seems to me that you have perhaps overlooked the primary reason for having castors.
That reason is not so you can move furniture easily.
It is so that the furniture stays where it's put but if you do have cause to move it then it will move with a bit less effort than if there were no castors.

I agree they need redesigning but making them easier to rotate is one of the last things that you want.
It seems to me that the offset of the shaft axis entering the furniture from the centre of rotation axis of the castor is part of the problem.
Too much weight on the furniture and the cheap and nasty casting of the castor will break or distort badly. And they also just break when you move them around too much.

Magnetic levitation is the way to go.
;)
 

Offline elegantlywasted

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Re: Reinventing the Wheel
« Reply #2 on: 30/12/2006 14:35:56 »
You both have excellent points, yet I am inclined to side with heliotrope, has anyone else been having a bit of fun atop a bed ona  hardwood floor? Quite frequently you notice when the play is done that the bed is about 6 feet from the wall and has knocked over your bookcase....
 

Offline Atomic-S

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Re: Reinventing the Wheel
« Reply #3 on: 06/01/2007 06:24:12 »
You both have excellent points, yet I am inclined to side with heliotrope, has anyone else been having a bit of fun atop a bed ona  hardwood floor? Quite frequently you notice when the play is done that the bed is about 6 feet from the wall and has knocked over your bookcase....
The solution to this may be in the kind of spring loaded wheels used on certain step-stools, which raise the stool up allowing it to roll, but as soon as someone stands on it, the spring retracts, letting the frame rest firmly on the floor.
 

The Naked Scientists Forum

Re: Reinventing the Wheel
« Reply #3 on: 06/01/2007 06:24:12 »

 

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