Magnetic force in two axes 1

[fredming]

I need to hold two small bars of acrylic (1 x 5 x 1/4) in alignment. I can only put the magnets into the large flat surfaces, between the bars. I have used 1/32 x 1/4 neodymium disks, and they work fine against lifting one bar off the other. But the bars can slide, one over the other.

Is it even theoretically possible to have a magnet hold in two directions at once????

 

[BobM3]

Do you have a sketch of what you are trying to do? Because acrylic is non-magnetic I assume you are trying to use the magnets to somehow clamp the acrylic. It may just be a case of not enough clamp load to hold the pieces together tight enough.

 

[IRstuff]

If you use two Halbach array sheet magnets and orient the arrays perpendicularly, there will be a cogging effect that will prevent small movements, but that's about much as you should expect.

Another option is to provide mechanical features like a pin/slot in the magnets you add that might provide some mechanical resistance to movement.

TTFN

FAQ731-376

 

[fredming]

"I assume you are trying to use the magnets to somehow clamp the acrylic. It may just be a case of not enough clamp load to hold the pieces together tight enough."

Right. I just want to hold them together and keep them from slipping relative to each other. Strongly enough that I can position them in a jig, but they won't move under light pressure from a finger.

I'll try a stronger magnet.

thanks.

 

[MagMike]

If the magnets are just in attraction through the acrylic, then they will always allow some sliding motion. Most of the attractive force between magnets is oriented along the gap between them. Forces in the transverse directions (sometimes called restoring forces) are much lower. Usually the main thing preventing transverse (sliding) motion is friction. It is far easier to slide a magnet off a stack of magnets than it is to pull it straight away.

Think of refrigerator magnets: If a refrigerator magnet is holding up a single piece of paper, the frictional forces between the paper and the surface of the refrigerator are high enough to overcome gravity. With multiple sheets, the attractive force decreases and gravity overcomes frictional forces.

There are some magnet arrangements (such as Halbachs, as IRstuff suggested) that'll help reduce sliding, but then economics comes into play. Bigger magnets are probably the cheapest/simplest method.