Working with magnets in an assembly

[ERIMechEng]

My objective is to design a non-frictional eddy current brake system using a series of permanent magnets affixed to a fixed plate that is held a short distance away from a rotating plate. I think the basic design concept will work, but I've never worked with magnets in an assembly before:
1) How can I affix the PMs to the fixed plate? Adhesive? Press-fit? I'd like to stay away from adhesive since the "distance between magnet and rotating plate" dimension will need to be held in close tolerance.
2) Any reason that I shouldn't use neodymium magnets? I was going to select neo PMs because of their strength, but if other types are easier to work with, I'm open to suggestions.
3) Any comments on the design concept?
4) Any online (=free) references that I can look up on my own?

Thanks!

 

[prex]

Look in the second site below, under 'LEM'

prex

http://www.xcalcs.com

: Online engineering calculations

http://www.megamag.it

: Magnetic brakes and launchers for fun rides

http://www.levitans.com

: Air bearing pads

 

[EdStainless]

It is best to use a steel backing plate and an aluminum face plate. Make the Al slightly thicker than the magnets and drill holes in it to hold the magnets. Then you only need enough epoxy to hold the magnets in place.

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

 

[bz2005]

Hi ERIMechEng,

What tolerance do you need between the magnet and the rotating plate? I know with Loctite you can easily control the glue line to under 0.005" or even smaller. Or, you can always grind flat after bonding the magnets to the fixed plate.

I would use Neo magnets. They tend to corrode with presence of water or moisture, so definitely nickel plate them if you can, or encapsulate them.

SmCo magnets can also be used. SmCo has much better corrosion resistance than neo, and doesn't need plating. They are not as strong, and more expensive.

 

[EdStainless]

I wouldn't use Neo in this application. These things get hot and the properties of Neo drop off fast with temp.

If you have to get the magnets closer than 0.050" to the disc then you need more field.

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

 

[ERIMechEng]

@ bz2005: I'm not sure of the tolerance I need. I haven't yet built a demonstration rig to prove the concept, so I don't have any hard numbers.

@ Ed Stainless: "...then you need more field." You mean I would need more / stronger magnets?

Assuming: 12 neo mags (1" dia) arranged in a 24" dia circle. Aluminium plate 0.1" away, rotating at 400 rpm. What kind of braking force can I expect (VERY rough order of magnitude)?

 

[bz2005]

Magnetic field strength drops quickly with distance, so place your plate as close to the magnets as you can, if you're after maximum braking.

Bo