Magnetic Holdowns

[Duffy]

I went to the local "Travelling Wood Show" yesterday. (Yes, I confessed and have been granted absolution!) What caught my eye were sets of magnetic holdowns for featherboards. They sure looked simple, but I cannot figure out how they work. There were two sizes, the smaller used 3/4'" rare earth magnets and the larger used 1" magnets. The body was either aluminum or potmetal, a bit larger than the diameter of the magnet, and there was a twist knob on top that obviously operated SOMETHING internally, I assume another magnet.
How DO they operate, and does someone have a plan for them? These were being sold for about $30.00/pair for the little ones, and i know that the magnets are only about $1.25 each.
Any ideas? Duffy

[rowbare]

I imagine they are similar to these: http://www.leevalley.com/wood/page.a...=1,42363,42356

There is a bit of a description there and a brand name there. A bit more digging found the patent: http://www.google.com/patents?id=O-N...age&q=&f=false

bob

[pcarpenter]

I have a pair of these from back when the bodies were made from Oak. There is nothing magic about them....it's a very powerful magnet embedded in the bottom just below the surface. The little lever at the tail end physically lifts the unit enough to get the base to let go.

http://www.rockler.com/product.cfm?p...s&cookietest=1

Paul