Breakaway torch carrier design

I use 1 or 2 magnets yanked out of old hard drives.

RNJFAB do you have those magnets on both sides, attracting each other or just a metal plate on one side? They're a LOT stronger if attracting each other. I've got 20x3mm and if I put just two of them together I can't pull them apart. I've got the kind with a hole in the middle.

But full disclosure I haven't built this yet. So I'll definitely update on how it goes.

Here's a design I made that's cheap, been working well for 4 years and >200k pierces with no accidental activations.

• Z-plate is aluminum, and there are 4/ea V-bearings mounted to it.
  • Two of the bearings are on eccentrics so they can tension the slider.
  • Float switch mounted on Z-plate, triggered by slider
• Slider is a piece of 1/8" steel plate
  • Edges are beveled/rounded and is captured by the V-bearings
  • 3 holes drilled in it to locate the bearing balls on the carrier plate
  • Microswitch (post-type), NC, triggered by the carrier plate being in place.  Switch wires are routed through the Z-plate and up the back.
• Carrier plate is aluminum and has
  • 3/ea 3/8" bearing balls pressed in to undersized flat-bottom holes.  Holes are just deep enoughso the ball stick out a bit - CAD helps here.
  • 3/ea 1/2"x1/4 magnets pressed & epoxied in

Holes in slider can be easily adjusted (chamfer, size) for an appropriate break-away force in all directions.  I found that to get a good 'feel', the balls should be buried about 1/3 the diameter of the ball when the magnets are touching the slider plate and slightly chamfered.

The dimensions are also important - the distance between the magnets top to bottom should be fairly short, otherwise you wind up with much stiffer break-away force front to back than rotationally.  The torch should have quite a lot of leverage.

Hope it helps.

-Ralph
     
 

There is another really simple torch breakaway and holder designed by seanp on the plasma spider forum.
It uses 3 ball bearings tig welded from the back that locate into holes on the front pieces. The magnets used  then don't really matter.

I am With Andy, Don't use more than 3 location points.

I just have the magnets onto a steel plate. 

when I tested mine made no real difference if it was onto the magnet or steel.