Re: Question about helmets & magnets.
What kind of helmet? If there is a pic, I can't see it due to work filters. What are you trying to attach/detach?
I have always used Magic Sculpt to secure the magnets to one side. I put them in place, and let get semi-hard (Magic Sculpt takes hours to harden completely), and add a little Vaseline to the surface so that my fingers don't stick to the surface while smoothing. I smooth it down to its near final shap and let harden completely.
Next: Vaseline everything that you don't want sticking, and mate new magnets to the magnets in the hardened Magic Sculpt. Then put the two maching pieces together and secure with tape or hot glue. The two parts need to be mated and secure (not able to move). Now come in with more Magic Sculpt and press it onto the new magnets, and form it to mate with the hardened Magic scupt. Again, use Vaseline on the Magic sculpt to get a smooth surface. Wait until hardened, and separate the two pieces. If you added enough Vaseline, they should come appart easily, and will return to their mated position and hold due to magnetic attraction.
There is a chance that some of the ridged Magic Sculpt might bind up and prevent smooth mating and unmating the two halves. A little sanding/filing will take care of it.
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PS: Be sure to use Rare Earth Magnets, and not just magnets!
www.k&jmagnetics.com