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I want to insert and glue 1/16" diameter rare earth magnets into holes I create in my plastic models. The purpose of the magnets is to make it easy to swap weapons/options on my Warhammer 40K models.

Regular twist drill bits leave a wide concave hole in the plastic, making it difficult to glue a magnet flush to the bottom of the hole.

Forstner drill bits create a flat bottomed hole (with a small concave hole in the center), but only down to 1/4" diameter holes.

Brad point drill bits create a flat bottomed hole (with a small concave hole hole in the center and a depressed ring around the hole) down to 1/16", but it seems brad point bits below 1/8" are not a "true" (?) brad point bit.

I have two cascaded questions: 1) does a 1/16" non-true brad point drill bit provide a good-enough flat bottomed hole for 1/16" diameter rare earth magnets? 2) if not, what is a workable method to create 1/16" diameter flat bottomed holes in plastic?

Update 2 Oct 2012: The root problem I am trying to solve is magnets being pulled out of their holes after gluing. I originally thought I had a tool problem (concave hole causing lack of contact surface area between magnet/glue), but CaulynDarr and Affe's comments point to a likely process problem. Experimentation and tenacity on my part will solve that. Thank you for your comments!

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just put a dab of greenstuff in the hole with the glue – Affe Oct 1 '12 at 15:52
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Oh also, protip, for vehicles and other places where it's possible, I put the magnet on the inside (sometimes still drilling a bit so the palstic is thinner and it holds better) so that when a weapon is on the magnets are pulling each other into the glue joint instead of trying to rip each other out of it. – Affe Oct 1 '12 at 16:05
@Affe Thanks! I like your protip, it makes good sense. – David Pointer Oct 2 '12 at 14:20

1 Answer

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I can't answer the specific question on drill bit types. I've don plenty of magnatizing, but haven't analyzed the tools I've used in that great of depth.

I've used Dremel's precision drill bit set in my 7.2 Volt rotary tool. I've never had too big a problem with the convex bottom of the hole they create. If you match the drill bit size close enough to the magnet diameter, the sides of the hole should provide enough surface area to hold the magnet in place with a little super glue.

A little super glue, epoxy glue, or an epoxy resin like Green Stuff or Milliput could be used to fill in the hole to an even surface.

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Thanks! I'm beginning to think I may have a process problem with my drilling, rather than a hole/tool problem. I'll keep experimenting. – David Pointer Oct 2 '12 at 14:23

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