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Does anyone have both a 4 minute recorder and a dial caliper or micrometer? I've been teaching myself how to machine sapphire rod and would like to try making some 4 minute styli but need to know the diameter. I'm assuming it's half the size of a 2M recording stylus, but knowing for sure would be preferred.

Thank you.

For those interested, it turns out the answer is .010" in diameter. The end of the sapphire rod is flat, cut at a 90* angle and has a small dimple in the center. I don't believe the dimple has any effect on performance.

I've read somewhere that the dimple is a true demi_spherical hole the stylus end, so it produces a cutting edge all around the perimeter of the stylus. The wax is cut by the edge and the cup launches it away while running.

Inigo wrote:I've read somewhere that the dimple is a true demi_spherical hole the stylus end, so it produces a cutting edge all around the perimeter of the stylus. The wax is cut by the edge and the cup launches it away while running.

That is true for 2 minute cutters but not this 4M. The 4M I bought has a very small dimple in its center, to small be affect the cut. I'd guess it's .001" - .002". The 2 minute cutters are concave almost to the very edge.