Our friend Ray (walleyeman) used an 'Engine Lathe' (Lathe for turning metal) for making his brushes.
He used metal and Inlace Acrylester. The acrylester came in rectangular pieces. He told me that the three pieces were joined with a small bolt. Here's a few pics that he'd sent me while making a custom brush. Note that he used some kind of a 'jig' to be able to make repeatable pieces--
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Ray said that he used a rag and Mother's Mag and Aluminum Polish to finish polishing the acrylic and metals in his brushes.