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Old 29th Jun 2010, 4:53 pm   #24
Aerodyne
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Join Date: Jun 2004
Location: Hampton Vale, Peterborough, UK.
Posts: 1,698
Default Re: Copying a control knob by moulding

I've 'got away' with tapping the resin. After all its a solid lump, not hollow as many control knobs are. I do agree that a brass insert would be preferable; it justs adds to the complexity. It would need casting in situ rather than retro-fitting, so some support for it would have to be created to secure it in place until the resin sets.
I don't tend to take home-made knobs on and off very often!
Another possibility is to cast-in a suitable (say, 4BA) nut or, as I have done successfully on occasions, grind a slot in the back of the finished casting to take a nut. I used a Dremel drill and slotting tool for this. THe grub screw hole should be drilled first, I consider. The nut spreads the loading pressure from the grub screw but accuracy of 'slotting' is essential or the resin might crack when the knob is in use.
-Tony
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