Older polisher modification

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I have a twenty five year old Black & Decker 6124 polisher/buffer. It is a single speed that seems too fast to me. Does anyone know about making the polisher into an adjustable unit. I’m too cheap to buy a newer polisher.
well if I were you I'd buy a new buffer If I remember that old buffer runs at 1800 rpm and the new compounds are not using more than around 1000 rpm. yea I'm to cheap to but if your trying to polish a car that is the way to burn it if your grinding trust me I've been there get somthing you can slow down