since posting this I have designed a unit to do the job and many more besides. if anyone is interested just let me know and we can work something out.
It's simple and very useful, I have etched flask's tumblers and other round objects, it has changed from the ply mock-up I started with to a fully functioning 3D printed, CNC machined parts that goes together real easy.
I'm selling them at £86 plus postage depending on your location, please ask.
as I make t order and some parts are purchased in the target dispatch time is two weeks from placement of order and payment received.
Full instructions are given and some fiddly parts are pre-assembled so as to make it easier for you.