Julian,
I don't want to appear negative here but with something as simple as this do you need plans ?
We have the internet for pictures and ideas, we have forums for help from like minded people, why do we need to be tied to an actual set of plans for something so simple.
You say you need to scale up so you are halfway there.
Now this isn't aimed at you but recently someone on another forum posted a picture of a rear tool holder, just a block of metal with a slot cut in it for a tool and 3 clamp screws.
So some Herbert comes gushing up do you have a drawing for this ???WTF ??
It's a block of metal with a slot and three screw holes the bottom of the slot is determined by your lathe, not any drawing.
You can't but drawings for everything you make, take that 'rotatable workholder' does it have a bearing in in, does you scrap box have ant bearings?
Can it index in steps for hexagons etc? do you have a scrap gear in your scrap box you can build one out of.
If Guy Lautard can ' design' one you can improve on it.
Rant over and no it wasn't related to you but every beginner, learn to think and you will climb that beginners hill faster.
JS.
