thank you very much. i've just finished a wing armature using this method.
its mainly down to the creating of a new ball, which allows the slot to be much thinner than it would have to be for balls without modding.
i must get myself a dremel, its something on my buy list. is there any that you recommend?
and your PPE tut explains it way better than i could ever hope to. it really is the go to guide for PPE.
i wish you luck if you try this, and if you have any questions, or get stuck at any point, feel free to ask 
My brother bought me a 300 series for my 21st birthday a couple of years ago tinyurl.com/krjpjnb It came with a huge selection of parts and once I'd played with them all I worked out what I needed - metal drilling parts, diamond engraving bits and more sanding attachments. I use the sanding attachments all the time to grind down cured resin overflow and flashing, to work with metal and wood, I used it non-stop through uni and I think it only cost something like £30-£40. The grinding parts are a little flimsy but I think I misuse them quite a lot, and I wonder if a more butch version would suit me more but I'm very happy with my little 300 series atm. It serves me well!
I'd like to get some of the big attachments you can get, like the workstation tinyurl.com/lw8v3zv or the flexitip thing but they aren't essential. It's pretty light, and because it's corded it doesn't run out of battery which can be irritating