Ok, so I have a dremel 300 series rotary tool and the other day I bought the multisaw attachment and failed to notice that it only could fit the dremel 400 series. I know stupid right?. Since I live in Mexico and bought the attachment in the US, returning it is not an option and to be totally honest, I was kinda pissed off that I'm obligated to buy another rotary tool in order to use the multisaw. Corporate strategy really sucks for consumers.
So in this instructable, btw my very first one. I will explain how to modify your dremel 300 to fit the XPR multisaw attachment and therefore maybe other XPR goodies.
Step 1: Identifiying the problem at hand.
So why doesn't the multisaw fit in the dremel 300?? it's the same diameter and everything. It's very simple really, as you can see in the first pic the multisaw has this two little keys that are supposed to fit into the dremel 400 keyways, as shown in the second pic. So our mission is to make this two symmetrical keyways as precise as possible in the dremel 300. I actually eyedball it and it worked out pretty damn good, you can go ahead and make it as close to perfection as you wish.
Next, required hardware...