well, a couple really.

1.) about what thickness of Ti is used? - im sure it varies, but what is used the most?

2.) on some i see a groove milled into the base of the lock, is this because the Ti would be too thick to operate the lock easily without the groove? at what point (in thickness) is Ti too hard to unlock?

thanks

1.) As you seem to have guessed, you can use any thickness that suits your purpose. On mine, I usually use 1/8th titanium but I think Chris Reeves' Sebenza is closer to 3/16ths. It just depends on how stout the particular knife needs to be,

2.) Yes, the grrove is there in order to make the titanium flex enough to be operable. If you are building the knife for yourself, and if you are built like Arnold, you might not need the groove.:D But, if your knives are intended for the general public you'll want the groove on a knife made with solid titanium slabs.

But, not all frame locks have solid slab handles. Some of mine (and lots of other guys too) use 1/8th slabs that have all the ti milled away down to about 50 thou except for the bolster area. When the lock is cut, the front end is still full thickness but the remainder is as thin as a normal lock and therefore needs no aditional groove. This type of frame lock would have scales mounted on top of the milled area....

My smaller gent's style knives have .090 slabs or sometimes .100. I also use a fair amount of .125 and have recently even made one big honker with .160. As Ray said, the relief scallop has to be milled or ground into the frame so that us mere mortals can unlock the knife. You want to leave about .060 of material for adequate strength. For now I use a dremel with the little sanding drums to grind my scallop in there but I'm getting a small mill very soon.