I was wondering if anyone could provide me with some ideas on how to cut clean 45 degree mitres using the track saw These mitres are 65" long. The White Oak veneered sheet is particle core and is 3/4" thick. I'm cutting along the grain, not crosscut. I've tried every Festool blade for my TS55. The problem is I cannot get a clean cut. Cutting at 90 degrees works great, it's only when I tilt the saw 45 degrees does the veneer starts to chip.

Thanks,
JC

My first thought is about the condition of your splinter strip. How long has it been since you replaced, or at least moved and re-cut it?
I have never had this problem and I do a lot of miterfolding, usually with HPL, but a good percentage of veneer too.
Most people's complaint in this area is actually about the bevel itself not being straight, so before you get to crazy about the finish of the cuts, be sure that they are straight. 65 inches is pretty long, you have to be pretty careful/diligent to get good fitting cuts like this.

Oak is fairly chippy in the first place, so maybe covering the cut line with blue tape could be helpful. You just have to be careful when removing it after. Pull the tape straight back and not upward, you could make it worse with the tape by using bad removal technique.