You should have used a non-expensive racquet to practice stringing with. It wouldn't be too smart to string a ns8k at 26lbs on your 2nd time stringing.
an expensive lesson, but likely won't be your last... it's broken. so you need to learn from this one. can you determine what happened that caused the break? did the racquet shift or move during the pull? is the racquet clamp loose, or not properly mounted? was there an awkward stress point? was there possibly even a stress fracture already on the racquet you did not see while removing the old strings. of course it's costly, but what has happened - has happened. you need to take the lesson learned here for the next job. but - just don't let this scare you away from future stringing jobs.
I broke one last Sunday. A CY VP700 racket. Broke at 8 clock point. I was trying to put 24/26lbs with a 2-point support machine. I added a support at 9 and 3 clock position to make it a kind of 4-point support. I finished main string at 24lbs. When I started to add 2 lbs at the 5th string of horizontal ones, the bottom half of racket became "fat". When I finished about half of horizontal ones, the frame cracked at 8-clock position. This is my 9th racket that I strung. I normally put 23/25lbs without any problem before. I guess the 2-point support machine isn't any good. But that is what I can get for the price.
I've been using 2 point machine for the past 4-5 yrs, and did not experience any cracks yet. A well made 2 point machine should handle the job without any problems. It might have more to do with: 1. The mounting. 2. The condition of the racket. 3. The stringer's experience. 4. The pattern. Seems you string top to bottom. A safer way to do, is to start from the middle.
I would like to echo what LB said. Also, I am very surprised to see a CY VP700 to crack at 8 oclock. Good news is it is covered by life time warranty. Go to the cybadminton website and follow the RMA direction and you should be fine. May I ask what make and model of your stringing machine? How do you add support at 3 and 9 oclock?
I do from the bottom to top with 2-point method (one string) or from the top to bottom with 4-point (two strings). How do you do from the middle for the cross string? Same as you do for the main? I might try it next time. But I am wondering because you need add 10% tension for the cross, if you start in the middle, will that put too much force and cause the frame top and bottom to deform because there is no string yet?
This broken one is already a replacement. I may hold on to later since I have enough rackets for now. If I bid on eBay, I may get one cheaper than the warranty could offer. I use Eagnas Hawk 15. I bought two long thread rod, add two piece wood rod at each end, make it a kind of rectangular, then put the racket in between, tighten four screws from both side to hold the middle portion of the frame at 9 and 3 clock position. Hope this will hold the frame when I put the main string. Anyway, it seems helpful for me.
Personally, I have 1 issue regarding this device. It's better have a "single action" adjustment than 2 separated one. Reason is, if 2 speparated ones, you have a hard time to see whether the "block piece" is moved evenly from top and bottom or left vs. right. Therefore, there's chance to create unbalanced force when you try to "hold". The blocking piece should look like "| |" from the side. if somehow, it looks like "\ /" or "/ \" or any combo of that, then your racket will be in trouble.
The best is to have two pieces of "< >" on each side, but I just haven't find anything that I can use. Anyway, this is not a long term thing and I need find something better than this later.