Next, it was time to finish mitering the chainstays and seatstays and drill vent holes in the BB and seattube before tacking and brazing the frame up. One thing I didn't take photos of was how I capped the tops of the seat stays. For this I basically just used some offcuts from the toptube to create scallops that I brazed on, filed to shape and mitered to the seat tube.

Finally time for some heat. I started tacking and brazing the seat tube to the BB. Then mounted it back up in the fixture to ensure it was all square and that the miters for the rest frame still fit nicely. Being that I brazed the seattube all the way around I ended up adjusting the miter on the downtube so it fit the ST/BB fillet nicely. 
Once I got the fit right I was able to tack up and braze the front triangle. Leading up to this build I worked on getting my brazing speed up while still achieving a good internal fillet. While putting heat to the actual frame I did my best to be quick and I was definitely working faster and laying down better fillets than when brazing up the previous frame, but there's still room for improvement. Once the front triangle was brazed up it was pretty quick work to get the rear triangle pieces tacked on and brazed up as well.

Finally all the main bits of the frame were attached together into one unit. After a soak (in our bathtub since I don't yet have a suitable soak tank) to get the flux off I got to work cleaning up some of the fillets.
For this frame I opted to keep the fillets mostly raw, as this is a prototype/experiment and I felt that spending many extra hours on filing and sanding fillets would be an unnecessary time waster this time around. Therefore I just removed some burnt flux and wire brushed the fillets and linished the tubes to clean them up.

The last thing I had to do before applying the gun blueing finish was to solder on the guides for the brake lines. I know that this should normally be done before brazing the frame, but waiting until now was a conscious decision for this build as I lacked the experience of having built other MTB frames to 'know' beforehand how I wanted to do the routing for the brake line.