Forgot to mention, to test the BH alignment either use an arrow spinner, or just stand the arrow up on its point and give it a good spin, works great on a piece or wood. Watch for either the end of the nock or the BH end to "wobble" at all. They should spin perfectly. If not, then either the arrow is bent or the BH/insert is not aligned perfectly with the shaft.

How do prevent the insert from being off centered?

Square off the end of the shaft before glueing it it. Then square off the end of the insert after the glue dries.

OK here is my whole process that I do. I started doing this after takeing my arrows to get cut at shops and they were always cut uneven ie slatted cuts. and bad. I got my own arrow saw I cut to my desired length. Then I take a arrow squaring device (ASD)to both ends. trust me I can see the difference useing it. Then I install the nocks and inserts I use goat tuff for this process. Then I mark the insert with a black magic marker just the very end and then use the ASD on the insert until its square which is when all the magic mark has been removed. Then I install my broadheads on 5 arrows and then I also use a slight right helical on my arrows for flight stability. I also align the blades of the broad head with the vanes themselves. My broadheads shoot the same as field points and I also spend alot of time to get my bow perfectly tuned. Some of this might be myth but all together I believe this make for perfect arrows. Since I started doing this alot of people have started getting me to build there arrows becuase they shoot so much better and are more accurate. Also tuning is a big key of broadheads because you just added wings in front so where ever it points is where it will hit.

I shoot light for speed. i am shooting 85 grain field tips and 85 grain thunderheads and they fly identical. try finding the same grain field tips as you are shooting broadheads