Hi, sorry about the old links. That's a problem when other sites move/change stuff.
First, WHAT tool do you have for doing bubble flares? It should come with instructions.
Second, check out Youtube videos. They are helpful. But, like the rest of the web,
THERE IS A TON OF WRONG / INCORRECT/ BAD / MIS-INFORMATION in some videos. So, just because some clueless person does something, doesn't die from their moronic act, and posts a video of it, does not mean that it's the smart or correct way to do something.
Basically, it's a
lot of work to do a flare
correctly! But, people HAVE AND WILL still do BAD/STUPID flares, not have them fail right away, tell others, and have others do the same DANGEROUS methods.
I try my best to tell people the
right way to do things. I like to think that I didn't waste all of my time in school and on the stuff that I've done professionally.
With the above said:

For flaring you should/must do the following
(most common errors)
o Use a sharp tubing cutter to cut the tube. You need a square cut.
Use a flat file to do a
very light cleanup on the tip.
o Ream the inside of the tube. I have a tubing reaming that takes me under 60 secs to do it right and correctly.
o Angle the outside of the tube. This is the hardest and most time consuming part since it requires an "artistic" eye and ability. And, I have ZERO artistic ability. You don't want me doing visible body work on any vehicle!
You'll end up with the end of the tube in a "V". Now, the thickness of that "V" is important. Regardless of any BS you read, experience is the only way to get it
Now, when you do the fold for a double flare, or the additional fold for an ASE double flare, the metal folds properly and without "bulges".
So, try a few flares. Take 1-2 hours to get it down right. Or, say *****-it, do a half-*ss job, and risk your life and the life of others. Now, what do you think makes more sense?
Do a Google search. Do a Youtube search. But please, be careful and don't trust everything you read. I think that it's ??Carcraft?? that has the moronic article on flaring (setting themselves up for a lawsuit among other things) . They say it's for flaring Stainless Steel brake lines, and they show it doing mild steel (typical) brake lines. A flaring tool for Stainless Steel brake lines costs at least ~$400 and is VERY heavy duty. It takes a LOT OF FORCE to do a
proper Stainless Steel flare.
As I mentioned, there is a ton of bad info out there! Most by people that are just repeating stuff they heard, or read, or done. That does
not mean that it's correct information.
Last, a bubble flare is "basically" half an SAE Double Flare. But, make sure you have the correct ISO
Bubble flare inserts with the correct angles.