I was reading one of Ron Fournier's books the other night, and it mentions that flaring dies (at the time it was written) are typically homemade but very useful. I'm in the process of mounting a fuel tank in a supermodified, and some of the tabs were screaming for dimples, and my tool budget is currently zero, so I decided to give making one a shot.
I decided on a 3/4" die, and made the OD 1-1/8". I was fiddling around with a circle template on paper, and it seems like adding about half the diameter of the hole to be flared makes them look right...so a 1" hole would end up with a 1-1/2" OD flare, 1-1/4" would be 1-7/8", and so on.
I made the OD of the die 1-1/2". Mostly because I had a chunk of 1-1/2" 4130 bar in the shop, but this also seemed to give a nice flat to flatten the sheet back out.
My flare angle is 35 degrees. This I borrowed from the Mittler Bros. aircraft style flares.
The biggest question I had was the clearance...If you make the OD of the flare the same on the male and female dies, it will pinch the sheet, making a big stress riser. That seems to defeat the purpose of dimples, so I actually fired up the computer to lay it out. Because I was planning to do 16 gauge (0.063") sheet, that's what I made my clearance for. This resulted in the OD of the flare on the male die being 1.054". I arrived at this from a drafting layout where I offset the angled part of the female flare by the sheet thickness, and measured the ID.
So here is the resulting die set after about half an hour of fiddling on the lathe...
I made the male die with a 1/2" hole down the center. This is so I could use a 1/2" bolt to squeeze them...I don't have a press just yet.
And here is a sample flare...
And finally, this is the piece that prompted the whole thing. Material is 16 ga (0.063") normalized 4130 sheet. I'm going to start a thread on this in the racecar fabrication forum once it's done.
I'm pretty psyched about the results. So much so I figure on making some more of them in other sizes. It's definitely not rocket science, and I wish I had done this a long time ago. Granted, my die isn't as nice as the Light Racing version, and not heat treated, but I have all of about $1 worth of bar stock and some time invested.
So, if you have access to a lathe and some time, it's definitely worth a shot to make these.