I have come up with a way of doing this out of need. I am not sure how others do it.
First the vertical main top is cut, shaped and welded together in the front.
This is then placed on a sheet of metal and traced around with about an inch extra.
The top plate is then cut out and dished to the desired shape. This top plate is now welded to the upper piece on the inside only.
The Beverly is used to trim around the helm crown and it is then ground with the right-angle grinder equipped with a tiger wheel, to fit flush.
A strap is rolled around the top and bolted in every hole. This strap will generally not lay down flat to follow the contour of the tapered helm so it is heated red and tapped into place with a polished hammer.
It is then removed and smoothed on the Grizzly belt sander. Then it goes to the motor mounted flap wheel, then to the buffing wheel. This finishing is important before the final riveting.
Now you know my secret. It works for me, your mileage may vary.
Hal
Ps: This is a pic of a similar helm with out the trim strap:
http://home.armourarchive.org/members/h ... /mine1.jpg
actually it was an evil scheme to shame you into putting this prize in my hands 
Apparently one that failed 
How, exactly, do you expect me to catch up to you when you keep producing awesome helm after awsome helm? Maybe you could take a couple decades off while I gain some experience?? 
How can you? Let's burn Tim the infidel at the stake folks! I'll get the wood.
