Thanks for all the answers chaps!
I was really hoping for some amazing answer that would mean I'll never get a crinkly bend again, but thats just wishful thinking.
It's a Rothenberger too!! Perhaps that doesn't mean much these days - probably owned and made by someone else anyway. Only a couple of years old and hardly used - maybe they get better with use?
I might try a little packer between the former and roller, that sounds like it might help, but you'd have thought they'd make it properly in the first place...
What bugs me is that on the same length of pipe, I can get a good bend on one section, turn it round, bend another bit, and get a crinkly one!! Isses me off.
So which is better at smooth water flow - a crinkly bend or a smooth elbow?
Any other ideas gratefully received. If I work out what I'm doing right/wrong I'll let you know.