Originally Posted by
3alarmer
Look at the
Sheldon Brown link for a visual, but the 2X4 on the ground thing will drive you nuts, because it's hard to control.
I haven't had a problem controlling the spread using a 2X4 and I use my foot. The only time I had a problem was when I tried the threaded rod method on a mixte, but I was able to straighten out the frame using Sheldon's instructions. I don't use a string as he recommends. I use a straightedge and digital calipers. I have a crude tool I made from a couple of axles for dropout alignment.
If you're not comfortable with Sheldon's method, don't use it.