On 2005-04-29, wrote:

I am about to try and hang my first doors and have learned from
various places [. . .] One suggestion I've read involved cutting a
1x2 brace of the final door width + 1.5in (2xwidth of jamb stock) +
say 1/8in for the hinge side gap and tacking that flush to the
outside edges of the jamb assembly while shimming to ensure that the
desired opening is maintained.

This sounds like a good idea, particularly for a non pre-hung door. A
small allowance for a gap on the non-hinge side should be made.

What also comes to mind (though I haven't read this anywhere) is to cut 2
braces of say 10" in length and tacking these so as to brace the top corners
in a 6/8/10 triangle thus ensuring the tops of the jamb assembly are square.

This could be done, and I've seen windows come this way, in which case
it makes sense to leave these braces on while installing the window.

However, for a prehung door, the usual simple way to do things is
this: remove the door from the jamb. Position the jamb approximately
correctly. Plumb, straighten, align, shim, etc. the hinge side of the
jamb. Reinstall the door and close it. Use the door when shimming
the non-hinge side of the jamb to get an even reveal between the door
and the jamb on the top and non-hinge side of the door.

Cheers, Wayne