Edit: 12/19/2011: I have written up a more concise and better illustrated narrative on how to install the Emmert Pattern Maker's vise here.
As a result of some of the comments I got from the last post, I wanted to show how the final product turned out, and write up a more cohesive and useful narrative for anyone who's planning on installing one of these, or building a bench around one.
If I were building a new bench, the top would be full thickness all the way across. I'd laminate all but the last 2", mount the vise, and then get ready to laminate one more piece of wood. I'd also spin the jaws on the installed vise to measure how much clearance I actually needed for the vise to rotate, and cut the last lamination accordingly. On a scratch-built bench, the clearance would probably be under an inch. and then thickness the last piece to be parallel to, and about 1/8" behind the extended plane of the rear jaw of the vise. I know this seems weird. It was in the original instructions for the vise, and it took me a while to figure out why. The jaws rotate. And there's a lot of mass that will be rotating. If you're off a bit, and you go to rotate your work, there's a chance you'll crunch your work into the top edge of your bench. Not cool. If you really need to clamp to the front of the bench, it's very easy to make an L-shaped shim to hang over the front edge, so you can clamp the work to the front of the bench. where the long arm of the L-shape rests on the top surface of the bench.
Another judgment call was the placement of the vise with regard to the left edge of the bench. In this case, I placed the vise to align with the dog holes that I have on the bench as it came from the factory. There's just over 2" of bench sticking out past the left-most edge of the vise. I don't think it's really going to get in the way of my ability to work, but on a new bench, I'd mount the vise all the way at the end, and drill my dog holes to line up with the vise once everything is in.
Notes on installing an Emmert or Emmert clone:
(edited on 1/27/11 to be more readable)
I assume that anyone who's trying to mount one of these beauties has done at least a little bit of homework first. There's a lot going on here. I also assume you've read enough to know to take most of the vise apart, and work on the install with the least amount of weight possible.
The most visually obvious thing that needs to be laid out is the recess for the plate, and the holes for the three screws. You do NOT want to lay out those screws until the absolute end of the install. There are two more hidden screws that will hold the vise up while you trim and shim to get it aligned and perfect. Once you get it in the way you want it, then you'll know where you need the holes to be, and you can lay out and drill.
I was really, and justifiably, concerned with getting the mount laid out and drilled just right. The placement of those three holes determines the alignment of the vise with regards to the bench, and if they're even a little bit off, everything will be thrown off, even if it's only a little bit. Given the amount of wood that has to come out just to mount the rear jaw, the thought of getting it wrong only after you've done irreparable damage to the bench top is pretty high on the list of things that can persuade someone to steer clear of the greatest vise ever made.
I think it's conceivable to measure and lay everything out so that it will be perfectly installed with no errors. I also believe that weird things happen, iron castings are reliably not 100% square or straight, and that the human mind and hand are both fallible. A bench top is a huge, expensive, ponderous expanse that will display every evidence of your failures if you aren't able to grapple a little bit with the process of mounting your bench vise. No pressure. : )
This is usually where I cringe, because as sure as the day is long, I'm gonna slip up somewhere, and I do NOT want to be the yuppie bastard Emmert owner who owns an Emmert vise, but botched the installation, thus proving that I'm unworthy. In the process of hanging this 90 pound monster, I learned the following: Have faith. There's a lot more wiggle room than you think.
In addition to those 3 big mounting screws, which render every error permanent, there are also 2 more mounting screws behind the rear jaw, in a horizontal orientation, which will give you the time to figure things out a bit. Those 2 hidden screws will give you the wiggle room you need to get the install done as accurately as you are hoping to. Do all of the underside excavation first, and rout out the recess for the mounting plate. You may also have to do some hand work to get the fit right... my mounting plate was tapered in thickness from back to front. Once the plate will fit into the recess, mount only the rear jaw, using only those two horizontal screws, and trim and shim until you're happy with the alignment of the rear jaw. You can keep removing the vise while you make adjustments to the notch, until everything is just right. There's room for trial and error. Once you have the rear jaw alignment dialed in, with those two back screws nice and tight, then you can mark out the three holes for the top screws in the mounting plate. Those three screws are just the punctuation mark at the end of the sentence... the finalizing step in the long process of getting it just right. They are not the leap of faith that I was terrified they would be.
I have to point out that accuracy in drilling is important here, because the nature of countersunk screws is to completely mis-align everything if you don't drill the holes just right. But if you've made it this far, you should be just fine...