Sadly, MDF jambs are seen more and more these days. I hate them. Just can 't stand them. But sometimes when I trim out a project, they are there... and since one of my hats is a "trim" carpenter... I use what is on site. I don't like them because they aren't rigid enough to keep the jamb from def lection, are more prone to movement due to humidity than wood, and worse, t hey take double the amount of time to shim them properly when hanging as yo u need twice the shims.
So, bad news. MDF comes in all types of densities, resin bases, and prep m ethods. Cutting with hand tools is tough. Cutting and maintaining the dep th you need to properly set a hinge is almost impossible with a chisel.
Porter Cable to the rescue! I bought this gadget several years ago and hav e used it to hang a couple of hundred (I do mean that literally) doors. Th e double headed nails are long gone, replace by fine threaded sheet metal s crews. It works well if you are patient, set your router right, and do a f ew test cuts to make sure you understand the setup and use of the template. And it even comes with a "perfect fit" router bit matched to the jig and will cut a nearly perfect radius for almost all hinges.
I dismissed this as a plastic piece of crap when I saw it, but my old comme rcial rep told me to try it, and bring it back if I didn't like it. Now it is a permanent fixture in my door kit with the attending router, hole saw kit and 1" paddle bit for latchsets and deadbolts.
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These are also available at some Home Depot stores, which is where I bought mine.
Robert