I'm sure there are half a dozen threads on this subject already, so if the only reply I get to this is a link to one I'd be grateful. I've been doing extract+specialty grains for a while with no real interest in doing all grain (too much time and money for me to commit right now). I do like the idea of controlling my beer more, though. Partial mash is pretty much an enigma to me beyond the basic knowledge of what's going on. I have just the basic questions right now:
What additional equipment would I need?
Will the cost-per-batch decrease?
How does one do it (in layman's terms)
Should I bother right now?
Who wrote the book of love?
For additional equipment, possibly none. I used a huge mesh bag, and just did partial mashing in my bottling bucket, until I got an MLT.
Yes, the cost should decrease, as grain is cheaper than extract. How much is really up to you. If you use, say, 5 pounds of grain at $6, and replace 3 pounds of extract at $12, that's $6 for one batch right there.
How you do it is simple. You take the crushed grain, and add it to water. The amount of water is 1.5-2 quarts of water per pound of grain, and you want to hold the mash at 150-155 so you would use water of about 165-168 degrees to do that. Hold that for an hour (wrapped it in a sleeping bag, or put it in a warmed and turned off oven), and then lift out the grainbag and pour 170 degree water over that, up to your boil volume. That's about it.
You should do it! Right away!
It's easy, and it makes great beer. Plus, you can use malts that are "mash only" malts or adjuncts- like flaked corn or oats, or Munich malt or Vienna malt.