Jointers and Planers
People often ask "...which is better to own: a jointer or a planer?"
In order the fully enjoy the benefits of either machine, you need both. They truly compliment each other. Actually, to properly prepare wood, you need three machines, a jointer, planer and a tablesaw (that's assuming that most people start off buying a tablesaw, some feel a bandsaw is more important than a tablesaw). A jointer will make wood flat (relative to length), either one flat edge or one flat surface. A table saw can make the other edge parallel to the flat edge produced by the jointer. A planer can make the other surface parallel to the flat surface produced by the jointer.
Think of it this way:
Or more thoroughly:
ONE WITHOUT THE OTHER
What if you used a jointer without a planer? Unless you've got patience and great skill and some luck, you'll end up with finely tapered wedges. Both surfaces will be flat, but they won't necessarily be parallel. So it won't be of uniform thickness or uniform width. What if you used a planer without a jointer? You'd end up with a board that was of uniform thickness or uniform width, but it wouldn't be flat nor straight.
COST SAVINGS VERSUS CONSITANCY
People often ask if they can justify the cost of a planer and jointer with the cost savings of buying rough sawn wood.
I initially thought I could justify buying a jointer and a planer by buying rough-sawn lumber. Then I learned that you buy these machines for the control it gives you. These machines let you control the consistancy of wood size that only comes when you do it yourself. A lumber mill is designed for speed, not accuracy. If you can find enough surfaced wood at a lumberyard or retailer for a medium size project, that is all all perfeclt flat and straight and exactly the same dimensions, then you are luckier than most woodworkers. These machines also let you compensate for natural board twisting that occurs due to moisture change, stresses after cutting, etc. I often take a piece of wood that started off flat from the jointer, and watch it become two bent pieces after ripping it in half. The internal stresses are often released in a board after it's ripped and cutting a flat, straight board doesn't always give you two flat, straight boards.
Additionally, you can't justify buying these machines by the price difference between rough-sawn and surfaced wood from the mill. Of course there's a huge price difference in price between wood bought at a HomeDepot of other retail places compared to a lumber mill. I used to buy red oak from a national chain home/building center for the equivalent of $8-9/BF and now I buy it for under $3/BF from a lumber mill. But many lumber mills sell surfaced wood for only a few cents more per board foot over rough-sawn wood. They often will surface wood for an additional charge, but the charge is usually not much and you won't be able to justify spending $1000 or $2000 on a jointer and planer. You buy these machines for he control and consistancy that you can only achieve with useing them.
I use a jointer and planer to prepare my own stock for CONSITANCY, not cost savings.
COMPARING JOINTER AND PLANER SIZE
I'm not sure why we start off buying a 6" jointer and a 12" planer, but we usually do. After a while it starts to make sense to have machines of equal size. If cost were no option, a 12" or 16" version of both would be ideal. But few of use have the $3500-$9000 it can cost for that size. Even the few combo jointer-planer machines in that size from Europe are very expensive.
In the beginning, I thought that I'd want a $500 6" jointer with a $1000 15" planer. So I bought my 6" jointer and bought a $350 12" DeWalt lunch box planer, thinking I'd upgrade to a Delta 15" planer when I had the money. I discovered something completely different. I decided I wanted a larger jointer, not planer. So I upgraded my jointer to an 8" DJ20...... And if I could, I would upgrade (and spend $2500-$3500) on a 12" jointer before I upgrade my little 12" planer. My advice to most hobbiest woodworkers (doesn't apply to everyone) is spend ALL your money on a jointer, and buy a little lunchbox planer. A little lunch box planer doesn't have the power to quickly process really rough sawn wood, like a big heavy planer can. But a bigger jointer can do that, leaving just a little surfacing neccesary that a small planer can handle easily.