As your woodworking skills expand, you'll want to consider adding a jointer and a thicknesser to your repertoire of tools. They both treat rough lumber in similar ways, but they aren't the same tool.
Most large woodworking projects require certain tolerances and exactness when lining up ends of lumber. Unfortunately, the wood you purchase from big box retailers and suppliers are never completely straight or flat. Warped, twisted, and cupped lumber are unsuitable for building furniture. A jointer and a thicknesser can remedy this.
A jointer is used to make a board perfectly flat and will remove warps and twists in the board. So you'd run rough lumber through a jointer first, and then a use a thicknesser (known in the US as a planer) to get the board to a consistent thickness and perfectly parallel.
Quality jointers like this one from Delta are available for $US288 but can run up to $US1500. A benchtop woodworking thicknesser like this one from DeWalt is a bit more expensive at $US399. You can also buy a combo unit from Jet that combines both tools, these run $2799.
By using both tools you'll end up with straight, flat lumber that is suitable for any woodworking project.
What does a jointer do? [Matthew Cremona (YouTube)]
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