The Thickness Planer

Smooth rough-cut wood stock with a planer.

Thickness Planers

Photo: dewalt.com

The planer is a tool for woodworkers who require large quantities of planed stock and who elect to buy it rough cut. A couple of trips through a planer and smooth, surface-planed stock emerges, often at a fraction of the cost of the milled boards sold at your neighborhood lumberyard. This tool is also known as a surface planer.

(Note, however, that in order to plane rough-cut stock successfully, the board must have one true face. If neither face is true, a jointer/planer can be used to smooth one face, then the other side can be planed parallel to the first on the thickness planer.)

The freestanding planer is a near relation of the jointer/planer. It, too, cuts with a cutterhead, but the planer smooths the face of much wider stock. Benchtop models will plane twelve-inch-wide stock, but some freestanding models will plane pieces with widths of thirty-six inches or more. The size of the machine is determined by the thick­ness of the stock it will plane. Most twelve-inch planers will plane stock up to six inches thick; eighteen-inch planers take nine-inch-thick stock. Planers of these sizes typically have between one and a half and three horsepower.

The cutting is done from above rather than from below. The workpiece is presented to the machine by hand, with one face against the feed bed. A pair of rollers, one at the front and one at the machine’s rear, then power the stock through the machine at a constant rate. Be­tween the rollers is a cutterhead with several knives affixed. The knives do the actual planing, assisted by a pair of bars that rest on the stock as it travels through the planer.

The first bar is called a chip breaker, and it helps prevent the grain from tearing out. The second, called the pressure bar, keeps the stock flush to the feed bed. The design of the machine – with the cutterhead contained entirely within the housing of the machine – means that, unlike the jointer/planer, with which this machine shares many de­sign elements, the surface planer is relatively safe to use.

Surfacing the Surface. The planer must be set to suit the stock to be planed. The feed bed is adjusted to the proper height, so that no more than about a sixteenth of an inch is planed in any one pass. Most ma­chines have a feed control wheel that adjusts the speed at which the stock glides past the cutterhead.

When setting up the planer, be sure to measure the thickness of the stock at the corners and at the piece’s midpoint. Set the planer to sur­face the stock at one sixteenth less than the maximum thickness.

If the stock tapers, lead with the thinnest end. As you feed the stock in, stand to one side. Support the stock so its weight doesn’t lever its top surface into the cutterhead. Once the planer has planed about half the length of the piece, go to the other side of the machine and support it there. Or, better yet, have a helper stationed to receive it as it emerges.

Again, keep in mind that if you’re planing to surface rough-cut stock (boards that haven’t been planed smooth, but have the toothy surface left by the big blades at the mill), you must be sure they have one true surface (or make one true with a jointer) before surface plan­ing.

If you’re planing thin stock (wood less than three-eighths of an inch thick), you will need to use a carrier board. A piece of three-quarter-inch plywood will do; make it the width of the planer and slightly longer than the stock to be trimmed. Compensate for the added three-quarters of an inch when setting the height, and feed the carrier board and the workpiece together. Be sure to set the carrier board aside for future use.

Most planers won’t take stock less than twelve inches long (the dis­tance between the rollers). If you need to plane shorter pieces, follow up the shorter one with a piece of scrap of the same thickness that’s twelve inches or longer. It’ll push the short one through.