Monday, March 15, 2010
Does a Planer Belong in Your Workshop?
In the “old days” (whenever that was) lumber was simply sawn out of logs and left to air dry. If you wanted to be able to see the grain so that it could be matched with other boards, it had to be planed. If you wanted it planed, you needed a long bed hand plane and a lot of skill. With the invention of the planer, no one needed to plane boards by hand any more and the practice stopped in the name of “progress.” Today, most boards are delivered already thickness planed and some are even straight line ripped on one edge, making things very easy for the woodworker. So, why own a planer?
Thickness planing does not end at the lumber yard. Lumber, once edge glued into panels is still uneven and the boards are never in perfect alignment with each other. Something must take this rough panel from, say, 1 7/8” down to its final thickness of , say, 1 ½”, smooth both sides. There are two ways of doing this that I know of: an abrasive planer (wide-belt sander or drum sander) or a planer that uses knives in a cutterhead.
A combination of a knife planer and an abrasive planer would be ideal but not always affordable. This is because planers have a way of tearing chips out of loose grain. They are, however, much faster in removing material than a sanding machine. A sanding machine will never tear out chips but it may use up a lot of valuable production time. So, in an ideal world, where money didn’t matter, you could do most of the thicknessing with the planer and then finish up to the final thickness dimension with the sanding machine.
In fact, if you have the money and need to do your woodworking on an industrial scale, there are machines with a planer head followed by two or more sanding heads. I had the chance to use such a machine for several years. A friendly competitor bought it for his woodworking firm in Hawaii and had it shipped in by ocean freight from the mainland.
This giant machine, made by Cemco, used 880 volt, 3 phase motors. A ten HP motor ran the conveyor belt and the one planing and two sanding heads each had 60 HP electric motors. It could plane and sand panels 52 inches wide. In size, it looked like a large, industrial printing press. My friend bought into a sawmill and had Hawaiian Koa wood shipped by barge from the Big Island to Oahu where he had constructed a dehumidification kiln next to the Cemco machine. Eventually, he over-extended himself financially and had to close his business. He found a buyer for the planer/sander but he had to ship the huge machine all the way back to the mainland because no one in Hawaii had a use for such a machine. Of course, I don’t know what your plans are for a planer but I’m pretty sure you won’t be buying a Cemco any time soon. That still leaves a lot of sizes and types of planers to discuss.
A planer/jointer uses the same cutterhead for planing as it does for jointing. It looks like a jointer but it also has a space underneath the jointer table where you insert boards for planing. You feed the boards in one direction on the jointer table, above the cutterhead, and in the opposite direction through the planer underneath the cutterhead. This is because the cutterhead only spins in one rotational direction. A planer, if it has molding capability becomes a molder simply by removing the straight knives and replacing them with profile cutters.
Most planers are constructed with the cutterhead mounted in the top part of the machine and a metal table with rollers underneath the lumber being planed. The thickness is adjusted by raising and lowering the table with relationship to the cutterhead above. The lumber is driven through the machine by the front roller or rollers which are usually serrated for better grip. The outfeed rollers are at the same height as the infeed rollers but they are usually not powered and are shiny and smooth. There are some large, expensive planers in which all rollers are powered.
There are three types of cutterheads: straight knife, spiral and helical. The terms “spiral” and helical are often used interchangeably although this is inaccurate. There are strong similarities between the spiral and helical types but there IS a difference as I will explain. Straight knives are used on most planers in the less expensive range. For the most part, straight knives are fine but they do have two drawbacks: they are difficult to align with each other after changing and they tend to tear out loose grain more easily.
Helical and spiral heads get around both problems to a large degree. It has been found that a bunch of small cutter blades arrayed in a spiral wrap around the cutterhead will minimize splintering. Helical knives are usually square or rectangular in shape and sharpened on either 2 or 4 sides. They are mounted directly onto the face of the cutterhead and, thus, require no adjustment to align them with each other. To change a cutter in a helical head, you simply remove the screw that holds it in place. If there are unused edges on the cutter, you can rotate that cutter to exposed the new edge to the wood and then replace the screw. You buy cutters by the box and replace them as needed: Sometime you replace just a few that have become nicked. At other times, all cutters have been dulled on all sides and it is time to replace them all.
The spiral cutterhead is different from the helical head in that Spiral Planer Cutterhead, a whole row of cutters, connected together in a flexible strip are attached to the spiral head, One row at a time. There are spiral tracks or indentations in the heads that locate the cutter strips. There may be three or so tracks on a spiral cutterhead. Helical cutterheads are much more common than spiral heads.
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©2010 Robert M. Gillespie, Jr