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Knife planer: technology shaves time and money.

Long associated as a woodworking workhorse, today's knife planers not only work harder, they work smarter.

One of the oldest pieces of machinery to be found in large or small shops is a knife planer. These noisy, typically cast-iron-base machines may in some cases have been manufactured before the last world war but they are still capable of producing a smooth finish. Some foremen will admit that the only repairs performed on their planers have been the replacement of bearings, knives or a motor. Still, they remain amazed at the paybacks their planers have given them.

Considering the rising cost of lumber and increased use of No. 2 common hardwoods, wood products manufacturers, in their quest to achieve maximum optimization of their raw materials, are closely scrutinizing all areas of production including knife planing operations. Once a wood products manufacturer puts his knife planing operation under the efficiency magnifying glass and studies the new equipment market, he will find that machinery manufacturers are responding with planers that offer smoother cuts, increased feed speeds, plane to tighter tolerances and reduce power consumption.

In short, woodworkers studying the marketplace will quickly discover that even if their venerable planer is not broken, replacing it with a new one might help improve their lumber yield capacities.

"Because of the new developments and technology used in today's planers, woodworking operations are able to increase their yields from eight to ten percent in their planing operations alone," said John Foster, sales manager with Newman Machinery.

Two main classes

When classifying single and double head knife planers, there are two distinct classes -- rough mill and finishing planers. The functions of both machines are similar, but their applications vary greatly.

"A rough mill planer is a machine that has to be built to take some abuse," said Claude Sutton Jr., owner of Sutton Woodworking. "Most are built of cast iron and they must be able to handle rough lumber that varies in width, can tolerate hitting knots and other foreign material, and be strong enough to hold down warped boards."

Rough mill planers also have higher feed speeds than their counterparts, often operating at around 300 feet per minute, and usually feature automatic loading.

Finishing planers, on the other hand, are designed to handle wood products such as glued up panels that need to be calibrated and are used on woodworking components that require tight tolerances.

"Most finishing planers use a small diameter cutterhead so that the chip breaker and pressure bar are closer together. Thus the panel can't lift and become thinner at the edges," Sutton said.

Operating at slower feed speeds, around 60 feet per minute, most finishing planer operations are hand fed because smaller parts are often involved.

Shaving time

A decade-old development that made its appearance in the knife planing industry has been the acceptance of the helical cutterhead. Unlike traditional cutterheads that use straight high-speed steel knives to plane surface material, the spiral design of the cutting blades on a helical cutterhead slowly circle around the cutterhead and approach the cutting surface at an angle. The action is similar to that of the old-fashioned reel type lawnmower blades.

"Since the planing blade is approaching the wood at an angle, the blade is actually milling the board versus a cutting action," said Foster. "It also causes the head to run quieter and with less vibration than traditional cutterheads. And if OSHA says quiet your planer down or shut down, the helical head is an attractive alternative."

Blade composites of helical cutterheads differ from those of traditional cutterheads. The cutting blade is constructed of individual carbide knives positioned adjacent to each other and held in place with set screws instead of a straight, one-piece strip of high-speed steel. The carbide cutters are also reported to offer longer life than their high-speed steel counterparts.

"Carbide blades only have to be sharpened every other month instead of every day like high-speed steel," Foster said. "But when resharpening the carbide knives, remember that for most cutting applications, carbide knives are ground at a different angle than high-speed steel."

Cutter bit hook angles can vary from manufacturer to manufacturer, but attention to the species of wood being machined and grinding the tool to the correct angle can result in an improved finish with less pick out, longer cutting edge life and reduced horsepower requirements.

"Hardwoods such as oak and maple, particularly bird's-eye maple, respond well to lower hook angles such as 7 degrees," said Jeff Machacek, vice president of sales with Northfield Foundry and Machine Co. "With softwoods, such as southern yellow pine, you don't have the rigid cell structure of hardwoods. So we use a 25-degree angle with a Tantung cutting surface because the Tantung resists the resins better than carbide."

Another plus about helical cutterheads is that a company does not have to buy a new planer to experience some of the benefits of helical cutterheads. According to Sutton, planers can often be retrofitted with a helical cutterhead after the standard head has been removed. But a company should contact its planer manufacturer to make sure the manufacturer can perform the refitting.

Faster feed speeds

Increasing feed speeds have been a goal of companies trying to increase productivity, yet one optimum feed speed rate for one company might not be best for another.

"The key to finding the optimum feed speed rate is running the planer at a speed that doesn't cause problems with your downstream handling equipment," said Phil Gusloff, chief engineer with Yates-American Machine Co.

Knife marks per inch can be relative to the quality of the finish and are also affected by feed rates and depth of cut.

"Generally, the more knife marks per inch, the better," said Foster. "For rough mill operations, seven to ten knife marks per inch is a good figure to aim for, while finish planing should range between 16 to 18 knife marks per inch."

Going digital

Many of the planers on today's market offer digital thickness control standard or as an option so that operators can more precisely control a planer's depth of cut. Advantages of digital thickness controls are higher yields, improved accuracy and ease of operation.

"Customers requested a planer that was easier to operate," said Machacek. "Manufacturers responded with digital measuring equipment that primarily eliminates errors and in some applications, allows push-button conversions from inch to metric."

Motor efficiency

Today's electrical motors have been designed to be more efficient than designs of the past. Design improvements such as enclosures filtering out pollutants like sawdust, while allowing a fan to cool the motors, have been credited with allowing the motors to operate as high as 95 percent efficiency.

"In some areas of the country if you want to apply for a business grant, one agreement could be that your equipment has to operate with high efficiency electrical motors to reduce the drain on the local power supply," Gusloff said.

Knife planer sanders

Another member of the knife planing family is the knife planer/sander, which has found a niche in the woodworking market. Knife planer/sanders offer the advantage of helical head planing and sanding in one pass, resulting in a quality finish that allows some end users to eliminate the necessity of having separate knife planing and belt sanding machines.

"The most popular configuration of planer/sanders with our customers has been the one cutterhead, one sanding belt setup," said Harold Kapaun, sales manager-woodworking division with Timesavers Inc. "But configurations with top and bottom cutterheads as well as one, two or three sanding belts can be constructed."

Uses of the knife planer/sanders have found their ways into a variety of industries because of their ability to meet high tolerances.

"The knife planer/sanders have the ability to meet tolerances from 0.003 inch to 0.005 inch," said Gene Brooks, marketing director with Cemco Inc. They can be used by panel manufacturers to sand glued-up panels and by panel mills interested in performing value-added services. The head design, feed speeds and rake angle geometries will allow for the machining of particleboard. Glue resin build-up on the blades hasn't been a problem.

In the past, abrasives cost on glue lines were higher with abrasive planers because there were problems with glue resin buildup. But this is eliminated by putting the cutterhead in front of the abrasives, Brooks added.

Some changes

When asked what trends were appearing on the horizon of planing technology, the responses varied. They include:

* More affordable electronic equipment such as measuring and quality control devices will appear on planing equipment.

* Feed speeds are expected to increase, and that will increase the amount of friction generated by the cutterhead.

* Expect to see additional cooling equipment, such as watercooled planer beds and fans to keep the planer cool.

Meeting the demands of tighter tolerances with minimum waste production will continue to be a challenge for planer manufacturers. But by working closely with these woodworking manufacturer customers, planer manufacturers stand a good chance to reach that goal.


If your planer is not squaring up correctly, here are a few tips to help bring it up to specification.

Problem: Feed restriction is caused either by the table rolls being set too low for roughing operations or from a low-pressure bar.

Solution: About 90 percent of the time, the pressure bar is too low. As the sharp edge of the planer knives wear, you must compensate for this wear by raising the pressure bar an equal amount on each side. Your first indication of knife wear is hesitation in feed of the material through the machine after it leaves the corrugated infeed roll on its way out. Turn the machine off, walk around to the rear and with a wrench, raise the pressure bar about a quarter turn on each side. The material should free up and run smoothly. Never attempt pressure bar re-adjustment with the machine running.

Problem: A very pronounced washboard finish appears down the full length of the board.

Solution: One knife is too high and is forced to do all of the cutting. Either grind the knives using the knife grinding attachment or reset the high knife.

Problem: Clip marks appear six inches from each end of the board.

Solution: The pressure bar is too high. Reset the pressure bar until it is slightly low to the point that feed will be restricted, then raise in quarter turn increments until the clip marks disappear, making sure that feeding is not restricted.

Problem: Snipes on the end of the material

Solution: The table roll is too high. Normally these snipes are more noticeable on the trailing end of the board than on the lead end. Lower the table rolls. This problem most often occurs during the planing of rough lumber. Table rolls must be elevated for running rough or resaw lumber through the machine. When material is turned over to surface the other side and you neglect to lower the table roll for the finished cut, then definite snipes will appear on the ends of the material.

Problem: Chatter marks on thin material.

Solution: Even at their lowest point, the table rolls are too high to handle the material. Solve the problem by either using a slave board or making the auxiliary table out of high-pressure laminate countertop material, cleating at each end of the table to keep it stationary.

Problem: Machine planes a taper across the full width of the board.

Solution: The table is not parallel with the cutterhead. The table requires leveling.

Problem: Stock twists in feeding through the planer.

Solution: Either the table rolls, infeed roll, chipbreaker, pressure bar or outfeed roll may not be level, causing material to twist. Place gauge on block on the table directly under the infeed roll and move the table up until light contact is made between roll and gauge blocks. Move gauge block across full width of table and check clearance on left end.

Repeat this process under the chipbreaker, pressure bar and outfeed roll until the problem is discovered. Generally the pressure bar will be out of level due to its constant adjustment to compensate for knife wear. At this point, level the pressure bar or other part of the planer and proceed with operation.

The following planer tips were excerpted from Powermatic's "Guide to Planing Excellence." To receive a copy Circle #216
COPYRIGHT 1993 Vance Publishing Corp.
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 1993, Gale Group. All rights reserved. Gale Group is a Thomson Corporation Company.

Article Details
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Author:Derning, Sean
Publication:Wood & Wood Products
Date:Nov 1, 1993
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