Proper Rate of Feed, Force Feeding, TOO Slow Feeding

OPERATION

PROPER RATE OF FEED

Professional trimming and edge shaping depend upon care- ful set-up and selecting the proper rate of feed.

The proper rate of feed is dependent upon:

nthe hardness and moisture content of the workpiece

nthe depth of cut

nthe cutting diameter of the cutter.

When cutting shallow grooves in soft woods such as pine, a faster rate of feed can be used. When making cuts in hard- woods such as oak, a slower rate of feed will be required.

Several factors will help you select the proper rate of feed.

nChoose a rate that does not slow down the trimmer motor.

n�Choose the rate at which the cutter advances firmly and surely to produce a continuous spiral of uniform chips or a smooth trim edge on laminate.

nListen to the sound of the trimmer motor. A high-pitched sound means you are feeding too slowly. A strained, lower-pitched sound signals force-feeding.

n�Check the progress of each cut. Too-slow feeding can cause the trimmer to take off in a wrong direction from the intended line of cut. Force-feeding increases the strain of holding the tool and results in loss of speed.

nNotice the chips being produced as you cut. If the trim- mer is fed too slowly, it will scorch or burn the wood. If the trimmer is fed too fast, it will take large chips out of the wood and leave gouge marks.

Always test a cut on a scrap piece of the workpiece wood or laminate before you begin. Always grasp and hold the trimmer firmly with both hands when trimming.

If you are making a small-diameter, shallow groove in soft, dry wood, the proper feed rate may be determined by the speed at which you can travel the trimmer along the guide line. If the cutter is a large one, the cut is deep or the workpiece is hard to cut, the proper feed may be a very slow one. A cross-grain cut may require a slower pace than an identical with-grain cut in the same workpiece.

There is no fixed rule. Proper rate of feed is learned through practice and use.

FORCE FEEDING

See Figure 8.

The trimmer is an extremely high-speed tool (25,000/min), and will make clean, smooth cuts if allowed to run freely without the overload of a forced feed. Three things that cause force feeding are cutter size, depth of cut, and workpiece characteristics. The larger the cutter or the deeper the cut, the more slowly the trimmer should be moved forward. If the wood is very hard, knotty, gummy or damp, the operation must be slowed still more.

Clean, smooth laminate trimming and edge shaping can be done only when the cutter is revolving at a relatively high

speed and is taking very small bites to produce tiny, cleanly- severed chips. If the trimmer is forced to move forward too fast, the speed of the cutter becomes slower than normal in relation to its forward movement. As a result, the cutter must take bigger bites as it revolves. Bigger bites mean bigger chips and a rougher finish. Bigger chips also require more power, which could result in overloading the motor.

Under extreme force-feeding conditions, the relative speed of the cutter can become so slow—and the bites it has to take so large—that chips will be partially knocked off rather than fully cut off. This will result in splintering and gouging of the workpiece.

TOO SLOW

TOO FAST

Fig. 8

TOO SLOW FEEDING

See Figure 8.

When the trimmer is advanced into the work too slowly, the revolving cutter does not dig into new wood fast enough to take a bite; instead, it scrapes away sawdust-like particles. Scraping produces heat, which can glaze, burn, or mar the cut, and can overheat the cutter. Dull cutters can also con- tribute to scraping and burning.

It is more difficult to control a trimmer when the cutter is scraping instead of cutting. With practically no load on the motor, the cutter will be revolving near top RPM, and will have a greater than normal tendency to bounce off the sides of the cut, especially if the wood has a pronounced grain with hard and soft areas. The cut that results may have rippled sides instead of straight.

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