Tip #19
Sharpening Woodworking Tools (continued)
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Pg.1-5, Pg. 6-10, Pg 11-15, Pg. 16-20, Pg. 21-25

Grinding Planer and Jointer Knives

Jointer and planer knives need occasional maintenance. This upkeep consists of a simple cleaning and honing of the knives on the machine (see the Jointer or the Planer Owners Manual).

However, this type of edge repair will only go so far before the knives need to be removed and thoroughly ground. The best way to grind jointer and planer knives is to use the Shopsmith Grinding Wheel and Knife Sharpening Accessory that mounts on the Mark V. Set up the grinding wheel according to the Owners Manual that came with the Grinding Wheel.

Select the proper hard wheel for the severity of the cutting edge damage (coarse for nicks and a badly worn cutting edge and fine for routine grinding).

Warning: Never use the soft rubber-bonded abrasive or all-purpose wheels to grind jointer or planer knives. The sharp cutting edge of the knives will dig into the soft wheel and cause the knife to be thrown from your hands, causing serious hand cuts and damaging the wheel and the knife.

Figure 24-37. First, grind the primary bevel. Then grind the strengthening secondary bevel.

Remove the knives from the cutterhead according to the Jointer or the Planer Owners Manual. Planer and jointer knives are ground in a two-step operation. First, the primary bevel is ground. Then a secondary bevel is ground on the front edge of the primary bevel (Figure 24-37). This strengthens the cutting edge and helps dissipate the heat during cutting.

After the knives are used, they can be either honed in the jointer or planer, or reground on the secondary bevel. You will be able to regrind the knives in this manner several times until the secondary bevel becomes either wider than the primary bevel or wider than 1/8".

Figure 24-38. Center the knife bevel on the wheel.

Grinding Wheel Setup--Set the primary bevel angle by placing the knife on the knife rest in front of the knife guide. Loosen the wing nut and tilt the tool rest until the knife bevel is centered on the wheel (Figure 24-38). Warning: Position the tool rest no further than 1/8" away from the wheel. Then tighten the wing nut.

Position the knife guide behind the knife so that it aligns the knife parallel to and just touching the wheel. Securely tighten the two screws that hold the knife guide in place. Remove the knife.

Figure 24-39. Hold the jointer knife with one hand while sliding it back and forth across the wheel.

Grinding the Knives--Be sure that the speed dial is set to “Slow” Turn on the Mark V and set the speed dial to “R” (3500 RPM). Hold the knife firmly on one end of the knife rest and feel for it seating solidly against the knife guide.

The 4" jointer knives are held with one hand and slid back and forth across the knife rest (Figure 24-39). The 12" planer knives are ground in three overlapping sections (Figures 24-40A, 24-40B, and 24-40C).

Figure 24-40. Planer knives are ground in three overlapping sections: (Top) grinding the left end, (Middle) grinding the right end, and (Bottom) grinding the center.

Slide the knife slowly across the knife rest and knife guide, and past the wheel. Caution: Keep the knife moving. If you hesitate, the wheel will heat up the knife and turn the edge blue. This will ruin the factory heat treating.

Grind the knives at this setting until the sparking stops. When the sparking stops, the knife should be evenly ground.

If some of the nicks are still showing on the edge of the first knife, or only part of the bevel is ground, you may need to reset the guide and continue grinding the primary bevel. But if the remaining edge damage is minor or all but a slight part of the bevel is yet to be ground, the secondary bevel grinding operation will grind away and true up the edge.

Grind the primary bevel on the other two knives at this setting. Then turn the speed dial to “Slow” and turn off the machine.

Figure 24-41. Reposition the knife guide so that the knife just touches the grinding wheel.

Set the secondary bevel angle by loosening the Wing nut and resetting the tool rest approximately 10° to 15° toward the wheel. Tighten the wing nut. Place the knife on the knife rest and reposition the knife guide so that the knife just touches the wheel (Figure 24-41). Repeat the knife grinding procedures explained above, It should only take one or two passes to grind the secondary bevel.

It is not necessary to hone the jointer and planer knives after they are ground. The burr that is left on the cutting edge is small, and will be knocked off at the first contact with the stock.

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