Tip #52
Shopsmith Jig Saw (continued)
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Piercing Cuts

Figure 16-24. Piercing is possible because the blade can pass through the work before it is gripped in the upper chuck.

As mentioned earlier, one of the biggest advantages of the jigsaw is that it can cut internal curves and designs in a workpiece without having to cut through the stock from the outside edge. This operation is called piercing.

To make a piercing cut, first drill a hole in the waste stock on the interior of the pattern. The diameter of the hole must be larger than the width of the blade. If you want to save the waste stock for later use, drill the hole near a corner in the pattern. Be careful not to drill through the pattern line.

Release the tension on the blade and loosen the upper blade chuck. Raise the hold-down and tension tube as far as they will go. Turn the drive shaft so that the lower chuck is at the bottom of the stroke. Then thread the upper end of the blade through the hole you've just drilled (Figure 16-24). If you need to, you can flex the blade slightly to one side. But be careful not to bend it so far as to kink the blade. Reinstall the upper end of the blade in the upper chuck, tension the blade, and ad-just the height of the hold-down.

Figure 16-25. Each piece to be cut out must have its own blade insertion hole. often, as shown here, the holes can be part of the design.

Cut out the waste stock from the interior of the pattern, being careful not to cut through the pattern (Figure 16-25). When the cut is complete, turn off the machine and let it come to a complete stop. Once more, release the tension on the blade, loosen the upper blade chuck, and raise the tension tube and hold-down. Finally, remove the workpiece from the jigsaw.

Figure 16-26. Cutting techniques to follow when the work has square corners. Click on image for larger view.

When a corner forms an arc, you can turn the corner in one continuous pass. If the corner is square, you can work as shown in Figure 16-26. Approach one corner from the blade insertion hole and then back out, either to the hole or far enough so you can make a second approach to clean out the corner. The third cut starts at the first corner and continues to the second one. Back out far enough so you can turn to approach the second corner from another direction. Continue to work this way until the cut is complete.

Figure 16-27. One continuous pass will cut out a circle. Drill the blade insertion hole close to the outline. Click on image for larger view.

The size of the blade determines how far you must back out and how big a turn you must make to get set for the second approach at each corner. The finer the blade, the less room you'll need for the maneuver.

Cutting out a circle is a much simpler matter. Just make one approach to bring the blade to the line and then continue around until the cut is complete (Figure 16-27).

Figure 16-28. If you preplan the cutting technique, you 'II usually save time and material. Click on image for larger view.

Two other cutting techniques are shown in Figure 16-28. In (A), the cut is the same as for a circle: one approach to the line and one continuous pass. In (B), the cut is made from the blade insertion hole to the corner. After backing out, the form is finished by cutting in the opposite direction; around the semi-circle and back to the point. It could also be done by drilling the blade insertion hole close to the point and cleaning it out by working as you would for a square corner, then finishing with a final, continuous pass.

Figure 16-29. The fence helps to produce accurate slots. End holes of correct diameter are drilled on a common centerline.

Internal slots are shaped as shown in Figure 16-29 with the aid of the fence shown in Figure 16-16. If the slots are to have round ends, first drill end holes with a bit that matches the slot width. Then, us-ing the fence as a guide, use the piercing technique to clean out the waste. Work the same way if the slots will have square ends; but, after the initial cuts are made, work without the fence to clean out the corners.

Continue to Cutting Circles
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