Concentric Boring

A round or a square workpiece, if it is not too long, can be positioned for accurate concentric holes by using the miter gauge and the fence as shown in Figure 11-17. The table height is adjusted so the drill point will be on the workpiece's horizontal centerline. The miter gauge, locked in place, maintains the workpiece's alignment; the fence serves as a backup.

Figure 11-17. A simple way to set up for boring concentric holes.

Figure 11-18. A V-block can also be used when doing concentric boring.

Figure 11-19. A V-block is used to hold the workpiece as shown here. Use the fence as a stop block and use a spacer when the workpiece is too short to reach the fence.

Another method requires the use of a V-block (Figure 11-18) which cradles the workpiece as demonstrated in Figure 11-19. When the workpiece is shorter than the V-block, use a length of scrap wood between the workpiece and the fence. The V-block can also be used to hold square workpieces (Figure 11-20).

Figure 11-20. The V-block can also be used to position a square workpiece for concentric boring.

Figure 11-21. An extension V-block is used for extra-long workpieces.

For extra-long workpieces, use an extension V-block as shown in Figure 11-21. The V-block is also used to grip short workpieces (Figure 11-22). The V-block, held in place by being clamped to the locked miter gauge or clamped to the extension table, is positioned so the vertical centerline of the spindle bisects the “V.” Table height is adjusted in relation to the diameter of the workpiece. Small auxiliary V's are used when the workpiece is too small to be gripped by the basic V-block. Figure 11-23 shows how the extension V-block and the auxiliary V's are made.

Figure 11-22. The extension V-block can also be used to grip short workpieces. Auxiliary V's are used when the stock's diameter is too small to be gripped by the basic V-block.

Figure 11-23. Construction details of the (A) extension V-block and (B) the auxiliary V's. The shape needed is actually a rabbet cut.

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