Understanding Guide Bushings
Figuring template offset
Offset is the distance from the outside of the guide bushing tube to the cutting edge of the router bit. This dimension determines where the bit cuts the workpiece.
To figure the offset, measure the outside diameter (OD) of the guide bushing tube and subtract the diameter of the bit. Next, divide this figure by 2 to determine the offset. In the example at right, subtract the 1/2" bit diameter from the bushing's 3/4" OD. You get 1/4". Now divide this number by two and you arrive at a 1/8" offset.
Know your alternatives
There are router bits capable of template routing without guide bushings. See the chart on the next page for comparison information.
Adapters and subbases are available from many mail-order sources, including the following:
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