Drill Guides and Bushings

[Barry Blitz]

What is the tolerance for fit? If a shaft is 10mm, is the inner diameter of the guide/bushing the same? If slightly larger bore is needed, then by how much?

And the same question for the hole needed for the outside diameter for which the bushing will fit (which will not be a metal bore, something softer like phenolic or plastic).

I am planning to make some jigs using press fit type P or H drill guide bushings.

[Paul F Franklin]

Typically, a drill bushing has a few ten-thousandths of an inch larger ID than it's nominal size, at least in the smaller sizes. You need to know the tolerance of your shaft to know if you need to order an oversize bushing or not. If you have a precision ground 10mm shaft, it should fit in a 10mm drill bushing.

Similarly, the od of drill bushings designed for press fit into metal are also a few ten-thousandths of an inch oversize so they press tightly into metal. Drill bushings designed for softer materials like wood or plastic are usually serrated to provide resistance to spinning.