Machining strategy and tool selection
As with cutting inlay
parts, the first step is to select a cutter diameter that is large
enough to give you the desired cutting speed, but small enough to
produce the level of detail necessary to accurately shape the pocket.
Often multiple tools, used sequentially, are required to shape a
pocket that will accept the inlay part with minimum insertion force or
When cutting pockets, a new cutting strategy
must be formulated. If the pocket is relatively large (20X the size of
the smallest diameter bit you plan to use), it makes a lot of sense to
rough out the pocket. This step should leave a minimum amount of
"stock" that will need to be removed in a clean-up pass
using a smaller diameter cutter to achieved the final size and shape.
For large pockets this two step process is almost invariably
shorter than a single, lower speed pass with a smaller diameter bit.
A key point in this strategy is to rough out
the pocket from the inside out. By "wallowing out" the
center first, you create an ever widening debris pocket, allowing the
flutes to run cleaner and cooler. This roughing pass will be
"climb-milled", moving the tool in a counter-clockwise
outward spiral. Inward bit deflection during climb-milling will result
in a pocket that is slightly smaller than planned.
Overlap between successive roughing passes
should be 20 - 50% of the tool diameter (assuming full plunge, single
pass machining). More overlap (larger percentage) yields a smoother
bottom, especially in softer woods, but results in a longer cutting
time. A little experimentation with the material you will be
pocketing will help you decide which overlap setting is right for your