RPM of the head and FPM (feet per minute) of the stock both combine to give the measurement known as KMPI (knife marks per inch). Too many KMPI will burn or glaze the wood; leading to premature dulling of the cutters and possibly failure of the glued joint. On the other hand, too few KMPI can lead to too rough a finish or tearout. The knowledgeable operator can fine tune the KMPI to achieve the best quality cut and the longest run times between sharpenings.

One of the best indicators of a proper feed rate is chip size. The presence of fine sawdust indicates that there are too many KMPI, and chip load is too small to effectively cool the cutters. The ideal chip should be well-formed and have the appearance of a shaving rather than sawdust.

Generally, good fingerjoints may be produced using a feed rate that yields around 30 to 60 KMPI. However it is recommended that one experiment a bit to find the best speed for local conditions.

The answer would be 40 KMPI...right in the range that works well in many cases...but remember ...

experiment yourself to find out the optimum feed rate for your wood species and location.