bent wrote:
But I do not know the teachings when it comes to these kind of profile bits.
What is the rule. Is there any difference from other bits?

If you are only talking about the depth setting on your router, then several
types of bits that produce beaded profiles, or joints - including dovetails -
cannot be routed in successive passes at increasing depth settings. If you are
talking about mounting the router in a table (or possibly using a guide fence),
then you have more options for making a larger cut using multiple passes.

When multiple passes are necessary depends on the amount of wood being removed,
the type of wood being worked, the size of the router bit and router, and how
good a cut surface you want. All decorative routed edges and routed joints
benefit when the last, or finish, pass through the router removes only a small
amount of material. This produces a smoother surface, better fitting joints,
less sanding, etc.

Router bits that produces joints such as -
http://www.infinitytools.com/products.asp?dept=1060
http://www.infinitytools.com/products.asp?dept=1062
or any bit where any part of the cutting profile toward to bottom of the bit
(away from the router) is a larger diameter than a part of the profile nearer
the top of the bit -
http://www.infinitytools.com/products.asp?dept=1234
http://www.infinitytools.com/products.asp?dept=1040
cannot have the router depth setting altered in successive passes. However, when
the router is mounted in a table, you can make successive passes using different
fence settings.

Dovetail sockets are routed to size in one pass, but a preliminary cut using a
straight bit that is smaller that the dovetail socket profile can be helpful.
This technique also works with T-slot bits, although here multiple passes can be
used if you need to deepen or widen the cut slot.
--
JeffB
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