... Possibilities...

1. Bent bit

2. As sonny said, bit isn't properly seated in the collet

3. Collet is worn or not properly seated

4. The bearings - the router bearings, not the bit bearings - are worn.

If neither the bit nor router is damaged, and the bit is seated properly, there is another possibility: The shaft flexes enough to produce a poor cut.

How big a bite is the bit taking? It might be too much for the router/bit combination.

Typically, machinists will make a "spring cut" or "spring pass" to compensate for any deflection of the cutting tool. They do this by using the same setting make a cut. Some will use a climb cut for this last pass.

You may want to test this on a sample and see what results you get.

Joel