I am wondering if an up cut spiral bit is the only way to go for ultimate dust collection when using the 1400 to create dados? Thoughts?
It is good but not perfect. It will help "clear the path" but can leave some fuzzy edges as it is "pulling" the wood up.
White side makes a combination bit that is excellent, but it is not cheap! Take a look for it and good luck. Again, the up cut bit is a good start, but there will be some cleanup after the fact. Really a preference thing. If you have a Rockler nearby, head on in and try both out.
EDIT: I forgot that you asked specifically about dadoes. What I referenced above was for trimming the edges for flush. I have these undersized plywood bits and they leave a very clean cut in ply and other woods. Again, pricey but the cut is clean. Having to clear the path isn't really a big deal.
Whiteside Router Bits 470 Undersize Plywood Dado 3 Piece Set with 7/32-Inch,15/32-Inch, and 23/32-Inch Cutting Diameter with 1/2-Inch Shank https://www.amazon.com/dp/B003UYSVYU/ref=cm_sw_r_cp_api_Uty6ybQCQT0T4
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