I discussed this with Zeb Whiteside a while back. He said that the bit itself is perfectly capable of cutting the fixturing slot in one pass, but that even commercial shops have their own preferences when it comes to pre-slotting. A lot depends on the rigidity of your routing setup. A big stiff CNC is likely to give better results with single-pass cutting than a light machine (or router table).
My own experience is all non-CNC. On my Shopsmith OPR router table, using the 3-1/4 hp Triton undertable router, a single pass works great in softwood or MDF. I also get good
results that way in hardwoods and BB ply, but the cuts sound rough, so I generally pre-slot these.
I’ve never tried handheld routing in a single pass. For that, I’m typically using my
WoodAnchor slotting guide, which works really well.
Here’s one other interesting takeaway from Zeb Whiteside. The specified 18,000 RPM speed limit for the bit seemed kind of low to me, as I have bigger bits that run just fine at higher speeds. It turns out that the issue is heat. Zeb said that higher speeds generate more heat without improving the cutting process. So at 18k, you should get better bit life and less workpiece burning.
I haven’t tried routing the slots with a Shopsmith, but rjent reports good results.
