Routing a Shallow Flute in a White Oak Stair Tread

Advice on router bit choice, hand techniques, and on maybe using a different machine for this. January 25, 2013

Question
I’m looking for some feedback on what the best router bit may be for routing clean 3/16" wide and 1/8" deep flutes in white oak. They will be stopped flutes that we will use a plunge router and jig on. I need clean flutes and little or no burn on the ends. I was thinking about a down-spiral carbide?

Forum Responses
(Solid Wood Machining Forum)
From contributor D:
I'm used to flutes being round bottomed and cut with a core box bit. I don't think they come in down-shear but that would be a nice solution if they did. I use 3/16" bits every day - two flute up-shear, straight bottom. Brand new bits will burn in white oak with the slightest pause routing by hand, even with very light passes.

I use a CNC machine and have worked out optimized feed and speed rates, but by hand I say pull up quick at the ends. You won't be able to be effective sanding in such a small groove either. A razor sharp chisel dragged in the groove can clean up burns pretty well, but it’s much better not to get them. The tylosis in oak burns readily and deep. I know I could cut these clean and crisp with a CNC but by hand I'd get a few burns without at least a few practice swipes on a piece of scrap. A lot of old timers think skill with a hand tool is king. Stopped flutes is where skill with a power tool is king.

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From contributor F:
If you have a shaper that would be my first choice. I'm not a fan of the modern round bottom flutes, just don't like the look. I use my shaper with knives ground to a more spade like shape to cut the flutes. The shape gives a feel for the old fashioned style fluting.

I simply use a long fence that I can clamp my stops to. Put the piece against the stop, plunge into the cutter, and run to the next stop. The other advantage over the router is it gives a nicer entry/exit slope than the router gives due to the diameter of the head.

If you don't have a shaper you could have a cutter custom made to do the same thing in your router table. It’s basically a rabbeting bit with the ends shaped. Otherwise you’re stuck with a regular off-the-shelf core box bit. For cleaning, simply grind the same profile into an inexpensive card scraper or other suitable implement and scape the flutes out after routing.

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From contributor C:
Have you looked at an S/C Straight flute? While a down-cut will probably work better this is a good choice as well (more hook). It may not have the burning issue as prominent also. We have the round bottom straight as well. Don’t have the round bottom spiral in down-cut as the machine cannot make those moves.

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From contributor G:
Also bear in mind a down-spiral wants to push the router up and it’s the opposite for an up-spiral which is more desirable. Granted it is a small cutter but there’s nothing worse than getting to the last one and losing it. Leave your part thick and overhead sand when done.

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From the original questioner:
Thanks Contributor G. What we are routing is a flat bottom groove in the front of
stair treads for traction - I believe that is the theory. We can leave it thick and sand off any chip or fuzz from an up-spiral bit.