How low can I go?

[Tuba Dave]

I'm going to give this a try. If I can get this off my honey-do list quick and easy, and still be left with a new cutter, I win twice.

 

[mmcmdl]

Just another idea . If you have a top notch holder , you could grind down a grooving insert to your .009 needed thickness . This would be an easier route .

 

[benmychree]

How about a woodruff keyseat cutter?

 

[Tuba Dave]

How about a woodruff keyseat cutter?

I ordered a T-slot cutter, I guess a similar tool.

 

[Huub Buis]

I like the idea of a t-slot cutter. If the size (width) of the grove is critical, get a smaller cutter so you can widen the slit until it fits.
I have a 1 mm thick HSS T-slot cutter that has a 6 mm shaft and a 10 mm cutter diameter. That can cut 2 mm deep at the max. I would prefer a cutter that can just a fraction deeper, 6 mm shaft and 12 mm outer diameter.
A 2 mm wide groove can also made using a 2 mm (or less) endmill. It just depends on the work holding.
You can make an arbor that has a press fit for the slitting saw. Just beware that the slitting saw has sharp edges so you need to cut (turn) the shoulder using a tool without a tool nose radius.

 

[whitmore]

A slitting saw is basically a washer with teeth; if you were to bevel the center hole, a flathead
(or flathead allen or flathead bristol spline...) screw could retain the washer without any
protrusion. McMaster.com sells Beveled-hole washers, that could presumably be toothed and do
the job in plastic...