I fiddled with the grill juuust a bit more - that outer slot is now 0.005" wider. The fillets are a little smaller too to allow for polishing.
Also fixed an error I had in the diameter of the raised ring that fits into the back of the iris so that it is now 0.49". The manufacturer 3d model has the inner diameter of the back face of the iris larger than the front (0.497 inches… is that what yours measures there?)
And the ring along with the faceplate connected:
^Shapeways thinks the innermost circle of the grill is a little suspect, but I might go ahead and order one out of pure curiosity about whether it is possible or not… If it succeeds it will be in the “raw” unpolished state, which isn’t awful, but it would involve learning how to polish out the print lines. Here’s an example of the before and after with their process: