A couple of complicating factors - I forgot to say that the part is printed with 30% infill to save plastic so it's not as stiff as it could be (there are three solid layers on the top and the bottom (1.1mm) and on the perimeters (1.5mm - I'm extruding filament 0.5mm wide and 0.35mm thick)) and the concave bending of the sides away from the planet gear effectively doubles the deflection.

I tried the new ring gear (still 6mm and 30% fill) and it moved but didn't skip (at moderate loads - see below) so I don't think it will be an issue - more something to bear in mind for any future modifications - I'll know more when I've managed a proper load test.

Testing at 2KG/metre resulted in a broken gear carrier and splintering of the wooden batten attached to it so they need to be improved next - I might make an aluminium carrier as I've just converted the milling machine to a CNC-USB controller but haven't cut any metal with it yet :-)

I think I've pretty much tuned out the oversized first layer problem by putting a slight relief on the side of the teeth next to the bed - the 15t gears look good and the 30t isn't far off - same technique should work on the ring gear as well and has improved the feel of the gears quite a lot.