Update: Here is one the bogies after 2 coats of Revell Enamel. I used Revel No. 9 "Anthracite" which is my favourite almost-black colour for underframes and bogies.
(Yes, I still have to paint the wheels and metal parts of the Hollywood Foundry bogie.)
On 1st February, I received 3D prints of my bogies back from i.materialise in Prime Grey. I am very pleased with the bogies, especially considering the complexity of the design, and the known limitations of Prime Grey.
(Note that the clear underframe is temporary, as is the bogie mounting arrangement. I have nearly finished the design for the 3D printed chassis and fuel tank. When finished, there will be less "daylight" between the underframe and bogie as there will be large I-beams running horizontally.)
The little clips I included to attached to the Hollywood Foundry bogies worked well. Hollywood Foundry published a 3D drawing of their bogie which I was able to stretch to the correct wheelbase, and include as a layer (actually, several layers) on my drawing to make sure it all fitted.
Because of the fine detail, i.materialise were not keen on removing the complex support structure necessary during the 3D printing process, and I agreed to do this, so it has been interesting to see the print as it comes of the machine with the support structure in place. It took me about 30 min. to carefully tear it away and clean up the tiny attachment points. It still needs a bit of cleaning up.
Below, is the bogie with the support structure still in place.
It is not obvious in the photos but, as the HF gearboxes are quite small, I was able to include the outline of the bottom half of the the traction motors in the print, so they will be visible when viewed at rail level.