These are STL files I used to replace the smoke unit on my G Scale Bachmann Shay with an ultrasonic "mister" aka, water vaporizer unit.

If you want a guide on how to do it yourself, please watch the video I made on my installation here:
https://www.youtube.com/watch?v=BI9Ihtu0PuA

Here is the parts list:
Shay-Reservoir
This is the tank that will sit inside the boiler/smokebox that will hold the mister head and the wick in place. Depending on your printer, you may need to enlarge or shrink the print a percentage or two so it holds the mister head and wick properly. This is intentionally designed NOT to be a tight fit inside the locomotive. You will need glue/tape/foam or something else to hold the reservoir in place once you have made sure the mister head is located at the correct location.

Shay-DiamondStack
This is a copy of the original diamond smoke stack that came with my locomotive, but without the spark catcher screen on the top and I increased the funnel diameter to minimize the chance of vapor condensing on the side and clogging the mister head.

Wick&Head Holder
This is a part I designed who's only job is to hold the mister head and wick together. This can be used if you want to mount your mister inside the diamond stack (as I showed at the end of my how-to video).

Tips & Suggestions:

Most 3D prints are porous and do not hold water well. I strongly recommend you test the water-tightness of your reservoir print by filling it with water and seeing if it leaks any after 2-3 hours. I decided to use some Gorilla Waterproof Patch & Seal Liquid to make sure my reservoir was water tight.

I printed the reservoir with the flat part on the print bed and used supports. Your printer and settings may prefer a different orientation, so do whatever works best for your setup.

The tolerances of my print worked for me, but you may need to increase or decrease the size of the print a bit for it to work with your printer setup.

I want to help out other hobbyists, so I don't charge for my designs. However, if you like what I created and find it helpful, a tip is always appreciated. Tips can be sent to: http://paypal.me/sukotto88