Prepare any applicable small container, which will actually serve as your miniature smoke machine container. One container typically used for this type of project is a small Styrofoam cooler. However, you can use any other small container that can effectively hold dry ice and hot water.
Wear gloves before handling dry ice to protect your hands from burns. Touching dry ice with bare hands can burn the skin because of its extremely low temperature. As an alternative, you can use tongs or a spoon to transfer a piece of dry ice from its original container to your miniature smoke machine container.
Fill your container with an ample amount of dry ice. Depending on how long and how much smoke you need for your miniature project, you can place a small, single piece of dry ice into your container or fill the container with dry ice pieces almost reaching up to the brim. As a guide, a 5-lb. piece of dry ice submerged in hot water can provide a decent smoke effect for about 10 to 15 minutes.
Add warm water to your container to enhance the smoke coming from the dry ice. You can use anything from lukewarm water to boiling water. The hotter the water, the quicker and thicker the smoke you'll get from your homemade miniature smoke machine. If you have access to a submersible water heater, use this so you can keep the water hot. This way, you can generate a continuous smoke effect for your project.
Position your miniature smoke machine somewhere near your miniature project. This position may vary according to your needs and preferences -- but it should be close. If using a miniature fan or regular fan for your set-up, position it according to the direction you want your smoke effect to go, then turn the fan on.
Slowly and carefully move your container horizontally up to about six inches from its original position. This helps spread the smoke effect without causing the water to spill from the container. If you need more smoke, simply add more dry ice and/or hotter water to your container.
Turn off the fan after working on your miniature project, then dump the water into the sink.