This another great idea I copped from sombody else’s web site. I learned a few things about it that are worth mentioning so here goes.

How to Make One

The fog machine is very simple - blow compressed air into mineral oil and it vaporizes into fog. I made mine from a plastic food bucket of about 2 gallons capacity that has a snap on lid (see pictures below). Bend about 2 feet of 3/8 copper tubing so it will sit in the bottom of the bucket, and drill a hole for it to exit from the lid. I clamped it to the lid so it would stay put. The end of the tubing in the bucket is pinched closed, and drill about 8 very tiny holes (1/32 or so) in the tubing so they face the bottom of the bucket. I ended up soldering some of them closed again so start with about 4 holes and if you need more fog drill one or two more. The tradeoff here is more holes need more air and this thing uses a lot of air.

The fog exits the bucket via an ABS tee fitting which helps keep the bubbling oil out of the exit pipe. You can attach a suitable pipe to the tee to send the fog where you need it. I used 1 1/4 inch corrugated black plastic pipe used for sump pumps.

How to Make it Work

Put enough mineral oil in the bottom of the bucket to cover the copper tube - this shouldn’t take much if you put the tubing right in the bottom of the bucket. Attach a source of compressed air about 30-40psi to the copper input tube and you should see fog from the exit fitting within 20 seconds or so.

Notes:

This thing uses a lot of air ! I used a 4HP compressor with a 12 gallon tank and it cycles about every 2 minutes if I leave the fog machine on. If you use fewer or smaller holes in the tube you use less air, but you get less fog too.

A cheap source of mineral oil is unscented baby oil. You can get half a liter at WAL-MART for about $2. I put about 1 liter in mine, which should last for about 10 years. The oil vaporizes to a very fine mist and it uses very little in operation. If you run it for a couple of hours you will detect a very fine oil layer at the exit of the fog tube but its not messy at all.

I’ve seen some questions as to the toxicity of the fog. I concluded there is less risk from this than a conventional glycol based machine but then again I’m no expert. Mineral oil is sold in drug stores as a laxative, so perhaps if you breathed it for long enough...

Pros:

Very quick and easy to make. Very low cost of materials and operation assuming you have a source of compressed air already. Produces quite decent amounts of fog, which is cool so it tends not to rise. The compressed air forces the fog out so you don’t need a fan. The small fog tube is easier to conceal than the much larger ones used on heater type fog machines.

Cons:

Uses a lot of air. Your compressor will run a lot which is very noisy (I put mine in the garage and ran an air line to the fog machine in the front yard). The fog machine itself is kind of noisy because of all the air hissing and bubbling thru the oil. On my Witch and Brew prop, this simply added to the sound effects !

Fog Cooler

Not really required but it makes the fog heavier which is the effect I wanted. Coil up some of the fog pipe and stuff it in a cooler filled with water and ice. Thats it !