Ive heard that grinding aluminum and steel with the same abrasive grinding wheel will cause a thermite reaction and cause an explosion. I am very interested in this considering I weld both steel and aluminum at my job and would like to know if this is an actual danger.

Work with ease! Just tested it for you, nothing bad happened to me. :P

just to let you know you need to have a good ration of filings, once you switch from one to the other in would have to miw the two-perfectly then keep the ration and super heat it. it will never happen

It has nothing to do with thermite! It has everything to do with contaminating the aluminum weld zone, You are never to use ferrous tools on aluminum. You should never grind aluminum on a pedestal type grinder with ferrous grinding wheels. as the aluminum cam clog the spaces between the grit. since most wheels are compressed together with out the benefit adhesive. It can cause an unbalanced in the wheel causing it the have a catastrophic failure. From the rpm's it is spinning. If you have been around when one lets go, you will never load up a wheel again whether it is aluminum,cork,rubber,wood or anything else!

That is why a stainless steel wire brushes are used for aluminum TIG welding. And not used for anything else.

Mjoat's exmplaination seemed accurate for the real reason why it should be done.

However, as for why it wouldn't create a thermite reaction is because steel isn't an oxide. For a thermite reaction you need a metal, and a metal oxide (typically iron oxide and aluminum).

if the steel is rusted, which any steel in the environment for more than a day is, that provides an Oxide since that is what rust is, or aluminum "rusts" or if you prefer develops an oxide on the surface