Hi Sherry,
I'm afraid there is no fool-proof method of doing this. You have two broad choices: define the three resources at one unit: for example - operator, machine, tool is one resource. When setting up the resource sheet - carry the cost for all three 'parts' to the one resource.

The second option is a work around of creating a task calendar that carries all non-working time from all three resources. The task calendar is then assigned to the task and it will schedule the task to occur during common working time.

If you are going to use the second option and use resource leveling - ensure you have the option "leveling can adjust individual assignments on a task" unchecked.

The ability to define equipment resources and "tie" them to work resources has been on the request list for many users for many years.

I hope this helps.