filed a provisional on an idea made of aluminum, weeks later realized i could make this in several different ways if made of plastic as well. Do i file another provisional with all the variation, including the aluminum version and abandon the first provisional..?
A provisional application helps establish a priority date so that someone else cannot file a patent on the same invention. If the variations are substantially similar and can be covered by one single patent application, then there should be no need to file two provisional applications.
It's not a good idea to restrict your claim to a specific material. In the Detailed Description part of your actual patent application, you can discuss various embodiment using different materials. However, in the Claims, you should just omit any reference to material, or simply refer to it as Rigid Material. And any material-specific variations should be referred to in more abstract terms, for example in your independent claim use the term fastening means while in you dependent claims specify welding in case of aluminum and clip-and-lock in case of injection molded plastic