[header] How to make a plaster cast of an arm [title] Realize that you'll have to remove the cast. [step] If you are making your own plaster cast, you'll have to be able to remove the cast yourself. Removing a plaster cast requires having access to either plaster shears or an electric cutter. 
It's highly dangerous to do this process yourself, so have a friend ready to help you. [substeps] Plaster shears are safer than electric cutters.