Re: Aluminium extrusion vs steel
Whatever you build from welded components that will later be machined in any fashion, and you want that component to stay true, flat and parallel, you are going to have to stress relieve it in some fashion. This is typically done in a furnace. Unless you stress relieve your "weldment", every time you touch its surface with a cutting tool it will change shape..it'll move. The foundation for any accurate machine, CNC or otherwise, is a accurate frame.
Stuart
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