I have to agree with Jim aka Syslight here, I finally tried 2 blades at once all last week and that worked just fine.... NO damage to either blade.
I would not recommend too many more in there depending on the size of the tumbler....

One of the guys I work with came up with an idea of how to do a vintage razor in the scales... I will try this tomorrow and see how this might work out... I don't even want to tell you how this might work, until I put a little more experimentation and thought into it but I will keep you updated on the progress or failure!!!!...