There are various mount methods mentioned on this site. I have a vertical mounting surface at the front of my mill (which requires an extra router and mount), other people use a hole cut into the table to mount material that way. Have a look at this thread: https://forum.sienci.com/t/altmill-vertical-milling-thoughts/14989/4 . I would like to point out that there are a number of joint types that do not require vertical mounting.