Its possible to route aluminium with these I have hgr20 on my build around same size as you plan ( http://www.mycncuk.com/threads/9678-...-Framed-Router ) , and cut aluminium regularly without problems, the general advice I am sure will be go for more expensive square rails which are indeed better at a price, when I sell up and move and get a proper workshop I may well build second machine and use top materials but for first build I am happy with performance of these and the price.