Steel frame cnc router design/build

[JAZZCNC]

No experience with Blackburns but if you haven't got a milling machine to surface standard plate then who ever you use I recommend you buy ground flat plate for key areas like Z axis and bearing plates. . . . It's more money but worth the expense because standard plate is never flat, it may look flat but it's not.!! So for critical areas like Z axis and bearing plates where surfaces must be flat and parallel to each other they must be surfaced flat.
I have the capability to surface plate and still I buy ground plate for these areas has it saves me hassle and time and even careful milling can't match ground surface quality.

Even Round rail which is very tolerant of bearing/rail miss alignment will bind and stick if plate is slightly cupped, less than 1mm cup, bow or twist over 300mm bearing plate length will be enough to totally lock the bearings when fastened to plate. Normal rolled plate can have that much error and I've seen plenty folks fall foul of this and corrected several bearing plates for people because of this.

If you can't get it from Blackburns then I suggest aluminium ware house because they cut to size and you can order just slightly larger than you need for those areas. Your Looking for ECOCAST at AW it's here. Aluminium Plate - Cut to Order - Aluminium Supplier | Aluminium Stock | Aluminium Warehouse

PS: For rest of plates like motor mounts and even gantry sides etc then normal plate is fine, if you have decent metal scrap yard near by it's worth checking them out has often they have offcuts etc from industry and some can be large and quality, most just charge scrap value.