Aluminium construction profile 40x20 T-slot 5 and 8, item

Steel T-slot plate 7030

I'm guessing you do not have access to a milling machine or you wouldn't have to ask your cheapest way for you to get a clean slot

steel t slot plate Spec Chart Of Stainless Steel T Nuts Stainless Steel Bolts, Studs Threads: METRIC, BSW, BSF, UNC, UNF or as required

steel t slot extrusion Your browser can't play this video Learn more Assembling V Slot Gantry Plate for Alumi