what grade of aluminium is best for fork yokes for a road going large capacity bikes ? I want to machine up some for my old cafe racer but don't know what to order to make them with as i have rarely worked with aluminium , mainly stainless steel.
6082-t6 will be fine. Like the 7xxx series mentioned several of the 2xxx series are stronger and machine very nicely but getting hold of 'em ain't as easy, especially if you don't want to pay dearly for the privilage and/or buy tons of the stuff. 6082 machines well in the T6 condition and is used for a lot of aftermarket billet bits on bikes (i'm pretty sure virtually of the ally products Scott0031 makes/used to make for bikes were carved from 6082)
Normal yokes are castings with silicon content in, thats why you dont see them anodised. LM6 rings a bell but can be pressure doe casted.
6082 in T6 is widely available and covers stuff for MOD to off the shelf round. Different number for plate for some reason! Its also same consistency for super high hydraulic tube. To give you some idea normal off the shelf 1 1/4" x 1/8" is rated at 70bar, 6082 will take 4800 psi (330bar.)
I work with 6082 all the time because its ok to machine not gummy like some and most of all anodises well.