I may be crazy Duncan but not that crazy
. I mill as much away as possible with a 1/4 inch mini mill, but then still have to do a fair amount of filing. I am not really equiped for this sort of thing so the whole process is a bit long winded. Probably about 12 hours start to finish cutting out of a 30mm bar end. I use that as its my only means of holding it in the machine vice. The bits of black steel flat sections I have are a bit rough quality ( lots of hard bits randomly spread throughout ) and tend to eat milling cutters.
Now if I had still been at work, I could have had the outline laser cut in a couple of minutes then only around an hour to mill the spindle slot and drill for the pin.
As an aside and in response to your ealier comment as to how much it might have cost ready made, I found Robert White doing the Arca version less plate, for £130 excl vat.
Link to a review of that particular item.
http://liaoyusheng.com/arca/
Don