My Downham Mini Borer has an unusual DA180-type collet system for which adapters are very hard to find. It came with a Morse 1 adapter for which chucks are available for drill bits of up to 8mm; chucks up to 13mm tend to come with a Morse 2 taper.
I made an adapter with the help of a machinist friend of mine. Unfortunately I don't have any 'making of' pictures so I can only show the finished product.
I'll add details on the dimensions soon.