I have one 16 mm ball nose slot drill and I have used for drilling, plunges better than straight slot drill. I have about 1,5t knee mill w/o pinole = feed is by cranking the knee. Speed 25-700 rpm about 3,5kW, 22 mm slottdrill will go trough hot rolled metal, but shakes the table.
I have been thinking of sharpening some chipped slot drills to "drills", but I don't have them in sizes I want. Positive thing is that ER25 chuck is pretty compact and MT3/16 mm collet is even more compact. IF there were some short drills with 16 mm straight shanks in 12-20 mm sizes it would solve many of my needs.
I don't like "Blacksmith Drills" most of them are pretty poor quality, I have some, but it seems to work better to start with a standards drill and turn down shank.
Googled some Rotabroach and there seems to be MT3 taper adaptors for them, with coolant union and all. Downside is that they get pretty long fast. But Rotabroach shank looks a little like weldon shank, but it is OD19,5mm, has two flats at 90 degree where set screws butts.
This sort of set looks fine:http://www.toolstop.co.uk/unibor-magnetic-drill-cutters-set-of-6-p72509
* Sizes 14S, 16S, 18S, 20S, 22S, 24S, pretty much most I will need
* One lengt/shank for all
* But I should turn own adapter from MT3 taper blank (not too hard), but if it needs trough coolant, it gets a bit more complicated.
Chipenter: What collet system you used? Did you use use 12-30 mm Rotabroaches? What rpm and how much coolant you need? I have no problem with low rpm or high feed, but coolant might be a issue.
Maybe I buy one locally (If I can find one after my work day) and make one adapter as a weekend project just to find out how it works out?