In the process of making Watch screws (14BA and smaller) from carbon steel, I have been experimenting with slitting them. Normally I use a screw head file, but this can be somewhat time consuming so I tried a slitting saw in the lathe. I mount the screw in a tapped brass block clamped to the vertical slide and run in gently at centre height to the slitting saw.
This sort of arrangement I find works well when making larger screws (4BA and larger), but with a 8 thou slitting saw and slow backgear performance was somewhat hit and miss; sometimes a beautiful slot was cut, other times the slot was very Vee shaped with ragged torn edges and in one case the slitting saw lost a tooth (but the screw was undamaged)!
I have a feeling that this may be because I am using a cutter of too coarse a pitch (the finest saw I could find had a tooth spacing greater that the diameter of my screw head and normally I try to ensure that at least two teeth are in contact with the work. I should be interested to know if this is a plausible explanation?
Alan