Always hold whatever you are cutting in a vice and have a good grip on the Dermel so you cut it square. Choose the cut-off disc properly as well as the spindle speed.
For hardened steel pins, use a brown disc (usually thin) at about 20k rpm (for a new one) to 30k rpm (for a used one that has a small diameter) and don't push too hard. Let the cutter flow through rather than push through.
For Ti pins, use a black disc (usually thick) and drop the rpms to between 10k and 15k. Give the tool a little push, but be very careful of heat build up as Ti is soft and can clog the wheel easily.
In either case, if the metal changes colour when you're cutting it, you have softened it and it will be weaker in that area. Providing that the nut goes past the softened end, it'll be fine. Ti will be OK, but try not to use the very end of the bolt or pin to take too much load.
Practice on a scrap bolt, cutting about 10mm off at a time. One thing to watch - if the cheapo Maplin tool slows down appreciably while cutting, you'll always have problems with a poor cut and overheating of the part and the tool. If it does that regularly, it won't last long. I've had two Dremels in the last 35 years, and the first one died because it ran out of copper on the commutator due to 28 years of excellent service, most of that building slot-race chassis!! HTH
