Got to ebay and look up arrow cutoff saws. Sometimes they have them under fletched arrows. You can get a new one for less than 30 bucks. One piece of advice if you do get one of these saws, CUT SLOW AND SMOOTH. They are small and work well.

The arrow needs to be cut off completely square for accuracy. Carbon dust is very harmful to breathe so be careful about that also.

All of the inserts I have ever used for both carbonand aluminum arrows are alligned by the insersts "fit" into the inside walls or tube of the arrow not with the "fit" to the end of the arrow. Where the insert contacts the end of the arrow serves as a "stop" rather than for alignement so although I would shoot for as close to a 90 degree cut as possible, I don't think it is very critical.