Bleeding
 

Usually when i SH the cuts are deep but dont bleed that much, but on a couple ocasions the have been bleeding alot producing a fast flow of blood.
The ones that dont bleed alot often appear to be alot deeper then the one ones that pour..
Why is this? & How do you know when its bleeding to much?

My guess is that cuts nearer the surface have lots of capillaries, deeper ones may be into fatty tissue and wont bleed as much. It all depends where your harming, but dont state where cos it cant be discussed with anyone other than FAA.

Always apply pressure and keep the wound elevated if you can, if it doesnt stop or significantly slow down in bleeding within 10 minutes you need to seek medical help.

Have you looked on the first aid articles?

if its fast flowing blood chances are you have nicked an arteriole which is one of the blood vessels under your skin. smaller wounds have a lot more capileris so can seem to bleed more.
you should put pressure on your wounds as soon as possible after cutting them to prevent too much blood loss.