I have cut two of the under collar on the bias and and ironed on appropriate weight interfacing which I cut on the same bias. I then marked on the stand collar with chalk. I will only do this for the undercollar. For the top collar I will cut it on the fold. I will not cut the top collar until I have done my next fitting, just to make sure that it fits on the jumpsuit and the model appropriately. Always check, check and check again!!