However, I have been doing my own framing for a while and here are a couple of other things to add:
1) Most samplers are not matted. A mat acts as a spacer between the glass and the fabric so that air can circulate and not trap moisture which can damage the needlework over time. If you are not going to use a mat, you should use spacers - this is what framers use and can be found at any framing place. They are small and fit between between the frame and fabric.
2) I have found that most store bought frames cant accommodate the thickness of foam board. (If you dont mind it sticking out in the back then its fine). I use acid free uncut mat boards as backing but you cant use the pinning method since it is too thin (you can try though). You just have to be careful to keep your fabric centered and taut while you sew it around.
chekccard