I went to About.com and found a picture of the side-by-side rulers. Let's see if this will work:
http://quilting.about.com/od/rotaryc...ing_strips.htm

OK, I checked it. It went right to it.

I had trouble with bowing too until I got the new ruler with the built in strip cutter.

It works the same way the circle ruler works, slits cut into a ruler every half inch the whole way across the ruler. When I lay the ruler on the fabric after lining up and ironing, it covers about 18 inches of the fabric. I got mine at Walmart but I have seen them at Joanns and a couple of other sites and I paid 13 dollars.

Hope it helps, it helped me.

Along with the alignment comments I have one that helps also. I use a wider ruler when cutting strips. 6 inches or wider helps in making sure that the line on the ruler is perfectly aligned with the fold of the fabric.

Happy cutting!! :D

That would have been my question. I usually hold the fabric selvage-to-selvage and see if it is skewed. Then I shift one selvage until the piece hangs even. I do not have problems with bowed strips when I use that method.

That's what I do. The grain has been set already by the manufacturing processes, so you're just concerned about getting a good flat fold. Then you can use the ruler to get a good 90 degree angle for the cut.

Unless you HAVE to have 45" strips, I cut the strips in half before piecing. You will have to make twice as many strip sets, but your sets will be easier to pieces and press.

**********************SUPER SIMPLE***************************

GO TO YOUR LOCAL QUILT SHOP. HAVE THEM SHOW YOU HOW TO DO IT CORRECTLY. THAT'S WHAT I WOULD DO BECAUSE I AM A VISUAL LEARNER. I HOPE THIS ...LET US KNOW WHAT YOU DO TO REMEDY THIS PROBLEM. :D

Yes. The longer the ruler is lined up with the fold, the closer you will be to an accurate 90 degrees. If you line up only 3 or 4 inches of the ruler with the fold, it's quite easy for the cut to be off 2 or 3 degrees at the other end of the ruler.

I agree with prism99. The folded edge is the key. I have to fold at least twice to make 4 thicknesses because of lack of space. I put the folded edge on a straight line on my mat. Then, using a 6" wide ruler, place a line going across the ruler on the folded edge/mat line, and cut on the long edge of the ruler. Move the ruler over counting squares on the mat, line up the width lines, and cut against the long edge. I saw this on simply quilts. Basically, you move the ruler, not the fabric. I, too, make sure the folded edge is toward me.

I never iron first. I smooth with my hands. I'm lazy. 8)