Originally Posted by Prism99

Bends are caused by not having your ruler positioned ***exactly*** 90 degrees from each fold. Since you are double folding, you have to make sure that the ruler is hitting *both* folds at 90 degrees.

Basically, before cutting, you need to measure from one fold to the other fold all across the fabric, making sure that the distance between the two folds remains the same. If it does, and if you get your ruler lined up at 90 degrees from one fold, it will also be lined up at 90 degrees from the other fold.

Incidentally, holding the selvedge edges together and sliding them until the fabric hangs straight has nothing to do with whether or not you get bends in your cuts. It's a nice thing to do to make sure that your fabric lies flat on the table, and may help slightly with keeping the cuts on-grain. That's it.

If you want to test out the 90-degree angle thing, take a few sheets of paper. Fold them (with edges matching or any which way). Be careful to position your ruler on the fold for the 90-degree angle. (This simply means that the cross lines on your ruler match up perfectly with the fold.) Cut. Now do another one with the ruler just slightly tilted off that 90-degree angle. When you unfold the two pieces, the 90-degree cut will not have a bend; the other will. The farther away your ruler is from 90-degrees to the fold, the bigger the bend will be at the fold.

You can double-fold some paper and test again. With one sheet, make sure that the folds are equi-distant from each other; with the other sheet, make sure the folds measure closer at one side and farther away from each other on the other. Cut both with the ruler positioned at 90 degrees from one fold. You will see how having the folds equidistant from each other are the key to not having bends in the cut strips.