OK friends...This is how to avoid the dreaded "V" strips when you rotary cut a full width of fabric.
First of all, press your fabric well so that the selvages are parallel to each other and there is no fullness between the selvages and the middle fold on either side. Preferably, you fabric will be starched, but it's not absolutely necessary. It is necessary that it's flat and parallel.
Lay the fabric on your cutting mat with the folded edge away from you and line it up
exactly with one of the horizontal lines of the mat.
Measure down about 11" from the fold and place a ruler horizontally across the fabric. If it doesn't reach to the other side, add another ruler so that the entire width of the fabric is
absolutely straight across the horizontal line of the mat.
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Carefully fold the selvage edges up towards the middle fold. You should be able to just barely see the horizontal line the entire length of this fold.
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Carefully remove the rulers from inside the fold and start your vertical cuts from either the left or right side of the folded fabric. With every cut, check to see that the folds are still lined up with the lines on the mat. Ta-Da! No more "V"s!!