Originally Posted by OdessaQuilts
I agree with Donna, I thought it could be your seams, but then I went back and re-read your original post. If I understand correctly, you are discovering problems when you put 2 pieces together to sew them, right? If that's where you're noticing the problem, there are fixes.
First, are you holding your cutter so the blade is straight up and down? You do not want to "angle-in" toward your ruler, as this will give you an "off" cut. If one cut is angled and the next one straight, your block is going to be "off".
Secondly, why are you only cutting one layer at a time? A 45mm blade can easily cut 4 layers without difficulty. If you've got your fabrics laid out nicely, you can certainly get accurate cuts easier (I believe) with more than 1 layer of fabric. (Please don't take this as a "snippy" comment, I'm just trying to understand...)
When you cut, how are you holding the ruler? Many people put a lot of downward pressure on the ruler, which can actually move it during the cutting process. Obviously, you don't want that "shift" to happen, so use a lighter touch. Also, one of the things I hit upon when I first started rotary cutting is to keep the heel of my hand and my little finger just off the edge of the ruler. This gives me a little more security in "feeling" if the ruler is drifting.
Don't apply too much pressure from the blade up against the ruler. This can also cause shifting of the ruler and therefore, a "wonky" cut piece.
A sharp blade is very important.
Also, if your pieces are off by a thread or two, it should be okay. Lay them together so they are as centered as they can be, and sew with a 1/4" seam just as you normally would. If you are seeing a thread or two of the underneath fabric, it's okay - just use that edge to line up on your machine/foot/line for your 1/4". If the two pieces are more than a couple threads off (like perhaps 1/8" or more), you should re-cut.
Finally, if these tips don't help you, I'd recommend that you go to your LQS, if you have one nearby, and ask someone there for some help. I wouldn't recommend a big chain store, because sometimes they're just too busy. But a LQS is there to provide SERVICE TO THE CUSTOMER. They WANT you to be happy and successful, because that is what will keep you coming back and their doors open! Ask if you can bring in some fabrics and your tools and have someone watch you cut. They may be able to pick up on something that we can't necessarily "see" from this board and the help will be invaluable to you.
I hope that this will help you to have a better cutting experience. Good luck and let us know how you make out!
Odessa