Inspiring Quilters, Stitch by Stitch
I have been teaching quilting for over 2-1/2 years. Here are some of my tips for more accurate rotary cutting. For those quilters who want their blocks to be "square" and their points to match, it starts with how accurately you cut the fabric. Fabric always has some stretch in it, so you have to deal with that even if you cut perfectly. Applying spray starch to the fabric when pressing it before cutting will help, but that is not a good option if you are doing fusible applique.
Accurate rotary cutting starts with the tools that you are using, particularly the rulers and rotary cutters. I never depend on the lines on the cutting mats when I am trying to make accurate cuts. The lines on the mats are usually much wider (and less accurate) than the lines on high quality rotary cutting rulers. Lines on the mats are suitable for less accurate cutting, like if you are cutting a 13" square of background fabric for applique, and plan to trim it down to a finished 12-1/2" square later.
A few basic shapes of rulers will take a beginning quilter a long way, without a huge investment. It is not necessary to buy a separate ruler for each size square or rectangle that you need to cut. Modern rulers are marked with accurate grid lines that make it easy to cut squares and rectangles of almost any size. Rulers can be taped together with blue painter's masking tape when you need a larger or unusual size, and you will still get an accurate cut.
Most new quilters first purchase a 6"x24" ruler. I have found that it is nice to have 2 rulers that are over 12" long but 4-6" wide to take instead of the 6x24" ruler, when I teach. I can carry these easily without risk of breaking them, because they fit in my rolling case. Then I tape them together with blue painter's masking tape to get the 24" length needed to straighten the edge of fabric. I have small hands, and the 4" width is easier for me to hold firmly.
After the 6"x24" ruler, the next purchase is usually a square ruler (or a set of them). Square rulers should be sized to include the seam allowances for the block, so for a finished 6"x6" block you need a 6-1/2"x6-1/2" ruler. Sometimes you need a ruler larger than 6-1/2" square, because you need to cut something wider than that. I have a 9-1/2" x 9-1/2" square ruler that I use often.
I bought a set of square rulers in sizes of 4-1/2", 6-1/2", 9-1/2" & 12-1/2". The ones used most are the 6-1/2" & 9-1/2" squares. The 12-1/2" square is valued when I need to square up a finished block or cut a WIDE piece of fabric for a border or background. (Often it is taped to other rulers with painter's masking tape for an accurate but wide cut.) I rarely ever look for the 4-1/2" square, as I can use the 6-1/2" square instead. (If I am making squares that small, I am probably strip piecing them instead of cutting individual squares.)
Recently some rectangular rulers have come out, that are 8-10" wide but 12-15" long. These give the capability for cutting squares (similar to the 9-1/2" square), but are also long enough to use for cutting strips. If you could only afford 1 new ruler, these might be a good option instead of a 9-1/2" square.
An important but often unrecognized difference in quality between rulers is the thickness of the plastic. High quality rulers are made with thicker plastic, but some of the lower cost rulers use thinner plastic. You can definitely feel the difference if you hold them next to each other (especially if laid on a flat table top). This DIRECTLY affects how accurately you can rotary cut! The contact area where the rotary cutting blade touches the ruler is what "steers" the blade, if you are holding the rotary cutter properly. So a thicker ruler gives a larger contact area with the blade, and makes it much easier to get a straight, accurate cut. I try to emphasize this to my quilting students, but many quilters seem to be unaware of it. I noticed this difference when I was beginning as a quilter, and stopped buying the thin rulers. I also prefer the larger diameter, 60-65 mm, rotary cutting blades for straight line cuts, because again I get more contact area with the ruler and thus more accurate cuts.
My favorite brand for basic rulers (i.e. squares & rectangles) is definitely OMNIGRIP, which is made by the same company as OMNIGRID. OMNIGRIP rulers have a nonslip coating on the back side, which makes it much easier to hold the ruler still while cutting! (This greatly improves the accuracy of your cuts.) The nonslip property is well worth the extra $1-2 in price.
When you buy rulers without the nonslip coating, you can apply something to the back side to make them less slippery. There is a clear plastic adhesive sheet (Clearfilm?) that can be cut to cover the entire back of the ruler. Or you can get adhesive dots made from either clear plastic or sand paper that can be spaced around the ruler. (You need to use lots of these dots - more than just 1 at each corner. Maybe place 1 dot every 6 inches.) I prefer something clear, so you can still see through ALL the lines on the ruler, but my friend swears by the sandpaper dots to prevent slipping.
I am also making a collection of triangular rulers (isosceles triangles, like an arrowhead, with 2 base angles equal). These are useful for a lot of quilt patterns, but can be hard to find with angles other than 45 or 60 degrees at the top. Often the size of the angle is not specified on the packaging. The Fat Cat ruler is 30 degrees at the top, but it is cut off there (i.e. blunt instead of pointed) so that I had to tape on a piece of cardboard to get the full use of the 30 degree angle. Some of the Dresden Plate rulers have angles of 18 or 20 degrees at the top. I just found a ruler with a 40 degree angle at the top at a quilt show, which is rare. I also found a right triangle with an 18 degree angle and cutting lines parallel to the short side. I bought 2 of these 18 degree rulers, because combined they make 36 degrees and I can tape them together! I can also use them with the 18 degree Dresden plate ruler to make a complete rectangular block. (My students say that I am too good at math & geometry...)
ROTARY CUTTERS & BLADES:
I cut mostly straight lines with my rotary cutters, for squares, rectangles & strips. I find that larger diameter blades allow me to cut more accurately for straight lines. Thus, I primarily use blades that are 60-65 mm in diameter. The 45 mm blades allow cutting gentle curves, but I rarely do that for quilting & piecing. When I need to cut curves, I drop down to a 28 mm blade, which is large enough to fit into the templates for circles but small enough to cut tight curves. I found that the 18 mm blade was too small to fit into templates for circles or to cut around plastic rulers. It is only useful if I am cutting freehand, and then it can be hard to steer. It was useful when I was cutting around shapes printed on paper patterns pinned to fabric.
Many options are available for rotary cutters. I tell my students to look for a brand where they can purchase the replacement blades locally. If they live in a small rural town, then their choices can be limited by places to purchase the replacement blades.
Personally, I prefer cutters where the blade latches into the open position for cutting. I don't like to have to squeeze the handle to keep the blade out while I am also pressing down & steering the blade to cut the fabric layer(s). I prefer to focus on 1 thing at a time if possible! I do want it to be easy to expose the blade (for cutting) and then cover the blade (when cutting if finished), preferably while using 1 hand on the rotary cutter.