I've had two or three folks having trouble with making their trees at 45 degree angles. There were comments on the Moda site and on my own blog post about it. This is SUPER important since the shape of the entire quilt depends on this. I am SO SORRY that folks are having trouble with this. I was intentionally a little vague in the original post because I knew that every cutting mat will be a little different and I thought I would save confusion by letting you figure it out on your own mat for yourself. CLEARLY, that was the wrong decision on my part. :) Please forgive me for the trouble this may have caused you. Hopefully this post will clear things up considerably.
Unfortunately, I no longer have the original quilt. My mother has it. 2000 miles away from here. So pretend that this crazy rainbow fabric looks like a Christmas tree. If you have toddlers like I do, it's not so hard to imagine after all. ;-)
Your 5 strips (2 1/2" wide) sewn together should measure 10 1/2" top to bottom now. For demonstration purposes, I cut myself a 10 1/2" wide strip of fabric.
Below is a picture of my cutting mat. The first time I made a tree skirt like this, my trees were not 10 1/2" tall; instead they were 12" tall. So the black ink you see on my cutting mat was originally for a 12" tree.
Do you see this right angle here below? That's 90 degrees.
A closer look for you:
Half of 90 is 45, so thisis a 45 degree angle below. My cutting mat already has this 45 degree angle on it and I believe most mats do as well. When making my 12" tree (remember: yours is only 10 1/2"), I measured from that top point down both sides of my 45 degree angle 13". In different words: from that top point to where both sides of the 45 degree angle meet the black line is 13". Across the base of this new isosceles triangle measures 10". In other words: the black line is 10" long. The height of this isosceles triangle is 12", exactly what I wanted at the time.
I can still use this black line to help cut my new trees in triangles that are only 10 1/2" tall. First, line up your fabric along the black line:
Cut diagonally like so:
From that top point to the lower right side point should measure 11 1/2":
If you're right handed, as all the instructions so far have assumed (!), just turn the mat around or walk to the other side of it.
See how in the above picture your tree top point is not lined up like it is in the picture below? In order to get that 45 degree angle to come to a perfect point, I pulled my 10 1/2" fabric down to the intersecting point on my cutting mat:
Zoomed out, it now looks like this, with my fabric pulled back from that original black line, but still PARALLEL to it:
Cut along the 45 degree line:
The base of your isosceles triangle should measure 8 3/4" inches:
The height should still be 10 1/2":
Ta Da! Wow, I hope this helps.