Hello I have looked up in my favorite 501 rotary cutting blocks book and it says how to make a 4" pinwheel ( by using 2 7/8" fabric for the squares) but I do not know if that includes seam allowance. how do I make it 4 1/2" it says to cut the fabric 2 7/8 inches to make the 4" block does this mean that once sewn it will be a 3 1/2 block. UGGHHH!!

forgive me I have had a weird migrain and I need to finish my moms vintage dresden plate quilt. I am trying to make it easy with strips and pinwheels in 30's print.

I would make a sample up and see what it looks like. Math is not my strong point.

Using 2 7/8" will result in 2 1/2 inch squares so it does include the seam allowance. Two 2 1/2" squares sewn will give you the 4 1/2" you need. I would recommend you use 3" squares and plan to trim the blocks to 2 1/2" when done. That 1/8" could make a difference in a block to small.

I don't understand that direction. I would assume the 4" finished pinwheel block is made from 4 half square triangle blocks. If this is the case then to understand then do what I had to do many years ago to understand the half square triangle concept.

So draw a square 4" and put the diangonal lines in as the finished pin wheel should be.
Each small half square triangle finishes out at 2".
Are You with me.
Then take the 2" square and draw on graft paper.
Put diagonal line. Then put your 1/4" seam allowance all around it. Then on the bottom from the square corner to the diagonal point measure. This will be 2 7/8"

When making triangles into squares you need to add 7/8" instead of the usual 1/2" to compensate for the angle.

So the directions are correct. four squares made of 1/2 square triangles with each triangle cut 2 7/8" will finish at 2 1/2" with seam allowances.

This should give you a 4 1/2" unfinished block. It will be 4" after sewn in the quilt. I agree to make a sample to be sure.

The math works. You always add 7/8" to what your FINISHED size will be. Since you need four half square triangles to make a pinwheel, each HST will measure 2 1/2". Once you sew all 4 together, you will end up with a 4 1/2" block, which will finish to a 4" block. At the same time, you could easily start out with a 3" square and trim each HST to 2 1/2", then sew 4 of them together.

Pinwheels are my favorite block. :lol: :D

Thank you so much for the advice. I will make it and see what happens when done will post tomorrow!! Thank you for thinking for me at least when I sew I don't have to think!

It will make a 4.5" unfinished/4" finished pinwheel. Most people would just cut the squares at 3" and then trim down the HST's (Half Square Triangles).

Know what you mean! Somebody asked me yesterday how I was doing and I said "OK, I guess, but my brain is tired!"...had been trying to figure out what somebody else did (or didn't do) in software I had not used in a long time.

So I made a trial and 2 7/8" square will make a 4 1/2" pinwheel. Whew! That was tough!