Hopefully my mistakes might help other newbies..
Started making my first ever pinwheels last night and struggled abit with getting them exact....this is what I have learnt
1. It is much easier to use a template block. I am using a 5inch acrylic template, but it could be plastic or heavy card I suppose which is giving me 81/2 squares (8 finished). Rotary cutting round the template seems much easier and more accurate than using a ruler.
2. Fold each square in half and iron down the middle of the dark square making sure points meet, open up and gently press with the iron, making sure you can still see the diagnoal pressed line.
3.Put a light and a dark sqare right sides facing together then sew 1/4 inch either side of the pressed line. Then cut down that line and you should have two exact triangles.
4. Press...one you've sewn a seam press it. I once read a tip that said you should never iron the fabric as it can distort but press down with your iron.
5. Opened up you now have two squares...join togethether and you have half your pinwheel.
6. Make the other half exactly the same and then join together.
What I learnt last night was the secret to pinwheels is accurate cutting ( hence a template) and pressing.
I have written this because having made one and been really proud of it my next was a totally different shape and the next !
Now they are turning out all the same an even 81/2 block and it is so much easier.
Everyone will have their own way of doing them but I think any tips can help so please post them...us newbies need them.