I made several of these pin cushions to fit into the space of a half block on my block pillows. This saves space on the pillow for moving bobbins and, because the pins are always in the same place, I don't need to look up to reach for them.
Draw around a half block on 2 pieces of calico or cotton. Draw a second line about 2.5cm outside of the first box. Sew the pieces together on the outside line, leave a space along the long side for stuffing.
Pin a pinch on the corner of the inside, unsewn box. Do this on both sides of the fabric.
Pull the two pins away from each other. Flatten the corner and sew between the pins. This creates a boxed edge corner.
Repeat on all corners. Trim off the triangle excess fabric. Turn box inside out.
Cut wadding (batting) into rectangles. Make them larger than the half block. Cut more than you think you need. You can use ordinary stuffing if you choose, but I found layers of wadding gave a more even cushion. Secure the pile with a few running hand stitches.
Stuff the box liner. Test firmness with a pin. If using stitched wadding, roll it tightly, push roll into box and unroll the wadding inside the box so it fits nicely into the corners. Sew up the open edge.
Cut some old blanket or felt to fit the top and bottom of the cushion. Use a running stitch starting in the centre, to compress the stuffing into a flatter block.
Measure around the block. Cut final layer fabric 3cm larger than this measurement and 3.5cm more at each end.
Sew along the long edge to make a tube with pattern inside.
Test how easy it is to fit the cushion inside about half an inch. If it is easy, sew a second line to make the tube narrower.
When it is really snug, trim excess fabric, turn tube inside out so the pattern is now on the outside.
I use two rulers to help pull the cushion inside. Hand sew the box ends
You could pin and sew the top cover by hand if you can tension the top fabric enough.
Sew the box ends up.
Hope these instructions make sense! I tend to just cut and make as I go along.
If you find your cushion is not high enough, cut a piece of exercise/camping mat and place it underneath the cushion.