I found this it might help
1 Using the tracing paper, draw a rounded triangle shape on the paper. The size will depend on how large you want your final speed bag to be. Remember that you will be sewing the edges together, so you will want the pattern to be larger than the size that you want it to be. You will need about four to six pieces, but you only need to make one pattern. After you have the pattern that you want, pin it to the cloth.
2 Use the scissors to cut the shape from the cloth. Pin the pattern to the cloth and repeat for every piece of the bag that you decide to cut out. Put the pieces together.
3 Sew the sides of each piece together with the heavy thread and sewing machine. After a few pieces, this can get a little tricky. The last seam might have to be sewn by hand, or you can turn the whole thing inside out and sew it.
4 Turn the bag right side out and fill with your desired stuffing. The wood chips will make for a softer bag, but the sand will give you a better workout. Fill up almost to the top, but don't fill it up all the way, as you will need to sew up the top of the bag.
5 Insert the tab of fabric inside the bag, leaving the top of the tab hanging out. Stick the metal ring inside the tab, so that it sticks out along with the top of the tab. Sew the top of the bag closed (you will most likely have to do this by hand), sewing the tab together along with it. The bag should be taut and not hanging loose anywhere. You should be left with a tab hanging out of the top and the metal ring attached to it. Hang the bag from any speed bag board, and you are done!