A shop near me has the perfect way to quickly make perfect HST! Sundays' Best in Ellerslie GA has their own line of stencils. Linda Camp, the owner, will happily mail you the sizes you need. Here is a link to her video.
http://www.sundaybestquiltworks.com/...etriangle.html. After purchasing several sizes I now have a Pinterest board devoted to HST quilts. They are fun, quick, and eye catching!
Be sure to tell her I sent you!