I use black electrical tape to create a scant 1/4" "jig" on my machine. Stack 3-4 layers of tape right on top of each other, with the bottom layer stuck to the plate of your machine, and you've got a nice wall to run your fabric against as it is feeding. This allows you to keep pressure on the outside edge of your fabric, while it is tapering to a point, without risking the seam getting wobbly or wider than 1/4". No starch, speed reduction, or special tools required! Works like a charm.