I started using titanium plated machine needles. They last much longer then regular needles. I can machine quilt several big size quilts with one needle. I can tell when the needle goes dull so it's not just a guess on my part. I buy these:
.... Most professionals recommend changing the needle every project or, if you count, every 8 hours. Imagine having a needle that will last 40 to 60 hours. This is equivalent to saving 80% on the cost of needles.....
http://www.superiorthreads.com/shop/...s/description/