I change my needle when it makes a 'thunk' noise, or when I am changing to a project that requires a differnt size or a thread that likes a certain needle. I just bought some "Inspira" brand that Viking recommends, and I won't do that again. They dull in about three or four bobbins worth of sewing, when I use the Schmetz will last for about a dozen bobbins. I don't like the singer brand needles any more, they used to be great, but now they seem a tad short and can cause missed stiches even in joining just two layers of cloth together. So yeah, about every dozen bobbins, or if my machine requests it, sooner. I have found that the 'organic' cottons (I had some from Birch and some from Jaycyn) that I just worked with dull the needles more quickly, too.

I change with each project, place the old needle in a pill bottle (lable removed) and when it gets fairly full, I fill in all the space with plaster of paris and just toss in the trash

I usually change out for each project. On my quilting frame I change out every 5 hours of stitching.

Yes I have to admit that's what I do too. I have a question for all you good people. What about sewing on Insulbrite? Does it dull your needle or actually sharpen it?

Jenny Doan (MSQCo.) said in one of here tuts that she doens't change her needle til it dies.

I change my needle frequently. I can see the difference a new needle makes in my sewing & piecing, so it's worth it! I use the type of needle that's appropriate for the job at hand. I buy my needles with coupons and when there is a "notions" sale. Like the Schmedt needles more than any other brands I've tried.

My husband has a sewing repair business and he always reminds me to change the needle. He says most problems are from old or improper size needles and not cleaning often enough.

I agree with your dealer but how do you measure 8 hours?! One tip that I was given is 8 hours is equivalent to 3 bobbin rewinds but I don't about things like that, everytime I quilt a project my sewing machine gets a good delinting a touch of oil, polish AND a new needle, I use size 14 Topstitch needles which is fab for FMQ, solves the breaking of thread and so easy to thread it you don't have a good needle threader. I don't use many dedicated needles as I mainly stick to ordinary quilting but I do use a metallic needle when use metallic thread, and for my piecing on my Bernina I am using my ordinary Organ needles until they run out and then will go totally Topstitch.

I learned in my sewing/quilting classes to change my needle for each new project - and to use the correct size needle for the fabric/thread/project I'm working on. Other than that, my machine starts to make a little sound like it's working harder - so I put in a new needle and it purrs like a kitten!

I don't know if i'm lazy or just plain cheap, I replace when they break. I never think of it till therews a problem. when emb. if I hear a loud poping sound, then i'll change it.