The popping sound is my cue to change it also. I don't go by how many hours sewn with them because some projects give the needle more of a workout, like paper piecing or making baskets for example. If I happen to bend one I change it right away.

When it bends or breaks.

I only change mine when I hear the popping or it breaks.

I agree. I have two industrial machines and have to special order needles. Thankfully they just seem to go and go!

I change my needle depending on the project I am doing and which sewing machine I am using.
My Viking Rose will NOT sew-- skips stitches, bundles the bobbin thread, etc- if the needle does not match the thread and the application. I could try to sew but it won't be fun.
My Pfaff is about the same. When I get tension difficulties, I change a needle, and usually that helps.
My vintage Singer can be stitching along for days. she seems to like certain needles.:)

I'd never thought about this before, but isn't it strange how so much to do with sewing machines has changed in design, style, and function along with other things, but needles are still the same as they were in the days of the treadle machine?

My needle sounds like it is popping through the fabric.

ok folks, here is a funny story. I think it is anyway. I was new to quilting about 4 years ago and I started out sewing on quilts for the church quilting group. One year I sewed 186 quilts. No joke using the same needle. When I heard that I should have been changing the needle between each quilt, I darn near died laughing. 186. That was sewing the squares together for bed sized quilts. LOL I'm still in awe at my lack of knowledge back then. LOL

I change mine for every project, usually; sewing machine dealer recommended changing after every 8 hours of sewing. I figure I'm pretty close.
Also, when a needle is getting dull, the machine sounds a lot more like thunk, thunk, thunk, than when a needle is new.