Hi,
I had the Sapphire 830 and it just didn't perform as I thought it should for the money. I was encouraged to upgrade and did to the 870. What a difference. I have no problems winding bobbins and it sews like a charm. The greatest feature for me is using a walking foot. I thought it was expensive, over $100 , but it was s-o-oo-o--o-o worth it. I was told not to use Coats and Clarkes thread soI purchased Sulky, Gutterman and Modera. It is real important to try to have the same thread in the top and the bottom also, unless you are using invisible and metallics on the top and regular in the bottom. I also find that the thread flows better when I place the spools horizontally, rather than vertically. Enjoy!!!