I know that I would use the same machine for a top from start to finish but it sounds like she was saying you had todo it her way or you were wrong. The seas may be different on machines. As for bobbin thread, I did not even know there was such a thing and I have been sewing for 50 years.

It DOES make a difference. Even the 1/4" foot on the same TYPE of machine (i.e. Pfaff 2170) will be different enough to make your seams a bit off. You don't have to specifically use bobbin thread, but don't change the type of thread throught the project. If you're making a block that you need to trim to size, this isn't so much of an issue. But better to be safe!

I have never heard of "bobbin thread" until now. I've always used the same on top and bobbin.

I agree about the ruler. I am one that no matter what I do my seams aren't perfect but if I use the same ruler and measure my 1/4" seam on each machine it doesn't matter what machine I use. The seams are the same mess on either machine lol..

I use bobbin thread all the time and have never had a problem. My favorite is Superior's Bottom Line in natural color. It is strong and well-made. The owner of Superior Threads gave a presentation at a LQS and he said it is good as the TOP thread, too, so I have been doing that and LOVE it! Since it comes on big spools as well as smaller ones, I sit and fill 10-12 bobbins at a time and then I'm ready to go! very economical.

Bobbin thread and prewond bobbins are usually polyester like serger thread, tex 25, but are lots stronger than cotton.Some prewond bobbins are also cotton, but are usually size 60. so is Coats & Clark dual duty cotton that we have used for years on both top and bottom for clothing, quilts, mending, etc.
The only thing we have to watch when using poly is not to iron the thread as it will melt, so iron, press on the right side only.
Bottom weight is made for bobbins for embroidery and prewond bobbins. I would not use it for top quilting.
Phyllis 81 yrs in Oregon

I have used bobbin thread only in one quilt and will never use it again, the seams did not hold up well. I am not trying to speak badly against a product but this was the experience I had.

I use Anton-Robison bobbin thread all the time and it is very tough even tho' it is thin. I have never had any problems with it and it sure goes a long way. Don't have to stop and wind so often!

I have never heard of bobbin thread either.

I like to use the same machine for all my piecing. Latley I've been doing my piecing on my FeatherWeight. I am not real picky with my thread except for garments. It's interesting to read other opinions.