Can the top thread and bobbin thread be different weights?
 

I was wondering if the top and bobbin thread be different weights for machine quilting, or do they need to be as close as possible. I was going to use a monifilament for the top, can I use a prewound bobbin for the bottom. I'm not sure what the weight is on the prewound bobbin, but it is quite a bit thicker then the monofilament. Any help would be greatly appreciated.

Yes it can be done. Make a practice piece with some of the scraps from your top, backing and batting so you can get your tension set. The prewound bobbin thread might not be "grippy" enough for the mono so you might try a regular thread for the back if the prewound is giving your problems. I usually use Mettler for the bobbin with mono.

Agree with Scissor Queen ... I actually have notes taped to the inside of my quilting thread box telling me which weights work nice together along with needle size and tension settings.

There are limits though ... even with fooling with both top and bottom tension I just can't get a 12wt on the top to work with anything lighter than a 30wt on the bottom. BTW .. I have a separate bobbin case to use just for "let's mess with the tension" sewing.

mine works better with same kind of thread in bottom.

Not on my machine

If you can get this to work it would be good -- used monofilament myself, and the last time winding the bobbin it actually got so tight the bobbin wouldn't release from the winder, had to take my sewing machine into the shop to see what was wrong. Removing all the mono solved the problem, it had actually cut the bobbin in halve...strong stuff. In the future will use a prewound for the back.

Funny that I was just reading through Diane Gaudynski's book about quilting threads. She recommends a 60 wt thread in the bobbin with .004 monofilament and a #70 needle. She says she never uses monofilament in the bobbin.

I think it depends on your machine, so you just have to give it a try. One of mine will work with anything, the other throws a tantrum (impossible to get the tension right) if I don't use the same thread top and bottom. They're both Janome machines, both supposed to be suitable for quilting.