More Help Needed in Sandwiching
 

I got my throw size quilt sandwiched with no wrinkles. I am doing the happy dance. But, boom, brain hit a brick wall. Do I trim off the excess batting/backing now before I quilt it, or after it's quilted? I'm working on UFO's and been awhile since I actually quilted something. Thanks for answering a basic question.

After is better imo.

I think you need to wait till you're finished. That's what I do and that's what I learned.
Quilting could make things spread out a little bit and you want to be sure there's something there.

I always trim after. Sometimes either to top or the back slips.

Generally after ... howeverrrrrrrrr .... it depends how much you mean by "excess"!

If the excess is excessive, for either or both,
you may want to trim some off before you start quilting.
Otherwise, the excess could create way too much bulk, be in the way and
all-too-easily fold over and get quilted into what you are doing.

i always trim after because the quilting can draw up the quilt top.

If I have a large amount of backing and batting. Then I trim to about 2-4", in case quilting takes up more.

What QuiltE said.

It's nice to have a couple of inches of backing and batting at least around the edges so you have something to hang onto while quilting at the edge and to also have a space to put a fabric scrap off the quilt to test your thread tension.

I would wait until later. You never know what may happen between now and then.

after quilting don`t trim your backing and batting flush with your quilt as it took me years to get a full binding leave a little as in this video i use Gale
http://www.mccallsquilting.com/mccal...ining_the_Ends

If you're using your domestic machine and not a long arm, trim off up to about an inch or 2. The reason is if you have all that fabric flopping around as you quilt, there's a chance it'll wind around and pretty soon you've quilted the flap up under your quilt. I tell you this from experience.....if I leave too much extra fabric on the ends, I always have to get my seam ripper out.

After - I like to have something to hang onto when I'm doing the border. I've never needed the extra to allow for FMQ, except with a fleece back. I pin about 4-5 inches apart.

After is best in my opinion.

Also, I do a really long basting stitch all around the outside of the quilt before I start quilting, and one horizontally and vertically down the middle of the quilt. I normally work from the center out on my small DSM. I spray baste so the quilt holds together really well.

Yep, after is the best time to trim!

How much excess are you dealing with? You should always leave a bit because things 'move' when you are quilting.
Better to be safe and trim when you are done. But, you don't need to have 10" hanging around and getting in the way when you are quilting the top.