I am trying the iron on tape now. I have the batting edges meet and iron the tape. Next when I move the batt around, I can see a tiny sliver of a gap where the batting edges pull apart. Do you iron the tape to just one side of the batting?
Thank you!

I also have the Janome 6500P and use my batting scraps to make a larger size for a quilt. For me, I barley overlap the edges of the batting and use a wide zigzag stitch with about a 3.2 length setting. Mine doesn't bunch up. Are you using the correct settings as indicated by the screen?

I use the batting seam tape. Right now I have a number of pieces pieced together in various sizes. I'm quilting smaller projects on the frame using up all these smaller pieced battings using one large muslin backing. Just keep adding the batting when I run out, rolling the muslin along, adding the next project. Great way to clear off my rod I keep all projects waiting to be quilted. I'm also quilting fabrics for various future projects such as dining table chair seats, toilet seat covers, etc.

That was terrific! Thank you.

I looked at JoAnn for batting tape, but it was all double sided.

I own a Janome 6500. I also piece batting all the the time. Using your regular zigzag foot, I set my machine at "7" - for zig zag width and "4" for the stitch length. Make sure that you are feeding the batting evenly as you sew, don't push or pull on it.

I use a stitch on my machine that looks like a broken zig-zag. (< >) something like this with a space in the middle. Never have any bulk. Always nice and smooth.

I hand stitch them together using a very long zigzag stitch. Have to be sure to know it at the beginning and end of a seam.

I would just iron it to one side. When you baste, don't stretch it, so that the edges stay together. Ultimately, if there's a millimeter of space there it probably won't matter once you quilt it, as long as the space isn't along a fold line in the finished quilt (folding right along there would make it spread more).

With pieced batting, I always try to quilt more heavily than I would with an unpieced one, to keep the joins from opening up.

I like the spray basting to the back technique that someone posted. Going to try that, think it would work with glue?

I have a Janome 8900 and use the largest zig zag both in length and width. The seam lays flat. I go slow so the two edges stay together and let the feed dogs guide the batting. I don't pull or stretch it. If the seams aren't meeting then before I start stitching I overlap the batting a little bit and cut with my rotary cutter, that way I have matching seams to butt.