I wouldn't call what you're doing as tacking. Tacking is a hidden stitch usually done to attach a facing to a seam allowance. You are needing to do an invisible seam. I will try to explain how I do one.

Fold both edges of you seam allowance down. Baste if you have to. Start on one end by inserting your knotted thread up through the crease of one seam allowance. Come out as close to you machine stitching as possible. Go directly across to the other side & insert your needle from the top side of the folded crease. Don't catch any fabric..just slide it a short distance in that fold. Come out & go to the other side & do the same thing. Just go back & forth from side to side doing the stitch with your thread in the fold. Make tiny stitches 1/8 inch or so. You will have a knot showing where you finish but that should be the only thing showing.

Thank you Joan. It wouldn't surprise me if tacking is the wrong desrription for what I'm trying to do. I think I can try your suggestion. I may go through more thread, but if it looks neater. I'm happy.

I need to question what we are talking about. In the UK tacking most often means the same as basting - a temporary stitch to hold the fabric in place while the actual seam is sewn, either by hand or machine.

The small invisible stitches you refer to Joan, I would call hand-felling or if attaching a collar by hand, "draw-break stitch".

If you are indeed trying to attach the pieces with a temporary stitch, it is no harm to use a knot, but if you go over the first couple of stitches you do, one ontop another, that is usual quite sufficient to hold it.

On the other hand, maybe you did mean an invisible seam!

Have I just further muddied the waters!?

Cheers,
AJ

Don't know what the stitch I do is called because lots of what I was taught at a young age was by my mother or her sister. They basically said "Do this" to finish stuffed things....creatures, pillows, ornaments or even lined things where the item was turned & an opening needed closing invisibly. So I still "Do this" today.

If you knot the thread a lot it is probably because the thread is too long. Try using shorter amounts of thread.
Colleen