|I was attempting to repair a raveling hem with my blindstitcher. I have one with a curved needle (not sure if this tip applies with the straight-needle models, I have not used one of those). Note - this is not a regular sewing machine, this is a dedicated blind stitcher.
The fabric was a very thin and slippery silk/spandex blend, just a touch heavier than chiffon. I couldn't adjust the machine to consistently take a small "bite" out of the fabric - the needle either would gouge a huge chunk with each stitch, or it would glide over the surface, missing the fabric altogether.
In addition, the folded-over part of the hem, the edge of which is supposed to align to the center of the sewing area, kept slipping out of place. Securing pins could get only so close to the needle swing area, and I didn't want to use washaway tape to keep it in place because the blouse is dry-clean only.
So. To re-hem the blouse, I did 2 things:
1) I cut a strip of tearaway stablizer and put that under the fabric. This pushes it up into place, allowing more consistent stitches. I initially thought the stabilizer would be incorporated into the hem on the public side (hence the tearaway), but the needle never touched it. It was thick/stiff enough that it nicely pushed the fabric into the correct position and the needle grabbed only the fabric.
2) I gave up on the foot controller and handwalked the hem. That way, I could see every stitch forming, and if I saw the folded part slither away from the center groove, I could catch it with a pin and maneuver it back in place before the needle came back 'round. If you do this, make sure you don't accidentally pull the thread off the looper.
I know this seems like kind of an arcane tip for a machine that few people own, but hopefully it will help someone in the future.