Blind hemming.

[wrenkins]

I have to hand stitch a band to a bathrobe and it's a mile long so I thought I'd learn how to blind hem! It looks easy.
I put on my blind hemming foot and set to with some scraps.
First go...perfect! Unfortunately it was all down hill from there. There seems to be a problem with tension somewhere and eventually after several goes the bobbin gave up the ghost altogether.
I tried adjusting the stitch width and had a little play and I seem to have upset it somehow.
I put everything back to how it was at the start and it's still acting the a**e on blind hemming but when I put on my 1/4 " foot and sewed a straight seam it was all perfect!
One thing I should add is that I'm using a cone for my top thread. It's not on the spool holder on the machine but in a cup and threaded up through a safety pin. This had also been working perfectly well until now.
What am I missing?
I'm going to handstitch the robe as my thread isn't a close enough colour and I don't want to make a mess but I have curtains waiting to hem and I really want to use my blind hemmer.

[Ohsewsimple]

I'm assuming this is just a foot on a sewing machine.  Personally I never like the result I get with them.  Always prefer to do it by hand.  Seems quicker too taking into account all the faffing around trying to get all the settings right. 

[wrenkins]

Turns out it was the bobbin! The case wasn't seated correctly so I hit it a smart tap and off it went. 
I prefer the look of hand stitched too OSS but it's miles long. I'll do the robe by hand because I'd like a decent finish but the curtains are still under threat! 

[BrendaP]

Blind hemming is the stitch which is 4 or 5 straight stitches and one zig-zag to the left - or 4-5 small zig-zags on the right and one bigger zig-zag to the left.
https://www.thesewingdirectory.co.uk/blind-hem-tutorial/
I don't bother with the special foot, I just make sure that the middle of the regular foot is exactly over the fold of the fabric.