hi Wysrd,
Thanks for the positive notes on my stitching. I can share a few tips for stitching by hand I've learned.
1) I bought two 4-prong stitching chisels in the same diameter and spacing. I took one of them and removed the outside prongs... producing a 2-prong chisel. This allows me to do curves much more gracefully. Whenever using the chisels, I make sure one prongs is in a previous hole, preserving the spacing.
2) I don't go all the way through my leather with the chisel... only into/through the top layer. I use a drill press to finish my holes (preserves vertical) using a drill-bit that is smaller than my groove, but just wide enough for cobblers stitching (typically 2mm-2.5mm diameter).
3) After every complete stitch (the hole has thread going in both directions), tension both lines in opposition to countersink the thread into the groove. To get the best results, it's key to make sure this is done after every stitch; waiting 2 or 3 will not provide the same results.
4) For the second pass through a hole, always enter on the leading side of the hole (between the previous thread, and the fore edge of the hole. This reduces/eliminates the chance that your second needle will pierce the first thread as the sharp point goes through.
5) Groove the top only after the entire sheath is glued, assembled, and the edges sanded. This gives the best chance for the groove to remain a consistent distance from the final edge.
6) Create a groove in the underside only after you've drilled/chiseled holes. This will give you control to make sure the holes are centered in the channel.
Hope this helps!
Cheers,
David