Are we talking about the same kind of groover? Like this:
or this:
I believe I’ve read of at least one maker who preferred to simply groove rather than cut an angled trench on the inside of holdfasts. Might have been DW Frommer II. Couldn’t say whether that was a groover like the above or a gum tool or scratch compass with a bigger cutter.
My experience has been that groover or gum tool will not reliably follow a curving, awl-scribed line on the insole leather I’ve used, either Baker or Panhandle. Your experience may differ! Mine has been consistent. I’ve needed pressure to make the little cutters bite the hard, wooly insole fibers. That pressure could drive the cutter off course from a simple scribed line. I’ve seen it done cleanly when the groove was split and opened.
As for spacing, I did my holdfasts a fixed distance from the edge of my insoles all around on my first pair, but I quickly moved to varying that distance, and therefore the distance from edge to channel, as well. Further in through the waist, especially on the medial side. With a welt, the groove’s a fixed distance off the edge, and the edge’s ideally perfectly straight.
I tried doing just a groove, too, without cutting any angled slope. I think that was my second original pair, though I don’t seem to have taken a good photo. It worked, but it made stitching slow. Without a little ramp on the inside, my bristles would often crash into the side of the groove and not slide through. It was also harder to feed them inside out cleanly. I was also snapping inseaming awl blades at an unfortunate rate.
When I managed to get sewing a little smoother, I realized I was pressing my inseaming awl into the side of the groove, essentially embossing in little ramps, and using those to guide the bristles. Much easier to carve out a little ramp beforehand. It’s quick work with a sharp knife, good moisture, and practice:
This is one of my favorite things on the Internet. Sorry to anyone seeing me link it for the umpteenth time.
@x24leathers, don’t let me talk you out of anything! Follow your instincts, take some photos, and share your experience. And feel free to start topics to discuss this specifically, or your projects overall.