Why does my swivel knife keep dragging when I cut small curves?

It's probably a mix of all three, but the drying leather is likely the biggest culprit. Veg-tan that's drying out mid-project is exactly when swivel knives start dragging and catching, especially in tight curves where the blade has to plow through fibers instead of parting them. When the middle of the panel has gone pale and stiff compared to the edges, that's your sign. You can re-wet just that section with a damp sponge or a spritz from a spray bottle, feathering the edges of the damp area so you don't get a hard water line. It won't ruin your tooled parts as long as you're not soaking them, but the casings will soften slightly, so let it sit ten or fifteen minutes and get back to that crispness before you cut. If you're nervous, do a test swatch with the same leather and try tooling a re-wetted area next to a once-dried area to see how much the detail shifts. On the angle question, upright is right for straight cuts and long sweeping lines, but for tight little curves a lot of people roll the barrel slightly, maybe ten degrees or so, toward the direction of the turn. That keeps the cutting point from biting in on the outside of the curve. What matters more is that the blade stays in the same plane as it moves. If your wrist is rolling the blade as you turn, that's when you gouge. And yes, turn the leather, not your hand. That's standard for anything past a gentle arc. Keep the swivel knife anchored, thumb and first finger steadying the barrel, and rotate the piece underneath with your other hand. It feels awkward at first but it's the only sane way to do tight rib and spine curves without cramping up. Some people put the piece on a lazy Susan or a rotating cutting mat for bigger panels, though for a wallet-sized piece you can just pivot it in your lap.

Last thing, if it's still catching after re-wetting and re-stropping, check the tip itself. Sometimes a tiny burr or a nick from hitting a hard spot is the real problem and no amount of stropping fixes it until you re-sharpen properly on the strop's compound side with a consistent angle.

One thing that helped me a lot with tight curves: don't try to cut to full depth in one pass. When I tooled a dragon spine panel last year I ran the ribs twice, first pass maybe half depth just to establish the line, then a second pass to finish. The blade catches way less when it isn't plowing deep through a turn, and if it does jump you've got a shallow groove to correct instead of a gouge. Also consider a finer barrel if you're working with a wide one, the tighter radius blades just track small curves better.

The thing that finally fixed tight curves for me was switching to a smaller barrel on my swivel knife. I spent months fighting a big heavy barrel trying to do feather work on a belt panel, kept rolling the blade every turn. A friend lent me one with a slim barrel and it was night and day, way less leverage fighting me on the pivots. Also on the drying issue, I got in the habit of keeping a scrap of damp cloth or some plastic sheet over the part of the panel I'm not working on yet. Slows the evaporation down a lot on bigger cased pieces so you're not re-wetting mid-session.

Update: turned out it was mostly the leather drying out, like the first reply said. I misted the middle section with a damp sponge and let it sit, then did the two-pass trick on the ribs, half depth first, then finish. The curves finally glide instead of catching. Still cramped wrist but way less gouging. Wallet panel came out clean enough to finish!