Sooo... I have some actual metal leather peening tools, albeit cheap ones.

I've been needing it for the last two days and cannot find it for the life of me, so I decided to just make one.

This isn't as ideal as a real one, as it will probably breakdown over time. If you peen rivets for leather regularly, this is probably sub optimal. However, if you just need to do a couple for whatever project or only do a couple here and there, this (potentially consumable) tool may help.

UPDATED- 3/3/24- I've added a slight tweak to the model to work with a common, cheap arbor press. The hammer version does work, as I'd test it earlier.

Current Iteration Settings--
10-15 walls for strength
10-15 Tops/Bottoms
75% infill
Using Super PLA+ from Overture
No supports needed for the normal one
Supports needed for Arbor press (I used quick tree supports--remember it doesn't have to be a perfect surface)
I recommend using Ironing to give the cleanest surface to the rivet-facing-sides, as print artifacts may transfer over to the rivets' faces
-Blend these to your needs, depending I suppose on how aggressive you press or hammer when peening

You -can- stretch the Z axis height to increase the domed finish if you wish to.

You can also use stacks of scrap paper on the faces to prevent marking up of the rivets. I think I'm going to glue on some small pieces of thin rubber/neoprene. Otherwise, works exactly how it should.

Bambu Labs P1P has it under an hour, at about 10.25g of material