ND10 filter came in today so I went back to the shop for more tests... I still can't capture great puddle flow
ND10 filter - ISO 12800 Aperture 4
https://www.youtube.com/watch?v=tdU9xOruZqY
I popped the ND8 back on and got a better shot. If you look below the welding area there's a reflection and you can actually see the puddle flow fairly well. (I believe it's a reflection between the UV ND filters being stacked together It shows up really well on my computer, after uploading to youtube it isn't as crisp because of the compression). And at the end I blew through the square tube.
https://youtu.be/iL4efaQPgtc
I have several other videos I didn't upload scrolling through the apertures trying to find something that worked well but its hard to dial it in by myself... I think there was a point where I was just having fun O/A welding and kept going trying to improve... Still got a long way to go.