Thanks for the perspective, Jon. On the bigger pieces, do you use an angle drill or a RO sander? I use both. The angle drill leaves pretty bad scratches vs. the ROS. I get the tough stuff with the drill, and then switch to the ROS for all the finish sanding.
I've tried powered sanding. I am not real sure what I think of it yet. I have both powered and inertial sanders for discs, and I've had similar problems with scratches...but, I think that depends on the wood, too. Softer woods are a lot harder to deal with regardless, I think? I am working with some live edge aspen blanks right now, and even hand sanding, I'm getting some scratch marks in the tighter corners that I am having a heck of a time getting rid of.
I mostly hand sand, and if I've done a good enough job with the tools, then the hand sanding goes pretty smoothly. The key issue is tearout...even small amounts that you may not initially see, will show up quite well once you start sanding. I've learned the key is, eliminate the tearout first, before moving to higher grits. If I move to higher grits before the tearout is entirely eliminated, then I inevitably end up back at the lower grit (usually 220 for me) anyway, and have to work through them all again once I finally manage to eliminate the tearout.
For tearout I DO sand with the lathe on, and that does produce radial scratches. However, trying to clean up tearout without power seems to be a futile endeavor...at least in my limited experience anyway. I think that a powered sander might help here, however I have yet to find a sanding disc I truly love. I normally use Norton brand sandpapers, which have a grit that just seems to do the job superbly well. I've never found a sanding disc, even abranet, that seems to do as good a job. So I guess that's probably one of the reasons I mostly hand sand. Once tearout is eliminated, then I can fairly quickly move through all the grits to achieve the finish I want. Once I start moving through grits, I'll alternate...lathe on, low speed, then hand sanded with the next grit to eliminate the scratches. On some woods, if they need it, I'll just manually hand sand through all the grits. I will usually sand up to 320/400 if I intend to use a penetrating finish, or maybe higher like 600 to even 1200 if I intend to use a film finish.
FWIW, I do think its best to try and eliminate tearout as much as you can with the tools first. Finishing cuts, sheer scraping (with a VERY sheer angle), a good french curve negative rake scraper for the inside of bowls, etc. are all better ways to deal with tearout. Sometimes you can really get it all, sometimes you don't see everything until you start sanding (I don't know why, sometimes the surface looks fine, but once you sand, I guess maybe the fibers shred and you can see tearout better?) If you see tearout once you start sanding, its still better to go back to the tools to try and remove it first, and use coarser (i.e. for me that's usually 220 grit) sanding to try and remove it before fully sanding.
For any tools, if you are going to try and clean up the wood surface, its best to sharpen right before you do, even for finishing cuts. A good, sharp tool will give you a cleaner cut than a not freshly sharpened tool, and sharp is key when trying to cut out torn out wood fibers. My weak spot is finishing cuts...I always seem to add ridges or valleys when I try to do finishing cuts...I can never quite seem to get that light, single-sweep, perfect cut that I see other turners using. So I usually end up resorting to a NR scraper or sheer scraping, which will usually do the job, just not as well.
