So I have created a door panel that has a herringbone design using 1" x 6" thin black walnut panels. I went through and filled small cracks with a glue / sawdust mix and then sanded it down as normal with a random orbital sander. It looks great when looking at it but feeling it, I can feel where I wasn't as even at the spots that had the putty. I want to of course correct this before applying finish.

What are some effective ways to take out these "wavy" spots? The random orbital seems to take forever even with a 60 grit so was hoping for something easier. Would a wide belt sander do a better job at leveling these out?

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    ROSs are basically finish sanders so they're not very suited to removing much material, but even with that fitted with 60 grit the rate of removal should be pretty decent. However I think the issue might be the foam backing of the sander, as this is soft enough to conform there's a tendency to remove softer material more quickly and leave harder areas sitting a little higher, inherently creating a sort of wavy surface. Does that sound like it might be the problem? Re. an easier method to get the surface very flat, do you have any hand planes or scrapers? – Graphus Nov 5 at 15:47
  • @Graphus No hand planes. I have a large powered planer but unfortunately my panel is too wide for it. Would a belt sander do a decent job to get it flat again? – Eric F Nov 5 at 15:54
  • Finishing scraper? It's what luthiers use to get both shaped and flat contours. – jdv Nov 5 at 16:31
  • Belt sanders are better at maintaining flatness, or achieving it in the first place. Part of this is the nature of the way the belt moves but a great deal of it is due to the hard platten the belt rides on so it won't conform to an irregular surface but instead skims the high points (same basic principle as in a longer plane flattening a surface). However, getting a dead-flat surface over a wide area is challenging with a belt sander. – Graphus Nov 5 at 16:36
  • You didn't mention a scraper, if you don't have any scrapers yet I highly highly recommend you give 'em a whirl as scraping is awesome. If you want to get a taste of what scraping can do without spending a dime you can scrape quite well using a long-bladed kitchen knife (this is what I learned to scrape with and still use sometimes). It works best if you steel the edge to leave a burr on one side but still works well enough if honed conventionally to a sharp edge. – Graphus Nov 5 at 16:37
up vote 3 down vote accepted

Some sort of planer or scraper is probably what you want. Sanding can take edges off bumps, but isn't actually that great for getting things flat. (Well, not unless you put sandpaper on something very hard and flat. e.g., when truing up metal surfaces by lapping them on fine grit paper attached to a nice flat surface.)

Since you are going to the effort of creating a nice piece of cabinetry, it may make sense to use a cabinetry finishing tool, and take off targeted curls of material where the bumps are, letting your hand and eye tell you when you've trued things up enough. As per the comment, use a straightedge to get an idea of where the high spots are. Mark these and take your time to get the panel down to reasonably true.

I actually wouldn't use a belt sander for this purpose, as it seems a bit overkill. Belt sanders, to me, are for taking off material fast, but as a finishing step I think I'd be afraid it was too aggressive. Not to mention that I think the main issue you are going to have is that the material you are trying to level is a mixture of hardnesses, so the softer material will always come off faster. Sometimes you end up chasing trueness as you gouge out the softer material faster.

Luthiers would use calipers to test thickness, making pencil marks where material should come off. Then they scrape, test, mark, repeat. You can do this, too, if you want a very nice true finish. This might be overkill for the purpose discussed here, but if you have marking calipers these can work similarly to a straightedge.

There is an art to using and maintaining scrapers for this purpose, but the results are way better than sandpaper (IMHO). Once you get the hang of it, it is super easy to target fine areas without touching areas around it -- something sanders are just not that great at.

You can find more details about scrapers by searching "finishing scraper" in your favourite web search. That got me enough results to fall down a rabbit hole of related information!

  • I do like the idea of using the scrapers. What is a good method for identifying the high spots if the panel is wide / long for calipers? – Eric F Nov 5 at 17:08
  • Also is getting a wide scraper better in my case or a narrow one like a 6" wide one? You have been super helpful so far by the way! – Eric F Nov 5 at 17:14
  • You can build deeper mouth calipers out of a few pieces of wood, a dowel and a little pencil that can be moved up and down in a friction-fit hole (or a set-screw). The idea is that you get an idea of your minimum in a given area, set the pencil depth to that, and then use it to identify high spots. This is not a place where you care about the actual thickness dimensions, but rather the relative thickness across an area. Your eye and hand-feel will tell you a lot, as well. – jdv Nov 5 at 17:15
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    (It occurs to me that "How can I gauge thickness across a panel when calipers are so often so small?" might make a good follow-up question. I've seen home-made panel thickness calipers in a few shops, so it must be a common trick.) – jdv Nov 5 at 17:20
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    @Graphus, agreed. I certainly intended for my second graf to be the full answer to the question at hand. If this were me, I'd use a straightedge to get an idea of how true things were, and then pretty much true things up by eye and feel until it just looked good. Working with wood (instead of, say, metal) has a lot of advantages, and one of those is that there is only so much accuracy available to the material. – jdv Nov 5 at 20:15

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