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I'm sanding a piece of white oak (originally flooring, if that matters, although this isn't for use as flooring). I have done this in what I think is the correct way: starting with 120 grit, then 220, then successively finer grits, down to 3000, to get a really smooth surface.

The wood is perfectly flat, so I used sandpaper gripped in one of those sanding blocks with a soft pad, and I moved in random orbits as best I could by hand.

The initial coarse sanding left very faint scratches that were not removed by subsequent finer passes:

enter image description here

Why would that happen, and how do you prevent it, and is there any way to save this piece?

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    Why did you sand to 3000?? That's never needed in normal circumstances (because it's of zero benefit, esp. on an open-grained wood like oak) and even the turners who sand much more finely than the rest of us may not even go much beyond about 1000. I wouldn't normally do this but I wanted to explain my downvote: how to sand wood properly is more than adequately covered by external sources!
    – Graphus
    Jul 5, 2023 at 7:03
  • I was trying to get that buttery soft and ultra smooth texture that I've seen on some pieces and I assumed it was created by very fine sanding, but I guess not. Do you have a tutorial on sanding that you would recommend? Jul 5, 2023 at 10:12
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    Well remember that furniture will have a finish on it. In most cases (not just with everyday commercial furniture) what that means is you're feeling the finish, not the wood. Even with penetrating finishes that don't build a distinct film on the surface you're still feeling the finish to some degree, as it's incorporated into the surface wood fibres.
    – Graphus
    Jul 5, 2023 at 12:33
  • Sanding is too broad a subject to be covered by a single tutorial. Which species? How plain is the grain? Entirely by hand (note that almost nobody does this on anything of any size) or using machines? If by machine which type? (Nearly all machine sanding is followed by some hand sanding, even if it's just a single pass.) And since it's always worth mentioning, there's scraping to consider also. We have a previous Q&A on that as a starting point to finding out why many consider scraping superior to sanding (for flat surfaces, less so with curves) not least because it's so much cheaper.
    – Graphus
    Jul 5, 2023 at 12:38
  • Chiming in to second scraping. Getting the hang of preparing the scarper can be tricky. But it totally eliminates the question of sandpaper grit for finishing. Done correctly a scraper delivers that nice smooth surface and offers a high degree of control. Plus, in the long haul it's cheaper than constantly buy sand paper.
    – YoStephen
    Jul 11, 2023 at 16:13

3 Answers 3

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Random orbits are only a good strategy when a machine is doing it. So in the future, sand with the grain.

To fix this, start at about 80, and work your way back up through the grits. Don't skip grits too quickly. (In other words, get the cross-grain scratches out with the 80 before you move up. You'll never fix issues like that with finer and finer grits.)

This might be a matter of opinion, but mine is that you're wasting time going past 400. Maybe your application really wanted 3000, but I'd love to know why.

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    No, it's not a matter of opinion :-) 'Only' 400 is way higher than necessary in normal circumstances (even sanding with an ROS which changes the picture slightly). Common advice is to sand to 180-240, although it depends a little on the intended finish – any penetrating or close-to-the-wood finish v. any film finish built up to a distinct layer (including shellac, although finer prep is more beneficial with shellac than varnish or lacquer).
    – Graphus
    Jul 5, 2023 at 7:08
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    Don't forget to mention, if you move to a finer grit and the deepest scratches aren't going away, move back to the last grit...
    – bowlturner
    Jul 5, 2023 at 12:31
  • Why would a random orbit sander (machine) do a better job of getting out the scratches? Of course it's moving faster, but this is a small piece and I really put some elbow grease into it and they didn't budge. I wouldn't think doing more of that and faster would help. Jul 5, 2023 at 17:55
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    "Why would a random orbit sander (machine) do a better job of getting out the scratches?" Because that is, literally, its job :-) "a small piece and I really put some elbow grease into it and they didn't budge" You weren't doing as much as an ROS, even on its lowest setting! Plus, by sanding randomly you were introducing more swirly cross-grain scratches every time you put abrasive to wood. All sandpaper leaves scratches, it's in its nature. The reason you shouldn't be able to see any scratches with conventional hand sanding [contd]
    – Graphus
    Jul 6, 2023 at 7:57
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    ...is they're lost in the grain of the wood, hence Sanding 101: sand in the direction of the grain. It's not quite as simple as that in practice (hence why I said sanding is too broad a subject to be covered by one tutorial) but it is the foundation of how to hand-sand wood. By comparison scratches that cross over the grain can be incredibly noticeable in certain lights, and are highlighted by stain and look absolutely terrible. Cross-grain scratches remain visible under a clear finish, plain to see under a fully build varnish or lacquer finish, even under an epoxy or other pour-on coating!
    – Graphus
    Jul 6, 2023 at 8:03
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Why would that happen, and how do you prevent it, and is there any way to save this piece?

It happened because you didn't sand enough to remove those scratches.

Sanding is a process of replacing scratches with successively smaller scratches. Large grit removes material faster, but leaves large scratches; small grit leaves small scratches, and a smoother surface, but takes longer. The purpose of working from large to small grit is mainly to save time -- you could start with 400 grit paper and just keep sanding until all the scratches are gone, but it'd take a long time and a lot of work to sand out all the larger scratches.

You can absolutely "save" the piece you're working on by simply backing up a bit and sanding more. You'll have to judge which grit you want to start with by the size of the scratches. I'd recommend using a random orbit finish sander for this -- it'll go much faster than sanding by hand.

However you do it, you'll need to sand until you get a uniform appearance with no trace of the previous scratches before you move on to the next grit size. It's a good idea to wipe or vacuum the surface each time you switch grits to reduce the possibility of some detached grit from the previous sandpaper grade being left on the surface and slowing down progress.

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  • This is a great Answer in terms of general sanding advice Caleb, but it too missed the key thing from the body of the Q (that @AloysiusDefenestrate addressed in his, right in the first sentence).
    – Graphus
    Jul 10, 2023 at 22:58
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The simple answer is you didn't start with a coarse enough grit.

Consider the sandpapers as producing a lot of tiny little cuts into the wood which average out over the course of dozens and hundreds of "cuts" producing sawdust which average out to a smooth surface. Each subsequent level of sandpaper grain produces a finer "cut" -- 60 grit sandpaper produces a 60-grit-sized cut, 120 grit produces a 120-grit cut etc. This refers to both the depth and width of the cut.

If you start sanding a gouge in a piece of wood with a 60 grit gouge with 120 grit sandpaper and then go from there, you're not going to remove the gouge. You're just going to polish it.

I have two suggestions.

One: get some coarser sand paper like 60 and do test patch up to 220.

Two: I recommend not using sandpaper above 220 or 300 on wood. It's not necessary in any application I can think of. The finest abrasive I can recall being advised in a wood working application is #0000 steel wool used in polishing finishes.

3000 grit sandpaper is used for polishing things like clear coat on a car or metal (okay so you could hypothetically sharpen a chisel but even then 3000 is in my opinion overkill just use a strop at that point I digress). Wood, being a porous irregular material consisting of miceometer-scale fibers can't physically be regular and smooth enough for such fine grits to be worth the money.

However 3000 grit is useful here though as an illustration of the "polishing the gouge" point though. 3000 grit makes a cut 7 microns deep, or about 10% the size of a human hair; 15% the size of the smallest object visible to the human eye.

Apologies for belaboring the point. I hope my extended discourse on sandpaper grits is of use to you and saves you some money at the hardware store in the future!

Best of luck on the project!

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  • Why the downvote? Is this not good advice? Jul 9, 2023 at 10:36
  • 24,48 and 60 grit sandpapers are kind of "off the radar" in most cases, but that hardly seems worth a downvote.
    – gnicko
    Jul 9, 2023 at 14:13
  • Yeah they're harsh measures. But these boards look pretty beat to heck. You're gonna need to do work to them and since I'm guessing you dont have a planer more extreme options should be on the table. @JoshuaFrank I'm sure I dont know! I always assumed etiquette demands an explanation for downvotes. I know I certainly thought it was sound advice.
    – YoStephen
    Jul 9, 2023 at 16:56
  • "Yeah they're harsh measures. But these boards look pretty beat to heck." I don't know which other pictures you have access to but the only one I can see looks like a perfectly level surface with (not too awful) cross-grain scratches. And from the body of the Question it would seem they're from 120 grit..... Nothing but the most gouged or rough-sawn boards imaginable (worse than from an Alaskan mill!) would call for grits below 60 in many a sanding schedule. Coarser than 40 is for gross material removal, maybe appropriate for heavily weathered barn wood but not for errant sanding scratches.
    – Graphus
    Jul 10, 2023 at 15:34
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    "I always assumed etiquette demands an explanation for downvotes." No, there's no requirement for a downvote to be explained, any more than there's a requirement for an upvote to be justified. Mouseover the arrows and see what the popups say. It's just "This answer is useful" and "This answer is not useful". So maybe think about it this way: if four members had thought this Answer was useful (like the other Answer currently) its score would stand at +3. That it stood at 0 before the downvote tells you something.
    – Graphus
    Jul 10, 2023 at 15:58

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