Too much sanding?


I see it recommended all the time - sand with low grits to shape then 220 grit for finish. But why stop at 220? I have used 320 (even thinking of trying 400!) on a ROS to sand surface areas to an almost glassy smoothness and I feel that I get a better final finish because of it. At least I THINK I do! So far I've only used clear gloss polyurethane and it's almost like a piano finish. I haven't been doing it long enough to know if there will be problems over the years. Maybe it's too smooth? Anyone have any ideas?
FoggyTown
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I usually sand up to 400 grit too. Never had any problems at least none that I can see on some projects that are well over ten years old.

I think I remember reading that if you don't sand carefully at the higher grits, you stand the chance of burnishing or burning your wood. I'd also hazard a guess that staining after sanding with a higher grit might give a slightly different result than that obtained with a lower grit. Anyone?
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There is a limit to how smooth you can get, due to the wood structure, pore size for example. If you sand further than that, you don't get additional smoothness for your effort. Different kinds of wood have different porosities. An additional factor is the kind of finish. Poly can be smoothed more than the underlying wood because it builds up. But there is no advantage to sanding the wood beyond its limit. If you use a finish like tung oil, which penetrates, the wood limit is the limit.
Steve
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Thanks for that information. Do you know of any online reference for different species of wood that one could refer to when deciding the proper grit for final sanding and finishing?
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I have seen a web page, but I don't remember where. If you want a reference, check http://www.taunton.com/store/pages/070302.asp . I almost always sand to 220, then use 0000 steel wool, apply tung oil with steel wool between coats. Sometimes, a final coat of wax. Customers like the finish.
Steve
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Well the varnish that you are putting on the surface is what you will be feeling. I never go beyond 180 when using a varnish. If you are simply going to add an oil for the finish where you will actually be touching the wood with your hands a higher grit paper will result in a smoother feel. It is extremely easy to have a glass smooth finish with 180 grit and 2 to 4 coats of a wipe on gel varnish.
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foggytown says...

I stop at 150, usually worn out 150. No matter how much you sand the wood, you will still need to sand the finish coats. That is where the action is as far as I'm concerned.
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Hax Planx wrote:

Oh I understand about sanding the coats of finish - usually I use fine steel wool between coats but that's more to cut down any dust nibs. I'm just wondering if stains, varnishes, etc. have a better marriage to the surface if the bare surface is 400 grit smooth as opposed to 220 grit smooth.
FoggyTown
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FWIW . . .
A lot depends on the wood, 'buildability' of the finish, and what YOU are trying to achieve.
Stains, in my engineering opinion, are most effective on 'raw' wood. {AND water soluble DYES are the most even}A quick hit with 80 to 100 grit to remove the 'whiskers' and even everything out, then apply. At this point, if you need a 'quicker' glass-smooth surface, apply a pore-filler. Then another stain application. This is what I did on the Maple top of a kitchen piece. This way the pores weren't exaggerated by the stain, or by 'dimplies' in the final finish.
The finish in this case was about 4 coats of water-borne clear Poly. A hard, tough, and relatively fast recoating film. The individual coats were 'scuffed sanded' with increasingly finer grits - 220, 320, 400, 600. It was then waxed & buffed.
The same general approach is used on boat trim. Depending on the wood and the function, I may start with 60 grit. For broad, flat surfaces maybe 120 is where I stop. End grain, especially if shaped with a router, may get 220. {This tends to inhibit the increased absorption, and evens out the staining}. Then the finish schedule. For exterior it's about 6 coats of a UV inhibiting Varnish.
Regards & Good Luck, Ron Magen Backyard boatshop
"foggytown" wrote ...

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If you power sand with extremely fine grits you can, as an earlier poster said, burnish and case-harden the surface. This cuts the penetration of oil and rejects particles of pigment in oil stains, forcing you to use glazes or pigmented varnishes. You do need some "tooth" to the wood, too.
In flat work we generally have the luxury of sanding with the grain for our fine paper, so we don't show crossgrain scratches like our turning brethren. 320 is enough for almost anything out there. The first coat of finish will be almost fully absorbed anyway, so why sand the surface with a higher grit than we'll be using on the finish?
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If I understand the posting earlier this year from Darrel.. he usually doesn't sand pat 180 of it's going to be stained.. that makes sense to me, since stain usually raises the grain and is than sanded lightly, right?
I've noticed a lot of bad things about over sanding on turned things, like not getting a uniform color, but I don't think that has as much effect as flat work..
mac
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On Mon, 25 Jul 2005 12:10:56 -0700, mac davis

Mac-
Are you staining, or is it a result of the grain orientation? I've got a couple of cherry pieces that show two apparently different colors because of the way the light reflects. The end grain is apparently much darker than the face grain, but they are only clear coated, and the apparent color changes if you turn the piece a little.
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turning cuts fibers and sanding "breaks" them.. and a broken (or, at least an over sanded) fiber seems to absorb more color from the stain..
mac
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On Tue, 26 Jul 2005 09:06:31 -0700, mac davis

The face grain is absorbing more color? Interesting- maybe I'll have to monkey around with some stain just to see that! It kinda of makes sense in an odd way, though. Have you had the same experience burnishing pieces, or is it just with the sandpaper?
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hmm... haven't burnished in a while, but I seem to remember that it sort of glazed over everything and stained pretty evenly, IF you could get the burnished/burned wood to absorb stain..
mac
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On Wed, 27 Jul 2005 09:24:32 -0700, mac davis

Like I said, I don't stain much, but I've gotten some really nice results by total immersion and soaking in Tung oil (Danish oil is next on the list) for several hours or days. Probably would work with stain as well, if you're so inclined.

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No such luck on stain. Remember that oil stains are pieces of pigment suspended in the vehicle. Just stir the can after it's been sitting for a while. If it were a homogenous mixture like dye rather than a suspension, might be more effective.
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buffing system.. seems much more even than stains and better penetration..
mac
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On Thu, 28 Jul 2005 08:44:08 -0700, mac davis

Definately- I gave up on stains quite some time ago, after ruining several otherwise very nice projects. The wife still uses them for her scroll sawing, but I shy away from them these days.
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My guess would be it depends on your finish. If I use a stain, I only go up to 220- much higher than that and it doesn't seem to penetrate correctly with some woods. With stuff on the lathe, I sand to 1500 or 2000 grit to get that shiny burnished look, and then just use a clearcoat to slow moisture exchange. Sanding until it's glossy really makes the grain pop even better than oils, IMO.
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