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I've been working on a bandsaw box today, and I started with some horrific grit like 80, and up from there. And at 120 grit, I'd just hold the piece up to the light and look for scratches. After that I went to 220 and the same thing. It was arduous.

Is the goal in sanding to remove all scratches left by previous sanding? If so, then why is it that most instructions I've read for finish say to only sand to 120 grit. I don't see how I could ever get rid of all the scratches with 120, heck, the 120 itself will leave tons.

It seems like there is a common thought of only sanding with 120 or maybe 150 before applying finish. Is that true?
 

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You do want to remove all the scratches from the previous grit with the successive grits. Perhaps 80 was too coarse for the current project? I usually start with 100 grit or 120, then up 150, 180, 220 and on some projects to 320. Also make sure to sand with the grain and that end grain sanding is very difficult.
 

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Above 150g for work you are going to stain is not good. You will actually prevent the stain from penetrating. Make sure you are sanding with the direction of the grain. Sanding across the grain will leave visible scratches when you put the stain on.
 

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Thanks for the help!

It wasn't for staining...I haven't gone that direction yet. So this was just for simple poly, wipeon or brush.

The directions for that poly said to sand with 120 to 150 before putting on the poly. So I didn't know why it would suggest maxing out at 150.

I think going against the grain was my biggest issue. This was my first box, and also first real sanding experience, so no surprise I had issues with the basics.

Thanks!
 

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If you are not removing tool marks and scratches, use new piece of sandpaper. Remove dust and broken off sandpaper grain often. Do not move on to next higher grit until you have removed all problems.

If you sand with dull paper you will never remove all tool marks and deep sandpaper scratches.
Applying too much pressure while sanding will not remove tool marks just dull sandpaper. Sandpaper is a cutting tool, so light pressure, removing dust and broken off sandpaper grains often will speed up the process and reduce amount of deep scratches.

Most finish manufacturers recommend not going higher than 150 to 220 grit sandpaper for most woods. Depending upon wood species some recommend stopping at 320 grit sandpaper.

I like to use cabinet scrapper to remove bandsaw blade marks if can.
 

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220 and above is for scuffing between coats of whatever finish you are applying. These grits shouldn't even be looked at until your workpiece is fully prepped no higher than 180 and your finishing and sanding between coats
 

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Generally speaking grits 100 and below are shaping grits. These grits help you achieve the final shape.

Grits 100 and 120 are ideal for removing tool marks. Some rather deep tool marks (e.g. Band saw) may require coarser grits to remove the tool marks completely.

You will use more 100 or 120 grit paper than probably all of the finer grits combined.

When sanding a glued up panel it is best to use 80 or 100 to level the surface around the glue joint. Then follow with 120, 150, 180 and usually 220.

I know that I will get a lot of flack on this but the best technique is to sand diagonal (45°) to the grain for all grits below the final grit. Alternate the 45° diagonal left and right when changing grits. When you have reached 220 grit, sand in the direction of the grain.

The advantage of diagonal sanding is that the next higher grit removes the scratches quicker and easier because the sanding is perpendicular to the scratch marks.

About the only other thing that I can say is, "Try it, you'll like it."
 
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....I know that I will get a lot of flack on this but the best technique is to sand diagonal (45°) to the grain for all grits below the final grit. Alternate the 45° diagonal left and right when changing grits. When you have reached 220 grit, sand in the direction of the grain.
I actually agree with that and do that in certain situations, though it seems to work better on harder woods.
 

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....and I started with some horrific grit like 80, and up from there. And at 120 grit, I'd just hold the piece up to the light and look for scratches. After that I went to 220 and the same thing. It was arduous.
Generally 80 grit is a bit too rough for anything but 'sculpting'. Keep in mind that you cant jump grits too soon. It takes 100 grit a long time to remove the 80 grit sanding marks. Then go to 120 grit when all of the 80 grit 'gravel' marks are gone. After 120 you should go to 150 to remove allof the 120 grit marks. Jumping directly from 120 to 220 is a waste of time and good sandpaper. After 150 go to 180 and that should be all you need to go. Tony B
Is the goal in sanding to remove all scratches left by previous sanding? Yes. Tony B

If so, then why is it that most instructions I've read for finish say to only sand to 120 grit. I don't know where you read that. Most of anything I read says go at least to 180 and 180 works for me. Tony B

It seems like there is a common thought of only sanding with 120 or maybe 150 before applying finish. Is that true? No...at least no commonly anyway, but I'm sure someone said that at sometime or another. Tony B[/QUOTE]

Another thing to keep in mind is that sandpaper (abrasive paper) wears out fairly quickly and most people have a tendency to use it way beyond its useful life wasting time and effort. Abrasive paper can get expensive but it's all part of it. When sanding, feel a new piece every so often and compare it's feel to the piece you are using. You will be able to tell the difference.
 

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There are only two steps to sanding bare wood whether using a machine or hand sanding.

Remove tool marks and level wood using coarsest grit sandpaper necessary to get the job done efficiently. Remove the scratches left by the sandpaper using finer grits. Sand with any given grit of sandpaper until you can see no improvement. Then move to a finer grit.

Using light pressure, remove sanding dust and sandpaper particles often. Not sure how many have already said, “sandpaper dulls quickly so plan on changing to fresh piece of sandpaper when needed.”

Do not get hung up on term sanding sequence. Whether you start with coarse, medium, fine or extra fine sandpaper depends upon the wood before you. If hand sanding do not skip grit, if machine sand it is okay.

When all else fails read finish manufacturers sanding recommendations. Most professional finishers only sand to 220 or 320 and higher if using an oil finish. Most stop at 180 or 220 for oil or water based finishes. Lot depends upon the finisher, wood species, and final finish.
 
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