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Thread: Sandpaper leaving dark marks on wood

  1. #1

    Sandpaper leaving dark marks on wood

    Yes, I'm another novice that is turning pens. I come from a long line of woodworkers, but never had much interest until my 30's. Now I live 4 hours away from my dad, so I have to turn to the Internet for guidance. I have crafted several things from wood, most often rings and picnic tables, but recently got into pen turning as a way of supplementing my income.
    On to my issue. I sand in this order: 220/500/1200, then go through all the micro mesh pads. I started noticing dark marks on my pens and thought it might be the micro mesh has surpassed it's life. I started another pen and stopped after the sandpaper. I still see them!

    I'm using (gulp) Harbor Freight sandpaper, maybe that's the issue? (Remember the income supplement? Harbor Freight is cheap). I'm willing to upgrade sandpaper, if need be. Maybe it's both the sandpaper and worn out micro mesh?

    Dark spots in question: http://imgur.com/a/jBxpNGL

  2. #2
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    if it is turning dark it is not cutting it is just getting hot and burning . yeah the harbor freight paper wears out quickly so that is why it is turning dark but a fresh abrasive piece will take it off , but I think as some woods when getting down to the really fine grits they kinda darken slightly. some will get a shine like you put finish on them.

  3. #3
    Thanks David. On the pen pictured, I tried making sure to use fresh paper. I think you're right... Harbor Freight is the culprit

  4. #4
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    It's actually possible that the sandpaper you are using has some metal content, and that metal is causing the tanins in the wood to darken. It looks like that pen could be Oak, in which case that is possible because Oak has a lot of tanin.

    Doesn't really look like burning to me.
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  5. #5
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    I had similar looking dark stains and it turned out to be from the pen bushings. Metal was getting transferred to the sand paper and redistributed on the pen blank. Particularly problematic on light woods. Now I just make sure that sandpaper never touches bushings and the problem has never returned.
    Dick Mahany.

  6. #6
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    Quote Originally Posted by Dick Mahany View Post
    I had similar looking dark stains and it turned out to be from the pen bushings. Metal was getting transferred to the sand paper and redistributed on the pen blank. Particularly problematic on light woods. Now I just make sure that sandpaper never touches bushings and the problem has never returned.
    I think this is your problem.

  7. #7
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    Quote Originally Posted by Jim Fulbright View Post
    Thanks David. On the pen pictured, I tried making sure to use fresh paper. I think you're right... Harbor Freight is the culprit
    I was also going to ask what kind of sandpaper, and, what lathe speed as well. I always sand with the speed quite low, maybe 100-200 RPM or so, always moving the paper and never with much pressure. If the sandpaper ever gets hot the speed is too high and/or the pressure too high. Too much heat can do bad things to the wood.

    After sanding with the lathe running I always stop the lathe and sand by hand with the grain, 90 deg to the scratches.

    Also, to me 220/500/1200 seems like too quick a progression, but I guess no problem if it works for you. Going from 220 to 1200 I would typically use 220/320/400/600/800/1000 (maybe) and 1200. Note that after removing any tool marks it only takes a few seconds with each grit.

    Good quality sandpaper can make a big difference. After much experimenting I usually stick to two kinds of paper: Klingspor Gold below 600 grit and RhynoWet Redline wet/dry for 600 and above. I buy the Klingspor in rolls and tear off short pieces as needed, and cut sheets of the Redline into 1" x 3" pieces. The Rhynowet is amazing - I think it cuts better and lasts longer than any others I've used.

    Also, some wisdom many turners have probably heard repeated over the years: Use sandpaper as if someone else is paying for it! In other words, trying to save money by continuing to use a piece after it quits cutting well is counterproductive. After trying it both ways I'm now quick to throw it to away and use a new piece.

    One thing else, probably unlikely: I've seen black grit come loose from cheap wet/dry paper and get embedded in the wood. But if this was happening it would probably be obvious.

    JKJ

  8. #8
    Interesting thoughts, John and Dick. I do touch the bushings from time to time when sanding the tapers and that could be it. The dark spots do seem linear along the grain. I can't vouch for the metal content to the paper, but that's possible, too. Would "spritzing" the blanks with a water squirt bottle between coats help at all?

  9. #9
    Quote Originally Posted by John K Jordan View Post
    I was also going to ask what kind of sandpaper, and, what lathe speed as well. I always sand with the speed quite low, maybe 100-200 RPM or so, always moving the paper and never with much pressure. If the sandpaper ever gets hot the speed is too high and/or the pressure too high. Too much heat can do bad things to the wood.

    After sanding with the lathe running I always stop the lathe and sand by hand with the grain, 90 deg to the scratches.

    Also, to me 220/500/1200 seems like too quick a progression, but I guess no problem if it works for you. Going from 220 to 1200 I would typically use 220/320/400/600/800/1000 (maybe) and 1200. Note that after removing any tool marks it only takes a few seconds with each grit.

    Good quality sandpaper can make a big difference. After much experimenting I usually stick to two kinds of paper: Klingspor Gold below 600 grit and RhynoWet Redline wet/dry for 600 and above. I buy the Klingspor in rolls and tear off short pieces as needed, and cut sheets of the Redline into 1" x 3" pieces. The Rhynowet is amazing - I think it cuts better and lasts longer than any others I've used.

    Also, some wisdom many turners have probably heard repeated over the years: Use sandpaper as if someone else is paying for it! In other words, trying to save money by continuing to use a piece after it quits cutting well is counterproductive. After trying it both ways I'm now quick to throw it to away and use a new piece.

    One thing else, probably unlikely: I've seen black grit come loose from cheap wet/dry paper and get embedded in the wood. But if this was happening it would probably be obvious.

    JKJ

    John, I apologize I completely missed your reply. The sandpaper I'm using is Warrior Wet/Dry from Harbor Freight. I used to have the lathe on the high setting, but for the last 10 pens or so I've had it on the lowest speed for sanding. There is no display, so I'm unsure as to the actual RPM. I know it's a faster progression but that's what the pack came with, unfortunately. The pens do seem to come out quite nice especially after using the micro mesh and Shellawax.

    You're right, I have been trying to extend the life of the paper as much as possible. I'll be better about that. Also, as you mentioned, I do tend to let the paper get hot as I'm sanding.

  10. #10
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    To keep from sanding the bushings, you can make a set of wood bushings just for sanding. These would be similar to the ones made from plastic, but could be made from cutoff pen blanks. Would cost nothing. Glue a 7 mm tube inside the wood to get it to fit your mandrel.
    The hurrier I goes, the behinder I gets.

  11. #11
    That's an excellent idea! Thanks!

  12. #12
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    There are a variety of different types of sand paper. Aluminum oxide, Silicon carbide and ceramic. When I've used silicon carbide (the dark stuff) I saw some of grit getting imbedded in to pores of light colored wood. Also silicon carbide includes some iron so it could be reacting with the tannin in wood. I would make sure that you are either using aluminum oxide (typically lighter colored) or ceramic paper.

  13. #13
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    My $0.02. Use quality paper. I've used *mart paper and they SUCK. Mainly because the 180 grit has 36 grit rocks in it, and you cannot sand that out. Personally I use Indasa RhynoDry paper. The thing I love is the grit quality. It is consistent, and no rocks in the grit. It's also white, and even if the grit gets loose and lodged in your precious thingie, you won't see it.
    You can wash MicroMesh. Well, maybe not, but I do. Cleans it out real nice. Will not "Fix" worn out MM......

    Light pressure, keep the paper moving.

    Pro sander, mediocre turner.

  14. #14
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    Looking at your picture I see dark spots, not going around the wood as what would happen with grains coming off of the paper and imbedding in the grain, you aren’t using steel wool by any chance ?

    I suspect it is iron reaction with the tannin in the Oak wood, do you have the same problem with all woods or only the Oak ??

    The question about the steel wool is that it will have the metal break off and you would then get the tannin reaction.

    The wet and dry dry paper also can give you dark particles imbedded when the paper breaks down.
    Have fun and take care

  15. #15
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    My suggestion is skip the sandpaper all together. Learn to use the skew properly and go from turning right to finishing and no sandpaper needed.
    John T.

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