Sandpaper leaving dark marks on wood

[Jim Fulbright]

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

[david privett]

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.

[Jim Fulbright]

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

[John Beaver]

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.

[Dick Mahany]

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.

[Marvin Hasenak]

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.

[John K Jordan]

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

[Jim Fulbright]

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?

[Jim Fulbright]

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.

[Tom Wilson66]

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.

[Jim Fulbright]

That's an excellent idea! Thanks!

[Brice Rogers]

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.

[Kyle Iwamoto]

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.

[Leo Van Der Loo]

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.

[John Terefenko]

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.

[Perry Hilbert Jr]

OP didn't say what kind of wood. For instance maple,, seems it develops surface scorching very easily. Some other woods are most likely the same. 1200 grit paper can gum up easily from natural oils and saw dust on the wood. then it just burnishes and burns. I don't sand some woods beyond 400 until after a coat of sanding sealer. Then a 600 grit to even out the sanding sealer. And maybe another coat and then the high grits to polish the finish. I have been turning a lot of bass and tulip poplar, both very soft and sanding beyond 400 grit doesn't seem to get much, except to burnish the surface. A coat of sanding sealer seems to harden the surface of the softer woods and then a nice glassy finish can be achieved. I don't have a lot of experience turning either, but from other wood working I came to realize that different woods have different "personalities." What works on one, doesn't necessarily work on another. Some contain a high amount of natural oils, teak for instance. decades ago I turned dozens of bowls from Teak. The beauty of it was that to get a nice glossy finish, all I had to do was hold a rag up against the wood and the heat would bring the oil to the surface and "bake" it on the surface. Looked like a finish with no finish being used. Some pine has resins that get hard as rock after a few years. (Dade county pine, an endangered species now I understand) Other pine is soft and and dry. Sassafras branches and roots contain a lot of oil. The trunk wood often has to have cracks partially around the interior rings because the rings can actually separate in a living tree when it flexes in heavy winds. Some oak is subject to having the fibers between rings tear our when turning, and it leaves a corduroy effect on end grain surfaces. Just throwing that out there. Could be the wood, and not the abrasives.

[Jim Fulbright]

No, not steel wool. I have noticed it on several woods that are lighter, not just the oak. I bit the bullet and ordered some new sandpaper, so let's hope that that coupled with not touching any bushings will alleviate this!

[Reed Gray]

Well, the wood and the abrasives could both be the problem... Sounds like you got the idea that high speed is not good. One reason is to get the abrasives to cut, you need traction, so think of a dragster. They burn off their tires to generate heat and smoke, but they are going no where. So if you stay in the proper speed ranges, then you get good cutting and no heat. Another cause of heat is pushing too hard. If your fingers are getting warm or hot, then that is too high of a speed and/or too much pressure.

Looking at the wood, you have spots, like Leo pointed out. With an open grain wood, the pores will fill in with what ever (try buffing ash with a pad that was used for black walnut, I like that effect). So, that wood appears to be open grained, and the fill in could be part of the problem. With abrasives, I never use the cheap ones, and learned that a long time ago. You pay less, and you get less. Money well spent.

robo hippy

[Jim Fulbright]

Thank you all for your help. I've upgraded sandpaper, used it like somebody else paid for it, and have tried staying away from the bushings. I tried covering the bushings in CA glue and then masking tape. Turned out to be much more trouble than it's worth. So far, with the new sandpaper and staying away from the bushings, my pens have been turning out much better. Thanks again for everybody's help!

[Bill Boehme]

John, I apologize I completely missed your reply. The sandpaper I'm using is Warrior Wet/Dry from Harbor Freight.


The sandpaper is the problem. The wet/dry paper is silicon carbide and is meant for sanding metal, not wood. The black grit gets embeded in the wood and there's nothing that you can do to remove it. Use aluminum oxide paper or ceramic paper designed for wood. And, cheap paper equals cheap results.