Sanding problems

[Alan Carter]

Okay. Here's another newbie question. I'm having major problems sanding. No matter what I do, I get sanding marks on the piece. As an example, I just finished turning a bowl. The tool marks from the gouges and scrapers were minimal but the surface was rough, especially on the end grain. So I began sanding, but I ended up with sanding marks all along the piece. It looks worse after I sand than before. It doesn't seem to matter what grit I use (I started with 100) or how hard or soft I press. I'm moving the paper so it doesn't stay in one place. I seem to be able to get it so the lines are very small and faint (using 600g) but they're still there.
Is it related to lathe speeds, degree of grit, how hard I press? WHAT? It's driving me nuts. Or am I just being impatient and not spending enough time with it?
Take pity and dumb down your answers as far as you need to so I can figure it out.
Thanks.

 

[Rick M]

Sounds like you may be talking about more than just that particular bowl, but I was wondering what wood(s) and how wet/dry they are? Is your sandpaper getting loaded up with sawdust?

As I understand the general process, each successively finer grit should "erase" the scratches of the previous grit, until the scratches become too fine to discern. This essentially means you don't skip over a grit in the sequence. Nor do you move to the next grit until you've sanded away all the scratches of the previous grit.

Of what little I've learned thus far, some woods respond well to reversing the sanding direction toward the end of each stage. I understand this helps with "breaking off" the ends of grain fibers that just "laid over" in a uniform direction during regular sanding. A few moments spent manually turning the work in the opposite direction is supposed to be enough.

How hard to press will affect how your sandpaper responds, as well as the heat produced and any burnishing effect or potentially unwanted drying of green wood (which can lead to cracking).

 

[rsser]

Yep.

100 grit can be pretty harsh and leave deep marks in soft wood or in soft growth rings.

Make sure you use quality paper. Brush out carefully between each grit and inspect the surface. Go up through each grit without skipping any. Make sure the paper hasn't gummed up. If nec. hand sand with the grain.

 

[MichaelMouse]

It sounds as if you are hand sanding, which is about the worst case scenario. Tough to get out those tool marks by using something that cuts the same direction they took. Probably why most of us sand under power with rotating disks.

You'll want to take the paper you are using along the grain to the greatest extent possible as you finish with each grit. If someone will please tell me what "skipping a grit" means, I'll change my comment, but don't waste time playing the 120/150/180/220/240 etc. game. Just because they make those grits doesn't mean you use 'em on all projects. Not to mention we in the 'States are plagued by the CAMI system and lots of the disk makers use the European system, which uses the same numbers for different sized particles. Don't press too hard, either, especially with fresh grit on paper backing. Gives you rogue grit breaking off and hiding in the pores of the wood until it's ripped out in a long scratch two grits later. Use softer backing so it doesn't crease and flake, low pressure so it doesn't burnish and harden the surface, and get the dust out often. Sanding from center to rim with rotating work will help keep the amount of trapped dust which is heating and burnishing to minimum.

I like sanding sponges at 220 and 320 (P400) because they conform to the contour better and don't scratch at the edges. I also like to set up the grain with water and sand along the grain but up hill. This is what the reverse rotation sanders think or wish they are doing. Do this at 220 and 320 and you'll do a couple of good things. First, you'll break any case-hardening so you won't end up with a scratch against a burnished background, second, you'll minimize any grain stand-up which might interfere with your finish. Third thing is sort of minor, but the wet rag will clear rogue grit, too.

Best of the best is to go to powered sanding. That way you can cut across the gouge marks initially, reducing them quickly with little pressure, and cut time per grit dramatically as well. Other thing, as Ern mentioned, is that starting coarse on some woods will give you scratches so deep it seems to take forever to get them out. Though I must disagree and say that it's not the easily-sanded softer portions I worry about, but the hard ones the next grit slides over without grabbing. Hard woods want better toolwork. Sharpen the tool and take the final pass so that you can start beyond 100. I cut for 150/220, though there are people who hone and fiddle finer. You figure where the break-even point is for your method and stick to it.

 

[Joe Greiner]

Switch directions of sanding. Alternate between rotary and with-the-grain. On bowls turned cross-grain, the grain direction is all over the place. Lightly sanding with the grain should remove the dodgy parts imposed by the rotary sanding, because they intersect the previous cuts at an angle. To sand with the grain, press the paper over the offender, and pull the paper with the other hand. In effect, this is a manual belt sander. It's a little trickier on the inside, but the principle still applies.

"Skipping a grit" needs better definition. I've had decent results with 150, 220, 320, 400, sometimes 600. Sometimes forgot 320, because I forgot I had any on hand.

Joe

 

[KurtB]

Sanding

My understanding of the 'skipping a grit' was that one can skip grits, as long as the jump was not more than double the previous grit, i.e., 80-120, but not 80-180; 120-220, but not 100-220, etc. It does make sense, however, that going thru each progressive grit will allow a greater chance of cleaning up the previous grit scratches.

 

[Rob Wallace]

Skipping Grits......one interpretation....

The "rule of thumb" often touted for advancing through the abrasive grits is that moving to the next higher grit should be no more than 1.5X (one and a half times) the present grit you are using. I use this concept myself, and have advised others to do so in my presentation on "Woodworking Abrasives". For me, "The 1.5x rule" works.

For example, if you are sanding at 80 grit, the next acceptable grit size would be 80 x 1.5, or 120 grit. Thus you could "skip" a sanding stage at 100 grit, and sand next at 120. After completing your sanding at 120, the next grit size would be 180 (120 x 1.5), and thus, you would "skip" 150, and so on up the line until you have achieved the surface acceptable to you. This recommendation seems to promote an effective (at least for me) and efficient series of sanding grits for most woods I've used. It also controls for the newbie temptation to jump too many grit sizes between sanding stages. There may be some variation in efficiency at certain stages, depending on abrasive particle sizes that differ in FEPA vs CAMI scales, but in practice these differences are minor.

I'll agree with Michael's comment: "but don't waste time playing the 120/150/180/220/240 etc. game. Just because they make those grits doesn't mean you use 'em on all projects.". I rarely run the full series of grits, whether hand sanding or power sanding. Good tool use and careful shear scraping often starts me off at 120 at a minimum, and I move up from there. Occasionally there is the need to use "the 80 grit gouge" (often for severe tear-out), but this is the exception.

The 'one-and-a-half times' rule seems to work well in my experience, and saves time and money.

Rob Wallace

 

[Gretch Flo]

Use of magnification

I have improved the quality of my work (but probably increased sanding time!!) by using magnification. Often I thought my work was good til I got it into better light, or after a coat or 2 of Danish oil was applied. Then I could see the scratches!! The last couple of years I use the protective glasses with bifocal magnification (about $12-15 in woodturning catelogs) and it has improved my abilities to see the scratches before I get to the final grits or worse to my finishing table. I still sand too much-spending more time than in actual turning, Gretch

 

[waltben]

I alternate between hand-held folded over quarter sheets of paper and wavy hook & loop. Depending on the wood, I start at either 80, or sometimes 60 grit and work all the way to 1200 and sometimes higher. By alternating, I can be certain I've removed all the previous (coarser) grit's sanding marks. For some species, this can take some time. I usually spend almost as much time sanding as turning, but that's in order to get the final finish and 'look' I want.

 

[Barry Elder]

I have read all of Russ Fairfield's articles on finishing and really got a good education on sanding. I use all the grits with Mirka hook and loop and my vsr drill and clean and examine after each grit. If I skipped a grit in between, I would just have to sand that much longer to clear the scratches.

Nobody likes to spend much time sanding, so sharper tools, better presentation and technique, maybe even honing, will give you a better surface to eliminate some grits to begin with.

 

[robo hippy]

It sounds like you may be having end grain tear out issues as well. Of course, the better job of cutting you do, the less sanding you do. For your final cuts, you want a freshly sharpened tool. If this doesn't remove the tear out, then wet the surface with water or finish oil, let it soak in for a minute or so, then cut it out using very light cuts, as in it will take a couple of passes to remove the wetted wood. Some times you just can't get it all out with cutting and have to sand it out.

The problem with finding scratches after you are done is common, and I still find them after 11 years of turning. Having a good light source is very important, and for me, getting glasses helped a lot as well. I don't know what kind of lathe you have, but sanding at slower speeds like 500 rpm or less works better than higher speeds. It also has the benefit of not generating heat which can cause heat checks even in dry wood. If there is tear out, stop the lathe and sand it by hand, working on the problem spots, then turn the lathe back on and sand again by hand. Having a sanding pad of some sort helps, like some meduim density foam like an old flip flop. Just having your fingers on the abrasives won't even out the bumps and humps you leave. Reversing the lathe spin helps as well. The fibers do tend to lay down in one direction. Sand till you have ALL marks gone, then sand a little bit more. Don't get it close and figure that the next grit will remove it because it won't. Then move to the next grit. I never bother to wipe off the bowl as I am sanding. Never noticed that it made any difference as the next higher grit would loosen up any remaining particles. As you get to the higher grits, I do wipe it off with my hands. The fine dust will get into any remaining scratches from the coarser grits and high lite them. I don't sand my basic bowls beyond 400 grit.

Of course, power sanding is much easier, and faster, but the same rules apply: slow speed, grit sequence (80, 120, 180, 220, 320, 400), and good lighting. If there are visible scratches left, it is because you didn't get them out the first time before moving up a notch.

The coarser grits like 80 and 120 will remove wood and even surfaces out, the higher grits will remove scratches only, and almost no wood.

robo hippy

 

[MichaelMouse]

The coarser grits like 80 and 120 will remove wood and even surfaces out, the higher grits will remove scratches only, and almost no wood.

robo hippy

How's that again? I had always assumed that the sandpaper removed the wood down to where the bottom of the scratch lay, sort of like grading a road. Pothole's still there unless you get down as deep as it lies with the blade.

Now the wood buffers might come close to your statement in what they do, because they round over the ends and edges of the scratches so that there's not a lot of refraction to draw the eye. Gentle slopes look much like flat places, after all.

 

[odie]

How's that again? I had always assumed that the sandpaper removed the wood down to where the bottom of the scratch lay, sort of like grading a road. Pothole's still there unless you get down as deep as it lies with the blade.

Now the wood buffers might come close to your statement in what they do, because they round over the ends and edges of the scratches so that there's not a lot of refraction to draw the eye. Gentle slopes look much like flat places, after all.

MM......

If I understand him correctly, RoboHippy is talking about evening the surface from the perspective of profile view....you know.....little tool marks and irregularities that go around the circumference.....instead of "potholes".



ooc

 

[odie]

Okay. Here's another newbie question. I'm having major problems sanding. No matter what I do, I get sanding marks on the piece. As an example, I just finished turning a bowl. The tool marks from the gouges and scrapers were minimal but the surface was rough, especially on the end grain. So I began sanding, but I ended up with sanding marks all along the piece. It looks worse after I sand than before. It doesn't seem to matter what grit I use (I started with 100) or how hard or soft I press. I'm moving the paper so it doesn't stay in one place. I seem to be able to get it so the lines are very small and faint (using 600g) but they're still there.
Is it related to lathe speeds, degree of grit, how hard I press? WHAT? It's driving me nuts. Or am I just being impatient and not spending enough time with it?
Take pity and dumb down your answers as far as you need to so I can figure it out.
Thanks.

Some good information here so far.......

Now, if what you are trying to describe to us, is sanding marks left by very fine sandpaper.....320, 400, 600, or so......and not scratches that should have been eliminated with coarser grits........you may want to check out the possibility of solving that problem by using a random-orbital sander.

Not all woods need random orbital sanding, but sometimes you'll get a piece that will frustrate you to the point of wanting to throw up your hands in disgust!.....This is because of the very fine sanding "streaks" left by the upper grits. Like I said, not all woods will behave the same, but since I got my GREX RO sander, there have been a few times that it's saved me a lot of aggravation and hair pulling!!!!!

ooc

 

[MichaelMouse]

MM......

If I understand him correctly, RoboHippy is talking about evening the surface from the perspective of profile view....you know.....little tool marks and irregularities that go around the circumference.....instead of "potholes".
ooc

So you really think that you can get rid of scratches without removing wood?

 

[Joe Greiner]

The debate over the exact nature of polishing probably won't be settled in my lifetime. It's been several years since the publication of an article on the topic in Scientific American. Seems to be a combination of removal and filling. I'm not sure if they even considered wood.

Has anybody asked our friend Google?

Joe

 

[odie]

So you really think that you can get rid of scratches without removing wood?

Nope.....not what I said MM......

What I did say is I think robohippy is talking about something completely different than what you interpreted his words to mean......but, until he clarifies, your guess is as good as mine. Maybe it's me who is mistaken, but I doubt he thinks you can remove scratches, or irregularities, without removing wood......

ooc

 

[Doug Reesor]

I always consider sanding like polishing of any material. I think of it as a mountain range instead of pot holes, but whichever way, whether you fill in the valleys or scrape off the peaks the important part is not to be in a hurry. In order to get to the next level, all the scratches from the previous coarser grit must be removed. Using the mountain range analogy, you need to get rid of the deepest vallleys otherwise you end up only polishing the peaks with finer grits. If you end up with a scratch, you need to move back at least to the previous grit level to ensure the valley was removed. sometimes the scratch requires moving up several grit levels because it was undetected earlier.

I also have to remind myself to let the sand paper do the work. If I am generating a lot of heat, that means I am applying to much pressure and that results in a lot of scratches.

The problem, as was mentioned with the quality of the sand paper, is that non-uniform paper can cause a deep valley which then requires a lot of time on the next grit level to remove. Cross sanding and lighting definitely help finding the scratches that have to be removed at each step.

Good luck.

Doug

 

[robo hippy]

Well, maybe this does need some clarification. If you need to use the 80 grit or coarser gouge, it can remove significant amounts of wood to even out all the hills and valleys that we leave behind. 120 grit can do it but takes much longer to wear things down. By the time you get to 220, it is for clean up work, not fix it up work. My drum sander manual lists 80 and coarser grit for stock removal, any thing above that is for surface dressing. Yes, you are removing some wood with the finer grits, but by the time you get to 220 grit, you are removing amounts that can't be measured by tools that most of us have. Ever try to round over a sharp edge with 220? You can 'ease' the sharp edge, but not really round it unless you want to spend a lot of time and several discs to do it. I guess another way to say it is 80 grit is for roughing, and 220 and above is for a finish cut.
robo hippy

 

[Ruth Niles]

This has been an interesting conversation, albeit redundant at times; which is not a bad thing!

Three things I've learned in my 17+ yrs. of turning:

1. Try to get the finest finish with the tool before using any sandpaper.

2. The more you sand, the more you have to sand.

3. What worked great on your last piece, may not work on your next piece...no matter what the wood may be.

Ruth

 

[Malcolm Smith]

A couple of points. Use high quality fresh sandpaper. The grit size is more likely to be uniform and it will tend to last longer. With hardwoods, the grit breaks down fairly fast. I doubt that money is saved by buying bargain priced paper.

If sanding the inside of a bowl with a turned in rim, clean out the dust with a cloth and the lathe turned off to remove any grit that has separated from the coarser grit paper before moving on to finer grit papers.

Malcolm Smith.

 

[MichaelMouse]

2. The more you sand, the more you have to sand.

Much truth there. Say you have CAMI 80, which is a mesh of 80 places/inch. Means the average groove is maybe 2/3 of that deep, if the grit adheres. Full depth and maybe more if it breaks loose and gets pressed in. Now use a 120/inch mesh grit, and you have to hit the same spots three times to get to the depth of the previous, or five, if you have the rogue piece. 150 is about the same, which makes it a "better" solution, since it still has to go three to five to remove, and leaves a lesser depth scratch of its own.

This is why fast-moving disks or combination of disk and work movements work better than slow. You get more chances to hit the right spots in the same period of time. Yeah, I know the slow-sand myth, just as I know the slow grind myth. It's just not good science, but a good story. Keep the touch light and the paper moving, preferably in a way that keeps you from burnishing with the dust you made, and scoring with any loose grit you may have knocked off.

 

[Alan Carter]

Thanks for all the great advice. I started using a pad with my drill to power sand and that seems to have solved the problem, at least on surfaces large enough and not too intricate, which at this stage of my turning experience is not an issue. (My sentence structures are more convoluted than my turnings.)

 

[Nate Hawkes]

This has been an interesting conversation, albeit redundant at times; which is not a bad thing!

Three things I've learned in my 17+ yrs. of turning:

1. Try to get the finest finish with the tool before using any sandpaper.

2. The more you sand, the more you have to sand.

3. What worked great on your last piece, may not work on your next piece...no matter what the wood may be.

Ruth

You speak true words of wisdom, Ruth!! I've only been turning a couple years, but I'm turning quite a lot of bowls, and if I had learned this (and really, really believed it, without having to prove it to myself over and over again), I could have saved myself so much time sanding so many bowls.....

 

[Paul Bennett]

Sanding a turning has always been my nemesis. Since I make my living turning the sanding part always seems to pick my pocket. I have always considered all sand paper is the same--80 grit is 80 grit. I finally found a paper that is different and the seller explains why it is different. I found it on vinceswoodnwonders.com It is Sia soft abrasives. I decided to give it a try. It was truly amazing this foamed back paper works better than anything I have used.

I will have to turn 100 to 200 pieces at a time. When I can cut a minute or 2 off each one it makes a big difference in how much you make. More than that the job is much better.

Very few time do I find something that really does what it says--this is one!