Looking for information on sanding

[jimlee]

I am relatively new to wood turning and looking for information on sanding. Specifically how to tell the difference between tool marks and sanding lines and how to tell between the series of scratches left behind by the different grades of sandpaper. For example if I am going from 80 to 120 to 180 and I am doing the 180 how do I know that the scratches I am seeing on the harder parts of the piece are not from my 80 or 120 sanding? Or to put it another way how do I know that all the sanding lines/scratches I am seeing are from the latest 180 session and I am safe to go on to the next finest grit? I find myself seeing obvious lines/scratches when I put on a finish and I don't know how far back in grits I need to go to remove them. I do rub on a shellac mixture after I sand at 120 as a test to see what I can see before going all the way to 4 or 600 grit. I sand at the slowest speed my lathe allows and I hand sand with 'regular' off the shelf sandpaper. Not using a rotary power sander on my drill. So all the scratches are concentric. I do not have a way to reverse my lathe. I to end the turning with tools with a sharpened scraper to remove as much tear out as possible depending on grain orientation.

Is it possible to end up without left over sanding lines? Maybe I am over thinking this but the finer pieces I see do not have sanding lines that can be seen through the final finish.

Thanks very much,
Jim Lee

 

[Bill Boehme]

I am relatively new to wood turning and looking for information on sanding. Specifically how to tell the difference between tool marks and sanding lines and how to tell between the series of scratches left behind by the different grades of sandpaper. For example if I am going from 80 to 120 to 180 and I am doing the 180 how do I know that the scratches I am seeing on the harder parts of the piece are not from my 80 or 120 sanding? Or to put it another way how do I know that all the sanding lines/scratches I am seeing are from the latest 180 session and I am safe to go on to the next finest grit? I find myself seeing obvious lines/scratches when I put on a finish and I don't know how far back in grits I need to go to remove them. I do rub on a shellac mixture after I sand at 120 as a test to see what I can see before going all the way to 4 or 600 grit. I sand at the slowest speed my lathe allows and I hand sand with 'regular' off the shelf sandpaper. Not using a rotary power sander on my drill. So all the scratches are concentric. I do not have a way to reverse my lathe. I to end the turning with tools with a sharpened scraper to remove as much tear out as possible depending on grain orientation.

Is it possible to end up without left over sanding lines? Maybe I am over thinking this but the finer pieces I see do not have sanding lines that can be seen through the final finish.

Thanks very much,
Jim Lee

Here are some of my thoughts about this. Some of the other guys are teachers and I'm sure have more in-depth answers.

• Tool marks run in concentric circles and will be much wider than sanding scratches. Your long term goal is for the tool marks to be barely visible, but that won't happen until you have turned long enough to have well developed tool control.
• If you apply heavy pressure to sandpaper and hold the paper still, letting the lathe do the work then the sanding scratches will be heavy and will also run in concentric circles -- therefore, that is NOT the way to sand.
• Start sanding with the finest grit that will remove the tool marks. Try a grit that you know is too fine and see how it does. You will know whether you need to go to a heavier grit. Don't force a grit that is too fine to do the job when it becomes apparent that you need to drop down to a coarser grit.
• If you sand with the lathe running, turn the speed down slow. Then keep the sanding pad moving quickly in a pseudo-random fashion. My idea of hand sanding is that I should be doing as much or more work than the lathe. If I see scratches that look like concentric circles then I am either running the lathe too fast or I am not moving the sanding pad enough.
• Make sure that you keep very light pressure on the sandpaper. Sandpaper wears out -- it really does and cheap people like me hate to toss sandpaper, but do it anyway as soon as it isn't cutting like new paper. I've heard others mention a cute saying about sandpaper -- use it like somebody else is paying for it.
• When you don't see any tool marks or tearout, it is time to go to the next finer grit. From this point forward, you are not sanding to remove wood, but to remove the scratches left by the previous grit. It shouldn't take long for each successive grit as long as you are using fresh sandpaper and not some old worn out stuff that you have been using on several bowls, but it still has a bit of grit left. BTW, I really like the Norton Pro-Sand paper. The Norton 3X paper is also very good.
• I cut each sheet of sandpaper into quarters and then fold each of these into thirds. For me that seems to be the perfect size for hand sanding.
• For the coarser grits, it is fairly easy to tell the difference in scratch marks from one grit to another. Blow the dust off frequently and examine the surface under good light to make sure that scratches from the previous grit have all been removed. If you advance too soon to a finer grit, you will never be able to remove the larger scratches. If you see large scratches by the time that you get to 180, it will be necessary to back up and work your way through the grits again. You can sand with 180 till the cows come home, but you'll never remove the scratches from 100 grit.
• Once you gt to the finer grits, you can't really see the scratch marks, but you can feel the surface with your fingers. You will also begin to see a slight surface sheen rather than a scratch pattern when you get to the fine grits.
• Where to stop? It's up to you. You will discover that a surface that seems smooth and scratch free may look terrible with a gloss finish. Nothing highlights scratches like a glossy finish.Adding more coats of glossy finish will only exacerbate the problem. You can get away with a less than perfect sanding job if you plan to use an oil finish or a satin film finish.
• I forgot to mention that there is more to sanding than just leveling out the humps and bumps which you are doing in the beginning. During your initial sanding, keep your eye on the upper horizon of the turning to spot areas that don't look right. Things that don't look right would include dips, kinks, and flats in what should be a smoothly flowing curve. Close your eyes and feel the curvature of the surface -- your fingertips can "see" surface irregularities far better than your eyes are able to see them. The curve should also be pleasing to the eye and "fit" the overall form of the piece. If things aren't satisfying looking after the first grit of sanding, it won't get any better as you progress through the grits. It's no sin to decide that you need to do a bit more refining with your turning tools.
• A lot of turners use power sanding, but I feel like I have much better control with hand sanding. A piece can go lopsided pretty fast with too much power sanding with coarse grits.

These are just some random thoughts off the top of my head. Hopefully, I've answered some of your questions. Also, sanding becomes sort of an individual preference thing so what I see as important doesn't mean that it is some sort of hard and fast rule -- it's just what I do.

p.s., Welcome to the AAW forum.

 

[robo hippy]

Yes, the 'Mystery' scratches.... I would say that is part experience, and part lighting. We have all, more than once, taken a piece out into direct sun light only to discover scratches that were not visible in the shop.... So, bright light (I prefer Blue Max lights) in the more natural spectrums show things the best because that is what our eyes have evolved to see best in. Other than that, get good glasses, not the cheap readers in the discount stores, which can also ruin your vision. The experience part is being able to know what to look for. Effective sanding means lower speeds. It is all about traction. For abrasives to dig in and cut, there are optimal speeds for best cutting action. Too fast, and you are like a dragster peeling out, lots of smoke, but going nowhere fast. How to figure out those speeds? Can't really answer that one, but on my slow speed drills, I never have the trigger depressed over half way. You can develop a 'feel' for it with lots of practice. Coarser grits a bit higher, finer grits a bit slower. Pressure is also important. Best bet is 'light' pressure. For hand sanding, if your hand is getting hot, so is the wood. Reduce speed and pressure. With a hand drill, no more than the weight of the drill.

Now, how to see what you have left behind. With hand sanding, it is more difficult, but if you can get a different scratch pattern, this really helps. For spindle work, you hand sand with the lathe spinning, then stop the lathe and sand along the length of the spindle. If the up and down scratches show no 'around' scratches, you can step up another grit. I do hand wipe the piece down as well, bare hand. This seems to work the fine dust down into the coarser scratches to high light them. I have never used any liquids to expose scratches. With bowls, if you are hand sanding, getting a contrasting scratch pattern is more difficult. I guess you could hand sand in a line from the rim to the bottom. More than anything here, I use the hand rub to see if that high lights any scratches. With power sanding, and maybe with the inertial sanders, it is more easy. I change from using the top of the pad to the bottom of the pad, or from using one side of the pad to the other. This will leave swirl arcs in a different direction. I do hand rotate the bowl while sanding a lot, and keep the light close. Most of the time, especially when just learning, you don't really see the 80 or 120 grit scratches till you get up to 220 or even 320, so you have to back track a bit.

One explanation for the 'mystery' scratches that I have heard is they come from grit pieces left and/or stuck in the wood from the coarser grit when you move up one notch. This has led to a practice of blowing off the piece in between grits. The more I think about this, the more I think it doesn't work. With my constant practice of hand wiping out the bowls between grits, I have never once felt any grit stuck in the wood. I think this is more from stepping up before all the previous marks are gone.

I do have a sanding clip up on You Tube.

https://www.youtube.com/watch?v=s4Pkr89STGY

robo hippy

 

[odie]

I missed this thread before now, and both Bill and Robo have invested a lot of thought and time in bringing forth some very good information. (I tend to fade in, and fade out with the online discussions)

I am bumping this thread back to the top, because some of this information is great knowledge they have imparted......especially for newbie consumption. Even though I don't consider myself a newbie, I tend to read information, because it reinforces what I already think, or sometimes makes me put into better perspective, things that I already know, but can benefit by clarifying my own experiences from another's point of view. Occasionally, I am exposed to information that alters my own course of action!

This is a good quote from Bill:

These are just some random thoughts off the top of my head. Hopefully, I've answered some of your questions. Also, sanding becomes sort of an individual preference thing so what I see as important doesn't mean that it is some sort of hard and fast rule -- it's just what I do.

He's right, in that there are fine points about sanding that seem to vary with individuals.....neither good, nor bad......just different ways of accomplishing the task.

For me, the "fault line" between power sanding and hand sanding overlaps at 180gt. The past few years have been very satisfying to me with the amount of improvements I've made in my "tool finish" prior to sanding. These days, I infrequently do any power sanding at all on bowl exteriors, but still have to use my power sanding on interiors nearly every time.

It is important to start sanding at the finest grit possible. Choosing the right grit for initial sanding is imperative, because if you go too fine, you'll be removing material that you wish you wouldn't have....if you have to do a back track in grits. At that point, if you do backtrack, you'll end up removing more total material as a result. The same is true, if you start too course a grit. In bowl turning, it's extremely important to start at exactly the right grit, because removing as little material as possible is the goal. This is the most important thing to consider, because by removing as little material as possible, is that which enables the details, and detail grooves to be uniform in appearance. The base surface is uniform throughout the circumference. This also enables intersecting planes meet at the most crisp of corner possible. These two sanding related things enable me to achieve results that become appealing to the observer in a very aesthetic sense. Tool usage is important to sanding, as well......in that the finest grit that can be used successfully to begin with, is a direct result of how refined your tool usage is.....obviously!

ko

 

[Jamie Straw]

Looking for opinions on the guideline that "the next grit" be determined by addinge 50% to the current grit. For instance 120 to 180 to ... well 300 (rounding up), that kind of thing.

 

[odie]

Looking for opinions on the guideline that "the next grit" be determined by addinge 50% to the current grit. For instance 120 to 180 to ... well 300 (rounding up), that kind of thing.

Hi there Jamie......

From the starting point grit, I usually go to the next higher grit, with one exception. That would be for a bowl that is showing that it sands very easily.....in which I may skip a grit. This is usually not the case, though. The progress is always the same......60, 80, 100, 120, 150, 180, 220/240, 300, 400, 600. At whatever the starting point one decides, it's nearly always the same old progression from that point on up to 600gt.

Unless it's that rare exception when you can get away with skipping a grit......it's always a good idea to use all the grits available to us. You'll spend much less effort, and the sanding process will take less time overall.

ko

 

[Owen Lowe]

Looking for opinions on the guideline that "the next grit" be determined by addinge 50% to the current grit. For instance 120 to 180 to ... well 300 (rounding up), that kind of thing.

Jamie,
Here is the sequence I have available: 80, 120, 180, 220, 320, 400, 600. There is a bit of grit skip, like 100, 150, 240. The key to the whole thing is that if the grit you are using is not removing the scratches from the previous grit – with relative ease* – then you need to drop to a coarser grit. I am also a firm believer in not mixing brands of sand paper; problems may be few and far between but I’d rather not have it crop up in the first place.

*relative ease = 3-5 seconds with targeted slow to moderate speed power sanding should have a very noticeable effect on the existing scratch.

 

[odie]

BTW, I really like the Norton Pro-Sand paper. The Norton 3X paper is also very good.

Bill.....what is the difference between the 3x and the pro-sand? I'm very familiar with the 3x, but never had the pro-sand. Is the pro-sand the same as the A275 Norton paper? The 3x is great paper, but my preference for the last decade, or so, has been the Finkat paper from Japan......

ko

 

[Bill Boehme]

Bill.....what is the difference between the 3x and the pro-sand? I'm very familiar with the 3x, but never had the pro-sand. Is the pro-sand the same as the A275 Norton paper? The 3x is great paper, but my preference for the last decade, or so, has been the Finkat paper from Japan......

ko

I believe that the ProSand is fairly new. The 20 sheet job pack says next generation 3X technology so it is related to the 3X. The grit for each size feels like it bites into the wood and cuts more aggressively than other sandpaper including 3X. I think that it also stays sharp longer than the 3X. I have a lot of the 3X so I will probably be mixing my use of the two, but I really do like the speed that the ProSand cuts. If I am not mistaken, the paper is heavier than the 3X paper.

 

[Dave Fritz]

Excellent thread - thank you.

D. Fritz

 

[odie]

I believe that the ProSand is fairly new. The 20 sheet job pack says next generation 3X technology so it is related to the 3X. The grit for each size feels like it bites into the wood and cuts more aggressively than other sandpaper including 3X. I think that it also stays sharp longer than the 3X. I have a lot of the 3X so I will probably be mixing my use of the two, but I really do like the speed that the ProSand cuts. If I am not mistaken, the paper is heavier than the 3X paper.

I see the pro-sand only goes up to 320.....but, is a little cheaper than the Finkat. Lately, I've been going through a lot of 220, 320, 400, 600.......

Still have some 3x on hand, and it's a good paper, nonetheless......

ko

 

[Bill Boehme]

I see the pro-sand only goes up to 320.....but, is a little cheaper than the Finkat. Lately, I've been going through a lot of 220, 320, 400, 600.......

Still have some 3x on hand, and it's a good paper, nonetheless......

ko

I have 400 grit ProSand, so I know that it is available. It goes down to either 60 or 80 grit ... I'm not certain, but I still have about 40 sheets of 80 grit in the Norton 3X and I rarely need to use it so I don't know when I will be getting any of the really coarse stuff in ProSand.

Here is a link to the ProSand brochure.