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Problems with lines when sanding

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Forum topic by Thuzmund posted 12-22-2013 10:08 AM 1252 views 3 times favorited 19 replies Add to Favorites Watch
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Thuzmund

88 posts in 373 days


12-22-2013 10:08 AM

Topic tags/keywords: question sanding turning

Hi all,

So I have noticed a scary pattern: often, as I sand, I leave light swirls and lines that won’t come out. In fact (and this is what scares me)—I can tell the lines are coming from my sanding, not my tools (though to be fair, I know my tools don’t leave a flawless finish). I can see the lines appearing and multiplying as I sand.

This implies that even if I can get a near-perfect finish, I am destined to mar anything I turn until I get to the bottom of this. I’ve attached a picture of a recent bowl to demonstrate my problem:

I had this sucker very, very smooth (for me) by “cheating” a bit with PSI Versa Chisels (Spindlemaster clones). So I was a little heartbroken that my work went for nothing.

How do others cope with or prevent this problem? Do I need new sandpaper? (I used Gator Grit with the palm of my hand 80-120-150-220, and I should note that lines form in the 120-150 range, not just the 80 range)

Any info is greatly appreciated!

-- Here to learn


19 replies so far

View Wildwood's profile

Wildwood

1232 posts in 879 days


#1 posted 12-22-2013 12:01 PM

Besides sharpening tools more often, learning how to shear scrap or how a pull cut can help also look into getting some power sanding equipment from these vendors.
Vince has some videos here too.

http://vinceswoodnwonders.com/

http://www.woodworkingshop.com/?inMed=WOODCNT09

You-Tube will have some videos on shear scraping, using pull cut, and power sanding too!

-- Bill

View bondogaposis's profile

bondogaposis

2741 posts in 1095 days


#2 posted 12-22-2013 01:41 PM

I sand to 600 grit on turnings. You have to sand to much finer grit on turnings because you are sanding across the grain for the most part.

-- Bondo Gaposis

View Nubsnstubs's profile

Nubsnstubs

258 posts in 474 days


#3 posted 12-22-2013 02:38 PM

Those lines look to me like they were created by your tools. After a certain point when sanding, you think you’re done with a coarse grit, you go to another finer grit. That’s when you start noticing lines. They are usually not from the sanding but from you’re turning technique.

My experiernce is lines appear because I’ve just sanded the material on both sides of the groove/cut/tearout caused from the tool and technique used to form the sides of the form.

I know this because I use an angle drill for sanding, and any lines caused by sanding are curved, rather than straight. I keep sanding through the grits until I see a straight line. I then go back a grit or two, sand and repeat going back and forth through the grits until the line disappears. ...... Persistance, smooth tool presentation and new sanding discs is the solution. ............ Jerry (in Tucson)

-- Jerry (in Tucson)

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Wildwood

1232 posts in 879 days


#4 posted 12-22-2013 02:58 PM

How much you sand woodturning depends upon the wood species, and finish going to apply. Sanding your woodturning all about removing tool marks and even out the surface without leaving notable scratches.
Fact, sanding does not always remove tool marks or repair torn end grain!

See grain direction & Importance of sharp tool videos;

http://woodturning.org/education/

Stuart is not a fan of the pull cut but most American turners do use it. Even using a push cut with sharp tools may need some shear scraping.

Everyone talks about sanding sequence and agree up to a point. Think need to work toward a goal of off the tool finish. No do not always achieve my goal, lot depends upon wood species and grain direction and not going back to the grinder before making last cuts.

Before selecting a sanding sequence evaluate, wood surface first! Most film finishes only require you to san to 180, 220, or 320. Oily woods will require you to sand to higher grits. If finishing with oil or oil varnish blend will need to sand to higher grits.

Simply trying to say only sand as much as needed to give a uniform scratch pattern on the wood! Start with highest grit needed to achieve that goal and not lowest grit.

Do not skip grits, and do not go to a higher grit unit scratch pattern on surface is uniform. If have a stray scratch here and there, next higher grit might not take it out. Goal of higher grit sanding is to lessen scratches left by previous grit.

Do not use dull sand paper, sand paper wears out, so use it like toilet paper. Yes, some grades & brand sandpaper last longer than cheap stuff. Find a brand that suits you best.

Lathe speed turn speed down for sanding. Sanding at high RPM’s just over heats sandpaper & burnishes wood surfaces, Do not press too hard while sanding.
I shoot for completing 99% of my sanding and finishing with wood still mounted on the lathe. Hate to admit have still found problems once piece came off the lathe that should could easily been corrected.

-- Bill

View dean2336's profile

dean2336

213 posts in 1653 days


#5 posted 12-22-2013 03:24 PM

that is tool marks.working with spalted material you have hard and soft grains .a soft touch on finishing passes
and a continuous stream of material off the tool should mean the surface is flat.

-- dean2336,nebr.

View a1Jim's profile

a1Jim

112814 posts in 2321 days


#6 posted 12-22-2013 03:41 PM

Along with the other suggestions I would spend a lot of time sanding with 60grit and then move through all of the grits with out skipping any of the grits spending a little less time with each grit up to 600 grit as Bondo sugjested.

-- http://artisticwoodstudio.com Custom furniture

View TheDane's profile

TheDane

3972 posts in 2407 days


#7 posted 12-22-2013 04:05 PM

I have recently switch to Abranet … it is not conventional sandpaper but rather is a mesh that, IMHO, does a better job. It doesn’t load up like regular sandpaper and seems to stay sharp longer.

That being said, I concur with the others above … I think your sanding is simply revealing the tool marks.

-- Gerry -- "I don't plan to ever really grow up ... I'm just going to learn how to act in public!"

View Thuzmund's profile

Thuzmund

88 posts in 373 days


#8 posted 12-22-2013 09:47 PM

These replies have been great, everybody—there’s a lot to take in! But it’s all good stuff, so let me see what I’m taking away from this.

So tool marks are left behind even when the surface appears “pretty darn smooth” by my beginner’s standards, which makes sense. Dean, that’s an interesting tip about how a continuous stream of feathery shavings indicates smoothness. I was quite pleased with myself to get a lot of wispy fluff on this project, but I do recall that the stream was often NOT continuous. That’s something useful to remember next time, and of course it also makes a lot of sense, even to a beginner. :)

Jerry, I will also try your suggestion of regressing periodically as I move through the grits of sandpaper. It’s an easy thing to try while I begin work on getting better results with my tools (which I suspect won’t come overnight). Jim, I will try 60—I was avoiding it mostly out of fear that it’d be just too coarse and rough, but I really ought to experiment with that hypothesis and see what it does on some practice turnings. For example, I have lately been experimenting with white cedar for spindlework, and even the sandpaper can cause tearout! This experience certainly contributed to my hesitation to use 60 grit with this “special” project.

I was chatting with a friend from work about this, and he suggested that cuts in wood also expose pores, which then fill with sawdust to different depths and degrees depending on how sharp the cut (which leaves pores more open than a burnishing action from duller tools) and how deep the groove that’s been created. That’s an interesting thought, and it might account for why these things “appear” when sanding. Perhaps the sanding isn’t actually creating the lines, but merely “lighting them up” with pale dust jammed into the wood grain/pores.

Thanks again, everyone, for sharing your experience.

-- Here to learn

View lumberjoe's profile

lumberjoe

2847 posts in 992 days


#9 posted 12-22-2013 11:08 PM

I hate sanding with low grits on a lathe. As others mentioned, practice scraping the surface smooth. I generally start sanding at 220. Depending on the finish, I will sand as high as 12,000 grit. I never sand below 1000 grit.

-- www.etsy.com/shop/KandJWoodCrafts

View Rick M.'s profile

Rick M.

4470 posts in 1124 days


#10 posted 12-23-2013 04:05 AM

I had that exact issue using cheap sandpaper. After switching to 3M and wiping down the wood between grits, the problem went away. The 3M cuts very aggressively, it’s the most aggressive sandpaper I’ve used based on the amount of dust it produces. Mineral oil keeps the dust down and I feel gives you a better surface.

-- http://thewoodknack.blogspot.com/

View Thuzmund's profile

Thuzmund

88 posts in 373 days


#11 posted 12-30-2013 01:45 AM

So Rick, you would put mineral oil on the sandpaper as you sand?

-- Here to learn

View PRGDesigns's profile

PRGDesigns

215 posts in 1057 days


#12 posted 12-30-2013 04:06 AM

Have you been raising the grain in between each successive grit?

-- They call me Mr. Silly

View Rick M.'s profile

Rick M.

4470 posts in 1124 days


#13 posted 12-30-2013 08:35 AM

I don’t always start with mineral oil but somewhere along the line I’ll wipe the wood with it or dribble some on the sandpaper.

-- http://thewoodknack.blogspot.com/

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Thuzmund

88 posts in 373 days


#14 posted 12-30-2013 06:51 PM

PRG, I have not been raising the grain. I see that some folks do that with a solvent-based product, and other just add water or mineral oil. Does that sound about right?

-- Here to learn

View Rick M.'s profile

Rick M.

4470 posts in 1124 days


#15 posted 12-31-2013 07:54 AM

You need water or alcohol to raise the grain. AFAIK, petroleum products will not do it. Mineral oil or wax acts as a sanding lubricant and helps fill the pores, I get a smoother surface using it especially on end grain.

-- http://thewoodknack.blogspot.com/

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