How To Identify Flaws In Your Turning Before The Finish Goes On

[Dom Garafalo]

As a new turner I'm just getting to the point of understanding and applying finish to the items I'm making.

I'm very careful to look closely at whatever I'm turning to see if any scratches or imperfections appear before telling myself its ready for finish. Though I have already discovered on a couple of items I've completed that it is easy to miss something.

So I wonder if there's a way to apply a sealer or some type of product that will highlight any areas that need more attention or sanding before you apply the actual finish?

I would appreciate hearing about any tried-and-true techniques others use.

Thank you

[Michael Mills]

I use mineral spirits to dampen the wood and shine a light parallel. A lot of marks show up with the shadows from parallel compared to light from directly overhead. You can use DNA but if the item is very big it may evaporate before you can rotate the entire item by hand; the mineral spirits should give you a couple of minutes to inspect it.
If appropriate, taking it outside to sunlight helps a lot.

[Steve Schlumpf]

Dom, you can spray some water on it. It will slightly raise the grain but will highlight any sanding marks that you missed. Once the wood dries (just a few minutes) then a quick hand sand with a high grit will smooth any raised grain. Good luck!

[Brice Rogers]

I do the same as Michael and Steve. Mineral Spirits (or naptha if you can find it) or water. Some times if I think that I have a burnish mark I'll wet it to raise the grain. Then when I re-sand (by hand) the mark has gone away.

I will also sometimes give the piece a coat of spray shellac as a sanding sealer. It will highlight some marks or blemishes.

I also sometimes use BLO to help pop the chatoyance in the wood. It may help highlight a blemish. After a coat or two of BLO, I may finish with oil-base poly, wax, Tung Oil, French polish, etc. I would probably not try to use anything waterbase after BLO though.

[Bob Bergstrom]

Dom, you can spray some water on it. It will slightly raise the grain but will highlight any sanding marks that you missed. Once the wood dries (just a few minutes) then a quick hand sand with a high grit will smooth any raised grain. Good luck!

As Steve says water will raise the grain and swell the wood fibers, plus if you hit it with compressed air it will clean out any sanding dust revealing any scratches. I use a strong LED outdoor spotlight mounted in my Moffitt fixture.

[Steve Harder]

Buy a pair of 6 power reading eyeglasses. Inspect after every grade of sand paper with an oblique light source.. If you find a machine or sanding mark rework that grade or go back one grade. Don't rush, by the time you get to 240 or 320 you will be home free.

[Reed Gray]

Well, first you should have good lighting. For me that is one lamp from Blue Max which is a full spectrum therapy type lamp and very bright. It comes pretty close to natural sun light. Another method is to take it out into direct sun light. We see better in that than we do in most man made lights because that is what our eyes developed towards. Having good glasses helps too. I did find that prescription glasses work better than the cheap reading glasses from the store. Other than that, I sand till I think every mark is out, then one last pass. When first learning, I would use power sanding then a hand sanding to get a different scratch pattern. I have found that I can do that with the power sanders by changing which side of the disc/pad I am using, like right or left, or top or bottom. Especially with the finer grits, I hand wipe the bowls off. If there are scratches from the coarser grits, it works into those scratches and high lights them.

robo hippy

[Marvin Hasenak]

Most important thing is buy the best quality sandpaper you can afford, and use it like someone else is paying for it. Don't waste your time sanding with worn out sandpaper trying to get that last scratch.

[Dane Riley]

How fine do you sand? For me 400 (not P400) seems like a magic grit. Imperfections show up that I didn't see before. Sometimes you have to go way back, even courser than where you started. Still better than finding out after the finish is on.

[John K Jordan]

Lots of good advice here.

- I agree with good lighting from the side, not from over your shoulder or high overhead. I like smaller lights sometimes called "point source" lighting, as opposed to diffuse (flat) or over-the-shoulder lighting which will tend to fill scratches with light and hide them. Examples of point source lights are smaller fixtures with individual bulbs (LEDs are good), preferably on adjustable swing-arm or gooseneck stands. Examples of diffuse lighting are indirect or high or long or widely spaced fixtures such as fluorescents. If the shop lighting is diffuse, you might try turning it off and turning on one or two point source lights while examining for defects. A bright flashlight held so the light hits the surface at a glancing angle also works. I have several smaller fixtures over my lathe, all powered by a single switch, that I use for primary lighting while turning - another advantage of lighting like this is it helps you better see and judge the compound surface curves in a turning.

- I like to wet the surface with naptha since it shows up defects nicely and evaporates in a few seconds without raising the grain. Raising the grain can be a useful step in the final sanding but not necessarily related to seeing defects such as sanding scratches. I bought naptha at Home Depot. I have used denatured alcohol in the past which does raise the grain somewhat but also evaporates quicker than water.

- Sanding technique is everything. The best way to get bad scratches is hold coarse sandpaper to the piece while it is spinning. The best way to keep bad scratches is to continue to sand with other grits while the piece is spinning. At minimum, make sure the paper is always moving. I tend to use little hand scrapers instead of sanding in many cases, but when I do sand I often do it with the lathe off. I also do one simple thing which has helped a lot to avoid problems: after sanding with a given grit in one direction, I sand across those scratches with the same paper before moving to the next paper. For example, after using 220 grit paper on a spinning piece I stop the lathe and with 220 paper I sand by hand across the 220 grit scratches until they are gone. My theory is: if I can't remove all the cross scratches with the same grit, I'll never get them out with a finer grit. This will eliminate the sneaky problem of a coarse grit scratch being hidden by the finer grits until it is finally obvious at the finest grits! I do this for every grit in the sequence. If at some point I see a scratch that can't be removed easily by sanding across it, I'll back up and use a coarser grit.

BTW, I have always disliked power sanding with a rotating disk. I don't like the clouds of dust. For bowls and platters and such I do almost no power sanding but instead smooth out tool marks with the small hand scrapers mentioned. That means I can often start with a much finer grit, say 220 or 400 instead of 80 or 100. Also, when I do power sand, I generally do it gently with the lathe off, rotating the piece by hand as needed. My new favorite sander is a tiny, light-weight pneumatic Grex random orbital sander. This takes the standard 2" disks with mandrels available for other sizes. The Grex can be run very slowly and gently. It does need a good compressed air source.

JKJ

[Dom Garafalo]

Thanks everyone for a lot of great suggestions that I know will help me.

Although I'm really getting hooked on turning, I continue to tell people that it is so much harder than I thought it would be.

[Brice Rogers]

John, Very good advice.

[David M Peters]

John, by "hand scraper" are you referring to a card scraper? Thanks for the information!

[John K Jordan]

John, by "hand scraper" are you referring to a card scraper? Thanks for the information!

David, sorry, I missed this message. I started using the scrapers years ago as a beginner, first to solve a problem with my second (or third) bowl. I was getting checking from too much sanding heat on Eastern Red Cedar. I cut off the tip of a curved card scraper so it would fit inside the bowl and it worked so well.

scraper_PB054025_s.jpg

Since then, I've accumulated a number of scrapers of different sizes. Here are some:

scrapers_.jpg

The gentle curve of the big one on the left is perfect for both the center and the wings, inside and out, of things like this which tend to have ripples from the interrupted cuts:

penta_plates_comp_small.jpg

I use these on the inside and outside of both face and end grain work, handheld, lathe on, turning slowly, or off (mostly off).

scraper_IMG_20150723_095603_525.jpg

I found a small flat edge works wonders in taming the chatter in long, thin tapers.

To remove tool marks it is usually better to use these with the lathe off, scraping with the grain (or figure, depending). If the piece is large enough, I even take the chuck off the lathe and work on the surface in a comfortable chair. (Hey, I'm elderly and feeble and need lots of rest!) This has the advantage of letting me see the surface better and avoid unpleasant surprises. Once I felt like throwing one of the small squarish platters in the picture in the burn pile or putting it in my Box of Shame - when I took it off the chuck I saw it had a series of gentle ripples near the center - I did not see them on the lathe due to the curvature but they really showed up in different lighting. Just a few minutes with the large curved scraper mentioned above and it was perfect, made a great wedding present!

Safety: perfectly safe inside a bowl or large form with the lathe running (slowly) - if you drop a small scraper it just goes harmlessly to the outside. Just don't do what someone reported years ago when we were discussing this on another forum - he stuck his hand into a form with a large scraper and when he dropped it it turned into a food processing machine...

BTW, I sharpen these just like a cabinet scraper and raise the cutting edge with a burnishing rod, except for the thinner scrapers I skip the first burnishing step, rolling the edge almost parallel with the face. Some of the smaller ones are useful but too thin - I do like the thicker scrapers better and have cut some out of larger, quality shapers. A pain with a Dremel and I'm afraid a large grinder would get the metal too hot and ruin the hardness - might be a perfect job for a water jet machine! Or grind with a coarse CBN wheel which makes less heat for some reason.

JKJ