How to sand "air" on the running lathe?

[Doug McKnight]

I turned a long narrow rectangular sushi plate thingy the other night. This involved turning a lot of "air" which was part of the fun. I discovered, however, that I did not have a good way of sanding the object while the lathe was running.

How do the experts do this? A block with a layer of padding? I was concerned that if I used something too soft as a backing for the sandpaper I'd just end up hitting the leading edge too much and end up rounding it off. This would spoil the shape.

Suggestions are much appreciated.
Doug

[Reed Gray]

Pretty much impossible without rounding over the edges and corners. I do power sand, with the lathe off, and very slow speed on the drill, like crawling speed. The edge of the disc that is cutting runs off the edge rather than into it, so it doesn't dig in, and very light pressure. Some will just power sand the inside, and hand sand the rest. Probably safer.

robo hippy

[Roger Chandler]

On the natural edge bowls that I do, I always have to turn the lathe off, and rotate the piece by hand, and power sand with the other hand........I am right handed, so that works well. As Reed mentions, a light pressure is needed, but most of us have a tendency to be a little heavy-handed with sanding anyway!

[david privett]

I have never done this but I think there would be a lot of exacting work , but could you make a exact solid insert and out side shell as far as that goes. and use multiple adhesive sand paper strips that way there would be no air sanding. I guess it would not be worth doing that unless many of the same item was to be made. just a thought.

[Reed Gray]

That method can work for the outside of natural edge pieces. Taking some thing like a credit card to a piece of formica/laminate and putting abrasives on it. It will bend into an arc, and has a bit of flex and is bendable to help it form to a convex shape. Pretty much impossible on the inside of the bowl because any thing that conforms to a concave form would have to be softer, which would roll the edges. On a rectangular form, if you had the sanding shape fixed it might work, but if hand held, when in air, it will move in and round over the leading edges as they hit the abrasive, but the trailing edge would still be fairly good. Maybe a sander on a articulated arm that you could dial in by increments....

robo hippy

[Doug McKnight]

Thanks, I think it will be just hand sanding for this one (I hate sanding...)

Doug

[John K Jordan]

Doug,

I do very little sanding on such pieces, lathe on or off. It's almost impossible to sand corners effectively after turning air. You can hand sand or power sand with the lathe off - the tiny Grex 2" random orbital sander is perfect for this. But what I do instead is use small cabinet scrapers by hand, with the lathe off. I keep a variety of these on hand with different curvatures. There is a reason fine furniture makers often use cabinet scrapers to smooth wood.

With these I can remove ripples and tool marks quicker than it would take me to sand and I get a better finish with more control. It is difficult to accidentally round over edges unintentionally so crisp detail can be preserved.

An example of smoothing after turning air is this maple dished platter/shallow bowl.

337083

Some of my scrapers:

337084

I have been using these for many years and they have almost eliminated power sanding and the clouds of dust for bowls and platters. They are perfect for removing any unevenness in the center of the inside of a bowl. I use them with the lathe running for some things (held by hand, no tool rest) and with the lathe off for others.

After smoothing with the scrapers, I usually don't need sandpaper coarser than 400 or maybe 320.

JKJ

[Robert Willing]

337089I used abarnet sanding sheets with 3M foam backed sanding pad with the foam as a backer out side and 3M scotch-brite pads as the backer on the inside. I also use the fine (gray 3M Scotch-brite) pad alone as a surface furnisher. There are other brands, but they are what we used to call horse hair rubberized pads. They come in different grades /colors. The Scotch-brite pads will burnish the wood surface and almost give it a gloss effect. In fact I use the Scotch-brite pad as a backer on almost all of my sanding, because it will dissipate the heat from the sheet and let the dust pass through the sheet.

[Thomas Canfield]

On large "air surfaces" I like to use my random orbital sander with lathe power off and hand rotate. That works well on flat and gradual ouside curves. Inside curves usually is done with power off and hand sanding with foam pad backing.

[Doug McKnight]

Scrapers! That's an interesting thought. These are tools that I've completely neglected in my thinking. I guess another potential advantage of scrapers is that they presumably don't have quite the same tendency to remove too much of the softer areas that sandpaper can.

Do you favor thick and stiff or thin and flexible?
Doug

[John K Jordan]

I guess another potential advantage of scrapers is that they presumably don't have quite the same tendency to remove too much of the softer areas that sandpaper can. Do you favor thick and stiff or thin and flexible?

Exactly - with a gentle curve you can remove just the high spots whether the wood is very soft or quite hard. I get surfaces that are smooth as glass with the right finish.

I don't think the flexibility and thickness matters too much since they are not flexed for cutting the same way you use a straight cabinet scraper on a flat surface. The biggest thing is keeping them sharp since most seem to be made of carbon steel instead of HSS. Fortunately they are quick to sharpen - I use the tormek or CBN wheels, file the profile flat, then roll over a burr with a tungsten carbide burnisher. I don't use the double burnishing technique taught for flat cabinet scrapers. The thicker scrapers do seem to hold an edge better.

I started using these long ago, making my first small curved scraper by cutting off the tip of a standard large curved scraper that is usually included when you buy a set of three scrapers. I was turning a bowl from soft eastern red cedar and with my beginner technique I struggled with tearout. The idea of the scraper hit me and it worked so well I've been using them on almost every piece since.

I found my first set of small scrapers at Highland Hardware in Atlanta, then bought some more later when Woodcraft started carrying them. I did find a set of high-quality large scrapers that had one with gentle curves (the one on the left in the picture) - that is the one I use on corners like the dished platter shown. I use the smaller scrapers that fit tighter curves on the outside or inside of bowls.

I turn a lot of long, thin spindles with the skew and discovered that a small straight-edged scraper was even perfect for solving a chatter/vibration problem with one particularly flexible shaft with soft and hard areas.

I've shown many people these but I don't know of anyone else who has started using them regularly. People often ask how I get the inside bottom of a bowl so perfect so I tell them or show them. They say "nice idea" then go back to power sanding. (I hate power sanding!) I should probably do a club demo on this some day.

JKJ

[Doug Ladendorf]

John, you have been so generous sharing your experience, I think this is another area many of us could benefit from. I for one would love to see how you go about sharpening and using the curved scrapers.

Doug

[John K Jordan]

John, you have been so generous sharing your experience, I think this is another area many of us could benefit from. I for one would love to see how you go about sharpening and using the curved scrapers.

Why thank you! If you ever find yourself near Knoxville TN stop in for a visit and we can play in the shop. I built my shop down by the barn so when we take a break from woodturning you can take a llama for a walk. :-) I often have people come for some beginning woodturning, how to weld, learn about beekeeping,... I retired about 10 years ago and my schedule is flexible!

This is a busy time of year on the farm but if needed I can try to take some pictures and describe sharpening the scrapers in more detail. Basically for sharpening or reshaping I grind the edge flat at 90 degrees by moving the scraper on the grinder rest, smooth the edge with a file and/or a stone, then turn over a cutting edge by applying a little pressure with a carbide burnisher, sliding it along the edge while holding at a slight an angle from the flat of the edge. A HSS turning gouge will work as well to burnish if you don't have a smooth carbide rod.

You can find a lot of information on the internet about sharpening card scrapers. I did a search just now and this was the first one that popped up: http://www.finewoodworking.com/tool-guide/video/how-to-sharpen-a-card-scraper.aspx
I mostly use this method but sometimes skip the initial burnishing for the small, thin scrapers. The curved scraper is done mostly the same way as in the video except instead of using a vise I hold the small ones in my hand and turn them while burnishing. You can easily feel the hooked edge after burnishing (and feel when it gets dull). I sometimes burnish several times for each time I grind and hone the edge. Since the edges don't last too long, I tend to sharpen a bunch at once and switch to a fresh one as needed.

I found a picture of my first small scraper for woodturning, cut from the tip of a larger scraper since the whole scraper was too big to handle:

337105

I mentioned the Grex small random orbital sander. I have learned dislike power sanding with a coarse spinning dish on an electric drill. I don't like the results or the clouds of dust. At the TAW symposium this year I think it was Rudy Lopez who endorsed the Grex sander. Instead of spinning, it is a random orbital sander. It is air operated instead of electric which may be a problem for some but perfect for me since I have compressed air outlets all over my shop. Since it is air operated, the thing is tiny and light weight. The sanding can be VERY gentle or aggressive as desired. For small areas I usually follow up the card scraping with hand sanding with 320 or 400 grit (lathe off), but for larger areas, such as on a platter, 400 grit on the Grex is often perfect. I bought mine from Amazon.

337104

BTW, for hand-sanding flat or gently curved surfaces I found the perfect backing medium. Instead of using my fingers or a soft backing pad which can limit the abrasion to smaller pressure points, I back up sandpaper with a Magic Rub eraser. This is flexible enough to conform to the surface but applies pressure evenly. I use this only with the lathe off.

337106

BTW, I learned the hard way about sanding and heat. On the same early ERC bowl that I smoothed with the little scraper I followed one guy's advice and held sandpaper against the spinning wood with a insulating backing to protect my fingers from the heat. Bad idea on ERC (and probably some other woods.) Turns out the cedar surfaced checked badly with heat. I read an expert later say that if the sandpaper is too hot to hold you are using too much pressure! (Same thing when backing up a spindle with the hand as steady rest - Richard Raffan said if your hand gets too hot you are using too much pressure with the cutting tool.)

I do sand with the lathe spinning where appropriate but I use low speeds and try to minimize pressure. Then I turn off the lathe and sand perpendicular to the scratches and/or with the grain/figure with the same paper until the circular scratches are gone. My theory is if I can't get, say, 220 grit scratches out with 220 paper, I'll never get them out with a finer grit! I really, really hate to see circular scratches in a finished piece.

Just for fun, this is the ERC bowl that got me started with the scrapers. I think it was my third bowl, but it was about 15 years ago so I might be confused. The finish is beeswax.

337115

JKJ

[Reed Gray]

I am finding with dry wood the negative rake scrapers are excellent for removing tiny tool marks. They are not as effective in wet wood though, and I have some wet myrtle that I have been doing a lot of 'experimenting' with. Have to try them on an air/wood piece though.

The thing with dust being thrown around is, to me, an 'it depends' situation. Of course first you need a dust collector. Then if you have a sanding hood like my 55 gallon drum hood that encloses 75% of the bowl, no dust escapes. If you use the drill sanders at high speed, that does throw off more dust, especially if you are sanding at high drill speeds and only have a hose or big gulp hood. I have tried one random orbit sander, not the Grex, and found that while it does work, it works best for the higher grits, 220 and above, which is not practical for my green turned pieces. Most of the time I have to start at 120 or 100, and that is some times for tool marks which seem to grow with shrinkage, or for oxidation which I want to try to balance out. The card scrapers are good for stopped work, and I can see that they would be great for this application to reduce the amount of sanding. I used them a lot for flat work, but not much for lathe work. I did have problems with getting a consistent cutting edge on them, which was mostly me. I would think that the CBN wheels would be excellent for any of the curved ones, then hone and burnish.

Wish you didn't live on the other coast John, a play date would be fun, and the walking with llamas...

robo hippy

[John K Jordan]

Wish you didn't live on the other coast John, a play date would be fun, and the walking with llamas...

Who knows, you might find yourself coming through East TN some day when you least expect it. We have a guest room and I know the way to the airport. And John Lucas is not far, that's a fun visit!

JKJ

[Col Smith]

Back to Doug's original question about "sanding air".
This is what I made & use . Easy to make.

Sorry I can't load photo...don't know why.
Anyway it is a 200mm x 25mm x 3mm strip of thin ply or hardboard etc. glue on a strip of Velcro the same size, & cut various sand papers to fit.

Just hold the strip top & bottom & gradually move in to make contact with timber. It will only sand the high spots so there is no rounding off edges.

Works really good.

HTH
Col

[Doug McKnight]

Thanks Col, I have been wondering if something like this would be worth a try. Your experiences have motivated me to head out to the garage and start raking around for some thin material to try this approach.

Regards,
Doug

[John K Jordan]

....Just hold the strip top & bottom & gradually move in to make contact with timber. It will only sand the high spots so there is no rounding off edges.

Do you have any trouble with the strip bouncing? That was the problem I had with sandpaper glued to nearly identical sized strips of wood when I experimented with the a few years ago.

Perhaps the shape of the surface was different. The problem I had was with a concave surface - perhaps a curved surface on the stick with a curvature the same or a little tighter than the curvature of the piece would work better, assuming I could hold the stick carefully enough. I may experiment more.


The flat sanding stick worked better on the outside (bottom) of my small platters where the surface is convex.


But even there I find advantages to the hand scraping.


JKJ