Scrapers - Good Finish - Woodworking Talk - Woodworkers Forum
 
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post #1 of 12 Old 08-31-2011, 08:10 AM Thread Starter
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Scrapers - Good Finish

I have just started to use scrapers in my woodturning projects and I just wanted to pass on some experience I've had with using them and see if you guys thought the same.
Scrapers are used as the last tool in turning to achieve a smooth finish. I had no experienec with these tools so had to find out the hard way. My first few attempts of scraping caused more damage to the surface of the wood that the job was ruined. My mistakes, i know now was that I wa snot using the very tip of the scraper. As soon as I mastered that the jobs came out 100% better.
As for grinding, my scrapers are normally ground with a cutting edge just off vertical: that is, at 80º to 88º with reference to the top surface. In fact it is the burr thrown up on the top edge by the grinding process that is the actual cutting edge, rather than the corner formed between the bevel and the top surface.
Hope this has helped anyone. I'm MORE than welcome for anymore toips myself as Im no expert by a long shot.
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post #2 of 12 Old 08-31-2011, 09:25 AM
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When you say grind - you mean burnish correct? I know getting the muscle memory down for burnishing can take a while but once you do a scraper will get you a great finish!
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post #3 of 12 Old 08-31-2011, 09:40 AM
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Well let me jump in here and give some insight to scrapers. First of all a cutting tool used properly will give a better finish than a scraper. A scraper scrapes wood, a cutting tool cuts wood. Cuts are cleaner. So ideally you practice with the cutting tools learning to get the cleanest finish you can.
OK, now the reality. Most people don't cut that clean. It does take skill, lots of practice and very sharp tools. consequently we learn to scrape. Now there are 2 kinds of scraping. With the tool held flat you get a scraping action. By the way the scraping edge needs to be lower than the handle or you risk a catch. The bar should be parallel to the bed or higher to be safe and you should be scraping on center of above.
The above method gives you pretty good control if you take really light cuts. Usually this is used to clean up tool marks or to smooth out curves where you have uneven thickness. As I mentioned above good cutting technique will eliminate these and the need for scraping but I'm going back to talking about scraping.
Shear scraping is different. The tool is held at a 45 degree angle (approximately) and pulled with the handle higher. this is really a cutting action because the burr on the tool acts like a cutting edge. You do have to sort of find the best angle but it doesn't take long. Cut with the lower 1/2 of the scraper to prevent a catch and keep the handle higher than the cutting edge.
Sharpening angles. I have switched to 45 degrees instead of the the old 80 degrees or so. The reason. I don't use it as a scraper very often and tend to use them as shear scrapers. it's easier to raise a good burr on a scraper sharpened at 45 degrees.
There is also a new thing on the market called negative rake scraping. If you have ever used a skew on it's side as a scraper then you have used a negative rake scraper. This is a scraper with a bevel on the top and a bevel on the bottom. This accomplishes 2 things. first of all it makes it easier to keep the scraper tip below the handle. This is called negative rake if your into metal working and that's why they call it a negative rake scraper. Secondly the forces from the wood pull a negative rake scraper down on the tool rest which means less force is going into the wood which gives you more control. With a regular scraper held with the handle up you are pushing into the wood slightly and don't have as much control as a negative rake scraper.
I hope this clears up of the mistique. don't be afraid of a scraper, they are good tools, very handy easy to use if sharpened and used correctly. However your goal should be to use cutting tools like bowl gouges and spindle gouges. You will have to do less sanding once you learn to learn to use these correctly.
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post #4 of 12 Old 08-31-2011, 09:46 AM
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Sharpening a scraper. Many people come directly off the grinder with scrapers. the metal piles up on the upper edge and forms a burr. This is usually adequate but it depends on the hardness of the metal and the grit of the wheel.
What many people do is use diamond hones to create a burr. this has the advantage of changing the quality of the burr. you can use a course grit and create a large rough cutting burr or you can use a fine grit and create a small very fine cutting burr.
To use the diamond hone I polish off the old burr by running the stone flat on the top of the scraper. then I push the scraper up the bevel from the heel to the toe. I do this until I feel a good burr. Usually just one to 3 strokes is all it takes.
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post #5 of 12 Old 08-31-2011, 10:09 AM
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OK, I'm not trying to be argumentative here, but I'm a little confused. Everyone in the woodturning arena always says scrapers don't give as good a finish as a good cut. I'm a relatively new turner and while my skills with a gouge are improving, I still get a better end product with a properly used scraper. On the other hand, flat work folks swear by card scrapers, saying it even removes the need for sanding in many cases. I've been learning to use one of these also and now that I'm getting the hang of it, I see that. So which is is it, does scraping leave a smooth finish or not?

Also, I see a lot of folks using these easy turning tools with the replaceable carbide tips. Aren't these merely fancy scrapers?

Anyway, the way I look at is there's more than one right way to do things and whatever works, works.

That bowl was perfect right up until that last cut...
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post #6 of 12 Old 08-31-2011, 12:11 PM
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Concerning card scrapers vs. scrapers for turning, I believe there is a large difference in semantics. On turning tools the “burr” is the metal remaining from grinding, normally jagged and weak compared to a card scraper. With a card scraper the edges are filed or honed completely flat (square). Then a hardened rod or wheel is used to raise a “burr” by physically rolling the steel up forming a sharp straight edge. This is basically the process which John described. I can’t imagine anyone in flat work trying to work wild grain with a burr raised by a grinding wheel…. But maybe some do.
So, imho, the burr from a grinder will work but not as well as a burr on a traditional card scraper. The sharper, harder, and cleaner the edge the better the cut. This comes back to John’s comment on cutting or scraping and Cellophane’s comment on burnishing. For those who have not done it, here is a good site on burnishing a scraper. http://woodgears.ca/scraper/index.html
You can do the same with a scraper for the lathe if you have a very hard steel rod.

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post #7 of 12 Old 08-31-2011, 01:14 PM
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Have scrappers and use them for inside boxes, vases, and bowls. Still use sandpaper before applying finish. Previous posters have already address learning curve in using a scrapper and sharpening them. With practice comes skill in using scrappers successfully.

I am one of those folks that think get better surface finish with gouge or skew than scrapper. Strive for off the tool finish, and no do not always achieve that goal. Can use either gouge or skew to scrap as well as cut. Learned to do that watching Del Stubbs video and lots of practice.

Many accomplished turners use scrappers on almost everything they turn. They also do a lot of sanding too!

Seen a You-Tube video of a man making duck calls and used a scrapper for 85% of his turning. Could see lines in completed duck calls from scrapper and sandpaper use. This guy sells many duck calls every year, has won several awards for his calls. He has the skills to get off the tool finish if wanted too! So would not tell him he is using poor turning and sanding techniques.

Have not used any carbide tools. Yes they are affective scrappers with easy learning curve. Can be expensive to buy and maintain or make your own
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post #8 of 12 Old 08-31-2011, 03:09 PM
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Well turning scrapers can be sharpened very similar to card scrapers in the way you raise the burr but we don't go to the extremes they do. Second of all most cabinet makers sand to 220. maybe the finer ones go further. turners often sand to 600 and beyond.
The other thing is a card scraper is used by hand so you make a cut of about a foot over a 1 second period. We are probably running the wood past the tool at about 10 or 20 feet in the same period.
In reality we are splitting hairs because I often use a shear scraper as my final pass on my hand mirrors simply because I turn the mirrors quickly. it's a production item. I have to make a choice. I can pull up a freshly sharpened tool and make a pass or two to clean up the wood or I can grab the scraper and make a quick pass. where I draw the line is the details in the mirror. If I have beads and coves it's very difficult to scrape and just about as hard to sand these areas and not lose some of the crisp detail. In those cases I make a concerted effort to cut more cleanly so I can start sanding with 220 or 320.
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post #9 of 12 Old 09-01-2011, 12:11 AM
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Very good info from John lucas and others.
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post #10 of 12 Old 09-01-2011, 03:29 AM
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This isn't about scrapers but it is about making wood smooth. I have in the past used a scrap of hardwood rubbed on the piece turned and it smooths pretty good. The hardwood will get hot so move it around so it don't scorch, try it on a scrap piece you are turning and see how you like it.

One of my buddies uses the hardwood after applying CA to his pens and it makes them shine pretty good. I can't say this is the way for you to do it but it works for me.

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post #11 of 12 Old 09-01-2011, 07:20 AM
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I often hear of using wood or shavings as a final finish on wood. All that's doing is polishing what's there. If you have tool marks or tear out your just polishing that, not getting rid of it. You also never know what grit it actually is. shavings contain both summer and winter wood and there is a difference in hardness. I did do that for several years because that's what I read and it seemed to work.
Now I prefer to use sandpaper and just go to the finer grits if I need a really glossy finish. I know exactly what grit each one is and how far to go. My finishes are far superior to what they were when I used the shavings or burnished wood technique.
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post #12 of 12 Old 09-01-2011, 05:32 PM Thread Starter
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Great feedback here guys thanks
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