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Thread: Scraper Questions

  1. #1
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    Scraper Questions

    I started turning bowls a little over a year ago. Mostly I have turned smaller bowls (no larger than 6") but am beginning to turn larger bowls. My lathe will accommodate up to a 12" bowl.

    Concerning scrapers . . .

    1. There are round and half-round scrapers. It seems to me that the round scrapers would be the most useful for me, but, in fact, which makes the most sense for the bowls I will turn (and possibly some plates)?

    2. Is there size that makes the most sense? I have seen 3/4", 1", and even 1 1/2".

    3. There are also different thicknesses of scrapers. I have seen 1/4" and 3/8" (maybe there are others). Which is the most generally useful?

    4. As for grinding angle, is there an angle which is best for smoothing the inside (and maybe outside of bowls)?

    Maybe I have not supplied sufficient information. Keep in mind, I'm a beginner, especially when it comes to using scrapers.

  2. #2
    I hope to have a new scraper video up before the Symposium, shooting next week....

    Anyway, as far as bevel angles, most are in the 60 to 70 degree range. I prefer about 1 inch wide scrapers, and I can stall my 3 hp Robust with them. If you are only getting one, then a round nose would be best, Main reason is you can sweep and shear scrape from either side, right to left or left to right. I find the 1/4 inch thick ones to be a bit bouncy/chattery. Doug Thompson (Thompson lathe tools) has a 5/16 by one inch wide one that is just right, though you have to grind the nose profile yourself, so having a 36 grit wheel helps, or at least having a friend with one... Dave Schweitzer (D Way tools) has a 1 inch wide by 5/32 thick one that is also 1 inch wide. I have a couple of 3/8 thick ones and just don't use them any more, as well as some 1 1/2 inch wide. It is a matter of how much metal can you stick into the wood at one time. My favorite is the Big Ugly tool, another scraper... I have a bunch of videos up on You Tube about scraper, shear scraping, bowl roughing, and bowl turning in general, type in robo hippy... Some think that the bigger scrapers reduce vibration. For me, I just move the tool rest closer to the work, and never hang very far off the tool rest.

    I hope to have a negative rake scraper video up later this year...


    robo hippy

  3. #3
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    Quote Originally Posted by Randy Heinemann View Post
    Concerning scrapers . . .

    Randy,

    For the inside of bowls and vessels where I can't get the tool rest close to the surface, I like to use the Sorby multi-tip tools, either the straight or the swan neck depending on the piece. Mine came with a 1/8" thick teardrop scraper that can be positioned as needed to smooth different shaped insides. I don't use these tools for hollowing.
    http://www.rockler.com/robert-sorby-...g-tool-rs200kt
    Sorby_multitip.jpg Sorby_teardrop.jpg
    I use the swan neck tool to reach in a closed form but not with the tip shown but with the same teardrop shaped tip.
    http://www.rockler.com/robert-sorby-...ollowing-tools
    sorby_swan_neck.jpg
    I usually use these tips slightly angled down or raise the rest a little and hold them flat.

    For the outsides and the insides of shallower pieces where I can put the rest close to the surface I far prefer some negative rake scrapers I ground from Thompson scrapers and a Thompson skew. These are 3/4" and 1" and are amazing, always held flat on the rest. I use these without handles. By varying the burr they will aggressively shape or take whisper-thin shavings for smoothing.

    scrapers_neg_rake.jpg

    Since you asked about scrapers, after I remove most tool marks under power with tools like these I switch to hand scrapers to perfectly smooth the insides and outsides and remove minor undulations or irregularities still in the surface, especially the hard-to-smooth center of a bowl or platter. I have a variety of shapes and grind cabinet scrapers into shapes as needed. With these I can eliminate sanding with coarser grits.

    scrapers_.jpg

    I hold these by hand without touching the tool rest, mostly with the lathe off but sometimes I use the smaller ones with the lathe turning slowly.

    JKJ

  4. #4
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    I have two Thompson 1-1/4" scrapers. I ground one for inside large bowls and the other for outside. I think between 1" and 1-1/4" is just a matter of preference. I only use tear drop scrapers for inside hollow forms. I have a inexpensive Benjamin Best 3/4" hook nose scraper that i like for smaller bowls. I sharpen these to 70 degrees and have not made any negative rake. I also have one re-purposed tool ground as a negative rake round nose at 30 degree (whatever is the lowest setting on the Robo rest) that is used for very light passes to cleanup tearout. You only get one or two passes with this before resharpening.
    When working I had more money than time. In retirement I have more time than money. Love the time, miss the money.

  5. #5
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    John,Do you use the StewMac scrapers on bowls

  6. #6
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    Quote Originally Posted by Bob Ballard View Post
    John,Do you use the StewMac scrapers on bowls
    I use a either the StewMac (the two curved ones) or the cabinet type scrapers or both, depending, on bowls and platters.

    scrapers_platter_IMG_20171111_161724_603.jpg

    I sometimes try several different scrapers until I find the one that works the best for that wood and shape. The StewMacs are great for certain woods - I want some different shapes so I bought some 1/8" O1 steel and plan on cutting some shapes and hardening. When I get around to it...

    JKJ

  7. #7
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    Question here.....
    JKJ, I have that Sorby teardrop, in addition to several other insert/hollowing scrapers. I sharpen my teardrop with a shallow (or steep, depending on your perspective) angle so it's no longer square. I think it cuts better. All this hype about Negative Rake Scrapers, and you mentioning that scraper led me to think, IF I held the teardrop scraper "upside down" and used it, is it a NRS? Just tried it, it barely cuts, can't even see the shavings, since the cutter is in the way. Perhaps if I made an even shallower angle it may work better? Thoughts? Perhaps if I installed it upside down and used the tool correctly, it would work better too......
    Random out of the box thinking. TIA

  8. #8
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    Quote Originally Posted by Kyle Iwamoto View Post
    Question here.....
    JKJ, I have that Sorby teardrop, in addition to several other insert/hollowing scrapers. I sharpen my teardrop with a shallow (or steep, depending on your perspective) angle so it's no longer square. I think it cuts better. All this hype about Negative Rake Scrapers, and you mentioning that scraper led me to think, IF I held the teardrop scraper "upside down" and used it, is it a NRS? Just tried it, it barely cuts, can't even see the shavings, since the cutter is in the way. Perhaps if I made an even shallower angle it may work better? Thoughts? Perhaps if I installed it upside down and used the tool correctly, it would work better too......
    Random out of the box thinking. TIA
    Kyle, if I understand how you sharpened and used the scraper upside down, it does technically sound like a negative rake scraper but perhaps a horribly inefficient one!

    I've resharpened most of my scrapers into negative rake scrapers and I'm generally pleased with the result.

    I think the "negative rake" label is just a way to describe the the angle the leading bevel has with the wood. With a given included angle, the tool can be sharpened in a variety of ways and it will cut the same if it is held so the leading bevel is the same. For example, the three NRS I showed ground from Thompson steel,
    scrapers_neg_rake.jpg
    are ground to about 60-deg included angle. I hold these horizontal, flat on the rest. (I use them without handles.) I could remove the same fine shavings by grinding a the scraper conventionally, with a flat top, and with a 60-deg bottom bevel, then just hold the tool so it is sloped 30-deg downward. HOWEVER, for me, at least, that would be a lot harder to maintain fine control than when ground as shown and held horizontally.

    I believe Sorby recommended grinding the teardrop scrapers with an angle a little less then 90-deg. I think I usually ground mine to about 85-deg or so but nearly any angle will work. I hold it tilted down a little (relative to the wood) on the inside of a vessel or bowl, mostly by twisting the tool a bit counter clockwise. This, in effect, makes it into a negative rake scraper. If I hold it flat but move the tool rest up so the scraper s contacting the inside of the bowl higher than the mid point, it again makes it into a negative rake scraper. Some turners actually grind these with a top and bottom bevel instead of a single bottom bevel and hold the teardrop nearly horizontal, perhaps erring on the side of raising the handle a bit.

    Cindy Drozda and others point out (http://www.cindydrozda.com/handouts_...20scrapers.pdf) that an included angle of greater than 90-deg won't cut at all. This sounds like what you have if you sharpen the teardrop to some angle then turn it upside down - it just won't cut. I've found that if I sharpen at very close to 90-deg the scraper works, but perhaps not as well as at a sharper angle. This, however, lets me flip it over and cut with either side. The StewMac scrapers, very similar to the Sorby teardrop in construction, are sharpened as close to 90-deg as possible. Doing this on a grinding wheel actually make the angle very slightly less then 90-deg because of the radius of the grinding wheel.

    I have a number of small negative rake scrapers I use on detail and on smaller turnings that are sharpened at nearly 90-deg that work very well, especially on end grain, giving glass-smooth surfaces in hard, fine-grained wood:
    scrapers_small_thompson.jpg
    (I use these without handles also.) They would probably cut better at a sharper angle but there is another tradeoff - the sharper the angle the less smooth the surface can be.

    There is another usually ignored factor that changes the geometry and "cutting" angle for both conventional and negative rake scrapers - the burr on the scraper. The burr can be from the grinding wheel, added by honing, or raised with a burnishing tool (a process that used to be called "ticketing".) The burr has the effect of creating a tiny but sharp cutting edge, almost like a microscopic gouge. All three ways of raising a burr have their advantages and disadvantages.

    1) Using the bur from the grinding wheel is the easiest, just sharpen the lower bevel last and there will automatically be a burr you can easily feel with the fingers. This will cut well but differently depending on the grit of the wheel, the type of steel, and maybe some other factors. The disadvantage is it doesn't last long. Look at the burn with a microscope and you'll see a ragged, fragile row of peaks and deformed metal. Every time this burr touches wood more of the cutting peaks are torn away until they are all gone and it quits cutting. Some people say they resharpen after 30 seconds or so of scraping to restore this burr.

    2) Creating a burr with a hone is about the same but results in a much finer burr capable of smoother cuts but much finer cuts - great for that perfect surface but not as good for removing wood. I think it lasts longer than a grinder burr but maybe because I use much lighter pressure with the finer cuts. This burr can make incredibly thin shavings that float through the air.

    3) The burnished burr is made by pressing a hard, usually round rod into the edge and pulling it down the edge on the bottom side at some angle greater than the bottom bevel. The sharp edge is smoothly deformed by the burnishing rod. Look at it under magnification and you will see a much smoother and sturdier-looking burr than one made by grinding. I find the burnished burr can last longer than the others, perhaps because it is smoother and stronger and chunks don't tear away as easily with use. With a light pressure and an angle closer to the bottom bevel, the burr can be very fine and good for light smoothing, or apply more pressure and a steeper angle and the burr will be bigger and more curved and cut more aggressively. Some burrs work better with some wood than other - I'm constantly experimenting to find what works best for a particular piece of wood.

    The way I usually work is to first grind the bevels with the lower bevel last and create a grinder burr. I use this until it quits cutting then I use an extra fine diamond hone to hone both the top and bottom bevels until the burr is completely gone. I keep a piece of resawn MDF with polishing/honing compound smeared on it for honing my skew chisels - I often use this on the NRS to give a nicely polished edge. Then I raise a burr with either the diamond hone or the burnishing rod to suit what I'm working on.

    I use the burnishing rod on all cabinet-type hand scrapers to raise a cutting burr very similar to that used by fine cabinet makers.

    BTW, the instructions for sharpening the StewMac scrapers (which are much like the Sorby teardrop scraper) are to hone the sides flat before grinding with the rest on the grinder perpendicular to the stone. The video on this page describes this: http://www.stewmac.com/Luthier_Tools...e_Scraper.html The last time I sharpened the teardrop scraper I used this method and it seemed to work fine.

    JKJ
    http://www.stewmac.com/Luthier_Tools...e_Scraper.html

  9. #9
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    Rudy Lopez has this on sharpening his NRS, similar to what I use but with a different curve on the tip: http://www.rudolphlopez.com/pdfs/Neg...and%20Info.pdf

    JKJ

  10. #10
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    John,Do you sharpen the StewMac on a CBN wheel

  11. #11
    Jimmy Clewes was a fan of the upside down sharpening for his scrapers, don't know if he still is. At the time I saw him chat about them, he didn't have CBN wheels, and I don't know if that still holds true or not. The idea behind that is when sharpened upside down, you get a much finer burr than you do if you sharpen right side up because the wheel is dragging the burr off rather than pushing into the top of the scraper. I did try it, and didn't think it performed nearly as well as the conventional grind on a CBN wheel. It was a very delicate burr, with little durability. Other than that, I have not been able to get any conventional grind scraper, no matter how high or low I hold the handle, to cut as well as any NRS. That included top angle does some thing, and I am not really sure what. I do get better and/or cleaner cuts than I can with a standard scraper. I am able to get much finer cuts with a burnished burr. I am able to get much cleaner cuts in dry wood than in green wood. For burnished burrs, the more conventional 30/30 grinds do not take a burnisher very well, the edge is just too thin and fragile to take the burnisher, no matter how light of a pass I take with the burnisher. You can actually hear the burr breaking/crinkling as you burnish. With an 80/30 NRS like the Sorby 'hardwood bowl NRS' it is difficult to get much of a burnished burr, and you have to apply a lot more pressure. The less that included angle is, the better the burnished burr is, as in sharper, longer lasting, and can be turned down and back up more times. I have them 80, 70, 60, 50, and 45, with the top angle being 30. It seems like the 45/30 is my favorite for now. More experimentation necessary.... Oh, V10, 1 by 5/16 inch from Doug Thompson, and M42, 1 by 5/32 inch, from Dave Schweitzer. The next size thickness in M42 is 3/8 inch, which is too thick for my tastes...

    John, I can't remember, but do they tell you what metal the Stewmac scrapers are?

    robo hippy

  12. #12
    I watched that Stewmac video again. I commented on it some time ago, maybe years ago and asked him if he had ever tried CBN wheels, and got no response. I would be willing to bet that a carbide burnisher would turn a burr on it...

    robo hippy

  13. #13
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    One other advantage of the negative rake scraper is it applies almost no force against the wood so you get less chatter than you do with a regular scraper. This is especially true on thin platters with wings such as natural edge bowls. I used to think that holding a scraper handle up high was the same thing as a negative rake scraper if they both had the same included angle to the edge. It's not. My older tear drop scrapers were ground about 75 degrees. So flipping them over does produce a negative rake but it still works like holding a handle high on a regular scraper. Sharpening a scraper to a more acute angle like 45 degrees and giving it a negative rake on top is a much more controllable tool and leaves a fantastic finish.

  14. #14
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    Quote Originally Posted by Reed Gray View Post
    John, I can't remember, but do they tell you what metal the Stewmac scrapers are?
    robo hippy
    The gentleman who returned my call about this question said it was "tool steel", no more details.

    It looked like the gentleman on the video was putting a lot more force on the test board than I would ever use on a turning. The steel seems hardened but I didn't try the file test. The sharpening method and burr that works the best for us might be different, worth experimenting. I could try using the carbide burnisher on one and see if it raises the burr. No wager needed!

    Another thing, his sharpening leaves a definite concave edge, making the angle less than 90-deg. Based on the size of his hands, to me the grinding wheel looks like a small radius, perhaps a 6' wheel worn down to an even smaller radius. With scraping hard, dry wood I'm happy so far with the edge ground with an 8" CBN wheel and both sides seems to cut about the same. But for other woodturning use, these scrapers might work better sharpened at 70-80 deg and used on one side only.

    JKJ

  15. #15
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    Quote Originally Posted by Kyle Iwamoto View Post
    Question here.....
    JKJ, I have that Sorby teardrop, in addition to several other insert/hollowing scrapers. I sharpen my teardrop with a shallow (or steep, depending on your perspective) angle so it's no longer square. I think it cuts better. All this hype about Negative Rake Scrapers, and you mentioning that scraper led me to think, IF I held the teardrop scraper "upside down" and used it, is it a NRS? Just tried it, it barely cuts, can't even see the shavings, since the cutter is in the way. Perhaps if I made an even shallower angle it may work better? Thoughts? Perhaps if I installed it upside down and used the tool correctly, it would work better too......
    Random out of the box thinking. TIA

    Kyle, I read your post again, and I think I misunderstood the first time - I thought you might be trying to cut what would otherwise be the bottom surface and the obtuse angle on the ground bevel. I think I see now you are referring to the acute angle between the bevel and what was the top face. Yes, I think that would make a negative rake scraper. Perhaps the reason it doesn't cut when held flat is the burr is not established, or rather, the grinder burr is upside-down. You might try it again after raising a burr with a burnisher, perhaps after honing away any existing burr. A HSS or hardened steel tool shaft should work fine. I use carbide rods mounted in handles:

    carbide_burnisher.jpg burnisher_IMG_6767.jpg

    One of these is a much larger diameter rod than the other but they both will work - the smaller diameter feels like it burnishes about the same but with less force because of the smaller radius. An interesting question is whether the larger rod could be gentler on the steel and make a more durable burr.

    JKJ

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