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Thread: I just don't get negative rake scrapers.

  1. #16
    Russel and Pete

    Please view the diagrams and explanation in the video below

    from 1 hour 32 minutes and pay particular attention to diagrams at 1 hr 38 mins

    https://www.youtube.com/watch?v=N7BjRcSDurM&t=3093s

    My understanding is the bur is on a different plane with a negative rake scrapper

    hope this helps

    regards Brian
    Last edited by Brian Deakin; 06-29-2019 at 7:16 AM.

  2. #17
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    NRS vs raising the handle

    Quote Originally Posted by Kent Weakley View Post
    Russell,

    The negative rake scraper is essential a regular scraper with a pre-installed downward pitch, also know as raising the handle.
    I thought the same thing at first. Then I experimented and found out for myself: raising the handle does not make a scraper a negative rake scraper. There are several factors to consider but the most important is the tool is held horizontally instead of tilted down. This not only keeps the "downward pitch" constant but provides much more stability and makes it easier to use.

    For example, consider the design I use, shown earlier, nearly straight for a bit on the tip then with a sweeping curve down the side, ground to a 60-deg included angle. The second picture also shows the little jig I made to set the grinder platform each time I sharpen.

    _scrapers_IMG_7778.jpg NRS_IMG_7907.jpg

    I think this shape is perfect for the curve on the inside of a bowl or platter, for flat or almost flat curves, for the wings when "turning air", and for the outside of bowls and such, especially with ogee or other curves. I like to grind the same bevel on both top and bottom so I can flip it over and use the curve either way by just changing the burr.

    It would not be easy or perhaps even possible to use a conventional scraper ground to this profile then by tilting it downward by raising the handle while at the same time sweeping it continuously along a inside, say, of a bowl shape. To keep the desired "downward angle" all the way up the inside of the bowl you would have to coordinate a twist while sweeping. The tool could easily become unstable. Grinding as NRS makes it extremely simple and easy to use.

    I recommend that anyone who hasn't tried these grind one, put a good burr on it, and see how it works. Many, many people have been converted to the negative side or "discovered" this on their own, some after using skew chisels as scrapers. Always remember, it will barely work without a good burr. If you can't feel the burr with your finger when you slide it down the bevel and away from the edge there is not a useful burr. Most people add a burr while grinding but I get a better burr that lasts longer by using a burnisher. To renew the burr, I remove what's left of the worn burr with a diamond hone then burnish again - I repeat the several times before going back to the grinder.

    JKJ
    Last edited by John K Jordan; 06-29-2019 at 9:47 AM.

  3. #18
    Just raising the handle on a standard scraper does not give the same type of cut that you get with a NRS. Best explanation I heard came from Woodturner's Resource. What you get is a 'trailing' cut. If you have used the card scrapers, you kind of rub the bevel, and then tip the card and burr into the cut. When it starts to cut, you stop tipping the scraper. If you tip it too far, it starts to tear rather than slice. This is pretty much what you get when you just raise the handle of a standard scraper. Perhaps it is best said that the burr is not at the proper angle to get that cleaner cut. I have been turning a bunch of madrone and bay laurel/Or. Myrtle wood. The madrone takes a very nice cut up the sides with the NRS. The bay laurel does not.

    robo hippy

  4. #19
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    Quote Originally Posted by Reed Gray View Post
    Perhaps it is best said that the burr is not at the proper angle to get that cleaner cut.... robo hippy
    Reed, a couple of years ago, when you attended a club meeting in Bremerton, you and I discussed sharpening a scraper upside down because there was a potential for a more effective burr. You said you'd give it a try and get back to me. What happened with that?

    My own thought on it is, yes, the burr might be more pronounced on the backside of the grind, but I'm also unsure about the idea of trapping the tool between the wheel and the tool platform.
    Russell Neyman.

    Writer - Woodworker - Historian
    Past President, Olympic Peninsula Woodturners
    West Puget Sound, Washington State


    "Outside of a dog, there's nothing better than a good book; inside of a dog it's too dark to read."

  5. #20
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    Quote Originally Posted by Russell Neyman View Post
    My own thought on it is, yes, the burr might be more pronounced on the backside of the grind, but I'm also unsure about the idea of trapping the tool between the wheel and the tool platform.
    I'm not Reed, but I'm with you. I don't like that idea either, one reason I think a reversible bench grinder would a useful!

    But as I wrote earlier, I've tried all kinds of burrs and by far I like the burnished burr and for two reasons, because it lasts longer and because it can be reformed several times before having to go back to the grinder.

    JKJ

  6. #21
    Brian, I watched it again, thanks.
    Quote Originally Posted by Brian Deakin View Post
    Russel and Pete

    Please view the diagrams and explanation in the video below

    from 1 hour 32 minutes and pay particular attention to diagrams at 1 hr 38 mins

    https://www.youtube.com/watch?v=N7BjRcSDurM&t=3093s

    My understanding is the bur is on a different plane with a negative rake scrapper

    hope this helps

    regards Brian
    Pete


    * It's better to be a lion for a day than a sheep for life - Sister Elizabeth Kenny *
    I think this equates nicely to wood turning as well . . . . .

  7. #22
    I do need to experiment more with the up side down burr. As for the potential for the tool being dragged into the grinding wheel, I am thinking that is pretty much impossible, more so because the blunt angle on the NRS. At least I would consider it far saver than the long extended V arm for sharpening the SRG... Can't remember if I already said it here, but this burr is more on the 60 or 70 bottom bevel, and 25 to 30 top bevel, rather than the shew chisel type. Eric Loffstrom did some micro photo or pictures of the right side/wrong side burrs. The more standard burr looked like little balls of metal kind of curled over, and the wrong side was more of a straight edge. What little experimenting I have done, the main feeling I have for it is that the standard burr is far stronger then the wrong side one, though the wrong side one is supposed to be sharper. I couldn't really tell any difference, but again, I need more experimenting. I do agree with John that the burnished burr is far superior to the grinder burrs. It is sharper. It is much longer lasting. Some times I use the grinder burr first, then when it is dull, I burnish it down then back up. I am experimenting with honing off the burr with a card type hone, then burnishing with the carbide rods. Actually, you can hone a very nice burr on the standard scraper, and the NRS. It seems like with the card hones, you never totally get rid of the burr, but it does get very fine. If I hone on my Tormek, then I can get most of that burr off.

    robo hippy

  8. #23
    The more I ponder this, it makes me wonder... I remember the days when the honed burr on a standard scraper was one way to smooth out the bottom of the bowl. I think that faded when the NRS became popular. So, does any one use a honed burr on their NRSs?

    robo hippy

  9. #24
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    Robo, I'm not even close to being a pro, but I do use the honed burr. Learned that on the Boxmaster site. Since most of my sharpening is done on my Tormek, that doesn't work well with NRS. I also have a regular grinder, 350 grit CBN, which does nicely and does make nice NRS burrs. But I do like the card sharpener and burnishing rod burr best. It lasts only a few passes, but to refresh the burr, just swipe with the card a few times and a couple passes with the burnisher, and back to business. Don't even have to move from the lathe. Just my $0.02.

  10. #25
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    I've been enjoying using a NRS for a while. I would like to add another dimension to this discussion: the type of steel.

    I'm wondering if really hard steel (IIRC V10 or M42, etc.) is better for NRS or is HSS or M2 better? On one hand the hard steel may keep the burr longer. But on the other hand, it may be a bit more difficult to raise the burr on the really hard steel. My tools are fairly cheap and are HSS. A few are only high carbon steel. So I don't have anything to compare to and would like the advice of others.

  11. #26
    Well, again, there is a lot of 'it depends'. The longest lasting burrs I get are on the Big Ugly tools. The tantung is much harder than any of the standard turning metals. I can also burnish a good burr on it. I would say that the V10 and M42 will have a longer lasting burr than the M2. The burnished burrs will out last the grinder burrs by a long time, and can be turned down and bought back up again several times. It is easier to burnish a burr on the M2, which can be done with a hardened burnishing rod, but it is difficult to burnish a burr on V10 and M42 unless you have a carbide burnishing rod. I am fairly sure the 'upside down' burr is the weakest of all, but not much experience with it...

    robo hippy

  12. #27
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    Most of my scrapers are 10V (CPM10V) from Thompson Tools. It is no problem to burnish a burr using a carbide burnishing rod or burnisher.

    JKJ


    Quote Originally Posted by Brice Rogers View Post
    I've been enjoying using a NRS for a while. I would like to add another dimension to this discussion: the type of steel.

    I'm wondering if really hard steel (IIRC V10 or M42, etc.) is better for NRS or is HSS or M2 better? On one hand the hard steel may keep the burr longer. But on the other hand, it may be a bit more difficult to raise the burr on the really hard steel. My tools are fairly cheap and are HSS. A few are only high carbon steel. So I don't have anything to compare to and would like the advice of others.

  13. #28
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    Quote Originally Posted by Brice Rogers
    I'm wondering if really hard steel (IIRC V10 or M42, etc.) is better for NRS or is HSS or M2 better? On one hand the hard steel may keep the burr longer. But on the other hand, it may be a bit more difficult to raise the burr on the really hard steel. So I don't have anything to compare to and would like the advice of others.
    I use two skews as NRS's for cleaning up the end grain on peppermills (one ground with a LH angle, the other RH). I use the burr straight off the 46 grit stone wheel on my grinder. I tried the burr off a 180 grit CBN wheel but didn't think it cut as well so went back to using the 46 grit wheel. I know the burr is bigger on a 46 grit vs 180 CBN, and for me and how I use them the 46 grit burr just works better.


    I do not hone at all. If the burr only lasts 20 seconds, how much longer does a honed burr last?

    I recently bought two M42 skews to replace my old worn out M2 skews. I hoped the burr would last longer on the M42 skews, but to be honest I really can't tell a difference. If anything it might be just a bit less on the M42. Maybe it's me, but I also seem to spend a little more time at the grinder trying to get a burr. With M2 it only took a pass back and forth, then flip and do the other side. With M42 it takes several passes back and forth. I've read so much from others that say M42 lasts so much longer between sharpenings than other steels that why would you buy anything else? These are my first M42 tools, and I will say I've been somewhat disappointed. Maybe if I used them like a skew was intended instead of scraping I would notice more of a difference. I wouldn't mind trying a M42 bowl gouge next.

  14. #29
    Pat, if your NRSs are the skew chisel type, same angle on both sides, then you already have a right and left NRS, it just depends on which side you sharpen on. I would expect little difference in burr durability on different metals with the skew chisel type of NRSs, mostly because there is very little metal under the edge to support the burr. With a 60/30 NRS, there is much more metal under the burr so it lasts a bit longer, though I don't know of any one who has tested to see just how much longer it will last. For sure, the burnished burr lasts a lot longer than any grinder burr. As for edge durability, I didn't really notice a difference with my bowl gouges until I had turned for while with the M42 and V10, then went back to M2. Huge difference in durability.

    robo hippy

  15. #30
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    I am relatively new to turning and, at first, didn't see the need to regrind my scrapers to turn them into negative rake tools. I actually still only have 2 tools that are negative rake; one a steel scraper that I reground, the other an Easy Wood Carbide with one of their new NR cutters. I love both, but only for finishing. I still use my other scrapers for cutting up to the last steps and my Easy Wood round and square cutters and my for hogging out large amounts of wood both inside and outside of bowls. I love my gouges for finish work and, so far, I can't find anything that gives me a better finish than gouges with light shearing type cuts. So, I get the NRS thing. We all use what we feel comfortable with and get the best results with.

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