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Raising a burr on a negative rake scraper

Discussion in 'Woodturning Discussion Forum' started by John Hicks, Mar 18, 2020.

  1. John Hicks

    John Hicks

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    I have a couple negative rake scrapers; a glenn lucas gl1, and a crown tools crown point scraper that I modified. I have a tormek t7, and a sorby pro edge. Neither one seems to raise a burr at all. Being an old school woodworker, I can raise a burr on a card scraper, or a stanley 12 scrapers with no problems, When I try using my burnishing tool on a negative rake scraper; I can not seem to get just the right burr. I'm slipping alll over the place trying to control the burnisher on that curved edge! Plus I don't seem to get the angle right most the time. Any suggestions?
     
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  2. Bill Boehme

    Bill Boehme Administrator Staff Member

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    It sounds like you might be applying too much force and making control difficult. The object is to get a very small burr. Before you try raising a burr with your burnishing tool, you first need to hone off any wire edge or ragged burr left by the grinding wheel. Unlike raising a burr on a standard scraper where the burnishing tool is presented a few degrees off the bevel, the burr on a NRS is created by holding the burnishing tool approximately perpendicular to the NRS. You will know that the burr is right when you can feel a tiny smooth burr with your fingernail, but it won't be anything like the large burr on a cabinet scraper.
     
  3. Don Wattenhofer

    Don Wattenhofer

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    Ditto what Bill said, but you have to hone the edge first and use a carbide burnisher since the burnisher that works with card scrapers is not hard enough to work on high speed steel. To control the burnisher on round end tools I clamp the tool in a vise and use both hands to guide the burnisher around the edge. The process is easier to show than to describe and the double angle scrapers have a blunt angle that is difficult to roll a burr on. (NRS I think is a misleading term since all burred scrapers must be presented at a negative rake in order to work)
     
  4. GRJensen

    GRJensen

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    Instead of a burnishing tool, I give it a couple of gentle swipes with either a diamond card or CBN hone.
     
  5. Jim Woods

    Jim Woods

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    I use a 400 grit diamond card. Can get 3 or 4 burrs before regrinding.
     
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  6. Raif Harik

    Raif Harik

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    There is a long and informative video on NRS and sharpening by the new owner of d-way tools look for it. It's the last one on the video page.
    It's worth watching and talks about three different ways to get a cutting edge and when to use each.
    Ah here it is

    View: https://youtu.be/YsatMuK1Ei8
     
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  7. Don Wattenhofer

    Don Wattenhofer

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    Back in 1990 I attended my first pro demo with Del Stubs and he was forming the burr using an india slipstone so yes it does work but I do believe that a Superior bur can be had using a honed edge and carbide burnisher.
     
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  8. Roger Wiegand

    Roger Wiegand

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    If you grind off the part of the scraper with the angle on top so you just have a flat surface it's a lot easier to get a nice burr. Then you just tilt the tool to achieve the same effect. :rolleyes:

    I hone with a 600 grit diamond and then raise the burr with a carbide burnisher. Almost never need to go back to the grinder, only when the hollow grind starts to disappear and it takes too long to hone. Raising a burr seems harder to do on the double bevel scrapers, though I don't see why. Honing the old burr off is certainly harder, with a flat scraper you just slide the hone on the big flat upper surface; with the double bevel you're trying to balance on a relatively tiny surface. Perhaps it's imperfect honing of the top bevel that makes raising the burr harder for me.
     

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  9. Doug Freeman

    Doug Freeman

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    John you dont say what angles your nrs’s use. As the included angle increases it takes more force with a burnisher to raise a burr. My nrs’s are ground with the same angle and ~ equal bevel lengths to allow a dia hone to balance on the edges of the hollow grind for easier honing and it makes it easy to flip them over for direction change.

    I have the Veritas turner burnisher - not at all required, purely a luxury item, it makes it very easy to repeat the burnish angle and control the force.
     
  10. Don Wattenhofer

    Don Wattenhofer

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    Roger it is apparent that you have been doing more than watching videos, but I wonder why you make flat top scrapers from double bevel. I myself was doing the burr on flat tops long before the so called NRS became popular so my one double bevel is made from a flat top.
    There are other points concerning the Boxmaster video and that is the top grind is almost flat so there is very little difference than the flat top and when he was using the NRS for a roughing cut that seams pretty ridiculous .
     
  11. John Hicks

    John Hicks

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    Does the veritas have carbide rods?
     
  12. robo hippy

    robo hippy

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    Well, due to the shut down of every thing, I have been working on video scripts, including one on the NRS. For a burnished burr, I tried the standard round card scraper rod, and I had trouble getting a burr on M2. With the triangle burnishing tool, I could raise a burr. I have long since switched to M42 and V10 tools. I don't think it is possible to raise a burr on them with the standard burnishing rods. You need a material that is harder than the metal you are trying to raise the burr on. This would be micro grained carbide. This would be old router bits, or some reconditioned solid carbide bits, and probably a few other options.

    I prefer the burnished burr to the grinder burrs or the honed burrs. They just last longer. Most of the time I don't bother to hone off the grinder burr, and use that burr till it is gone, burnish it down, which usually breaks it off, and then burnish a new one up. You can hone the grinder burr off first if you are being really picky, and that can be necessary some times. I haven't experimented a lot with a honed burr, but I would think they would out last the grinder burrs, perhaps more so if you use a finer hone. For the grinder burrs, I raise then in standard method, sharpen the top bevel, then raise the burr by sharpening the bottom bevel. Some prefer and claim that the upside down burr is sharper, which means that when you raise the bottom side burr, you have the grinder platform at a negative 60 or 70 degrees, or there about... As for the veritas burnishing tool, it is made to be screwed down to the bench top and you use a pivot point. The angles of the rods are intended for scrapers with about a 70 degree bevel. I would think that hand held would be better. Depending on your angles, it may take more or less pressure to raise the burr. It really takes very little pressure to raise the burr.

    I am curious as to what angles you are using. Are your NRSs like the skew chisel, in the 30/30 range, or more like the standard scrapers in the 70/30 range? I have settled on 60/30 for my angles. The more blunt bottom angle leaves more metal to support the burr...

    robo hippy
     
  13. John Hicks

    John Hicks

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    70/30 is what I ground it to. I think the gl1 is 35/35
     
  14. Roger Wiegand

    Roger Wiegand

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    Hoping the smiley would indicate it was a joke. I'm not an NRS convert, but I haven't messed much with the one I have. It's a really nice piece of steel, so I've thought about it. Also thought about making the top bevel longer like the Boxmaster ones to make it easier to hone. But haven't done anything yet.
     
  15. Don Wattenhofer

    Don Wattenhofer

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    Roger sorry I missed the smiley face I just got excited that someone else had seen the NRS fallacy.
     
  16. Doug Freeman

    Doug Freeman

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    Yes, 3 of them. From vertical, The pivot rod is 0 deg, a 5 deg, and a 10 deg. I dont use the pivot rod, its removed. Hand pressure is enough, but I use the Stuart Batty 30/30 bevels which will turn more easily vs steeper included angles.

    Still playing with 5 vs 10 deg. Mine is not screwed down to a table. I screwed a ~ 1-1/2” square piece a few inches long of wood to the bottom that can be hand held or clamped in a vice. I find its a real advantage with hss inserts ( like a Sorby teardrop) I use with a 45 deg sheer scraper handle I made. Put a spacer on the burnisher surface to get the edge up to the cone of the rod and push it into the rod. Allows access to all of the insert OD. Hard to burnish those mounted on the handle.
     
  17. Doug Freeman

    Doug Freeman

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    Care to elaborate on what this “fallacy” is?
     
  18. Don Wattenhofer

    Don Wattenhofer

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    All burred scrapers are negative rake simply because that is the only way they will work. The latest craze of calling the double angle NRS appears to have blinded many turners to the full range of positions possible for using the burr. The double angle or double bevel is primarily used flat on the tool rest which is easy to do but it does not allow for the introduction of shear angle.
     
  19. Doug Freeman

    Doug Freeman

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    There are many situations where a flat top cannot be held at a 25-30 deg angle, especially inside a bowl or HF. Lifting the handle and/or Rotating the tool can be impossible or a bit unsafe. Scraping a flat surface such as a platter with the handle at a 25-30 deg angle can be difficult. An nrs is much less “grabby” and less prone to foul the surface.

    A double bevel does not preclude use of the tool as a sheer scraper as I do it often.

    Since starting to use nrs’s several years ago I cant remember the last time I used a flat top flat on the tool rest (handle up) - I use them to sheer scrape and an nrs when the position of the cut requires it or to refine the sheer scrape more (dang little lines I leave). I see a very practical use for the nrs concept, not at all a fallacy.

    Now if you want to call the mktg around the nrs, that folks need to buy “my” nrs tool that has these features, a fallacy, I agree with that. Any flat steel bar of appropriate material and dimensions can easily be ground to desired shape.
     
  20. Russell Nugent

    Russell Nugent

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    While you may present a traditional scraper at a negative rake it's still a traditional scraper. I don't think calling a double bevel scraper a negative rake scraper is wrong as it's a scraper with the negative rake ground into it.
     
  21. Don Wattenhofer

    Don Wattenhofer

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    I suppose its all in how you look at it, from my point of view I didn't have any traditional scrapers that I hadn't raised a burr on before the NRS became popular and they work just fine as long as I present them at a negative rake. The go to shear scrapers for me are 2 skews ground from 1 side only with the burr raised toward the ground side but I would never use them flat on the tool rest.
    It sounds like you are limiting yourself to standard flat bar type tools but with a little imagination it is easy to attach a small piece of tool steel at an angle on the end of bar such that the burr can be presented properly to the inside of a side grain bowl.

    Lifting the handle is the last thing you would ever want to do, that is almost guaranteed to catch or at the very least produce a very poor surface.

    Yes I didn't mention before but I have found times when the double bevel did a nice job as a shear scraper.

    Well it was not my intention to get into a fight I was just trying to get people to see more possibility's.
     
  22. John Hicks

    John Hicks

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    Me want cookies
     
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  23. Fred Belknap

    Fred Belknap

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    I use NRS a lot. I like how they give a smooth cut to clean up a piece that I cut most of the wood with a gouge. I have RoboRest on my grinder and I grind my NRS upside down. It put on a decent burr and is easy and quick. I have burnisher and diamond hones but doing the grinding upside down is by far the easiest. I use CBN wheels on the grinder. I saw this on a video somewhere, forgot where. I made a template to set the bevel on the grinder.
     
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  24. odie

    odie

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    Is the actual cutting edge of a NRS any different than a standard scraper?

    Answer that question ^^^^^ before you tell us how great they are. :D

    If it isn't, then it's all a matter of presentation.....and, your skill level. :eek:

    To tell you the truth.......I tried NRS's a number of years ago, and I felt there was no advantage to them.......o_O

    -----odie-----
     
  25. Doug Freeman

    Doug Freeman

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    Just seems there is a lot of misunderstanding/confusion of nrs vs flat top vs actual orientation of the cutting edge to the wood surface in both axes.
     
  26. Don Wattenhofer

    Don Wattenhofer

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    If by standard scraper you are not depending on a burr then yes the edge is different.
    I didn't think I was saying they were great.:D
    It is just like any turning tool presentation:eek:
    Practice, practice trial & error more practiceo_O
     
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  27. odie

    odie

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    Yes, absolutely.......time in the saddle is what makes the difference! :D

    My standard scrapers, for general use, have a ground burr, straight from the grinder....for fine cuts, I'm using a manually raised burr.

    -----odie-----
     
  28. robo hippy

    robo hippy

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    The standard scraper, which to me is a 70 degree bevel, is not the same thing as a NRS, and it can not do the same cuts, no matter how high you raise the handle. Ed Weber, over on Woodturner's Resource commented that when you raise the handle that high you are getting a 'trailing cut'. Think of it this way, if you use the card scrapers, which are common in flat work, you use a burnished burr. To get it to cut, you flex/bend the care a bit, and push or pull, and gently tip the card in the direction you are going until it starts to cut. This is about a 5 or maybe 10 degree angle at most. If you keep tilting the card till you are at 30 or so degrees, you are getting the 'trailing cut' which is closer to raking rather than slicing, and that tends to dig in more than slice. This is some thing that I couldn't figure out until Ed commented on this point. I use scrapers far more than most other turners, and they are my go to roughing tool, but the standard scraper and the NRS are two remotely similar tools, but very different in how they cut. It doesn't matter what type of burr you raise on them, or even if you totally hone off the burr on a standard scraper, you can't get the same cuts from these two tools.

    As I said earlier, they work excellently on end grain, and are highly variable in bowl turning. I do like them for sweeping across the bottom of a bowl, and coming into the transition. I get better results with them in these areas than I do with a standard scraper.

    robo hippy
     
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  29. Fred Belknap

    Fred Belknap

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    Odie the NRS I use are modified regular scrapers. I grind the main bevel 80° and the top bevel 25°. You can use them in just about any position and they won't catch. The top bevel on mine is smallish. They will cut pretty fast if you use considerable pressure. I use them mostly for finish cuts (after the bowl is round). I use them to cut NE with bark because you can control the cut better. I'm pretty much a fan, I have the scraper I got from you ground for NR.
     
  30. Bill T Tucker

    Bill T Tucker

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    Interesting discussion! Remembering a demonstration using NRS, the point was repeatedly made to keep the included angle less that 90 degrees (65/23, 60/25, 70/15). Have ya'll found this true or is my memory false like my wife says? What included angle do you prefer? Do you always use the same set of angles or change them for different applications? This short duck in the tall weeds could use some more guidance.
    Thanks
     
  31. Fred Belknap

    Fred Belknap

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    You probably noticed that the angles I use are 80° & 25° this equals 105°. The less than 90° is wrong. I have experimented with different degrees and settled at 80° and 25°.
     
  32. Doug Freeman

    Doug Freeman

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    There is little agreement on nrs angles. I wanted equal angles each side to make the tool “ambidextrous”. Stuart Batty uses equal bevels and recommends an included angle of 50-60 deg. I use 30/30 with a honed and burnished edge. Experimented with 35/35 which doesnt work as well.

    Primary benefit claim for a steeper lower bevel is edge life, but those folks also say the edge doesnt last long. One of these days I’ll do some testing to see for myself.
     
    Last edited: Mar 22, 2020
  33. robo hippy

    robo hippy

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    Well, the burnished burr is very long lasting, the grinder burrs are not. I have seen Jimmy Allen of D Way and Boxmaster tools use his NRS to hollow out a box, which is a slow process, but fairly simple for beginners and far less intimidating. I always use the lightest pressure possible when using a NRS, which to me is the purpose of this tool, to smooth out a surface that has some bumps and humps in it. Lots of variables, including which metal is involved...

    robo hippy
     

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