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Thread: Negative Rake Scraper Angles

  1. #1
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    Negative Rake Scraper Angles

    Just saw a video indicating that the total of the top and bottom angle on a negative rake scraper should equal 90 degrees. Is this correct?

    My scrapers (not negative rake) have an angle of about 65 - 70 degrees, which is about the angle that they were ground to when I bought them. If the above is correct, that would mean I should put a top angle of 30 - 35 degrees on the scrapers to turn them into negative rake scrapers.

    Or doesn't the top angle matter much?

  2. #2
    The link below has some useful information

    http://www.woodworkersemporium.com/c...ion-Manual.pdf

  3. #3
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    Not meaning this as a slight on you, but have you tried Google? It will produce an amazing amount of vids and articles on NRS. Most "famous" IMO is Stuart in the link above. Also worth taking a look is Boxmaster tools for a completely different approach. They all have different "rules" for angles. So bottom line I guess is there are no "rules". Find one you like and give it a try. If it doesn't work, find another. I do use Stuart's method. I recently gave the Boxmaster tools method a try. It also works, but not as good as Stuart's for me. I'm still learning......

  4. #4
    My negative rake scraper is about 75 deg on the bottom and about 15 deg on the top. I doubt either angle is critical, it is cutting with the burr and I have no way to measure the angle of that.
    _______________________________________
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  5. #5
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    90 degrees is wrong, that's way too blunt. Keep your 65-70 degrees that you use now (same angle that I use).

  6. #6
    For the last 3-4 years I have been using a Thompson skew on which I just rounded the tip slightly and continued the same grind in a curve down the side of the tool, so as it turns out, it is about what Stuart Batty says is the minimum included angle of 40*. It works extremely well and I can roll the burr either way and use the NRS on the inside or outside of a bowl/form.

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  7. #7
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    I only have one so I am not proficient in its use but when I converted a Crown 1.5" wide into one I followed the lead of many.
    Mine is "about" 63 (somewhere between 60 and 66). It has the same angle on both sides so the tool rest does not need to be adjusted; just flip the tool over.
    May not be the best but pretty easy to change the combined angle to try different if you wish.
    "I became insane, with long intervals of horrible sanity." - Edgar Allan Poe

  8. #8
    When Glen Lucas was at our club he recommenced two different grinds, one for hard wood blind for hard wood around 90 included and more like 66 included for soft wood. Haven't tried these, just reporting what he said.
    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 . . . . .

  9. #9
    There are two 'styles' of NRSs. One, which is probably the original is like a skew chisel, same grind on both sides, generally in the 30/30 range, but some variations either way. The other is more of a 70/20 grind, so more like a scraper with a top bevel grind on them. I will get around to that video later this year... For the skew chisel type, if you use them on bowls, you want a rounded tip to fit into the transition area of a bowl. You grind and leave the burr. If you want to use the other curve, you flip it over and grind the other side. For the 70/20 type grinds, one side always stays up, and you grind the 70 degree bevel. You do cut with the burr with both variations. It is a high maintenance tool. The burr is very fragile, and if you start a sweep in the center of a 12 inch bowl, and pull to the rim, I start with the nose, and end up on the heel of the NRS, and it is dull by the time I get to the rim.

    I don't use them on bowls, other than to maybe sweep across the bottom of the bowl. The shear scrape does still cut better, most of the time, on the walls of the bowl. Since a NRS is a scraper, it does 'pull' on the fiber rather than slice, and while it does reduce tear out, it doesn't eliminate it. Some will disagree. They do work better on harder woods than on softer woods. I have found them to be excellent for end grain boxes and I can get a 220 grit or finer finish off the tool. On boxes, I use a 70/25 most of the time, and a burnished burr. The burnished burr doesn't work as well on the skew type NRS because the edge is so acute you can hear it fracture as you burnish, kind of like krinkling up cellohpane type plastic. The burr on the 70/25 is very sharp and much longer lasting than the grinder burrs. Probably sharper too. The burr can be turned down and bought back up a couple of times before you need to hit the grinder again. You do need a carbide burnishing rod for the M42 and V10 metals, which are pretty much all I use. You can get a burr on standard M2HSS with a card scraper burnishing rod, but the triangle ones work better than the round ones. I do need to play with a 60/25 or so for forming the burnished burrs. I have probably tried every different angle from 30/30 through 80/25. Some where around 50 or so degrees, you can get a nice burr, and with the 80 degree bevel, it is difficult to get any burnished burr to form, just too blunt.

    Stuart has said a couple of times, that the NRS and a shear scrape are pretty much the same cut. Once he clarified that they both don't catch. To me, they are entirely different cuts as one is a scraping cut with the cutting edge at 90 degrees to the spin of the wood, and the other is at a high shear angle. The shear angle generally is better at gently lifting the fibers as you cut rather than pulling at them which is what happens when you scrape. Finish cuts on end grain forms like boxes are very clean, on bowls, not so much.

    robo hippy

  10. #10
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    Depends

    Quote Originally Posted by Randy Heinemann View Post
    Just saw a video indicating that the total of the top and bottom angle on a negative rake scraper should equal 90 degrees. Is this correct?
    My scrapers (not negative rake) have an angle of about 65 - 70 degrees, which is about the angle that they were ground to when I bought them. If the above is correct, that would mean I should put a top angle of 30 - 35 degrees on the scrapers to turn them into negative rake scrapers.
    Or doesn't the top angle matter much?
    Randy, perhaps the 90 degrees number is meant to refer to the maximum included angle. In my experience the NRS won't work well and perhaps not at all if the angle is NOT less than 90 degrees. But the "correct" angle is what works for what you are doing.

    I do have some smaller NRScrapers at closer to (but less than 90, probably 80-85) that I primarily use on end grain of fine-grained hard woods (for example on things like lidded boxes. They leave a surface almost like glass. On these I grind the top angle different than the bottom.

    scrapers_small_thompson.jpg

    Here are the three I use mostly on bowls and platters, for face grain, side grain, and general work, sharpened at 60 degrees included angle. The middle one is standing on edge so you can see the angle. (I ground it from a Thompson skew.) I grind the top and bottom bevels the same so I can flip them over and burning a new burr going the other way if needed.

    scrapers_neg_rake.jpg

    A lot of turners seem to sharpen NRScrapers like this except those I've seen have rounded tips. I find that a short flat on the tip does a much better job at taking out tool marks on flat, mostly flat, and some convex areas. They are perfect at smoothing the wings on pieces like this, top and bottom:

    penta_maple_ellis_c_IMG_5435.jpg IMG_7515_ce.jpg

    You might try sharpening different ways and see how they work in different circumstances. I keep a box of old, cheap tools perfect for experimenting with grinds.

    JKJ

  11. #11
    Join Date
    Feb 2018
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    Sparta Tn
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    just ran the camera for Ashley Harwood and she of course studied under Stewart Batty. She said the negative rake scraper should be 70 degrees or less. I got home and checked and both of mine are slightly less than 70. Not sure why I chose that angle at the time, possibly because I ran the camera for Stewarts demo last year.

  12. #12
    Join Date
    Feb 2017
    Location
    Northern Illinois
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    350
    I certainly have looked on YouTube and Google many times. The problem is that there are wide range of guidelines; many different from each other. I never know, when I'm researching techniques online, which are good ones and which should be avoided. From most of my research, I believed that there was no "correct" angle for scrapers or negative rake scrapers, but the recent video I saw indicated a total angle of 90 degrees between the 2 bevels. I thought maybe I could verify or not on the forum; my only reason at this point for coming here. Seems like there is no "perfect" angle. That's all I really wanted to know.

  13. #13
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    Quote Originally Posted by John K Jordan View Post
    Randy, perhaps the 90 degrees number is meant to refer to the maximum included angle. In my experience the NRS won't work well and perhaps not at all if the angle is NOT less than 90 degrees. But the "correct" angle is what works for what you are doing.

    I do have some smaller NRScrapers at closer to (but less than 90, probably 80-85) that I primarily use on end grain of fine-grained hard woods (for example on things like lidded boxes. They leave a surface almost like glass. On these I grind the top angle different than the bottom.

    scrapers_small_thompson.jpg

    Here are the three I use mostly on bowls and platters, for face grain, side grain, and general work, sharpened at 60 degrees included angle. The middle one is standing on edge so you can see the angle. (I ground it from a Thompson skew.) I grind the top and bottom bevels the same so I can flip them over and burning a new burr going the other way if needed.

    scrapers_neg_rake.jpg

    A lot of turners seem to sharpen NRScrapers like this except those I've seen have rounded tips. I find that a short flat on the tip does a much better job at taking out tool marks on flat, mostly flat, and some convex areas. They are perfect at smoothing the wings on pieces like this, top and bottom:

    penta_maple_ellis_c_IMG_5435.jpg IMG_7515_ce.jpg

    You might try sharpening different ways and see how they work in different circumstances. I keep a box of old, cheap tools perfect for experimenting with grinds.

    JKJ
    Thanks John. Very helpful. I guess I wasn't clear that I meant the included angle being 90. Unfortunately I haven't been turning enough to own any cheaper old tools. Most of my tools I use regularly. You, Reed, and others verified for me that what I thought was true is; namely that the included angle isn't crucial except for the extremes. I am new to NRS so all the info is helpful. Sometimes I'm not sure that what is on the internet is correct.

  14. #14
    Quote Originally Posted by Randy Heinemann View Post
    Sometimes I'm not sure that what is on the internet is correct.
    Now, there is a rule to live by!😉

    Left click my name for homepage link.

  15. #15
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    Quote Originally Posted by Randy Heinemann View Post
    ...Unfortunately I haven't been turning enough to own any cheaper old tools. Most of my tools I use regularly.
    None of the several dozen tools in my "cheap tool" box are those I bought new. I pick up old tools as give-aways, for cheap at club auctions, and have bought some here on Classifieds when the price was right. Some were rusted, some not properly hardened, and some just real cheaply made. But I have enough to loan or give to beginners/students, let people practice grinds, and try out grinds for myself. (I hate to make major modifications to an expensive Thompson tool just to try out a wild idea for a scraper grind!)

    Some of the old tools are perfect when I want to make something specialized such as a tiny 1/64" parting tool and a dovetailed recess cutter to use where it's too tight to fit another tool.

    ... Sometimes I'm not sure that what is on the internet is correct.
    Gasp, is that true??? Why didn't anyone tell me? No wonder my doctor didn't seem impressed when I told him the treatment I read on some forum.

    JKJ

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