What angles do you grind your turning tools?

Discussion in 'Woodturning Discussion Forum' started by Tim Leiter, Oct 21, 2017.

  1. john lucas

    john lucas

    Joined:
    Apr 26, 2004
    Messages:
    5,832
    Location:
    Cookeville TN USA
    interesting. Yea I accidentally ground my flat scraper to a negative rake and forgot the 90 degree rule. It wouldn't raise a decent burr. When I reground the underside to give me less than 90 it worked. Now I'm talking about measuring the angle from the top bevel to the bottom bevel. That's what I call an included angle. Just so we are on the same page. You are much more in tune with scrapers than I am. I only use them in a pinch to clean up some area I have difficulty with.
     
  2. Jamie Straw

    Jamie Straw

    Joined:
    May 28, 2015
    Messages:
    1,440
    Location:
    Bainbridge Island, WA
    Well, I'm sure as heck glad to hear it's not 39° :D:eek::D
     
    odie and Tim Leiter like this.
  3. RichColvin

    RichColvin

    Joined:
    Mar 13, 2016
    Messages:
    130
    Location:
    Dublin, OH
    Tim,

    I've felt for a while that there is a need for cataloging sharpening information in a way much like Machinery Handbook provides quick information for machinists. So, I put this together as a web site that shows information to answer many of the questions you've asked.

    You can get the information at www.SharpeningHandbook.info. There are no ads or flash; it's just the facts.

    I use a Tormek to sharpen, so it also shows how to get those angles using the Tormek jigs (where there is one).

    Good luck,
    Rich
     
    Last edited: Oct 24, 2017
    Tim Leiter, odie and Bill Boehme like this.
  4. Tim Leiter

    Tim Leiter

    Joined:
    Oct 19, 2016
    Messages:
    25
    Location:
    Central Michigan
    Thanks a bunch Rich. I don't use a Tormek so the jigs and process is not helpful to me but it shows different suggested bevel angles and their usage which is what I was looking for. I use the Wolverine System and also sharpen by "eyeballing" it and checking the angle with a gauge, but this will be very helpful.
    Tim.
     
  5. john lucas

    john lucas

    Joined:
    Apr 26, 2004
    Messages:
    5,832
    Location:
    Cookeville TN USA
    odie and Fadi Zeidan like this.
  6. robo hippy

    robo hippy

    Joined:
    Aug 14, 2007
    Messages:
    1,872
    Location:
    Eugene, OR
    John, the NRS's that I use that have included angles greater than 90 degrees, are mostly used for insides of boxes or slightly closed forms. The grinder burr works on them, just like on a standard scraper, but I am preferring the burnished burr for that tool. Cuts cleaner and lasts longer...

    robo hippy
     
  7. Bill Boehme

    Bill Boehme Administrator Staff Member

    Joined:
    Jan 27, 2005
    Messages:
    8,151
    Location:
    Dalworthington Gardens, TX
    Home Page:
    While watching Stu Batty demo the NRS at SWAT, he explained the reason that the included angle works much better when it is 80° or less and that is the bur that can be raised is bigger. He also demonstrated the difference in durability of a grinder bur and a raised bur. The grinder bur only lasted a few seconds while the raised bur was good for about 45 seconds. An included angle of 60° seemed to be the optimum value for strength and size of the bur.
     
  8. robo hippy

    robo hippy

    Joined:
    Aug 14, 2007
    Messages:
    1,872
    Location:
    Eugene, OR
    Hmm, I haven't done any real duration tests on burrs on the 30/30 NRS. With the more blunt NRS, the burnished burr lasts a lot longer than 45 seconds. My guess is that there is more metal to back up the cutting forces than there is on the 30/30. As I said in an earlier post here, when I burnish on a 30/30 NRS, you can hear the burr and edge kind of breaking rather than just turning.

    robo hippy
     
  9. Bill Boehme

    Bill Boehme Administrator Staff Member

    Joined:
    Jan 27, 2005
    Messages:
    8,151
    Location:
    Dalworthington Gardens, TX
    Home Page:
    The more blunt the the angle, the smaller the bur. Making the angle more acute enables you to raise a bigger bur, but there is a practical limit limit dictated by durability. When the angle is too acute then the bur is too large and breaks off because of not enough supporting metal for the force being exerted by the wood. Conversely, a large angle results in a much smaller bur that isn't as effective. Somewhere in between is a happy medium. I remember SB saying don't use an angle greater than 80° and I don't recall exactly the minimum angle, but I think it might have been around 45 or 50°. With the more acute angle the bur would be easier to break which I would interpret as use lighter pressure for very fine finishing cuts. I haven't tried this myself and, of course, this is from SB using his signature NRS steel. Maybe the two of us need to corral SB for a show and tell. Actually, I'll be the watcher while the two of you show me.
     
  10. robo hippy

    robo hippy

    Joined:
    Aug 14, 2007
    Messages:
    1,872
    Location:
    Eugene, OR
    If there were Star Trek transporters, I would try to organize a big play date so we can swap tools, ideas and techniques. Need to get Tom Wirsing, and a micro camera in the 1000X range for burrs. Or maybe we can transport John Lucas's micro camera thing he uses to the play date... My take on burrs, is size depends on several factors. For sure, with more acute angles, it is easy to raise a really big burr, but that burr, either burnished or from the grinder has no strength. The size of the burnished burr depends on angle of the burnisher to the metal. If it is almost parallel to the bevel, then you get a better more functional burr. If you are at a steeper angle to the bevel, you can get a big hook that doesn't cut as well. If you just brush the edge, you can still get a long lasting burr that cuts very cleanly. Most people put way too much pressure on the burnishing tool. Then, you can also take the grinder burr, turn/burnish it down, then back up and get a burr that is just about as good as one where you hone off the grinder burr first. The grinder burrs on my 70 degree scrapers with either V10 (I think Stuart uses V10) or M42 are good for roughing out a 12 inch diameter bowl, both inside and outside without having to go to the grinder. With the Big Ugly (70 degree bevel) and tantung or stellite, the burr, either from the grinder or burnished, is good for half a day of turning. The traditional card scraper used for flat work is a 90 degree bevel.....

    robo hippy
     
  11. Bill Boehme

    Bill Boehme Administrator Staff Member

    Joined:
    Jan 27, 2005
    Messages:
    8,151
    Location:
    Dalworthington Gardens, TX
    Home Page:
    Order an extra large transporter for John's camera since it is a scanning electron microscope. The test article is placed inside a chamber and then a hard vacuum is pulled and the it is bombarded by an electron beam ... not your average point and shoot camera. :D

    I saw an old used one on eBay for $68K, but if you have some extra pocket change you could get THIS REFURBISHED ONE that has all the bells and whistles. :D
     
  12. Raul McCai

    Raul McCai

    Joined:
    Oct 29, 2014
    Messages:
    416
    Location:
    nj
    I gotta confess. I pay absolutely no attention to the numerical representation of the angles I use. Not a bit. I just set my grinder to the angle that looks right a wail away.
     
  13. john lucas

    john lucas

    Joined:
    Apr 26, 2004
    Messages:
    5,832
    Location:
    Cookeville TN USA
    The only reason I pay attention to the angles is when I demo or teach everyone seems to want to know. I started off saying it doesn't matter, whatever works for you but that seemed kind of rude. Now I try to at least give them an idea.
     
  14. robo hippy

    robo hippy

    Joined:
    Aug 14, 2007
    Messages:
    1,872
    Location:
    Eugene, OR
    I was chatting with Doug Thompson about the NRS yesterday maybe, can't remember for sure, and he was telling me about an Ashley Harwood 'signature' NRS with a 40/20 grind that she got from some Brit bowl master I had never heard of before. It is supposed to be better than the symmetrical grinds... Now I have to experiment again. If it does work better, that might fit in with my theory that a more blunt bottom bevel can make for a stronger burr... Have to experiment some more...

    robo hippy
     
    Tim Leiter likes this.
  15. Bill Boehme

    Bill Boehme Administrator Staff Member

    Joined:
    Jan 27, 2005
    Messages:
    8,151
    Location:
    Dalworthington Gardens, TX
    Home Page:
    That sounds a lot like the Robert Sorby hardwood scraper.
     
  16. robo hippy

    robo hippy

    Joined:
    Aug 14, 2007
    Messages:
    1,872
    Location:
    Eugene, OR
    Well, I googled that one and theirs is an 80 degree bevel on the bottom, and about a 25 or 30 on top. All of my standard scrapers are 70 degrees on the bevel, and I have one or two 70 degree bevels with about a 30 on the top. These are better for the insides of goblets. Interesting that they used them on spindles and more of a peeling cut than scrape.... Have to cut up some wood and play some more...

    robo hippy
     
  17. Bill Boehme

    Bill Boehme Administrator Staff Member

    Joined:
    Jan 27, 2005
    Messages:
    8,151
    Location:
    Dalworthington Gardens, TX
    Home Page:
    I would need to measure it on the top, but I'm almost certain that it is no more than 10°. I hardly ever use it.
     
  18. robo hippy

    robo hippy

    Joined:
    Aug 14, 2007
    Messages:
    1,872
    Location:
    Eugene, OR
    You have one??? That top angle could be less, but I don't know, just glanced at it... In looking at their video, the first shots of it in use show it taking a pretty hefty cut for a NRS. Not so later. When using it on spindles, it looked like they were doing a peeling cut, so rub the bevel, raise the handle till it starts to cut, and continue. Depending on the burr, that would make it similar to a card scraper. I may have to watch it again, because they may have been doing a peeling type cut on the bowl.

    robo hippy
     
  19. Tim Leiter

    Tim Leiter

    Joined:
    Oct 19, 2016
    Messages:
    25
    Location:
    Central Michigan
    I sure wish I knew what you expertly experienced fellers were talking about concerning the different uses and grinds for an NRS. I don't have any idea how to use one on spindle work but I am going to try if I can figure out the grind angles on the top and bottom of the scraper. I'm so glad that excellent conversations are happening on my originally posted question. Great to read all of this.
    Tim.
     
  20. john lucas

    john lucas

    Joined:
    Apr 26, 2004
    Messages:
    5,832
    Location:
    Cookeville TN USA
    Well you would use a negative rake scraper on a spindle held flat. Done that for years before I learned about cutting tools. Ever used a skew on it's side to shape a bead. Same thing as a negative rake scraper except we usually put a burr on a scraper and the skew won't have a burr or at least extremely small one. I did a test for the editor of woodturning magazine a few years ago. Someone wrote an article about using a scraper in a bevel rubbing mode and she wanted to know if that was safe or feasible. I tried. Because the edge was reasonably blunt compared to a spindle gouge it didn't leave as good of a surface. I tried it with and without a burr. Pretty much the same surface after turning. Of course held flat like most scrapers it leaves a worse surface but then is also doesn't catch when used correctly (meaning handle higher than the cutting edge).
     

Share This Page