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CBN Safety Lesson

Discussion in 'Woodturning Health & Safety' started by Davis Stevenson, Jan 15, 2019.

  1. Davis Stevenson

    Davis Stevenson

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    Hi All,

    I just wanted to share a safety a lesson my wife and I learned, especially since I've seen numerous online videos showing a similar, potentially dangerous setup:

    My wife was sharpening a short-handled continental gouge using the V-arm pocket on our new KJR CBN wheel, with a bevel angle near about 40 degrees. This method is pretty standard, I think, for matrix wheels. Even with minimal pressure, something dug in, causing a nasty catch that took a big chunk of the tool tip off, as well as a nice chunk off the side of the CBN wheel.

    The instructions do warn about sharpening a Spindle Roughing Gouge this way, but that warning should probably hold true for forged, short tang tools.

    Use the platform, not the V arm pocket!

    Thankfully, there was no blood, no broken bones. Just hurt pride and a lighter wallet. Ken is awesome, felt bad, and made us a great deal on a new wheel. So definitely consider ordering from him!


    There are numerous youtube videos showing people sharpening on CBN with a big ole' Spindle Roughing Gouge in the pocket. Don't do it. If you actually read the instructions (I was being a typical man and I hadn't read the instructions) there are warnings about possible dangerous catches, and sharpening this way voids the warranty.
     
  2. John Torchick

    John Torchick

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    "Real men don't read instructions!" I messed up a pen once and got rather upset. My grandson went upstairs and told my wife, "All he needed to do was read the instructions." That is now the inside joke in the family and the shop.
    Davis, thanks for sharing the situation and the warning at the bottom of the thread.
    Edit- love the bowl grain in your avatar.
     
  3. Bill Boehme

    Bill Boehme Administrator Staff Member

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    Thanks for the safety warning. I never sharpen by putting the back of the tool handle in the V pocket. There are just too many opportunities for something bad to happen. A short tool increases the risk. I have also seen a new gouge flex because it wasn't properly glued into the handle. Don't even think about sharpening a scraper this way.
     
  4. Roger Chandler

    Roger Chandler

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    This is a great thread! Especially for the newer turners coming along who have not had a real good introduction to sharpening by a seasoned turner who knows the real scoop on things. This thread may just save someone an eye or a nasty cut.......thanks for bringing this to the forum!
     
    Bill Boehme likes this.
  5. Davis Stevenson

    Davis Stevenson

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    You're welcome! The amount of videos of people who seem like they know what they're doing and are sharpening like this is quite large. Hopefully this, or the other advice against sharpening that way, will pop op when newbies search for sharpening tips.
     
  6. robo hippy

    robo hippy

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    Hmm, must have missed this one... First time I ever saw that V arm set up, I looked at and said 'OH #### NO!' This was before I was making platforms.... Just too risky, and don't know why anyone would promote it...

    robo hippy
     
  7. Karl Loeblein

    Karl Loeblein

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    I thought V arms are OK as long as the bevel is steep enough, and the tool long enough to keep the bevel riding well above the center point on the grinding wheel, no? I suspect the catch mentioned above had more to do with tool being "short-handled" vice a 40 degree bevel. Thus, sharpening a long handled scraper in a v arm is still dangerous because the bevel rides to close to the center of the wheel.
     
    Bill Boehme likes this.
  8. Karl Loeblein

    Karl Loeblein

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    Hopefully your wife was wearing safety glasses/shield while grinding, or at least is reminded use eye protection from now on.

    Here's another safety precaution many people including professionals often overlook regarding grinding:

    Grinding Steel without a Mask

    Ref: https://www.reddit.com/r/metalworking/comments/1rkp5m/grinding_steel_without_a_mask/

    ...As you can see it's mostly rust with trace other elements. Chronic exposure through inhalation can cause organ damage or cancer.

    Some of the things that you can inhale when grinding won't be absorbed, some will. I believe a minor amount of iron can be absorbed, but things like silica and carbon won't. Silica causes silicosis, carbon causes black lung. They add up over time, so you don't have to grind week in and week out... each time you grind more gets added.

    All of the above is just for steel. Something like stainless steel is a completely different problem, and much more dangerous. That's because it contains chromium (so do other alloys like cromolly). If you heat it by welding or even produce a lot of fine dust in grinding, you can release hexavalent chromium, which can give you cancer in a single exposure if it's concentrated enough:

    ...So if you're grinding steel, you might be ok without a mask, but you WILL be ok with one.
     
    Bill Boehme and Davis Stevenson like this.
  9. Clifton C

    Clifton C

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    I had the same Thoughts as Robo. As to who would promote it? Oneway shows a pic of a spindle roughing gouge in a V arm. The "pinch" factor does give me a pucker factor but I've noticed a few other issues over the years, one being that sometimes the SRG itself is not inline with the handle, making it difficult to get an even grind. I show this by laying the gouge across the bed ways (or any flat surface), rolling it side to side and and showing how the end of the handle scribes an arch. Another issue has to do with sharpening spindle or detail gouges in the pocket, the tip eventually starts to look like a pencil point. I feel the pinch is a danger, but not going to say "you can't" or "you shouldn't", I just feel it's easier and safer to get a better edge using the platform for the SRG and the Vari-grind jig for spindle and detail gouges. I have "heard" the pinch, then got to see the results. I wanted to mount the wheel, SRG and the skivvies on a board for display but was voted down... can't imagine why...
    c
     
    Bill Boehme likes this.
  10. Bill Boehme

    Bill Boehme Administrator Staff Member

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    Maybe it was the board that was the problem ... I'm sure that a tastefully done display case would have would have won everybody's nod of approval.
     
  11. Ricc Havens

    Ricc Havens

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    Interesting discussion. I can picture what ou mean by the "pinch" factor. But it brings to mind some questions.:

    - Why does Oneway show a roughing gouge in the vee arm pocket if it's a safety issue?
    - It would seem to me that it would be more a pinch factor safety issue with friable grinding wheels as they wear. the CBN wheel is solid and doesn'e wear from down smaller than it's original diameter. So wouldn't the friable wheel be a bigger concern with possible "pinching" and a catch maybe even causing the wheel to break part with a nasty catch?
    - I know his videos were made a long time ago, but I just borrowed pro turner Eli Avisera's dvd from our club library. He shows sharpening a roughing gouge with the vee arm and a 45deg bevel. So if a possible pinch is a concern why do some pros teach it
    - also, in regards to Eli Avisera's video- after sharpening the main bevel he shows moving the vee arm to sharpening a second bevel to remove the heel. As a result he ends up with a 2mm usable bevel that he teaches. So when he goes back to resharpen and places the handle of the gouge in the vee arm pocket and brings the bevel to the wheel he really only has that small 2mm touching the wheel That seems more pinch/catch prone to me. (although in the video when he has the roughing gouge in the vee arm and is sharpening his 45deg bevel he is high up in the wheel so maybe that's his "safe" way of doing it.

    I have to admit I have always used the vee arm with the roughing gouge. Both on the white friable wheels and on my CBN wheel. So far never had a catch. But I do sharpen higher on the wheel and I think my bevel is somewhere around 40-45deg. The only time I ever had had issues with catches on a grinding wheel is when I did the swept back grinds on my bowl gouges and went off the edge of the white friable wheel. Haven't done that sine I got the wider CBN wheel.

    I did try grinding the roughing gouge using the platform like you guys mentioned. I had a tougher time keeping a consistent grind/edge. as I rolled the gouge I had trouble keeping it in place and it would slide down the rest just a small bit. So I will need to practice more.

    Ricc
     
  12. hockenbery

    hockenbery AAW Advisor Staff Member

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    If the tool is above the center line of the wheel an inch or more and the pocket arm is locked securely it is relatively safe to use the pocket for the handle or the varigrind.
    However using the platform is safer because the Vee arm may not always be locked. Do you check it every time? If the pocket should slip the tool is now lower. And that is a big problem.

    The main issue is the steep angles ground on bowl gouge for cutting the inside bottoms of bowl.
    With the 80 degree angle it is real close to the center of the wheel whether you use the handle in the pocket or vegrigrind. There is not margin for error - any movement of the pocket, flex in the tool or handle mounting, flex in the wheel, etc and the tool will come down the front of the wheel and push off to one side pulling your hand into the wheel.

    Lots of old videos will show turners not wearing face shields.
     
    Last edited: Feb 5, 2019
  13. Clifton C

    Clifton C

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    It is an interesting discussion. I scribed a circle (paper experiment) and found that a 45 degree angled gouge would be hard to pinch, just because of geometry, and less, as in 40, 35 etc would be farther up the wheel so would be above center line and less likely to pinch. So, to me, the obverse would seem to be true, 50, 55 60 etc. seem to be asking for trouble. After one pinch incident the clamp block was loose, but the pinch is so fast and violent, it could have come loose because of the pinch, not caused it. Another pinch, the guy said he thinks the V-arm moved out causing the pinch. In both instances the gouge got loose and skipped around the studio. I feel it's in the understanding of the forces that help us decide. 45 yes, 47 no? I admit, I am biased, I like the platform...
     
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  14. Ricc Havens

    Ricc Havens

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    For me it's always checked and locked. I have to move the vee arm all the way in when no in use as my shop is too small. So it definitely gets locked when I slide it out to sharpen.
     
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  15. Bill Boehme

    Bill Boehme Administrator Staff Member

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    A grinding wheel can remove steel really fast and the closer the tool gets to the "pinch" the faster it removes steel. I think that I used the V-arm once many years ago and decided that I preferred using the Varigrind or platform. It's scary just thinking about a tool getting jammed into the grinding wheel.
     
  16. Emiliano Achaval

    Emiliano Achaval Administrator Staff Member

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    I wonder if the V arm comes with the standard sharpening package or it's an add on? I have mine, have not use it in decades, so I can't remember. It's a good tip to let beginners know in case they have the V arm...
     
  17. Davis Stevenson

    Davis Stevenson

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    Emiliano,

    The V arm is included in the set. In the ads/listings, it even shows the a spindle roughing gouge in the V arm pocket.

    After playing around with the setup my wife had, even with the more acute angle, the tool was old, ground short, and had a short handle, which put it barely above centerline, but definitely in the 'pinch' zone.

    Playing around with my SRG at the 40 degrees I have a hard time seeing how it would pinch without something being loose. Blunter angles I could see it getting close to iffy.

    Also, I had no idea anyone would try to sharpen a scraper in the V pocket? Literally the easiest thing to sharpen on the platform.
     
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  18. Emiliano Achaval

    Emiliano Achaval Administrator Staff Member

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    Thanks for taking the time to answer my question. Glad your wife is ok. Happy and safe turnings! Aloha
     
  19. John Torchick

    John Torchick

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    Good reason to buy more tools, IMHO. One reason is as good as the next!
     
  20. Davis Stevenson

    Davis Stevenson

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    Do we even need reasons to buy more tools? Isn't the correct number of tools n+1, where 'n' is equal to the number of tools currently owned?
     
  21. John Torchick

    John Torchick

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    Davis, that is the new math. Coincides with E=mc(squared).
     
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  22. Mike Johnson

    Mike Johnson

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    E=mc(squared) that is equal to the equity left on your master-card credit squared.
     
  23. Dennis Weiner

    Dennis Weiner

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    Although the physics places various forces at the tool and wooden joint depending on the angle of the bevel, the real issue is the how strong is your joint between the tool and the handle in addition to the angle of presentation when v arm sharpening.
    The blade must be deeply inserted in the wooden handle to withstand potential flexing at the joint. The Short tang of the roughing gouge carries a higher risk of eventually coming loose. We have all experienced gouges that loosin up from time to time. These are not good v arm sharpening candidates.
    Like using a tool rest for turning, a platform secures mechanical advantage countering the strong forces between the grinding wheel and the tool. The V arm places the force along The axis of the tool and the connected handle. If it flexes or vibrates, the tip may cause a dig or catch especially if contact falls below the 90 degree wheel quadrant. So platform grinding may be a safer methodology.

    It is interesting that the CBN wheel chipped and sent a piece airborne. Most grinders do not have a guard to contain a broken cbn wheel as does the stone wheels. I’m wondering if this is a new concern that is overlooked as well.
     
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