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Thread: Heat damage to blades when grinding...

  1. #166
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    Dave at D-Way told me that he felt soft metal could be cleaned off a CBN wheel simply by grinding a harder steel. Dave seemed to think just about anything could be ground on CBN wheels. Ken at WoodTurner's Wonders (WTW) said he felt softer steels could be a problem and grinding a harder steel might help but not be a totally reliable solution. I think Ken felt washing the wheel with soap and water might be an even better solution.

    The reason I bought a 350 CBN was I felt from my discussion with Ken that it would smooth out the deeper grooves made by a 80 or 180 CBN. Ken offers a 220 CBN but that may be a little too close to a 180. I think Ken uses his 350 CBN for finishing lathe tools. I believe Dave told me he could not tell a difference in how his lathe tools worked coming off a 80 or 180 CBN, used right off the wheel. I believe both felt that grit changes on CBN wheels are not as significant as grit changes in many other stones.
    Last edited by Mike Holbrook; 11-08-2014 at 11:49 AM.

  2. #167
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    Just to convey what are probably the sort of tolerances typical of Eastern made bench grinders - I measured up my recently bought fairly generic 8in low speed UK originating example (i think the cheaper model that Derek mentioned first trying in Australia) tonight to see how it might do with CBN wheels on. It was picked as the smoothest out of a batch, and while not tightly toleranced by the standards of a good electric motor turns out not to be too bad. It runs smoothly with the grinding wheels off.

    Unlike many US grinders which have a 5/8in nominal (solid) shaft it's a nominal 18mm dia in this case - so the WTW CBN wheels which have a nominal 5/8in bore (just under 16mm) will require re-boring.

    The shafts measure from about 17.92mm to 17.97mm dia depending on the end and where measured. Very similar to stock grade bright mild steel shafting, but a fairly loose tolerance by motor shaft standards. To provide something to compare it with - changing the clearance (measured as diameter difference) from 0.029mm to 0.035mm takes the fit of an 18mm dia shaft in a bore from about as tight as is possible while still having a sliding fit, to a slightly less snug but still well located slding fit.


    Runout is OK, about 0.025mm (0.001in) one end, and 0.05mm (0.002 in) the other - which is about at the upper end of what's permitted by the IEC standard on a standard quality electric motor.

    The motor shaft is offset a little to one side of the grinder - so that the step on the motor shaft that locates the stepped sleeve that mounts the wheels is inside the line of the end face of the housing on one end by about 1mm, and proud of it at the other by about 2.5mm. i.e. a stepped sleeve is needed to clear the motor housing.

    What's not so good is the fit of this stepped sleeve - the bore is about 18.1mm, meaning there is potentially plenty of slop to throw the balance out. The stock grinding wheels in turn seem a pretty appoximate fit over these sleeves, but were not measured.

    Depending on how the tolerances add up after assembly, a given example running stock wheels could be moderately smooth running, or quite rough.

    It seems though that the CBN wheels when bored accurately to fit directly on the shafts will probably run very close to true. A pair of self aligning washers and some ground (hardened and flat) shim washers will also be required too to set up the spacing since there's about 50mm (2in) of shaft length available each side for a wheel width of 32mm ...
    Last edited by ian maybury; 11-08-2014 at 8:20 PM.

  3. #168
    Quote Originally Posted by Derek Cohen View Post
    Hi Ian

    I am still trying to work out what advantage you find with a flat ground primary bevel over a hollow ground primary bevel. Why? It certainly complicates matters - possibly unnecessarily.

    Regards from Perth

    Derek
    Absolutely agreed. If you are sharpening your tools because you are working wood, then sharpening is ancillary to the woodworking. I want fast and effective sharpening so that I can stay "in" the project. A hollow grind fits this bill. I have yet to ruin one tool regardless of construction by using a hollow grind. The hollow grind allows me to register the bevel to the stone by feel in a moment, a few careful strokes and back to the woodworking. Reduces "stiction" too I should add.

  4. #169
    Do you guys hollow grind to the final bevel angle or do you hollow grind to 25 degrees and then lift the handle for subsequent honing at the workbench?

  5. #170
    Quote Originally Posted by Chris Fournier View Post
    Absolutely agreed. If you are sharpening your tools because you are working wood, then sharpening is ancillary to the woodworking. I want fast and effective sharpening so that I can stay "in" the project. A hollow grind fits this bill. I have yet to ruin one tool regardless of construction by using a hollow grind. The hollow grind allows me to register the bevel to the stone by feel in a moment, a few careful strokes and back to the woodworking. Reduces "stiction" too I should add.


    just because you haven't had a problem with it doesn't mean it hasn't happened to other people.
    -Dan

  6. #171
    Quote Originally Posted by Reinis Kanders View Post
    Do you guys hollow grind to the final bevel angle or do you hollow grind to 25 degrees and then lift the handle for subsequent honing at the workbench?
    The latter, but either way works. It takes less effort to hone using the second method, or honing the flats with a coarser stone and then lifting the handle a little for the fine stone.

    I've always found a much higher low-effort hit rate with the edges lifting the last stone a little, and using a very fine or slow stone for that part of the edge-making as it removes less metal and leaves you better set up for the next go around.

  7. Quote Originally Posted by Reinis Kanders View Post
    Do you guys hollow grind to the final bevel angle or do you hollow grind to 25 degrees and then lift the handle for subsequent honing at the workbench?
    I don't always do it the same way.

    for very low angle tools I use what approaches a flat bevel with just a little bit of a microbevel.
    for thick tools with a high angle, I'll generally hollow grind and follow with a honed microbevel.
    for a lot of the stuff in between it is similar to what Paul Sellers advocates: a convex bevel that pretty much includes the microbevel. but when it starts getting too rounded I go ahead and give it a bit of a hollow grind to get some of that metal out of the way. I freehand grind, so I'm not stuck with a hollow grind at the radius of the grinding wheel. it's easy enough to work the chisel around on the stone to produce a hollow grind that is really close to flat, and after a few times at the stones it ends up slightly convex. but I don't obsess over the shape of my primary bevels. as long as the edge is as sharp as I need it to be and is as straight or curved as I need it to be I'm happy.

  8. #173

    I never stated that others don't have problems...

    Quote Originally Posted by dan sherman View Post
    just because you haven't had a problem with it doesn't mean it hasn't happened to other people.
    I'm not sure exactly what your point is Dan? I know that other people are having troubles.

    My point is that you don't have to have a problem. If someone is hollow grinding and ruining their tools in use then I think that the problem is operator error and that can be fixed with study of the basics and practice. Watch your bevel angle, matching it to the task at hand, and hollow grind to your hearts content, there need not be a problem. I am not a magician, just a woodworker who has applied principles and practices laid out by those that came before me and I have earned the skills with time on the tools and patience accepting that failure is always a possibility.

    Personally I think that a lot of what we discuss around here comes down to folks who watch a you tube video or a blog, try it a couple of times themselves and then throw up their hands in disgust or dispair when they don't get perfect results inside of 30 minutes. Perseverance in this instant gratification age is a quality that most of us are lacking. It keeps these forums humming.

  9. #174
    Quote Originally Posted by Chris Fournier View Post
    I'm not sure exactly what your point is Dan? I know that other people are having troubles.

    My point is that you don't have to have a problem. If someone is hollow grinding and ruining their tools in use then I think that the problem is operator error and that can be fixed with study of the basics and practice. Watch your bevel angle, matching it to the task at hand, and hollow grind to your hearts content, there need not be a problem. I am not a magician, just a woodworker who has applied principles and practices laid out by those that came before me and I have earned the skills with time on the tools and patience accepting that failure is always a possibility.
    I was responding to your comment on hollow grinding regardless of construction. I don't mean to single you out, your post just triggered something i think needs to be said.

    The creek has lost some objectivity in my opinion, and fallen into what I would call "do what we do because it works for us" mentality. It seems, gone are the days when people discussed the caveats of why one method might be better or more appropriate than another.


    for example:

    Japanese chisels, can be hollow ground, but several caveats should be considered before doing so.

    1. is the chisel laminated? not all of them are, traditional woodworker for example sells solid hss versions.
    2. what type of steel is it made from white steel, blue steel, other? White is more brittle and temperature sensitive than blue.
    3. how will the chisel be used and what angle will it be ground to.
    4. what diameter wheel is it being ground on? a 6" wheel produces a much less supported edge than a 10" wheel for a given bevel angle.

    So, while someone might not have any problems taking paring cuts with a blue steel chisel hollow ground to 35 degrees on a 10" wheel, a person making light mallet cuts with a white steel chisel ground to 30 degrees on a 6" wheel could have all kinds of problems.


    I guess i just wish people espoused understanding the details/cavets over general rules of thumbs.
    -Dan

  10. #175
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    Guess as is often the said 'the devil is in the detail'. Or more to the point - only your specific case is your reality. Rules by definition are standardised one size fits all procedures...

    This post is actually just to say that my 80 and 180 grit CBN wheels have arrived from WoodTurnersWonders, and to offer some thought on boring them to suit the grinder shaft size.

    The stock 5/8in bore on the WTW wheels requires opening up to the 18mm nominal of the (UK market) grinder shaft in my case. (actually a shade under - measure each shaft end in several places with a micrometer before deciding on the required bore size - roughly 0.001 - 0.0015 in clearance -diameter difference- should deliver a precisely located sliding fit at this shaft size) Some of the other CBN wheel makers bore their wheels oversize, and offer reducing sleeves to suit common US shaft sizes. I'm planning to bore both wheels to the same diameter to suit the smaller end of the grinder shaft (both ends are not quite the same diameter on my grinder), and to adjust the fit by reducing the diameter of the larger end using emery cloth - so that either wheel can go on either shaft end/side.

    It's maybe worth putting up a few thoughts on boring wheels like these - feel free to add views/options. On the basis that there's potentially a few pitfalls in getting the job done right. It's important that both wheels end up running true - both in terms of runout, and of side to side wobble. (the WTW wheels grind off their side faces as well as the periphery to do flat bevels as well as the hollow ground variety, and are 6061 aluminium)

    The simple way would be to try it under a drill press, but unless everything is very well set up indeed there's for me an unacceptably high risk of the bore ending up misaligned - plus unless a machine reamer is used after an undersized drill there will likely be problems in achieving a correctly sized hole too.

    One method is to use a small boring bar on an accurate engineer's lathe - making sure to check for wobble and runout first (that the wheel is accurately centred, and chucked square) using a dial gauge in both directions. (soft jaws bored to suit in a 3 jaw chuck are a good way to get concentric) Hitting the diameter with the boring bar and setting the chuck requires a skilled machinist, but has the advantage that it by definition finds the true centre of rotation.

    It's easier to bore in the lathe using a Morse taper drill and then a machine reamer off the tailstock (and it's certainly the simplest way to accurately hit a given diameter), but there's a risk of inaccuracy if the tailstock is not accurately set up/aligned or a floating tool holder is not used. Which isn't always the case on lathes in less precision oriented machine shops, or on older/worn machines.

    The other task is to dig up four sets of 18mm + bore self aligning/spherical washers (M16?) to go at each side of both wheels. This reduces the risk that a less than perfectly square cut thread or shoulder on the shaft will tip the wheel out of alignment when the retaining nut is done up....


    Last edited by ian maybury; 11-20-2014 at 11:32 AM.

  11. #176
    Quote Originally Posted by ian maybury View Post
    The simple way would be to try it under a drill press, but unless everything is very well set up indeed there's for me an unacceptably high risk of the bore ending up misaligned - plus unless a machine reamer is used after an undersized drill there will likely be problems in achieving a correctly sized hole too.

    A potentially more reliable method is to use a boring bar on a lathe - making sure to check for wobble and runout first (that the wheel is accurately centred, and chucked square) using a dial gauge in both directions. The boring bar requires a skilled machinist to hit the required diameter within the required 0.001in or so tolerance, but has the advantage that it by definition finds the centre of rotation.

    It's easier to bore in the lathe using a drill and then a machine reamer off the tailstock (certainly the simplest way to accurately hit a given diameter), but there's some risk of inaccuracy creeping in if the tailstock is not accurately set up/aligned. Which isn't always the case on lathes in less precision oriented machine shops, or with older machines.
    I'd recommend chucking it up in a 4 jaw on the lathe and getting it running true. Then Drill, bore, and finally ream. The drill removes the bulk of the material, the Boring bar insures the hole is true, and the reamer ensures accurate size.
    -Dan

  12. #177
    Quote Originally Posted by ian maybury View Post
    Guess as is often the said 'the devil is in the detail'. Or more to the point - only your specific case is your reality. Rules by definition are standardised one size fits all procedures...

    This post is actually just to say that my 80 and 180 grit CBN wheels have arrived from WoodTurnersWonders, and to offer some thought on boring them to suit the grinder shaft size.

    The stock 5/8in bore on the WTW wheels requires opening up to the 18mm nominal of the (UK market) grinder shaft in my case. (actually a shade under - measure each shaft end in several places with a micrometer before deciding on the required bore size - roughly 0.001 - 0.0015 in clearance -diameter difference- should deliver a precisely located sliding fit at this shaft size) Some of the other CBN wheel makers bore their wheels oversize, and offer reducing sleeves to suit common US shaft sizes. I'm planning to bore both wheels to the same diameter to suit the smaller end of the grinder shaft (both ends are not quite the same diameter on my grinder), and to adjust the fit by reducing the diameter of the larger end using emery cloth - so that either wheel can go on either shaft end/side.

    It's maybe worth putting up a few thoughts on boring wheels like these - feel free to add views/options. On the basis that there's potentially a few pitfalls in getting the job done right. It's important that both wheels end up running true - both in terms of runout, and of side to side wobble. (the WTW wheels grind off their side faces as well as the periphery to do flat bevels as well as the hollow ground variety, and are 6061 aluminium)

    The simple way would be to try it under a drill press, but unless everything is very well set up indeed there's for me an unacceptably high risk of the bore ending up misaligned - plus unless a machine reamer is used after an undersized drill there will likely be problems in achieving a correctly sized hole too.

    One method is to use a small boring bar on an accurate engineer's lathe - making sure to check for wobble and runout first (that the wheel is accurately centred, and chucked square) using a dial gauge in both directions. Hitting the diameter with the boring bar and setting the chuck requires a very skilled machinist, but has the advantage that it by definition finds the true centre of rotation.

    It's easier to bore in the lathe using a Morse taper drill and then a machine reamer off the tailstock (and it's certainly the simplest way to accurately hit a given diameter), but there's a risk of inaccuracy if the tailstock is not accurately set up/aligned. Which isn't always the case on lathes in less precision oriented machine shops, or on older/worn machines.

    The other task is to dig up four sets of 18mm + bore self aligning/spherical washers (M16?) to go at each side of both wheels. This reduces the risk that a less than perfectly square cut thread or shoulder on the shaft will tip the wheel out of alignment when the retaining nut is done up....


    Are there any small machine shops near you? I'd imagine that since the core of the wheel is aluminum, they could chuck it and drill and ream it pretty easily. I agree that a drill press is a no-no since there is no such thing as truing it again once it's on the wheel. You wouldn't like the wheel if you only had a small contact patch touching the tool.

  13. #178
    This thread is absolutely mind boggling to me. Spending hundreds of dollars for cbn wheels, and then they need to be modified at a machine shop before they can even be used? And hundreds more spent, no doubt, on tool rests and other paraphernalia. All to accomplish a mundane task that can be done with cheap, off-the-shelf equipment. It's like the woodworking equivalent of a hair shirt.

    People can do whatever they want, and spend their money however they want, and it's no skin off my nose. But I worry about about the newbies who come to this site looking for advice. I hope to high heaven none of them are seriously thinking about going down this road. To them I would say: ignore almost everything you've read in this thread. Get a modestly priced 6" grinder and use the stock wheels, or get some $40 friable wheels if you really want to live it up. And then, spend your free time learning how to use it. I submit that would be a more productive use of time than endless hours of forum posting and internet "research" trying to find some skill-free technology that will solve all your problems.

  14. #179
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    Yeah, but isn't that one of the points of a place like this? A forum where people can discuss methods of work, that go beyond the basics? I personally have trouble grinding on a wheel, no matter how much I practice. I doubt I'm alone.
    Paul

  15. #180
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    Nobody is claiming that CBN is the way to go for all Steve - although if the wheels last almost indefinitely as has been claimed, don't throw grit everywhere, and meanwhile don't wear/change dimensions then longer term in 6in form they may not be such bad value or such an indulgence at $149 a pop: http://woodturnerswonders.com/produc...20-grit-6-inch These prices are already dropping, and seem likely with wider adoption to drop further.

    The thread though isn't about setting up basic bevel grinding capability, or even just about re-grinding existing bevels. As before it's 100% clear that hollow grinding on a stock bench grinder is a cheap and very cost effective route to this - one that combines many advantages.

    It's about trying out some possibilities, and sharing some experience. Which for some of us happens to be a fun activity that draws on other aspects of our backgrounds. But which may not work out.

    There's been a few cross purposes, but the thread has from the start been about seeking a set up that can handle jobs from re-grinding to remove a honing bevel right up to the heavy work of putting a new bevel on a blade blank, or re-angling a bevel - all to a high level of accuracy and a good finish, and with speed and minimal risk of overheating. With in this case the ability to be set up to grind flat bevels, or to hollow grind - with the aim for the moment of enabling single bevel sharpening and subsequent honing with a guide.

    The boring of the wheels is relatively easy in my own case (David), it's a matter of getting an hour on a friend's lathe. They come in 5/8in bore as stock, which fits many US grinders anyway.

    It meanwhile seemed worth posting the piece on boring wheels - to help reduce the possibility of anybody that did find themselves needing to bore wheels (or indeed anything else similar) running into trouble...
    Last edited by ian maybury; 11-19-2014 at 8:16 PM.

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