My Evolving Thoughts on Sharpening

Discussion in 'Tutorials and Tips' started by Jeff Gilfor, Jul 14, 2014.

  1. Jeff Gilfor

    Jeff Gilfor

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    As I have developed my woodturning skills, in addition to falling prey to EVERY new and improved tool, I have moved from slow speed AO wheels, to slow and then fast speed CBN wheels; then to flat ground sharpening with a belt sander; and now have evolved to the Tormek system.

    My thoughts and discussion starter are these:

    I definitely see that my tools stay sharper much longer when I sharpen to a higher grit.

    I think that I get better tool control and finish with flat ground tools than those sharpened on 8 inch wheels.

    I have not used the T7 long enough to draw a conclusion yet.

    Any thoughts or comments and experience from others would be greatly appreciated, and I apologize in advance if this has been discussed before. I have not been able to find a thread that deals with these topics specifically though.
     
  2. hockenbery

    hockenbery AAW Advisor Staff Member

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    Jeff,

    You did not mention what type of turning you do.

    I sharpen my spindles gouges with a near flat bevel on a 8" wheel by walking the tool down the wheel as I sharpen. I think it gives me better control than the hollow ground bevel.

    My bowl gouges I use with the hollow ground bevel off the 8" wheel.
    I have a 1/4" bowl gouge with the convex Michelson grind I use for some finish cuts.

    With sharpening everyone evolves to their own best solution there is little consensus among the experts.
    Many prefer 60 grit wheels others prefer 120 grit wheels a few prefer the tormek.

    For bowls and hollow forms in domestic hardwoods I'm happy with a tool surface I can sand with 220 or maybe 180.
    Spindles, finials, I want a tool surface I sand with 320 or 400 to keep the details..

    Al
     
    Last edited: Jul 14, 2014
  3. john lucas

    john lucas

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    Well I'm experimenting right now and have 3 sharpening systems set up. Well 4 if you count an Aluminum oxide wheel on one side of the grinder and 180 grit CBN on the other side. I'm learning that the sharper the tool is the longer the edge lasts, maybe. When turning spindles I can tell the difference. I'm still not sure on bowls because I haven't done enough back to back to really tell.
    What I'm learning from all of this so far is that it's not just how sharp the edge is. It also involves the total sharpening system. How easy is it to use. How long to the belts, wheels, etc last and how expensive are they to replace when they wear. The sharpening angles of each tool effect how it's used, and how does a convex grind work vs flat grind vs concave.

    Now in reality my tools are almost all ground on a round wheel except those that I use on the belt sander. My main bevel, that is the one that actually does the cutting is so short on my tools that I don't see a bit of difference in concave, convex or flat. The cutting portion of the tool is usually less than 3/16, sometimes as little as 1/8" depending on how much time I take to sharpen. I did do some testing with a bunch of skews where I purposely left the bevel very long. My concave bevel really isn't since I hone the skews so there is a very short flat bevel at the point of contact which may be why I find very little difference in actual use from all the different sharpening methods. When I sharpen my bowl gouge I sharpen the main bevel, then move the Wolverine jig forward in the V arm and grind the secondary bevel which leaves the main bevel very short, the I pull the tool out of the jig and grind a 3rd bevel below the first 2 to simply round off the sharp edge on the bottom and in effect giving me more of a convex over all grind. This is not very different from the Michelson grind except his angles the first bevel in more creating a more convex acting grind.

    I have some difficulty justifying sharpening lathe tools on the tormek but it's because I use it for other tools and the wheel has to stay flat. If you flatten it often with the truing system it of course eats up the wheel and they are very expensive. For that reason I stated using my 1" strip sander for lathe tools. I can play with diffferent grits to learn more about sharpening with higher grits. A 600 grit belt leaves a finish that looks better than my Tormek which is supposed to be 1000 grit. Not sure why that is but it's almost a mirror edge straight off the belt. As the belt wears it's even shinier and more polished but it's very easy to blue the steel, which of course won't hurt the HSS tools but still tells me the belt is worn. The belts only cost me $3 and last a fiair amount of time but if you were to use these in a production shop it might get expensive.

    That brings me to the CBN. Mine is 180 grit and leaves a very clean looking edge and cuts great. Based on my experiments with the other sharpening systems I would love to try a CBN wheel of about 400 grit if anybody has one. I think it would give me the advantages of a sharper longer lasting edge. The wheel wouldn't wear out as fast and always stays flat. The also cut very cool so it may not blue the metal as fast but that's guessing on my part. Since the 180 grit CBN cuts away the metal as fast as my 100 grit Aluminum Oxide wheel, a 400 grit would still remove metal fast enough to reshape an edge a little although you might still want to keep an 80 grit handy if you really need to change a grind.

    I'm currently working on a project to see which metal actually sharpens the sharpest. I have aquired 3 tool blanks, one of Particle metal, one of HSS, and one of High Carbon steel. I will be grinding them at the exact same angles. I will be sending them off for final sharpening to a professional knife sharpener to get a keener edge than most of us every sharpen to. Then I'm going to look at them through a microscope and hopefully have them photographed so that we can see if one is superior to the other in the quality of the edge when all 3 are sharpened to the same high degree. My experience based on sharpening my skews to a hair shaving edge is that they will all be the same but I hear the argument all the time that one is superior to the other. Stay tuned. I'm having some medical issues to deal with right now so this might take a month or two do achieve but I'll get back with everyone on my results when i get them.
     
    Last edited: Jul 14, 2014
  4. Jeff Gilfor

    Jeff Gilfor

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    Sorry, yes, I do mostly bowls, with some HF, platters and spindles tossed into the mix. Do not do pens. I generally turn larger items (8 inches and larger in diameter).

    I agree that the 600 grit (Trizac) belt gives almost a mirror finish that rivals the fine gritted Tormek stone.

    I really like the idea of a finer grit CBN wheel, and wish that I could get a CBN belt. That would be the best of all worlds for me. I absolutely think I turn better with a flat grind. Even though I use a secondary bevel on all my gouges, the mail cutting bevel is still large enough for me to feel the difference. Also, it makes it easier for me to hone true to the bevel angle in between trips to the sharpener.

    I have ordered a CBN wheel (280 grit) for the T7. Hoping that the larger diameter (10"), coupled with the slow speed CBN, will yield a relatively flatter grind without wasting a lot of steel with each pass. I haven't found a lot of references to this type combination, and will be sure to report back after I've played with it for a while. If only I could find a 400 grit CBN wheel that fit the Tormek!

    Like I've said in the past: I been blessed with more money than sense.
     
  5. Bill Boehme

    Bill Boehme Administrator Staff Member

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    John, the only tool that has a visually observable difference between concave, flat, and convex is the skew. And, with the skew when it is cutting, there is only about 1/16 inch or less of the steel behind the edge that is contacting the wood. I would suggest that since the difference between the three different bevel types is not measurable except at the microscopic level, there is no performance difference. However, here is something for you to think about when sharpening and trying to compare performance: it is easy to get mislead about what really is the angle at the cutting edge. This is because we generally measure the angle using the entire width of the bevel surface because it is something that we can see and use a gauge to measure. However, if you were somehow able to measure the angle based on no more than 1/64 inch behind the edge, that is really a more accurate measure of the true cutting angle.

    The flat grind would be easy. Making a convex grind, we typically start with something flat or concave and then gently move the tool back and forth to give the bevel its shape. But, when we do that, we have changed the bevel angle ... maybe much more than we assume. measuring a concave bevel angle is more difficult because the tool for measuring needs to be short enough that it isn't influenced by the heel of the bevel yet long enough to see what we are doing.

    I have heard demonstrators say that a convex grind is stronger than a concave grind because it has more supporting steel behind it. They overlooked something very important ... they weren't looking at the angle right at the cutting edge ... instead they were basing that on using the entire length of the bevel as the measurement of the angle, which it isn't.
     
  6. john lucas

    john lucas

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    Bill I feel the same about the strength of the concave edge vs flat or convex. The only way it would be weaker would be if you sharpen the concave all the way to the tip, which no one does. You might do that at first but then most of us hone to make it sharper and that turns the micro bevel into a flat or convex edge.
     
  7. dbonertz

    dbonertz

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    I have found that sharpening for rough turning that a sharper edge does not last as long. I have 180 grit CBN and 80 grit CBN neither of which last as long as my old 60 grit pink norton wheel. Having said that I would not give up my CBN wheels for anyone. The sharper edge seems to last longer when finish turning but not rough turning. The dust factor alone will keep me from going back to the old wheels. I use the 80 grit CBN for my 3/4" and 5/8" roughing gouges for a more serrated edge when rough turning bowls and even then it isn't very serrated. Hard for me to put into words why but the 80 grit just lasts longer than the 180 when rough turning with bark, air/wood interruption and etc. When finish turning the 180 grit seems to last longer but also the keener edge gives a cleaner cut.
     
  8. hu lowery

    hu lowery

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    a thought on sharpening

    A master knife maker I once knew did all of his hollow grinding on the bottom wheel of a belt grinder. We could go to a big wheel on a belt grinder to get a gently curving concave bevel on our tools but I have also thought that replacing the flat surface that the belt rides on and we usually grind against with a gently curved surface would give us possibly the best of both worlds, a gently concave ground bevel and quick and cheap abrasive changes. The bevel arc could possibly be the same as a 24" or bigger wheel would give. Not much gain on narrow bevels but perhaps a substantial improvement when sharpening wider bevels.

    Don't know, just something I have been curious about. I own half of a one inch belt grinder off in storage somewhere I believe. Maybe I will play with it if I ever get down that way.

    Hu
     
  9. john lucas

    john lucas

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    Hu interesting thought. The way I sharpen right now my primary bevel is so short the difference between a flat platten and a 24" wheel or even an 8" wheel would make almost no difference. The main bevel is about 1/8" or less so almost no arc no matter what wheel you use.
     
  10. hockenbery

    hockenbery AAW Advisor Staff Member

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    Think beads, coves, and flats and gouge bevels

    Cutting beads there is little bevel contact whether the bevel is flat, convex, or concave.

    These are subtle and things you might not notice because our brains compensates as we cut.
    Cutting spindle coves there is tendency for the convex bevel to cut a little deeper too quickly which ruins the cove.
    The convex bevel has a tendency to come out of the cut too quickly which allows correction
    The flat bevel follows the straight line cut and and is a tiny bit easier to control as the curve of the tool and it's roll follow the cove

    Cutting flats
    Concave bevel tends to dig in
    Concave bevel has a very small contact and will cut as pointed, straight, dig in, or not cut.
    Flat bevel cuts the straight line.

    Working inside bowls ( a big cove) the flat and concave bevels tend to cut too deeply.
    Removing the heel of the gouge approximates a convex bevel.
     
  11. robo hippy

    robo hippy

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    Hmm, lots of thoughts here.

    If you have watched a Stuart Batty demo, when he is sharpening, he does make a distinction between the bevel angle from the heel to point, and the actual angle from point to just back of the point. It is a slight measure, maybe a degree or two.

    When turning bowls, for me, tool control comes from having the cutting edge as close to the bevel contact point as possible. On a convex/bows out surface, no matter how long the bevel is, there is very little space between these two points. When cutting the inside concave surface of the bowl, if you have a long bevel, there is a lot of space between the two points, which is why a lot of us remove at least half of the heel. I think this is similar to Johannes Michaelson's micro bevel on his swept back gouges.

    Now, actual sharpness and edge durability: Since I do all of my bowl roughing with scrapers, I don't know how a bowl gouge edge holds up, but I would expect it to wear faster than a scraper edge and burr when doing heavy roughing. Main reason is the more acute/pointy bevels we have on most gouges compared to more blunt bevel angles on scrapers (most of mine are at 70 degrees). The more blunt bevel has more steel backing up the edge, so it will be more heavy duty than a gouge angle, which ranges from 30 to 60 or so degrees for most gouges. The more fine/pointy the bevel is, the easier it is to bend over. One other difference with gouges is the nose bevel angle, and the wing bevel angle. I think most wing bevel angles, even if the nose is at 60 degrees, will be more like 40 or 45 degrees (can some one measure this as I don't think I know of a way to do it). So, this would mean 2 different wear patterns.

    Now, grits... I have 80 and 180 grit wheels on my grinders. Omnigrind has 400 grit wheels available, either from them direct where you can get the 1 1/2 inch wide wheels, or from Craft Supplies with their Raptor wheels which are 1 inch wide. I had a 320 grit CBN wheel which was the matrix type with 3/16 inch of a mix of abrasives and matrix bonded to an aluminum hub. The matrix type CBN wheels will leave a much more shiny surface when compared to a same grit electroplated CNB wheel. I used to use it for all my gouges, and it left a nice edge, but I think the 180 grit electroplated wheels leave a better cutting surface. I do try the 80 grit some times, and can't say I really feel any real difference. Same when I tried the Tormek black wheel on a few gouges. No real difference. This could be because of how I use my gouges though. 90% of the time I am only finish cutting, and I will touch up the edge before each finish cut. Seldom do I go more than one bowl with the same edge, unless they are small. I probably could, but it is habit.

    Which can get the sharpest: Well, this continues to crop up over the years. The metal heads discuss it a lot, and it seems to me that their general conclusion is that you can get pretty much the same edge with all of the steels, but it is much easier to do with the softer carbon steels than with the harder V10 and V 15. Me, I don't know. I do know how to grind though.

    John, hope it isn't any thing serious. I hope I can make it to Pittsburg next summer and meet you and some of you other easterners...

    robo hippy
     
  12. john lucas

    john lucas

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    Reed I've played with the wings on my various bowl gouges. Depending on the flute shape and whether or not you rotate the sharpening of the flute you can get angles that are very sharp or somewhat blunt. I have one that I use to use a lot on my mirrors. The flute was very U shaped and using the wolverine jig I could get the wings to be something like, 25 degrees while the tip was more like 50. This allowed me to do a pull cut using the wing and really clean up problem woods. It didn't hold an edge very long when doing a push cut and taking a lot of wood off where the wing is doing a lot of the cutting, but boy for shallow pull cuts it left an incredible finish.
    A stewart Batty grind on a slightly open U leaves the wings the same angle as the tip. The advantage of this is if you rotate the gouge to change the angle of the flute and consequently where the bevel is rubbing you change where its cutting on the gouge tip or side. The cut remains exactly the same because the angles are all consistent. This allows you to go down through a bowl and you can rotate the gouge to introduce a freshly sharpened area and get cleaner cuts all the way to the bottom.
    the Ellsworth grind leave the wings kind of rolled over so they are sharpened at an angle closer to the tip. this seems to hog off wood and stay sharp longer. I can't remember what the flute shape was on that one, I borrowed it to see how it worked.
     
  13. Jeff Gilfor

    Jeff Gilfor

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    Really good discussion folks. That was my intent when starting the thread.

    As a relatively new turner (5 years), but one who spends a LOT of time in the shop (ask my wife), I can attest to the dizzying array of advice, opinions, and science tossed around.

    I do believe that my CBN wheels on the Jet (1 hp) high speed grinder gives a very acceptable edge on my tools, and the repeat ability is also acceptable if I use my varigrind and don't continue messing with the angles.

    When I purchased the belt sharpening system (Sorby), I felt that that was a noticeable improvement in sharpness and tool control. Like I've said, I do grind a fairly robust secondary heel bevel, leaving maybe an eighth inch micro bevel as the cutting edge. Still, the flat grind seems better. Maybe just my imagination along with dissidence reduction for having spent the money for yet another tool. I don't know. Also,met fine grit belt leaves such a clean edge, that it lasts about twice as long as the edge from my grinder. Granted,might is only with the gouges. My scraper burr still dies after 30 seconds or so before needing a refresh.

    Now, with the Tormek, I really think I've got a nice balance. Not only is the edge sharper (no question), but the finer finish makes the tool finish smoother than either if the other two methods.

    Still, probably due to some OCD, I am trying to find an even better method, so I have ordered a CBN wheel for the Tormek (280 grit). My goal is to waste as little metal as possible, while having the sharpest and longest lasting edged tools.

    I have access to an operating room microscope at the hospital (my day job is an anesthesiologist). I will bring some tools in to do some micro photographs comparing the sharpening methods. I will also compare the burrs on scrapers from the various systems. Will post them when I get them done. I am interested in seeing with my eyes, what I can only claim I feel with my hands.
     
  14. robo hippy

    robo hippy

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    I haven't heard of a 280 grit CBN wheel for the Tormek. Is some one making one specifically for the wet wheel systems? Link? Pictures?

    Now, I am wondering about your burrs on your scrapers. I can use my scrapers for heavy roughing on bowls, and one burr is great for hogging out the outside of a big (14 inch diameter bowl), and can take out the inside as well. So, are you using a negative rake scraper? Are you honing the burr? Are you turning the burr with the scraper up side down?

    robo hippy
     
  15. Jeff Gilfor

    Jeff Gilfor

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    The wheel is from Ausie woodturning dealer Jim Carroll. The page link is:
    http://www.cwsonline.com.au/shop/item/woodcut-cbn-wheel-250mm-x-40mm-x-180g

    Although they reference the 180 grit wheel, I am getting a special ordered 280 grit wheel. The 180 wheel was very well received (according to Jim), but the 280 grit shall be better still! These wheels are supplied for them by Woodcut. It was NOT cheap. Especially when you add the shipping cost. I just have to know though.

    I sharpen my scrapers on my 80 grit CBN wheel. I have not needed to burnish them, and I really only worry about a fresh burr when doing final sheer scraping cuts. I tend to hone with a diamond card in between grinder visits. Do that about three times before a regrind is needed. I do have several neg rake scrapers that I use for the insides of deeper bowls. One has a 30 degree back angle with a 60 degree front grind. The other has a 25 degree back and a 30 degree front (for an included angle of 55 degrees). Both are round nosed.

    I sharpen scrapers on the grinder with wheels going the conventional direction (towards the tool). I plan on experimenting with the Tormek and the reverse sharpening direction for them this weekend.
     
  16. john lucas

    john lucas

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    Jeff would love to see those photos when you post them. Start a seperate thread with a title like sharpening edge photos or something so we will not miss this.
     
  17. Jeff Gilfor

    Jeff Gilfor

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    Going to wait until the CBN wheel for the Tormek comes, so that the photos can be a complete side-by-side comparison. Give me a week or two.

    Will start a new thread for them when they are ready.
     
  18. john lucas

    john lucas

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    I will try my best to get the 3 tools ground that I am sending off to have an expert sharpen and get photos. maybe we can learn something from our experiments. Will be fun.
     
  19. Jeff Gilfor

    Jeff Gilfor

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    @John: who is more expert in sharpening turning tools than an experienced turner?

    Can't wait to compare these photos! It will be interesting.
     
  20. odie

    odie

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    Howdy Jeff.......

    My grinder is pretty much just a method of removing metal for all gouges and skews. I rely on honing with 600gt diamond hones on both sides of the grind. Essentially, my cutting edge is completely done with the diamond hone......so, it's not really important what method is used for removing metal, because the diamond hone is the key to sharpness. A finely honed gouge will last through about five to ten re-hones, until the tool is brought back to the grinder for regrinding the bevel. The key to when the tool needs regrinding, is dependent on the secondary bevel created by the honing process. It's less critical on the exterior of bowls, than the interior, but more appropriate to think convex and concave with more complex surfaces. I'm using a Norton SG 80gt wheel for my grinding, and I'm very happy with this wheel......but, any wheel, or belt will do the job, since the very tip of the edge is done by honing.

    For scrapers, the Norton SG wheel does a good job of leaving a good burr for general scraping cuts. I sometimes use a carbide Veritas unit for preparing the burr for sheer scraping. The Veritas is optional, because I've found that this fine scraping is more subject to tool control than using optional methods of fine tuning the burr.

    I very sparingly use a scraper as a roughing tool on exteriors of bowls, and never use them for roughing interiors of bowls. For everything up to the final fine shaping, gouges do a better job, but shaping the bevel in several grinds are necessary to do all of the necessary cuts with precision. For final detail shaping and promotion of the finest surface preparation, a scraper in the sheering mode, in combination with super sharp gouges give the best surface......meaning minimal sanding.

    Getting a finely made cutting edge is important, as well as tool handling skills......but, I feel another important aspect to a great skillfully made cut, is how well your tool slides across the tool rest. Here is another thread that discusses this, and I see you posted to this thread, but am mentioning it because it fits the theme of this post:
    http://www.aawforum.org/vbforum/sho...ide-on-the-tool-rest&highlight=slip+and+slide

    Another part of the equation is to use a cotton fingerless glove, when the ultimate of slip and glide is needed. Post number 82 of this thread shows the gloves I use. I have both a left and right glove for this, depending on the need of the moment:
    http://www.aawforum.org/vbforum/sho...olving-shop-quot-photos/page9&highlight=glove


    ooc
     

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