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The geometry of gouge sharpening

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I am a nerd, I confess it. I like to understand the "why". I bow to our more experienced turners who have the steady hands and years of practice who can grind their gouges by hand and eyeball, but I'm like most of us who use jigs. I have been using the Vari-grind jig for years, and for several years in combination with Don Geiger's adjustable height Pro Sharp (I think that is the name, his new device is the Pro Sharp Supreme).

I like making my own grinds and experimenting, but also like to have a base to start from. I have a list of my grinds on a clip board hung by my grinder. I might set the leg of the VG to the 4th notch and the four position (in/out) peg to "red" to set the height of the V notch so that the nose bevel is 60 dgs. (the test bar Don provides). Then I might grind at a different leg setting on the VG, and a different peg on the V notch.

Sounds complicated, but it really isn't, and it has served me well as I can duplicate any grind I've come up with with a brief pass, saves me a lot of steel. But it has always bothered me when I see different set ups, particularly the extension of the gouge tip from the VG - and I've wondered about the effect. I got back onto this question a couple of days ago when I saw Don's new device, and his advocacy of Doug Thompson's grinding chart using a 1 3/4" extension - my older Geiger Pro Sharp has a built in socket for a 2" extension (no criticism Don, just investigating).

Let me explain one matter of jig geometry. The angle of the leg does not define the angle of the gouge as you roll it, the pivot point on the gouge is not the tip. The Ellsworth jig has a fixed leg, the VG a variable leg, but each of them have a different distance from the tip, even with the same extension, due to the location of the pivot. This affects the steepness of the side grind as you roll the tool - and that is the shape I like to play with.

I am attaching a diagram, and I hope it will come through readable. You will have to tilt your head to read it, sorry about that but I've tried to reorient the scan of my drawing. I was amazed, as I'm sure you will be, at the very small difference in effective grind between the 1 3/4" extension and the 2". My numbers aren't exact, nor is my drawing, as I was not using drafting tools (and my compass doesn't go to 6 1/2").

I'm going to work with this drawing and see if I can come up with a true geometry for the rolling of a gouge with a jig. My guess is that a 45 dg. angle from tip of the gouge to the foot of the leg would give an equal bevel from tip to sides. It is not an easy concept, the bevel reverses in a three dimensional way.

Your comments encouraged, your complaints accepted.
Best, Jon

image.jpeg
 

john lucas

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Here it is rotated clockwise. Hope you don't mind. I'm not a math person at all so hard to make much sense out of it. I used to play with the leg angles a lot but in the last 10 years just use 1 3/4" extension and leave my Varigrind arm in the second notch. I even drilled a hole in it so that when students move my arm I can repeatedly get it back. I now only have 3 wing postions. The standard grind from Doug Thompson's site, the Stewart Batty 40/40 hand grind and a sort of modified Wolverine/hand grind that has a very long left wing on one gouge. that was a grind I came up with years ago to better use a pull cut on my hand mirrors.
 

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Most of the tools I turn use the same geometry and tool angles for the turning process. I usually turn a couple of bowls each week and the tools used for these items are usually the same "go to tools" for bowl turning. Using the same grind (geometry) on the tool repeats the angle of approach for the tool working the piece. Over time this turns into muscle memory simplifies the turning process on repetitive items. Most production turners learn to use a minimum number of tools to streamline the turning process and minimize the number of moves in the process. For those unique one of kind pieces you sometimes need a different tool geometry to make the needed cuts and it takes time and extra focus when using a tool with a different geometry if you don't use it often. I have a number of bowl gouges on the wall and usually use the same one on all of the bowls I turn. I like to be relaxed when turning a piece and using a "new" tool with a different geometry adds an additional level of concentration and focus required during the turning process. How many hours of tool usage does it take before you master it's full potential? How many tools do you have on the wall? How many years do you have left on this planet? How many tools are hanging on the wall that you have not used this year?
 

Bill Boehme

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Jon, there was another thread a couple months ago about various bowl gouge jigs that you might find interesting although I'm not certain whether anything was resolved. In the fourth post, I have a picture comparing the old Ellsworth jig, the Varigrind jig, and the Vector jig. I leave my Varigrind in the middle notch and with a tool protrusion of 2" it's very close to the Ellsworth jig. While the jig controls the angle between the grinding wheel and tool, it can't control the shape of the grind. The person doing the sharpening must control the shape. Even with a jig one can over grind the wings and ruin the shape.
 

Dennis J Gooding

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I would like to add a few comments to the subject. I have had occasion to review two articles/videos on sharpening for the AAW Woodturner and in the process have had to delve into the details of the geometry of the Varigrind jig and its work-a-likes.

First of all, there are three adjustments available: Gouge protrusion, Varigrind arm angle, and V-arm position. However, there are only two independent parameters that actually affect the grind. I will call them Angle A and Angle B. Picture a line drawn from the tip of the gouge to the tip of the pivot that sits in the V-arm. Angle A is the angle between that line and the shaft of the gouge when the gouge is against the grinding wheel and in the central position. Angle B is the angle between the shaft of the gouge and a line tangent to the wheel at the point of contact, again with the gouge in the central position. In other words, angle B will be the nose angle of the sharpened gouge.

Changing any one of the available adjustments affects both of the essential parameters. This is why one has to alternately adjust two of them repeatedly to match an arbitrary existing grind. In principle, it could be any two of the three, but in practice the ranges of adjustment would limit free choice and one usually uses the Varigrind angle and the V-arm position adjustments to obtain the desired match. Any reasonable gouge protrusion setting can be accommodated exactly by appropriate choices of the other two adjustments. Therefore, it makes sense pick a single value for all gouges. The common choices are 1.75 inches and 2.0 inches but it can be larger or smaller without affecting the resulting grind. The only significant limitation is that if the gouge protrusion is too small, the jig will strike the grinding wheel when grinding the wings. For the following discussion assume that the gouge protrusion value is frozen.

Now consider the Varigrind arm angle. For any given setting of this angle, the V-arm can be adjusted to produce any desired nose angle exactly. Therefore, if one wanted a straight grind (no fingernail), it does not matter what Varigrind arm angle is used. Furthermore, if the tool is swung from side to side a bit to provide a slight fingernail shape, it turns out that the result obtained is nearly the same for any of a wide range of Varigrind arm angles. Any differences are small enough as not to negatively affect performance. This seems to be well recognized. Kirk DeHeer at Craft Supplies advocates using a Varigrind arm angle of about 23 degrees for both spindle and bowl gouges. Doug Thompson uses an angle of about 38 degrees (as best I can measure) to grind all of the gouges that he sells. Clearly these are quite different values and yet both yield satisfactory results. However, in both cases, all of the grinds used are short grinds in which the length of the grind is about equal to the gouge diameter or less. It turns out that if one attempts to extend the grind to form longer wings, the Varigrind arm angle becomes more important. For any given arm angle, as one extends the wing, it folds over more and more and eventually becomes too blunt. I find that for long side grind bowl gouges, say 1.5 times the diameter or greater, the 23 degree Varigrind arm angle is much too small, while the 38 degree angle works well. Personally, I have settled on the latter value exclusively for all of my gouges.

If one sets fixed values for the gouge protrusion and the Varigrind arm angle, then the only adjustment needed is to set the V-arm to get the desired nose angle regardless of what kind of gouge is to be sharpened.

As has been stated previously, the settings of these parameters do not establish the grind, but only the framework. The grind is up to the user.
 
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For bowl gouges, using 2 inches (just because), I use the Varigrind leg to set the nose angle, then set the V-arm (pocket) to determine how far the wing angle "folds over", not to set how long the wing is. How long the wing is seems to depend on how long, or how much I decide to grind on the wing. I notice that some turners prefer the wings sharper, as in standing more straight up, and their V-arm is closer to the wheel, my wings are "folded over" a bit, so I move the V-arm farther out from the wheel. The idea that there are two camps, as in, the Varigrind-leg can effect the nose angle or the wing, or, the V-arm the nose angle or the wing is interesting, as always, it's the results that count. I teach "Varigrind-leg = nose angle, V-arm = wing angle, and length of wing is up to the person grinding". I'm not trying to be bull-headed, I just can't grasp how the varigrind-leg effects the wing angle, folded over, as opposed to more straight up, not how long the wing is.
Jon, I hope this is not highjacking your original post...
c
 
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Reading this makes my head hurt.... Most likely because I sharpen on a platform, and never use jigs... I would guess that another factor, and why 'individual results may vary' is the exact setting of the jig relative to the center of the grinding wheel and/or axis/motor shaft. If I put a 1/2 inch piece of plywood on my platform, it changes the angle on the tool by about 5 degrees, so a 45 degree setting would get a 40 degree actual grinding angle. The Oneway is supposed to be set (correct me if I am wrong) at between 6 1/4 to 6 1/2 inches above the base of the Wolverine base. This could have the effect of 5 degrees difference in actual angles. Wing angles are another matter. With the jigs, you are limited, with a platform, you can roll as much as you want.

robo hippy
 

Bill Boehme

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Reading this makes my head hurt.... Most likely because I sharpen on a platform, and never use jigs... I would guess that another factor, and why 'individual results may vary' is the exact setting of the jig relative to the center of the grinding wheel and/or axis/motor shaft. If I put a 1/2 inch piece of plywood on my platform, it changes the angle on the tool by about 5 degrees, so a 45 degree setting would get a 40 degree actual grinding angle. The Oneway is supposed to be set (correct me if I am wrong) at between 6 1/4 to 6 1/2 inches above the base of the Wolverine base. This could have the effect of 5 degrees difference in actual angles. Wing angles are another matter. With the jigs, you are limited, with a platform, you can roll as much as you want.

robo hippy

Are you overlooking that the angle is set by the extension of the V arm of the Wolverine. You set it to whatever makes the nose angle of the gouge fit flush against the stone. Once you have that set, other things like the height of the Wolverine WRT the grinder is completely irrelevant as long as the Wolverine fits under the wheel guard and the wheel guard doesn't interfere with the swing of the tool. I think that the Oneway mounting requirement was primarily for anybody using the Wolverine with a 6" or 7" grinder.
 
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Thank you gentlemen, I enjoyed all the posts.May I point out that I realized, after going to bed, that my post was a bit premature as I've a bit more work to do. I was so surprised by the tiny variation in Angle A (thanks Dennis) between the 1 3/4" and the 2" protrusion that I couldn't resist posting. I'm glad I did jump the gun, your posts are helpful.

Bear with me, I'll be repeating myself a bit and expanding a bit. I am fully aware of the advantage of "muscle memory" by having only a few tools- in my 15 years of turning I've wasted a lot of money on buying the "latest thing". I now have my "go to" tools, but also do a variety of turnings where a different shape works better. I buy bowl and spindle gouges from PSI for the specialty tools, they are decent steel and cheap - so I don't mind regrinding them to a purpose. My object is to understand the "angle of the dangle" to get the shape I want without too much experimentation. Purists please note: I know that cheap tools are expensive in the long run, but these cheap tools aren't for the long run - they are for a purpose.

I have been tangling with this geometry for years, not so much in order to grind a gouge to a standard - more that, as I mentioned, I'm a bit of a math nerd. Dennis lays it out nicely, but I have another basic adjustment. I mentioned I use Don Geiger's ProSharp V-notch arm - it allows both a height and distance (from the wheel) adjustment, so there are four degrees of freedom rather than three (there are two degrees of freedom in the V-notch).

That latter jig sounds overly complex, but in Don's defense he designed it with simplicity in mind. The V-notch has a round peg in the notch parallel to the arm with four position settings, and the distance from the wheel is set so that position #2 (red) is 7" from the wheel. He provides a "setting jig", a 5/8" round bar (top flattened, to orient it) and ground to 60 dgs.. The four peg settings (distance from the wheel) change the tip bevel by 10 dgs (giving 50, 70 and 80 when for #1, #3, and #4 when #2 is set to 60). I think his intent was for variations on the Ellsworth.

Once I started using that set-up I found a lot of versatility in it. Using the 60 dg. bar to set the tip bevel is very accurate, far more so than matching a gouge tip as it makes more contact with the wheel (and is never reground so errors aren't compounded). I started playing with it and found that by setting the V-notch height using the 60 dg bar at some leg angle, and at some peg position (distance), I can make an entirely different tool that is exactly reproduced by changing the leg and the peg. That is what brought me to thinking of the geometry.

Now to expand. Dennis is right about Angle A and Angle B, but I think he is incomplete. I think there is an Angle C, and that is defined by the leg angle. To his credit he specifies that his Angle A and B are when the gouge is in the central position. Angle C is when the gouge is not in the central position. If the leg is at a shallow (flat) angle the butt of the gouge travels in a small arc, if it is more upright it travels in a wide arc. The side grind is different depending on the leg angle.

One of the important aspects of an Ellsworth, or other long side grind, is the side bevel and its relationship to the size of the work piece. For a small bowl one might want a steeper (or shallower, never know which word to use) side grind to do his internal finishing cut. Let us just say that the radius of the bowl changes the most effective side grind angle. I make a lot of small bowls from green wood and scraps - I'm 81 with one leg and the other bothered by a left side stroke some years ago, I no long go into the wood with my chain saw for stock. And this for Robo Hippy, I concur that there is more flexibility in grinding from the platform rather than a jig, but that same left side stroke left me a bit one handed - no way I can free hand a gouge.

OK, no answers necessary yet. I am going to continue this geometric exercise and will be back to you on this thread with the results. For Dennis, and others, who speak of the small difference in side grind from the angle of the leg - think of other legs. Think of a 90 dg. leg, with Angle B set at 45 dgs. Now roll the gouge. Think of a 0 dg. leg, with Angle B at 45 dgs. Now roll the gouge. Different side grinds, same tip bevel. And each could have the same Angle A. The problem is three dimensional, the usual solution is two dimensional. The wheel itself is round. so the Angle C comes into play as we roll the gouge.

One more thing, I got started on this when trying to exactly duplicate an Ellsworth grind using my 2nd generation Ellsworth jig. The square bodied one Bill B. shows in his link has a fixed leg drilled at an angle into the block, I had a problem with my 2nd generation jig in that the leg is bent, and the socket parallel to the gouge line, and epoxied in. The leg loses its angle and the two sides end up ground differently. My gouges were losing their basic shape. When I got a new one I spent a lot of time duplicating the grind on with my Vari-grind. I came up with different numbers than most others, but I got perfection. Leg at 4 1/2 (1 shallowest, the half being the obtuse side of the VG notch) and protrusion at 2" and V-notch at 7" from the wheel). Took a lot of experimentation and magic marker on the gouge surface and hand turning of the wheel.

That said, should any of you want to discuss particle physics or climate chemistry or any other topic I'm here <g>. I bought a 5/8" rod from Home Depot today and have cut it into six inch lengths. I'll flatten the tops and use my Ellsworth fixed jig and my Vari-grind to look for Angle C, and to see if it is significant. I would prefer to be at CERN in sub-atomic physics, but I don't think they'll take me. But then, they don't know how to make beautiful things out of trees. Thank you for your patience with an old fart who loves to talk.
 

Bill Boehme

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All I can tell you is that if you don't do it the way I do it, then you aren't doing it my way.

When I was in the army I learned there was three way to do things -- the right way, the wrong way, and the army way. And, you're going to do it the army way.
 

Bill Boehme

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... That said, should any of you want to discuss particle physics or climate chemistry or any other topic I'm here <g>.....

So, now that the Higgs Boson has been observed at CERN, is there anything left for physicists to do? Or should they all go home and take up something more challenging like woodturning?
 
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I believe the Wolverine was designed for the 8 inch grinders, but not positive on that. No matter because every grinder has a different height from the table. Some people seem to get very caught up in having exact perfect angle measure, while for me, close is good enough and a degree or 3 from any angle still works fine, and the actual differences it makes are almost non existent to the point where 99% of us would never notice.

robo hippy
 

Dennis J Gooding

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. ....... I mentioned I use Don Geiger's ProSharp V-notch arm - it allows both a height and distance (from the wheel) adjustment, so there are four degrees of freedom rather than three (there are two degrees of freedom in the V-notch)......

........ Dennis is right about Angle A and Angle B, but I think he is incomplete. I think there is an Angle C, and that is defined by the leg angle. To his credit he specifies that his Angle A and B are when the gouge is in the central position. Angle C is when the gouge is not in the central position. If the leg is at a shallow (flat) angle the butt of the gouge travels in a small arc, if it is more upright it travels in a wide arc. The side grind is different depending on the leg angle.......
.



Jon, a few comments if I may. I never heard of the Pro-sharp V-arm before, but it sounds like a needless complication for gouge sharpening. My recommendation for most turners would be to firmly settle on fixed values of gouge protrusion, Varigind arm angle and any other possible adjustments except V-arm extension. If you plan to use long side-grinds, I would recommend a Varigind arm angle in the mid range region. With these constraints, you only need to set the V-arm extension to obtain the desired nose angle for a given gouge and you are done. It does not matter what kind of gouge you are sharpening.

I am not sure that I understand what the parameter Angle C is that you mentioned. It sounds like it is an angle that changes as you rock the gouge/Varigrind assembly to move the point of contact with the wheel from the toe to the wing. If that is the case, then I would call it a variable, not a parameter. Its value at any given position would be uniquely determined by Angle A and Angle B. The only other independent parameter that I can think of is the diameter of the gouge. It has a minute effect on the grinds that can be obtained.
 

Bill Boehme

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I believe the Wolverine was designed for the 8 inch grinders, but not positive on that. No matter because every grinder has a different height from the table. Some people seem to get very caught up in having exact perfect angle measure, while for me, close is good enough and a degree or 3 from any angle still works fine, and the actual differences it makes are almost non existent to the point where 99% of us would never notice.

robo hippy

I reread my last post and realized that what I typed wasn't keeping up with my thoughts. :D To fill in the missing part, I agree that Oneway's design of the Wolverine was optimized for 8" grinders and that the height range probably covered all or most existing 8" grinders.However, by specifying the optimum height range the Wolverine could be used with other grinders by shimming either the grinder base or the Wolverine fixtures.

The closet that I come to measuring angles is eyeball matching the bevel against the stone. Of course, that isn't perfect and over time I have noticed a substantial drift in the bevel angle ... Almost always the angle grows larger until my slicing cuts look more like scraping cuts and I know it's time to reset to a known angle.
 

Bill Boehme

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I'm with robo. My head hurts. :)

I'm most likely less experienced in terms of bowl turning than anyone involved in this discussion so far. I am only contributing, really, because I believe that is the case. I am on a few forums and without fail, the subject of sharpening, jigs, angles, platforms, etc. gets discussed at least once every few months on each of them. While I commend and thank all those who attempt to demystify the sharpening process, I would also like to say that after reading the discussions, I am generally much more confused and frustrated than I was previously. I don't want to offend anyone in saying that. If I do, I apologize.

What I have come away with is the following:

1. there is no right/best/only nose angle for bowl gouges. Batty say 40 degrees and if you're off by 5, it's wrong. Others say 45 is optimal. Still others say 60. And on and on. Clearly, much depends on your turning style = how you want to use the gouge.

2. I am mostly confused by varigrind leg angle and wolverine extension in terms of which affects the nose angle and which affects the side grind angle, since it has been argued either way by very experienced turners/teachers.

3. Ditto for what to set the leg angle on the varigrind to achieve an ellsworth grind. Some say at the very top, others say somewhere in the middle of the range.

4. Ditto again for protrusion. Some swear by 1.75 and say nothing else is correct. Others say 2. I believe that Michelson says 2.625 for his jig.

5. Finally, no matter what setting I use, what jig I use, or what tool I am grinding, I am lousy at it. I seem to either grind too much on the wings or too much on the nose. I don't think that I'm a stupid person, but I would not have thought this was rocket science either. I do know for sure that I turn less often than I would ideally like to because sharpening takes much of the fun out of it. I'm not to where I'll go with easy tools and forget all this sharpening stuff, since I still cling to the hope that I can master sharpening, but I can only afford to waste so much good, expensive steel.

Tks for reading.
 

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Grant, the only really important thing is to have a sharp edge. All of the other things are personal preferences or refinements that have Perone become popular. None of them are the one remaining obstacle standing between struggling along and greatness.

Several things could be the cause of grinding away too music much steel to get a sharp edge. I think that the most common problem is the grindstone. If the stone is out of round and causes the grinder to vibrate then that can lead to grinding too much steel because it is impossible to use light pressure. If the stone is gray silicon carbide that hasn't been dressed recently that can make it hard to get a sharp edge.

Edit: spell checker went berserk.
 
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To me the most important aspect of any grind on a gouge is that it have a continuous convex curve on the cutting edge from wing end to wing end. No dips. It can be straight for the traditional grind.

The convex edge is formed by continuously changing the contact point with the wheel to the edge.
The varigrind, Ellsworth, and many other jigs help do this by rolling the edge over the wheel.

I keep the tool moving when it contacts the wheel or it will grind a flat against the curved gouge that will have a dip in the middle. Geometry

Two common grinding errors with jigs on side ground gouges are
1. A dip on the wing
2. A dip in the nose

The dip on the wing is usually caused by stopping and letting the wheel grind the wing in one spot.

The dip in the nose is usually caused because a tighter curve on the nose has the effect of less metal to resist the grinding. One way to overcome this is to grind the each wing twice rolling the tool from just off the nose to the wing edge and the back to the just off the nose never stopping the rolling of the tool an lifting the tool off the wheel at the end.
Then one final pass rolling the tool from wing end to wing end. This last action sharpens the nose and blends in the wings.
Some may find grinding each wing once and then the sides to side work better for them.

Regardless of the bevel angle a gouge will cut effectively if it has a continuous convex edge.
More acute bevel angles cut faster sometimes too fast.
 

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Grant, take a couple of aspirins and don't give up hope. Things are not as bad as you might think.

Regarding your Item 1: I believe you are right, there is no one best nose angle. It depends on what kind of bowl and what kind of wood you are trying to turn. I will leave it to the production bowl turners to recommend a best one or two nose angles to have on hand. However if anyone tells you that only one particular angle is acceptable, I expect that they are trying to sell you something.

Regarding your Items 2, 3, and 4: The Varigrind arm angle, the gouge protrusion, and the the V-arm extension all affect the grind, although not necessarily equally. This is not a matter of opinion, it is a matter of geometry. Another fact is that small changes of any one of these adjustments can be exactly compensated for by small changes of the other two adjustments. (The only restriction is that you don't run out of the useful adjustment range of any setting.) What is opinion, shared by many, is that you can set the V-arm angle and the gouge protrusion to fixed values and produce an acceptable grind for spindle and bowl gouges with any nose angle of interest. Read my earlier posts for some specific recommendations.

Regarding your Item 5: You nailed it. The jig only sets some constraints on what you can grind. The hard part is grinding the right amount at each point in the side-to-side swing of of the jig to get the profile you want. It might help to find pictures of the grinds you are trying to achieve and keep them in view as you try to approximate them. Bear in mind that in most cases, close is good enough.
 

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Grant Mostly it's developing a light touch and then only grinding where it needs it. And no 2, grind until the edge is sharp. After that it's all just learning to use the tool you just sharpened.
 

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John made me think of another tip for developing the light touch.

Sharpen with the grinder turned off.
Turn it on and let it come up to full speed.
Turn it off and sharpen while the wheel spins down.
Most grinders will run long enough to sharpen a gouge with a light touch.

If you apply too much pressure the wheel will stop before it eats away much metal.
Also you can practice rolling the tool with the wheel,off several times before you sharpen.

call it a polisher not a grinder...

It will all fall into to place for you.
 
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Well, after listening to and watching Stuart a number of times, the 40 degree bevel has less surface area on the nose, so it has less resistance when pushing through wood. Seems legit. Stuart tends to hold his tools more level like I do, and we both use a push cut. If you try the same cut with a 60 degree bevel, and a wide nose, you get more resistance. If you try it with a swept back grind, 60 degree bevel, and the handle dropped, you get a higher shear angle and less resistance. I do hold my gouges more level, so like a more open flute design for a bigger sweet spot. I rough with scrapers, and only use gouges for finish cuts before shear scraping. Since I am only removing small amounts of wood, there is minimal resistance compared to roughing cuts when you are trying to hog things off. I have tried 60 degree bevels for push cuts and roughing, and they just don't 'feel' right, and no idea why. Hardly any one uses scrapers like I do.... Different, and proud of it...

robo hippy
 

john lucas

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Reed I've been grinding my normal gouge with a very short main bevel. I think that this gives me more "feel" for how the tool is cutting so I have less tendency to force the cut.
 
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John, by very short main bevel, does that mean you are grinding off the heel? On concave shape, you need to grind off the heel, on convex, it doesn't make any difference. I do force the cut when I am removing stock. That does make it more of an effort to let the bevel and cut float when doing finish cuts.

robo hippy
 
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I would like to thank you all for your advice. To reply to just a few observations: my wheels are balanced and run true, so that excuse for bad sharpening is out. Too bad. :) One of my wheels is a CBN so another excuse for bad technique is lost.

The big thing I seem to consistently do wrong is over grind the wings. I get a nice convex edge shape from nose to end of wing, then proceed to gradually turn it into a straight line over a few sharpenings. Even knowing what I am doing wrong does not stop me from repeating my error. (Sign of madness??) As an aside, SB, with his 40/40 grind says that the edge should be a straight line, not a convex curve. So, as everyone here agrees, there are no absolutes.

This conversation has helped in that it has made me realize that I should simply pick an angle,and a way of repeating it consistently and quit trying to see if I can be a better turner by following the advice or opinion of the latest guru whose article I have read or whose video I have watched. That is not take away at all from the expertise of those fine turners, but my search for the holy grail is something of a fool's errand.

When I first started turning, I took 2 @ 2-day sessions with Bill Grumbine, a few years apart. His approach to sharpening with the Wolverine/Varigrind set up was to extend the tool "about that much" and to set the nose angle to "about that angle". I had a lot of fun learning with Bill and I had a lot of fun turning after my sessions with him. Many can argue with his sharpening philosophy, I suppose, but in the end, it produced a sharp tool, which, as everyone here has stated, is the objective after all.

Thank you again, everyone.
 

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Grant,
May be semantics.
I do think there is an absolute on having a continuous convex curve on the gouge and that curve may include straight or near straight parts and be a continuous convex curve.

The SB and the Glaser grinds have a continuous convex curve from wing end to wing end.
Both profiles have a wings that are straight or nearly straight when viewed from the side

The main point is any dips will cause trouble because it will impede rolling the gouge.
 

Bill Boehme

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Grant,
May be semantics.
I do think there is an absolute on having a continuous convex curve on the gouge and that curve may include straight or near straight parts and be a continuous convex curve.

The SB and the Glaser grinds have a continuous convex curve from wing end to wing end.
Both profiles have a wings that are straight or nearly straight when viewed from the side

The main point is any dips will cause trouble because it will impede rolling the gouge.

The words concave and convex seem to be overused in describing different aspects of tool sharpening. I think that everyone is on the same page when we are describing the bevel. In describing the cutting edge, I prefer the terms crown, straight, and dip. I think it's easier for someone to visualize what we mean if we say that the side profile of the edge on a wing is crowned or is straight or has a dip.

In looking straight down, we use terms like straight across and fingernail (with modifiers like long, short, pointed, and broad).
 

Bill Boehme

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When I use Convex it means no interior angles GT 180.
But I realize a lot of folks don't share that usage.

:)
We sure do need a Boehme's Woodturning Terms
:)

That definition just gave me an acute headache. :D At least you're not being obtuse even though the angle might be.
 
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If you have slight concave, or convex wings, it doesn't matter, you can turn till dull, then do a better job next time. The only bad grind that made the gouges difficult to handle is when the nose is kind of snaggle toothed.... Major convex can cause problems, but for me, most of the time, my wings are short so it doesn't matter, and I tend to cut more with the nose...

Synonym: word you use when nothing you type clears spell check.....

robo hippy
 

Emiliano Achaval

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Now I know why it took me so long to learn how to sharpen, even with the varigrind. However, some people here are over thinking it... We are not metal workers, a few degrees here , a few more there, still works... That been said... I remember calling David Ellsworth, sending pictures back and forth, around maybe 1995 or 96... I could not get the distances right, and was ruining the signature gouge. Finally David asks me where exactly do I live in Maui? He tells me a friend is going to call me. 5 minutes later, a turner that lived 5 minutes from my house called me. He showed me the "Jig for the jig" LOL, he showed me, and I bought the Don Geiger solution... That shows you how crucial it is to do the initial set up just right... I agree with the comment above, you still need to know what you want in your gouge, the varigrind is not fool proof... Aloha from Maui
 

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The only bad grind that made the gouges difficult to handle is when the nose is kind of snaggle toothed.... Major convex can cause problems, but for me, most of the time, my wings are short so it doesn't matter, and I tend to cut more with the nose...

robo hippy

I believe this is truth what Robo is saying here........I'm only attempting to put it in other words that mean the same thing, but the transition between nose and wings, as well as along the entire length of the available cutting edge should have a smooth curve.......sort of like what a "french curve" would represent.......(no "snaggle tooth" edges!) :eek:

If the other turners on this forum are using their gouges with any similarity to the way I use them.......then, any abrupt changes in the transitional curve of the entire cutting edge, or surface, represents an obstacle to the smoothness of the resulting cut that can be achieved with that particular shape of the grind. This is more apparent when transitioning through a curved profile cut, and rotating the gouge along it's longitudinal axis while doing so.....:)

ko
 
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lathe photo, Chip.JPG lathe photo, Chip.JPG lathe photo, Chip.JPG
Jon, a few comments if I may. I never heard of the Pro-sharp V-arm before, but it sounds like a needless complication for gouge sharpening. My recommendation for most turners would be to firmly settle on fixed values of gouge protrusion, Varigind arm angle and any other possible adjustments except V-arm extension. If you plan to use long side-grinds, I would recommend a Varigind arm angle in the mid range region. With these constraints, you only need to set the V-arm extension to obtain the desired nose angle for a given gouge and you are done. It does not matter what kind of gouge you are sharpening.

I am not sure that I understand what the parameter Angle C is that you mentioned. It sounds like it is an angle that changes as you rock the gouge/Varigrind assembly to move the point of contact with the wheel from the toe to the wing. If that is the case, then I would call it a variable, not a parameter. Its value at any given position would be uniquely determined by Angle A and Angle B. The only other independent parameter that I can think of is the diameter of the gouge. It has a minute effect on the grinds that can be obtained.

Pardon my delay in answering, I have been distracted by some medical matters. And for Bill B., I confess to fascination with the Higgs boson - and will add that there is plenty more to discover at CERN.

Dennis, I'm not sure if I got the name right on Don Geiger's Pro-sharp V-arm - he has a new version of that name and the old one is off the market so I assumed the old one had the same name, different version. The new one is "simpler", and a lot more expensive, and basically designed for "fixed" grinds - as was the original. Allow me to describe why it is not a needless complication, at least from my point of view.

We all like to remove as little steel as possible when touching up a gouge, and that involves getting the tip bevel as perfect as possible as well as a consistent side angle. As the wheel wears down the V-arm extension for the desired tip bevel changes, and that subtly changes the side angle. Don's original "Pro-sharp" arm (I'll use that name) allowed for a vertical adjustment of the V notch to refine the tip bevel angle while using a fixed distance from the wheel (set by a jig that could be be mounted into the V-arm riser). I will try to add a photo, but not yet as I don't want to lose my "immortal text" <g>. Along with the V-arm he provided a 5/8" bar as a gauge (with a flat top to mimic the flutes and orient the bar) ground to 60 dgs. Don was mainly setting up for the Ellsworth bowl grind. That almost full round bar made setting the tip angle perfectly quite easy, a bit of magic marker and a full face and hand turning the lathe - just as we all do with the gouge in place- made for an almost perfect replication of the grind. The small surface area of the actual gouge tip makes it almost impossible to duplicate the original grind.

I expect to hear comments saying that no grind need be exact, and I agree. I don't care if my 60 dg. bowl gouge is 60, or 58, or 62 - I won't notice the difference. What I care about is that I don't gradually shift the grind away from the original and then have to take excess steel to get it back. The use of the gauge makes it easier to match the exact tip bevel.

The second version of Don's "device" (the "Pro-sharp") offered a V-notch with a horizontal peg in the V. The peg has four positions set by a side pin. This device was a bit more expensive, but as I was a recent purchaser of the original he sent me the conversion parts for about 20 bucks. Not perfect for me, but I modified them to give a wider range of Varigrind leg settings. The four peg positions give about a 10 dg. tip bevel change. Setting the #2 at 60 dgs. gives 70 at #1, and 50 and 40 at #3 and # 4.

Wow, aren't we getting complicated! Not really. When I move my V-arm from my coarse stone to my fine stone all I have to do is shift it over, set the distance (I use 7") with the jig, then fine tune the height of the V-notch using the 60 dg. gauge at peg position #2. Now I'm aligned for all sorts of shapes with a single leg angle on the Varigrind. But that isn't all. By changing the leg angle I can get any shape that can be done by free-hand sharpeners.

My spindle gouges are Thompson detail gouges (the regular, not the shallow). I like a 30 dg. tip bevel and a long wing. I've found a shape of the wing I like. My notes say: Set up VG 6 1/2 red, Grind VG2 green. Translation: The peg positions are colored blue, red, green, yellow but Don uses lousy paint so they are 1,2,3,4 now. I call the flattest of the VG leg positions 1, the steepest 7, and the slanted edge of the notch 1/2 (it ain't exactly a half, but it is a good mark).

Why do I go through all this exercise? Yes I'm a nerd, yes I love details - but most importantly I like to save money. I have a small shop, a PSI 12" midi and the associated tools in my bedroom. I like to move from one piece to another, as an 81 year old fart my attention span is limited. When I'm not sure how I want to finish a piece I'll dismount it and work on another. For that reason I'm also often changing tools, and therefore my "touch up" grinding setup. With this set up on my stones I can easily shift from grinding a new shape on the coarse wheel to touching up another tool on the fine wheel. Two passes, or at the most three, on the fine wheel and I have a clean edge and bevel - even if I shifted the V-arm from the coarse to the fine (my last tool on the fine might have been a skew or a roughing gouge using the platform).

Finally, I call that Angle C a parameter, although I accept your suggestion that it could be called a variable. I got into all this nerd stuff when I bought a CBN wheel with a rounded edge to use on my Ellsworth style hollowing tools. I was tired of re-establishing the edge curve as I trimmed down the stone wheel. I fell in love with the CBNs, and a year later bought a course wheel as well. I recommend the CBNs, but not as an immediate substitute. When your grit wheel gets too small spend the bucks to replace it with a CBN, it will save money in the long run. Not a diamond, they get dull, the CBN.

Angle C is the radius of the swing of the butt of your tool as you roll it with the VG, it changes the steepness of the side grind. This is irrelevant if you generally work with bowls, or spindles, of similar size (radius) - but becomes relevant with the tightness of the curve.

May I suggest that you not argue with this presentation, just leave it open for later discussion. I'd really like to test my theory, and need to find a machinist to make my test blanks for a couple of bucks before I can justify my thesis - or say that I'm wrong (which I may be). I shall return (for those of an age).
 
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