Good luck with your enterprise Jon. From one old fart to another (I have a couple of years on you), I hope we are both still alive when your CBN wheels wear down enough to make those adjustments necessary. 
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The geometry of gouge sharpening
- Thread starter Jon Murphy
- Start date
But I will be willingly wading, unlike the General who wanted to be taken to a pier so he could retain the crease in his trousers. He returned to the ship immediately to change clothes after declaring his return. If you detect a certain undercurrent in my comment, I'm a former seagoing Naval officer. I "tugs me forelock respectful" to the Beachmaster (a junior Naval officer who felt that the use of the pier to land supplies was more important than the dignity of a General).
We shall be, Dennis. We shall take on Methuselah for the record. I see the fine and delicate work on the shelf behind you, my compliments.Good luck with your enterprise Jon. From one old fart to another (I have a couple of years on you), I hope we are both still alive when your CBN wheels wear down enough to make those adjustments necessary.
I didn't realize the photo I attached in my last would be gigantic, I was trying to make it my avatar photo. The lad is my grandson visiting from Texas, the face in the doorway of my bedroom shop is unrelated. But it does make the point that a small shop can do more than pens - that small lathe is a 12" swing.
I have to thank you, our discussion on the "angle of the dangle" led me to some experimentation. This evening I re-calibrated some of my settings for my gouges to work off a basic setting of the height to the center of the wheel and distance from the wheel of the basic V notch, then the selection of the four position "distance peg" in the Geiger device. I have to take a photo of the setup, I thought I had one, it is quite a simple device (unlike Don's latest production).
The re-calibration allowed me to use a standard of both height of the V notch and distance of the V notch with the same "peg" setting for set-up (using the same leg setting on the VariGrind). A few tests, using only the change in the four position peg (variable distance from the wheel for the toe of the jig), allowed me to duplicate exactly (or so close as to be fully functional in my handing of the tool) the grinds I'd made with a more complex process - and then duplicate them perfectly.
I can move my V notch arm from my coarse to my fine wheel with the height set, and use a simple (supplied) jig to set the distance from the wheel. Now I'm set up. I can touch up a bowl gouge, an old style spindle gouge, and my preferred detail (shallow flute) gouges by merely changing the leg angle on my VariGrind and which of the four V notch peg positions (distance from the wheel). My grind is an almost perfect duplicate, even when I change gouges or wheels.
But I repeat my thanks, your suggestion supporting the vendors (like Thompson) who find the middle range of the VG leg to be best set me on a new course, that of trying to make a single standard set up with the VG leg near the middle that would allow me different "wings" and "tip bevels" using only the four position "distance" and the leg adjustment of the VG. i was successful for the Ellsworth bowl gouge shape, and my preferred shape for detail gouges (30 dg. tip bevel, medium side grind). I'll be back to you, you fellow old fart. Perhaps my efforts are irrelevant, but perhaps they may be helpful. I have lived a reasonably long life, with years to go, as an annoying nerd.
Please note my email address and web site, MurphSays.com. About 55 years ago I used to drive, or ride (depending on whose turn it was), from NYC to Vermont for skiing on winter weekends with a bunch of buddies. There would always be the question as to what we would find for weather and snow conditions. I had a tendency to announce the details of the weather patterns - the low coming up the coast, the high from the west (or vice versa, or whatever). My lads shut me up by saying "that is Chapter 13 of Murph Says". OK, I'm still Murphsays, and took the domain name in 1995, and proud of it. But I'm also open to objection, with a grin, to the details.
The details of the grind are not important to the use of the tool, but the duplication of the grind you like with the least effort saves expensive steel, and preserves the grind you like. The gradual shift in shape by approximating the grind using the tool its self as the model can get confusing. I just bought a new Ellsworth signature, mainly as my old one was getting short in the flute, but partially as my shifts of jigs and such over the years had corrupted my shaping. I have immortalized the initial grind in my notes, using a quantity of Magic Marker and my set up.
David Ellsworth is not a god, but I like the gouge shape he settled on. I may decide I want a variation on that shape, but once you vary a shape you lose the original. By making a set of fixed variables for a specific shape one can return to that shape. Our scrapers and skews and other tools are basically linear, although two dimensional in some ways. Our gouges are three dimensional, and changes in the grind change the use of our hands in using the tool. OK, it ain't the shape of the tool, it's the touch of the turner.
As an ancient warrior I'm still ready to adjust my skills, but as one who lives on Social Security and does his turnings as gifts (despite their magnificence <g>), and has a wife who takes every bowl as a new place to put pennies, or something, I have to save expenses where I can. The expense of the CBNs is a saving in tool steel.
Howdy Gents. I've gotten a bit further in my experimentation, and would like to compliment Dennis on his initial analysis (dated Feb 18). I'm going to bounce off his comments, with full respect to my fellow antique <g>. In that initial post Dennis mentions Angle A and Angle B as parameters. "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 (added, the line from tip to socket). 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."
In a response I proposed that there was an Angle C that involved the leg position on the VariGrind - in Dennis's response (Feb18) to that he suggested that was more a variable than a parameter. After experimenting I propose that it is a parameter as it has a significant effect on the angle of the wing. Allow me a bit of 3D geometry to explain.
Angle A and Angle B are 2D matters, and can be duplicated with any VG leg setting combined with the distance of the V notch from the wheel (I'll be back that, with regards to vertical and horizontal, suffice to say that either is equivalent). But as one swings the tool to make the wings, whether long or short, one is dealing with a cone, a 3D figure in geometry (and in life). The butt of the tool makes a segment of a circle of greater or lesser diameter depending on the VG leg setting, and therefore a different angle at the tip of the cone (the contact of the tool with the wheel).
I'm sure you all realize that, but have not thought it important - but it was the darned thing that got me into this exercise. Let me relieve the suspense. I have in my hands (not at the moment, I use both hands for typing) an old bowl gouge that had little flute left. The wings are radically different (I ground them with different leg angles but the same Angle A and Angle B). I intended to try a number of angles, but didn't have enough flute for the VG mounting to do other than the extremes.
Pardon my being Murph Says, but I've been that since I learned to talk in 1936/7. Dennis speaks of a VG leg angle of about 23 and 38 degrees - I agree with the "about" as it is difficult to measure the angle. I number the notches from 1 to 7 (with 1 the flattest"). At the "notch" the leg is perfectly aligned with the straight side of the notch, at the "half" it is aligned with the "top of the V - which isn't really a half, but is easily duplicated. Thompson's setting, from his picture, is a bit more than 4 - an undefined visible gap. Wow, ain't that detailed - and it is quite insignificant. The significance is the ability to duplicate the setting so that one is taking the least steel to touch up a grind. By using the exact line of the notch, or that tip of the V, I get the same setting every tome. BTW, the 23 degrees is about notch 3, the about 38 is notch 4 (which is my favorite for most of my gouges).
Back to the experimental gouge. I ground it with Angle B (the tool to the tangent) at 60 dgs, the angle of my Geiger "gauge") and the VG leg at notch #2. I used the length of my V arm to set it. I ground the tip and left wing to the "horizontal" swing of the VG. I then did the same with the leg at notch #7 at the tip and the right wing. The difference in the result is significant, very significant. i take my "half and half gouge" in hand and look at it from the top. I can barely see the left side bevel, it is nearly vertical. The right side bevel is quite easy to see. It is almost impossible to measure the angle of the side bevel, but the angle at the nose (looking down) is measurable and is a part of the "swing" of the bevel. The sidewise nose bevel using VB leg notch # 2 is about 20 dgs, using notch #7 it is about 45 dgs.
Dennis correctly says that the difference in VG leg angle changes the position of contact with the wheel, and therefore Angle B slightly. I tested that first, marking the point of contact. I was about to give up my thesis as the difference of the level on the wheel was small. Should anyone be wondering how I stabilized the wheel position, I put a level on the top of the hex nut to ensure accurate measurement. When I actually made the two extreme grinds I was surprised as to the extent of the difference.
I also tested the use of height of V notch (with my Geiger V arm) versus distance. They equate, you can get Angle A and B either way, the variable/parameter beyond that is the leg angle that defines the diameter of the "cone", but once Angle B is set by height and distance the "cone" defines the wing shape. Protrusion is a minimal matter, unless you are extreme. Refer to my original chart.
All that said, I'll basically agree with Dennis and many of the rest of you. For almost all gouges a VG leg setting in the middle range of the notches is the most practical and useful. I happen to have a brand new Ellsworth signature Pro-PM from Crown, and I assume it is perfectly ground to David's specs. I did the magic marker test and found I could regrind it perfectly using my "Geiger 60 dg. gauge" and a VG leg setting of 3 3/4, but there is no mark for 3 3/4, At notch 4 leg setting, with the perfect 60 dg. tip bevel, I wiped out the magic marker with a few spins of the wheel (ok, I started the power then turned it off - it was more than a few spins, but it wasn't a significant change of the side bevel). I'll use the VG 4 leg setting for my Ellsworths, and if I'm working on a series of small radius bowls I might regrind with a VG 5 so as to better ride the bevel on a finishing cut.
My goal in this exercise was to understand the geometry of our gouges, and the way to grind what we may want for a specific purpose. I think I've accomplished it, but I'll never be finished. I bow to Dennis, his comments led me to shift my thoughts a bit. I use a 2" projection as my Geiger V notch arm (I won't put a name on it as it is not in production, but it is the predecessor of the Pro Sharp Supreme) has an integral 2" gauge (actually a bit less, I had to shim the face to get 2"). The difference between 1 3/4" and 2" is imperceptible in Angle A. Another of my problems was the second generation Ellsworth jig, the round one. The leg is at a fixed angle, but it sockets into the jig parallel to the tool (a bend in the leg). It is glued in, it tends to shift the vertical angle. I don't know how many times I tried to reglue it to get both wings even. In fact that was another trigger for this exercise, a way to duplicate David's grind exactly using my VG.
Now to the matter of the perfect grind - we all know there isn't one. There is no perfect hull for a fast sailboat, and no perfect shape for an airplane wing. They depend on the usage. But there are defined shapes that work. As we test our variations we need a base point to work from. If we like a pattern then we want to duplicate it perfectly as we retouch the tool. If we gradually reshape it we can end up with a very different shape and wonder why it doesn't work like it used to.
I'm all for variations, I'm a musician - but to vary a theme you have to know the theme, else you lose the basic theme.
I like my Geiger V arm, even though Dennis considers the height adjustment redundant. Dennis is right, you can make the same Angle A and B adjustment with distance. It also has a four position peg to adjust distance by exact increments. It is totally unnecessary, but it is convenient. I'm not comfortable with the New Geiger Pro Sharp Supreme - too fancy, and with no more variability, and a lot more money. The first version had the height adjustment, the second the four position pin (and I got the parts for the second at cost and made the conversion). I wish he were still selling that, I'd recommend it. Obviously I've digressed, but by now you should know I do that.
In summary, the "angle of the dangle" of the VG leg makes a significant difference in the side bevel angle, although for most standard grinds a middling leg setting gives a good balance of tip bevel and side grind, whatever the length of the wing. It's hard to go wrong with notch # 4 (about 38 dgs), A good "setting gauge" is a real help for setting up when combined with a device for a fixed change in distance. The gauge that came with my Geiger setup may have been the best part of it, a 5/8" rod with a flat machined on top to imitate the flutes when mounting in the VG. It is ground to a perfect 60 dgs, and the nearly full face with the curve of the wheel makes it easy to perfectly set the tip angle, more surface than the tip of the gouge. Now we have Angle A and Angle B. A fixed change in distance can give me another Angle B, and a nearly perfect reproduction of the new B grind.
For those who want to use the standard V arm to adjust the distance it would be easy to make gauges for the various tip bevels, provided you can find a machinist friend. Buy a 5/8" rod (the max for the VG) and have the machinist flatten a face to the depth that approximates the flutes of a US 5/8' gouge (about a half inch wide, or a bit more). Cut segments from it and put them in your VG and grind to your chosen tip bevel angles (leave a bit of length for errors, you will have to take a bit of time to get the angle right). Now you have a full faced gauge that will rest on the wheel, you can easily adjust your distance for your tip bevel with a normal Wolverine arm at whatever height the V notch is.
This is not a silly exercise, even the best of us can't exactly match Angle B to an existing gouge, there isn't enough face to be perfect. A home made gauge can make an excellent match. That said, I'm happy with my Geiger system. I can shift from wheel to wheel more quickly using that system - just did it tonight to do my testing. But were I a newbie reading this I'd save a lot of money by making "tip gauges" from cheap stock. A 36" rod can make me 6 "gauges" for perfect tip bevels for the price of the rod and a couple of passes by a machinist - who will probably do it for a six pack of beer in his spare time.
Enough, Dennis and the rest of you are right in that there is little difference in the effect of the VG leg angle for most purposes. But I am right in that it is quite significant at the extremes. Knowing the extremes is the best way to understand the norms, it allows one to gently shift in one direction or another. I happen to use some "extremes" in my detail gouges, the wing shape becomes quite important in a shallow gouge. I thank you all for your comments, I think I have gained an understanding of the geometry through them, and my experimentation at the extremes.
In a response I proposed that there was an Angle C that involved the leg position on the VariGrind - in Dennis's response (Feb18) to that he suggested that was more a variable than a parameter. After experimenting I propose that it is a parameter as it has a significant effect on the angle of the wing. Allow me a bit of 3D geometry to explain.
Angle A and Angle B are 2D matters, and can be duplicated with any VG leg setting combined with the distance of the V notch from the wheel (I'll be back that, with regards to vertical and horizontal, suffice to say that either is equivalent). But as one swings the tool to make the wings, whether long or short, one is dealing with a cone, a 3D figure in geometry (and in life). The butt of the tool makes a segment of a circle of greater or lesser diameter depending on the VG leg setting, and therefore a different angle at the tip of the cone (the contact of the tool with the wheel).
I'm sure you all realize that, but have not thought it important - but it was the darned thing that got me into this exercise. Let me relieve the suspense. I have in my hands (not at the moment, I use both hands for typing) an old bowl gouge that had little flute left. The wings are radically different (I ground them with different leg angles but the same Angle A and Angle B). I intended to try a number of angles, but didn't have enough flute for the VG mounting to do other than the extremes.
Pardon my being Murph Says, but I've been that since I learned to talk in 1936/7. Dennis speaks of a VG leg angle of about 23 and 38 degrees - I agree with the "about" as it is difficult to measure the angle. I number the notches from 1 to 7 (with 1 the flattest"). At the "notch" the leg is perfectly aligned with the straight side of the notch, at the "half" it is aligned with the "top of the V - which isn't really a half, but is easily duplicated. Thompson's setting, from his picture, is a bit more than 4 - an undefined visible gap. Wow, ain't that detailed - and it is quite insignificant. The significance is the ability to duplicate the setting so that one is taking the least steel to touch up a grind. By using the exact line of the notch, or that tip of the V, I get the same setting every tome. BTW, the 23 degrees is about notch 3, the about 38 is notch 4 (which is my favorite for most of my gouges).
Back to the experimental gouge. I ground it with Angle B (the tool to the tangent) at 60 dgs, the angle of my Geiger "gauge") and the VG leg at notch #2. I used the length of my V arm to set it. I ground the tip and left wing to the "horizontal" swing of the VG. I then did the same with the leg at notch #7 at the tip and the right wing. The difference in the result is significant, very significant. i take my "half and half gouge" in hand and look at it from the top. I can barely see the left side bevel, it is nearly vertical. The right side bevel is quite easy to see. It is almost impossible to measure the angle of the side bevel, but the angle at the nose (looking down) is measurable and is a part of the "swing" of the bevel. The sidewise nose bevel using VB leg notch # 2 is about 20 dgs, using notch #7 it is about 45 dgs.
Dennis correctly says that the difference in VG leg angle changes the position of contact with the wheel, and therefore Angle B slightly. I tested that first, marking the point of contact. I was about to give up my thesis as the difference of the level on the wheel was small. Should anyone be wondering how I stabilized the wheel position, I put a level on the top of the hex nut to ensure accurate measurement. When I actually made the two extreme grinds I was surprised as to the extent of the difference.
I also tested the use of height of V notch (with my Geiger V arm) versus distance. They equate, you can get Angle A and B either way, the variable/parameter beyond that is the leg angle that defines the diameter of the "cone", but once Angle B is set by height and distance the "cone" defines the wing shape. Protrusion is a minimal matter, unless you are extreme. Refer to my original chart.
All that said, I'll basically agree with Dennis and many of the rest of you. For almost all gouges a VG leg setting in the middle range of the notches is the most practical and useful. I happen to have a brand new Ellsworth signature Pro-PM from Crown, and I assume it is perfectly ground to David's specs. I did the magic marker test and found I could regrind it perfectly using my "Geiger 60 dg. gauge" and a VG leg setting of 3 3/4, but there is no mark for 3 3/4, At notch 4 leg setting, with the perfect 60 dg. tip bevel, I wiped out the magic marker with a few spins of the wheel (ok, I started the power then turned it off - it was more than a few spins, but it wasn't a significant change of the side bevel). I'll use the VG 4 leg setting for my Ellsworths, and if I'm working on a series of small radius bowls I might regrind with a VG 5 so as to better ride the bevel on a finishing cut.
My goal in this exercise was to understand the geometry of our gouges, and the way to grind what we may want for a specific purpose. I think I've accomplished it, but I'll never be finished. I bow to Dennis, his comments led me to shift my thoughts a bit. I use a 2" projection as my Geiger V notch arm (I won't put a name on it as it is not in production, but it is the predecessor of the Pro Sharp Supreme) has an integral 2" gauge (actually a bit less, I had to shim the face to get 2"). The difference between 1 3/4" and 2" is imperceptible in Angle A. Another of my problems was the second generation Ellsworth jig, the round one. The leg is at a fixed angle, but it sockets into the jig parallel to the tool (a bend in the leg). It is glued in, it tends to shift the vertical angle. I don't know how many times I tried to reglue it to get both wings even. In fact that was another trigger for this exercise, a way to duplicate David's grind exactly using my VG.
Now to the matter of the perfect grind - we all know there isn't one. There is no perfect hull for a fast sailboat, and no perfect shape for an airplane wing. They depend on the usage. But there are defined shapes that work. As we test our variations we need a base point to work from. If we like a pattern then we want to duplicate it perfectly as we retouch the tool. If we gradually reshape it we can end up with a very different shape and wonder why it doesn't work like it used to.
I'm all for variations, I'm a musician - but to vary a theme you have to know the theme, else you lose the basic theme.
I like my Geiger V arm, even though Dennis considers the height adjustment redundant. Dennis is right, you can make the same Angle A and B adjustment with distance. It also has a four position peg to adjust distance by exact increments. It is totally unnecessary, but it is convenient. I'm not comfortable with the New Geiger Pro Sharp Supreme - too fancy, and with no more variability, and a lot more money. The first version had the height adjustment, the second the four position pin (and I got the parts for the second at cost and made the conversion). I wish he were still selling that, I'd recommend it. Obviously I've digressed, but by now you should know I do that.
In summary, the "angle of the dangle" of the VG leg makes a significant difference in the side bevel angle, although for most standard grinds a middling leg setting gives a good balance of tip bevel and side grind, whatever the length of the wing. It's hard to go wrong with notch # 4 (about 38 dgs), A good "setting gauge" is a real help for setting up when combined with a device for a fixed change in distance. The gauge that came with my Geiger setup may have been the best part of it, a 5/8" rod with a flat machined on top to imitate the flutes when mounting in the VG. It is ground to a perfect 60 dgs, and the nearly full face with the curve of the wheel makes it easy to perfectly set the tip angle, more surface than the tip of the gouge. Now we have Angle A and Angle B. A fixed change in distance can give me another Angle B, and a nearly perfect reproduction of the new B grind.
For those who want to use the standard V arm to adjust the distance it would be easy to make gauges for the various tip bevels, provided you can find a machinist friend. Buy a 5/8" rod (the max for the VG) and have the machinist flatten a face to the depth that approximates the flutes of a US 5/8' gouge (about a half inch wide, or a bit more). Cut segments from it and put them in your VG and grind to your chosen tip bevel angles (leave a bit of length for errors, you will have to take a bit of time to get the angle right). Now you have a full faced gauge that will rest on the wheel, you can easily adjust your distance for your tip bevel with a normal Wolverine arm at whatever height the V notch is.
This is not a silly exercise, even the best of us can't exactly match Angle B to an existing gouge, there isn't enough face to be perfect. A home made gauge can make an excellent match. That said, I'm happy with my Geiger system. I can shift from wheel to wheel more quickly using that system - just did it tonight to do my testing. But were I a newbie reading this I'd save a lot of money by making "tip gauges" from cheap stock. A 36" rod can make me 6 "gauges" for perfect tip bevels for the price of the rod and a couple of passes by a machinist - who will probably do it for a six pack of beer in his spare time.
Enough, Dennis and the rest of you are right in that there is little difference in the effect of the VG leg angle for most purposes. But I am right in that it is quite significant at the extremes. Knowing the extremes is the best way to understand the norms, it allows one to gently shift in one direction or another. I happen to use some "extremes" in my detail gouges, the wing shape becomes quite important in a shallow gouge. I thank you all for your comments, I think I have gained an understanding of the geometry through them, and my experimentation at the extremes.