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40/40 grind (Read 293 times)
 
Leo De Bruin
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40/40 grind
May 3rd, 2020 at 10:04pm
 
So what is the big deal with this grind on bowl gouges? I have watched a couple of youtube videos(Ashley Harwood, Sam -the wyoming woodturner) and I am note seeing any advantage to this grind over the 60 degree Ellsworth grind I presently use?

Any comments?
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Don Stephan
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Re: 40/40 grind
Reply #1 - May 4th, 2020 at 7:29am
 
The grinding angle - 40 versus 60 - is a huge difference in how the tool is presented to the wood, and how convenient the angle of the tool to say the inside of a bowl just below the rim.  Also, how quickly the bowl strikes the rim when passing through the transition zone. 

But you probably are well aware of these points, so I am curious as to the reason for asking.

Sometimes I wonder if a more blunt bevel, 60 as opposed to 40, would dull to the point of ineffectiveness less quickly.
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Ed Weber
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Re: 40/40 grind
Reply #2 - May 4th, 2020 at 8:35am
 
Leo De Bruin wrote on May 3rd, 2020 at 10:04pm:
So what is the big deal with this grind on bowl gouges? I have watched a couple of youtube videos(Ashley Harwood, Sam -the wyoming woodturner) and I am note seeing any advantage to this grind over the 60 degree Ellsworth grind I presently use?

Any comments?


Short answer, not a big deal to me at all. I honestly don't care what others use. I use what works for me.
It's nice to see what 'experts' or professional turners prefer for something to try but if it's not right for you don't use it.
Once again it boils down to what and how you turn, your personal method of work.
JMO
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robo_hippy
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Re: 40/40 grind
Reply #3 - May 4th, 2020 at 11:23am
 
I am a big fan of the 40/40 grind. I also don't use the swept back grind at all. Yes, I am 'different'....

So, the idea behind the 40/40 grind is that it takes less effort to make the cut than it does with the 60 degree bevel. If you take about a 1 inch dowel, and cut a 40 degree angle on one end, and a 60 on the other, then lay the bevel flat on the lathe bed and push, using just your fingers to hold up the other end of the dowel, it takes more effort to move the 60 degree bevel. This can add up over the course of a long day of turning.

The 40 degree angle is also the natural angle of a beaver's tooth. I prefer it for the outsides of bowls, and for down the wall on the inside of the bowl. It does work better with a more open flute. Doug Thompson's V and the D Way gouges work fine with this, but I think the parabolic flutes might be a bit better. Once I get to the transition, I switch to a 70 degree bevel tool, of which I have several variations, but most have a ) shaped nose profile. The 40/40 has to be done on a platform, though I did hear of one method for doing the 40/40 with a jig, and it used a 3 inch protrusion rather than the more standard 2 inch. I learned platform sharpening at a work shop with Allen and Stuart Batty, and never went back to jigs. I have noticed that many who use this grind have the flutes more sideways, at 3 or 9 o'clock rather than more vertical, and they cut more with the nose than with the wings. The handle tends to be held more level rather than dropped. With the dropped handle, you are cutting more with the wings.

Does a 40/40 cut cleaner than a 60? I have heard that claim, but don't think it is really true. The clean cut depends more on the wood and sharpness, along with presentation. Presentation, to me, is a case of a higher shear/slicing angle will cut cleaner than a scraping cut which has no shear angle to it at all. The exception here is with end grain cutting. I have heard claims that the 40/40 will leave a tear out free surface on bowls. Even with Stuart's bowls at demos, you may not be able to see noticeable tear out, but if you spin the bowl you can feel it. When you go uphill against the grain, you will get tear out, every single time. How much tear out you get varies a lot, depending more on wood, presentation, skill level, and tool sharpness rather than a particular grind.

Why don't I use the swept back gouges? Well, in part I consider them more of a tool that does a lot of things fairly well, but some times the more specialized tools can do the individual jobs better. I can take a wider shaving with a swept back gouge, but not as thick of a shaving as I can with a 40/40. This probably is a case of how fast you can hog out a bowl depends more on how much horse power you have, than how much metal you can put into the wood at one time without stalling the lathe. I do think the swept back gouges will do a better job of shear scraping than the 40/40, but that is because it has more surface area on the wing. I prefer to use specialized scrapers for the shear scraping.

On the inside of a bowl, if you are going for the finish cut in one pass, you can't do it with a 40/40 grind. You have to use a 60 or 70 degree bevel, and probably most important, you have to grind off over half of the heel of the bevel. I always keep that grind rounded rather than a secondary flat bevel. Fewer tool marks...

For a long time, with my sharpening platform, the 40/40 setting on the platform just 'felt' too pointy, and the 45 angle setting 'felt' better. Turns out that the 45 degree setting is almost a perfect 40 degree angle. Since the platform is a protractor, and every thing 'worked on paper', I have no idea why that setting is off. I am some one who turns by 'feel' rather than by specific mechanics and settings.

Best way to figure out how well this grind can work for you is to have a play date with some one who uses it and try out  their tools.

robo hippy
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Ed Weber
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Re: 40/40 grind
Reply #4 - May 4th, 2020 at 12:36pm
 
robo_hippy wrote on May 4th, 2020 at 11:23am:
So, the idea behind the 40/40 grind is that it takes less effort to make the cut than it does with the 60 degree bevel. If you take about a 1 inch dowel, and cut a 40 degree angle on one end, and a 60 on the other, then lay the bevel flat on the lathe bed and push, using just your fingers to hold up the other end of the dowel, it takes more effort to move the 60 degree bevel. This can add up over the course of a long day of turning.

I hate to always sound contrary but I think the statement is a bit misleading
1. you don't push straight into the wood
2. with every different grind angle, there is an optimum cutting angle in terms of ease
There are simply too many variable involved to say one is better

I think you could argue that any angle has benefits over another, it's that individual.
There may be some geometry involved in determining an optimal angle but again, with a hand tool, with everything else being equal, everyone is different and no two people will have the same experience.
I really have to urge people to find their own grind angles and not simply use what some well known turner uses. If you try their grind and like it, great but don't simply use it because they do. Just because it works well for someone else does not guarantee it will be comfortable when you use it and as a result, you may not get the results you envisioned.
JMO

I'm not sure where the beavers tooth came into this but a beavers tooth angle is about 27 degrees
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robo_hippy
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Re: 40/40 grind
Reply #5 - May 5th, 2020 at 11:23am
 
Well, I will agree that you don't push straight into the wood. You rub the bevel and cut through the wood. I am some one who turns by 'feel'. I can feel a difference, in both roughing and finish cuts, with the 40 compared to the 60 degree bevel angles. Agreed that "All of the creator's children are different, and some of us are more different than the others."

As for the beaver tooth angle, I could be mistaken. I do have an old beaver tooth medallion some where, and I did see Chris Stott demo, and he held up a beaver tooth to his 40 degree bevel gouge, and they appeared to match pretty closely. I had wondered about applying the beaver tooth angle to wood turning tools. I may have to check some beaver trees right next to my house, but I think they chew more around the tree, rather than up and down, which would make a difference in which angle would work better. Now I am wondering of the upper and lower teeth have different angles....

robo hippy
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Mike Nathal
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Re: 40/40 grind
Reply #6 - May 6th, 2020 at 8:05am
 
If you ask 10 beavers what their grind angle is, you get 11 different answers
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Ed Weber
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Re: 40/40 grind
Reply #7 - May 6th, 2020 at 10:14am
 
robo_hippy wrote on May 5th, 2020 at 11:23am:
I am some one who turns by 'feel'. I can feel a difference, in both roughing and finish cuts, with the 40 compared to the 60 degree bevel angles.

I understand since I'm similar in that way.
Most every grind (bowl gouge) used has a different angle at the nose than on the wings. This is determined by how it is ground AND the shape of the flute. Te "angle" you're cutting with varies depending on what part of the cutting edge is presented to the wood and at what angle.
This is why when people say I use a ## grind angle, I find it misleading because it's only a small part of the equation.
You almost have to turn by feel to optimize your cut.
JMO


robo_hippy wrote on May 5th, 2020 at 11:23am:
As for the beaver tooth angle, I could be mistaken. I do have an old beaver tooth medallion some where, and I did see Chris Stott demo, and he held up a beaver tooth to his 40 degree bevel gouge, and they appeared to match pretty closely. I had wondered about applying the beaver tooth angle to wood turning tools. I may have to check some beaver trees right next to my house, but I think they chew more around the tree, rather than up and down, which would make a difference in which angle would work better. Now I am wondering of the upper and lower teeth have different angles....


I did provide a link.
If we could get our gouges to continuously grow like a beavers tooth, now that would be nice.
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robo_hippy
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Re: 40/40 grind
Reply #8 - May 6th, 2020 at 11:38am
 
I think that the biggest difference between free hand/platform sharpening is that the angles are more consistent from nose to wing with platform sharpening than they are with jig sharpening. No clue as to how much actual difference that makes when turning.

The actual 'applied' angle also changes, much more so when you are cutting with the wings, when you drop the handle. A 40 degree wing with the handle dropped to 45 degrees rather than level, could be in the 20 degree range or less since your cutting angle is skewed to the bevel rather than square to it.

I have also wondered if the same thing applies to skew chisels. If the tool handle is more square to the work, or at a skewed angle, and the grind angle is skewed to that as well..... Oh, it makes my head hurt... Too much thinking...

robo hippy
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Ed Weber
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Re: 40/40 grind
Reply #9 - May 6th, 2020 at 1:10pm
 
robo_hippy wrote on May 6th, 2020 at 11:38am:
I think that the biggest difference between free hand/platform sharpening is that the angles are more consistent from nose to wing with platform sharpening than they are with jig sharpening. No clue as to how much actual difference that makes when turning.

That's one heck of a claim
I think it has more to do with who is doing the sharpening.
Everything I said is still relevant, it's just with freehand/platform sharpening the operator can easily change the rotation of the tool which changes the angle on the grind everywhere except dead center. Whether this is perceived a sa good or bad feature is up to the individual.
robo_hippy wrote on May 6th, 2020 at 11:38am:
The actual 'applied' angle also changes, much more so when you are cutting with the wings, when you drop the handle. A 40 degree wing with the handle dropped to 45 degrees rather than level, could be in the 20 degree range or less since your cutting angle is skewed to the bevel rather than square to it.


This is the same thing I mentioned above
"The "angle" you're cutting with varies depending on what part of the cutting edge is presented to the wood and at what angle. "

This is why I say experiment and find what works for you whether you use a platform or a wolverine type of system.
You don't need to actually know the geometry involved in all the aspects of the cutting (I only roughly know what angle my turning tools are ground to) as long as you can repeat the grind that works for you.
I use a wolverine jig but there are so many ways to configure the grind, tool protrusion, jig angle, jig distance, etc the possibilities are endless.
I just write down the settings when I find what I like but I never actually measure the angles.

To the OP, I'd say give the 40/40 grind a try, some people seem to like it. It may fit with the way you turn.
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John Hicks
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Re: 40/40 grind
Reply #10 - May 21st, 2020 at 11:38am
 
Just do your own experimenting with different grinds. Very simple. You may prefer one grind/angle with green/wet wood; and another for dry hard wood. I have 3 5/8 bowl gouges that I have tried multiple grinds on. For general bowl making(dry wood), I prefer my own Frankenstein grind.
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« Last Edit: May 21st, 2020 at 11:39am by John Hicks »  
 
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John Grace
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Re: 40/40 grind
Reply #11 - May 22nd, 2020 at 8:32am
 
Ed Weber wrote on May 4th, 2020 at 12:36pm:
I'm not sure where the beavers tooth came into this but a beavers tooth angle is about 27 degrees
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I'm siding with the beavers on this one...after all, they do have millions of years of evolutionary testing on their side.
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Ed Weber
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Re: 40/40 grind
Reply #12 - May 22nd, 2020 at 10:31am
 
If you read the paper, it tells you how beavers actually go through the wood.
They bite with the top teeth and the bottom teeth scrape away a small thin layer at a time. So the whole notion of finding the angle of a beavers tooth and applying it to woodworking doesn't really apply.

"In general, rodents need an edge on the material to serve as abutment for gnawing, and the upper incisors are used mainly as an anchor ( Wilsson 1971 ; Maul 2003 ). Also Zhijiang et al. (2003) showed that the upper incisors moved only slightly during incising wood. When the upper incisors are fixed at an anchor point, the lower incisors can perform gnawing movements similar to a planer and in this way create more or less parallel corrugations in the wood"

I'm not aware of any wood cutting tool, hand or machine, that cuts in this way.
Leave the beavers out of it  Grin
JMO
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robo_hippy
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Re: 40/40 grind
Reply #13 - May 22nd, 2020 at 11:53am
 
You had to say 'Leave it to Beaver' didn't you......

robo hippy
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Ed Weber
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Re: 40/40 grind
Reply #14 - May 22nd, 2020 at 12:26pm
 
Cheesy
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