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Theory about 40/40 gouge evolution....

Tim Tucker

Tim Tucker

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Nov 4, 2018
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This is as much quest for the actual reasons as much as a supposition based on evidence I can find:

When we look at the 40/40 grind - we know it came from The Batty family, and as I have been told, Alan Batty's father may have been the first to begin working with it. And when you watch the push cut being done by Stuart, or Ashley Harwood (Emiliano - my apologies I have not seen your demo...) one commonality is the bowls produced tend to be taller in depth and more vertical walled than a lot of other demonstrators using a different grind. Now, if we consider that the era in which the 40/40 was birthed....from what I can find - lathes were virtually all fixed head lathes.

So my postulation/theory is that the body mechanics+ fixed head lathe design make for best use of the 40/40. The push cut adds to the tendency of the bowl design to quick to make a closer-to-parallel - to the - bed wall.
This is not to slight the Irish grind at all. Just a different method that seems to be less dependent on the elbow being fixed to the side while making the push cut = and the 40/40 angle on the grind apparently aids this approach.

Ideas? Comments? Questions? Smart remarks...?:D
 
Perhaps the best place to start is Stuart Batty's explanation of why 40/40 is the "best" grind.

1st ~15 min covers quite a bit, but worth watching the whole thing.
View: https://www.youtube.com/watch?v=QMVGankeK0I&t=236s


It's all about wood grain direction and the best way to cut a thin wall with no tear out. Can't remember if its in this video, but he has also discussed making heavy cuts with no tear out. Those are his stated reasons for the 40/40 grind. The body mechanics he uses are for "fixed head" lathes, and the body mechanics necessary for the tool edge to correctly move/cut through the wood - I think you have the cause/effect backwards, ie the tool drives the body mechanics not vice versa. Nothing says the HS can't be slid down or pivoted out and the tool motion replicated with more body movement vs arm movement. The finish OD cut must be made the way he does it - with a jam chuck to prevent vibration. The cut could be made off the end of the bed or pivoted out.

IMO the concepts are applicable to about any shape bowl, and are best demonstrated with the larger/deeper bowls he typically demonstrates. The longer wall of these types bowls are more difficult to cut - tool and vibration control are more difficult. He readily admits the grind is not good for the ID bottom, which a large shallow bowl would have a lot of. That's where the bottom bowl gouge comes into play. The OD, from bottom to rim, is a 40/40 grind push cut.

The wing angle plays an important role in peeling the wood. Sweeping the wing further back removes this cutting action. The "suicide cut" you reference in the other thread is another approach to it. I have compared the quality of cut of a 60° Michelsen grind "suicide cut" and a 40/40 down the ID wall of a bowl to the "1/2 way point", and the 40/40 cuts cleaner. I have not tried the suicide cut with a 40° Michelsen grind.
 
Timothy White said:
@Doug Freeman: would you explain “suicide cut” ive never heard that before. But then I’m only 67 years old
Click to expand...
Flute at 12 o'clock, shaft level, nose bevel contact a bit left of center. Go to 57:00 min mark of this video. Nicknamed the "suicide cut" because if the flute is rotated left to 11:59, there is a loud bang and an "oh sh**" as the entire left wing edge feeds itself into the bowl, possibly exploding the bowl, and you get to start a new one.

View: https://www.youtube.com/watch?v=wGupR8Lt9E0&list=PLdWw7w_lu91Qokw9Fu91Po5P7hrZOTKRW&index=1&t=3410s
 
I ground a P&N 5/8 gouge last year to a very close 40/40. Found it is really nice on entry cuts for natural edge bowls. Quite often with a regular grind BG tend to get some tear out and it is much less with 40/40.
 
Well, Stuart's body stance and arms out away from the body to turn are adaptations to turning bowls on a long bed lathe. It keeps you from having to lean over or brace yourself up against the lathe. I use the 40/40 grind for the outside of a bowl and for the walls on the inside, down to the transition area of the bowl. I also turn with the sliding headstock all the way to the end of the lathe, or on my Vic 240, with the headstock pivoted to the 30 degree setting.

I don't know how the 40/40 came to be. I would guess it is as old or older than Alan Batty. Back in those days, spindle turning tools were also used for turning bowls, and the 40 degree bevel is not wrong for the old continental style gouges or the spindle detain gouges. BOB tools seem to be more of a modern invention than one going back to the early days. Not sure though....

robo hippy
 
It's possible that the "arms out-swing gouge toward body" method is not secondary to the long bed, but intentional on Stuart's part. Everyone focuses on the gouge grind, but part of his method involves minimal pressure on the tool, especially the bevel. For example, the only contribution of the left hand is downward pressure on the shaft of the tool. The purpose being to allow the gouge to slide freely. Holding the handle of the gouge up against one's trunk would involve adding restriction to the movement of the gouge. I don't know if avoiding "handle against trunk" is purposeful or not, but it might very well be.
 
I saw Stuart this weekend at Totally Turning in Saratoga.
heard is explanation of 40/40 and have stuck with my conclusion that if I was starting out, I'd probably try it and adopt it.
but after 40 years of turning....I'm pretty comfortable with my grinds for my basic tools (gouges, skew, etc.) and it does not make sense to change.
while now I have the muscle memory to think about my bowl shape and LESS (not completely none) about my tool presentation, if I were to change the grind, it would reverse that balance.
May be wrong...may be old and stubborn (definitely old....maybe stubborn) but that's my thought.
(OK...definitely stubborn too)
 
egsiegel said:
I saw Stuart this weekend at Totally Turning in Saratoga.
heard is explanation of 40/40 and have stuck with my conclusion that if I was starting out, I'd probably try it and adopt it.
but after 40 years of turning....I'm pretty comfortable with my grinds for my basic tools (gouges, skew, etc.) and it does not make sense to change.
while now I have the muscle memory to think about my bowl shape and LESS (not completely none) about my tool presentation, if I were to change the grind, it would reverse that balance.
May be wrong...may be old and stubborn (definitely old....maybe stubborn) but that's my thought.
(OK...definitely stubborn too)
Click to expand...
I think your reasoning is sound. If you are happy with what you are producing as finished work - then I see no incentive for change. On the other hand there are those folks among us ( o.k....ME) that may suffer from a medical condition referred to as "Terminal Curiosity"....:). It does not mean I will abandon a given method I currently use, rather - I always want to know about, observe and analyze the use of other methods unfamiliar to me. Perhaps this is the primordial crave for "shiny" things - that which is new and foreign.....but, I try to learn at least one thing and hopefully more - that I can adapt to my turning abilities from everyone I encounter. Sometimes it is a grind or cut method. Sometimes a tool storage idea, etc....
I learn by agglomeration. After enough collection and adsorption/adoption of other's methods and practices - I may tweak or combine 2 or more things and find something new.
 
Curiosity about how/why things work resulted in a degree and 40 years in engineering. While “if it ain’t broke don’t fix it” has merit, I have to analyze whether something new to me can improve some aspect - woodturning, motorcycles, fly fishing, etc. Many times its a technique, free except for the time to learn it, sometimes a different grind that I can try out on a cheap tool, etc. Curiosity killed the cat because it didn’t think it through thoroughly.
 
Well, no matter which tool you are using, if you are rubbing the bevel, that pressure is 'the bevel should rub the wood, but the wood should not know it'. The pressure from the second hand, left for most of us, is also minimal. The statement about 'anchor the tool on the tool rest' doesn't register with me since the tool stays on the tool rest just fine. I guess the key is 'tool stability' for fine control. My first day in Thai Chi class, which was maybe 10 years after I started turning, the motions we did were pretty much identical to what I did when turning. Keeping the tool in close to my body provides a more precise movement than having my arms extended out. Perhaps explaining it another way, it provides a shorter lever. I have never found it to be limiting. I did try Stuart's methods, and just didn't care for them. Part of that could be that my methods work better for me, and his methods work better for him.

For me, I am one of the 'if it ain't broke, take it apart and fix it anyway' types. I am always experimenting with different techniques to see if I can learn some thing new to add to the mix. I do on occasion turn a bowl with just gouges instead of my normal rough it with the scrapers, then clean it up with a gouge. I also will take and turn a bowl with just a 60 degree bevel gouge. That experiment informed me that unless I had a short bed lathe, I would not want to turn bowls that way, it really makes a big difference in where you hold your tools. I guess I can say that since I am out of production work, I am experimenting more than usual. I spend a lot of time in the swimming pool. There is always some little thing that needs 'adjusting'.....

robo hippy
 
robo hippy said:
Well, no matter which tool you are using, if you are rubbing the bevel, that pressure is 'the bevel should rub the wood, but the wood should not know it'. The pressure from the second hand, left for most of us, is also minimal. The statement about 'anchor the tool on the tool rest' doesn't register with me since the tool stays on the tool rest just fine. I guess the key is 'tool stability' for fine control. My first day in Thai Chi class, which was maybe 10 years after I started turning, the motions we did were pretty much identical to what I did when turning. Keeping the tool in close to my body provides a more precise movement than having my arms extended out. Perhaps explaining it another way, it provides a shorter lever. I have never found it to be limiting. I did try Stuart's methods, and just didn't care for them. Part of that could be that my methods work better for me, and his methods work better for him.

For me, I am one of the 'if it ain't broke, take it apart and fix it anyway' types. I am always experimenting with different techniques to see if I can learn some thing new to add to the mix. I do on occasion turn a bowl with just gouges instead of my normal rough it with the scrapers, then clean it up with a gouge. I also will take and turn a bowl with just a 60 degree bevel gouge. That experiment informed me that unless I had a short bed lathe, I would not want to turn bowls that way, it really makes a big difference in where you hold your tools. I guess I can say that since I am out of production work, I am experimenting more than usual. I spend a lot of time in the swimming pool. There is always some little thing that needs 'adjusting'.....

robo hippy
Click to expand...

I'm pretty darn early in my woodturning life so, I when I tried Stuarts methods I picked them up relatively quickly (and believe me when I tell you that I'm definitely no expert at them). They just seemed kinda natural to me at the time.

I'm right there with you with the 'if it ain't broken, take it apart and fix it anyway' philosophy though!!!
 
If I was starting now, I'd probably do things differently...because I would be taught differently.
For example, I'd probably have a beading tool. I learned to turn beads with a skew. I can turn a bead in 2 minutes with a skew....why would I need to buy a dedicated tool for something I can already do comfortably in 2 minutes?
But if I was learning now....I would "have to" put in the practice time (and flying shards) to practice to the point where I can do it with a skew...there are newer (better?) ways to do it.
 
egsiegel said:
If I was starting now, I'd probably do things differently...because I would be taught differently.
Click to expand...

That statement is probably a "universal truth".....and, it begs the question: Would you want to do it differently?

There is a lot of generally accepted knowledge that is a "given" in today's turning world. Much of it wasn't part of the knowledge base in earlier times. The real question is: Is what is accepted as common practice now, actually expanded knowledge, or is it simply different knowledge? (As I see it, the answer to that, is......yes, and no..... but those who have "vision" based on knowledge of what preceded current trends, may, or may not analyze the evidence of woodturning evolution a little differently than your average newbie.) What was common knowledge in earlier times, is now mostly rejected for a more modern philosophy.....and, lost or forgotten, in the abundance of current evolving opinions, techniques and, the mountain of "new and improved" tools and gadgets.

-----odie-----
 
I am a 40/40 geek. I took Ashley's bowl turning class and it changed my turning.

The key like anything else is practice. My group at her class did a 30 day challenge to turn a bowl per day. It helped a lot.

As for the stance and arm movements, it takes a while to get used to. Instead of a woodturning dance I call it woodturning yoga.
 
I believe Stuart's arms away from body is the result of his desire to not move his feet during the cut. If you watch him turn he positions is body for the end of the cut, and you can see him point his gouge at the cut end. Then he pivots his trunk and swings his arms out to place the gouge at the cut start. This requires a "not totally comfortable" position at the end and start of the cut. It allows a single smooth continous cut without moving the feet. It does not feel as secure as a handle against the body.
 
Hmm, food for thought Steve. Most of the time, when turning bowls, I do not move my feet other than on the outside of a big bowl where I can't space my feet far enough apart to make one continuous cut. Some times it is me forgetting to space my feet apart. Process is similar for both styles, move with your body, not your feet, and for me, not with my arms.

robo hippy
 
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