Bowl Gouge Flute Descriptors

[Neil Strong]

Part 1 of 8

Warning: Long multi-post starter to this thread… and some folk may prefer to be spending their time out in their workshop turning wood than engaging in pedantic stuff about flute profiles and names… :~}

The focus of this thread is neither turner preferences for one flute profile over another, nor is it about which flute profile might be better suited to a particular grind for one use or another.

My focus here is entirely on flute descriptors in order to reduce the confusion that I’m seeing over those in our woodturning community.


–o0o–

Elliptical

Back in the early 70s when I began woodturning the flutes on bowl gouges had simple names like shallow and deep, which were easily understood. I can’t recall anyone giving the flute on the deep bowl gouges any other descriptor than that, but looking at the flute on the forged bowl gouge that Peter Child included in his 1970s book it might have been called elliptical (https://en.wikipedia.org/wiki/Ellipse)…


493485

And here is how Roy Child (Peter Child’s son) drew that elliptical flute profile that they were using back then in his later 1999 article http://www.peterchild.co.uk/info1/sflute.htm (http://www.peterchild.co.uk/info1/sflute.htm)


493486
There was then a period when elliptical was more widely used to describe a flute profile that had a continuously changing curve and Henry Taylor Tools described the gouge that they made to Roy Child’s design as having an “elliptical flute cross section”, which they called the SuperFlute. The ellipse is a precise mathematical curve derived from Conics (https://en.wikipedia.org/wiki/Conic_section) and where a flute is elliptical it would be appropriate to call it that, but few are.

Here is how an elliptical flute would look in a round bar…


493487
Roy Child himself neither named his flute design the SuperFlute nor described it as elliptical. In his own words he simply described it as follows, “it has a large radius at the sides blending into a small radius at the bottom of the flute.” Here is a diagram drawn by Roy of his flute profile design alongside the SuperFlute made for him by Henry Taylor Tools…


493488


So, as can be seen, the Supeflute is neither a true ellipse (as specified in Conics) nor is it a parabola (more on those later), although it is much closer to a parabola than some bowl gouge flute profiles that have been described as parabolic. It is in fact closest to the catenary profile (https://en.wikipedia.org/wiki/Catenary) as seen in the example of a chain suspended from two level points or arches like the St Louis Arch that might be seen by some of you on your side of the pond.

[Neil Strong]

Bowl Gouge Flute Descriptors - Part 2 of 8

Catenary or Parabolic

There are only small differences between the catenary and parabolic curves. For comparison, here are those two curves superimposed on one another, the parabolic in red and catenary in black…


493489


For the purposes of woodturners they are close enough to be used interchangeably, however, catenary is not a term in common use and there is already too much confusion around parabolic as a descriptor to muddy the waters any further by introducing another descriptor. By default parabolic has become the descriptor for flute profiles that are close to either catenary or parabolic. Relevant to the distinction between those two and the V profile are the continuous curves in the upper sides of their flutes. This is more obvious in the catenary and, although the upper sides of a parabolic flute start to straighten out, they never become fully straight as they do in a V flute.

The Parabola (https://en.wikipedia.org/wiki/Parabola) is a curve that is derived from Conics (https://en.wikipedia.org/wiki/Conic_section) and, although very precise in its parameters, it can have many manifestations, eg….


493490

493491

493492

What we see on bowl gouges is a flute that is usually closer to the middle curve (F=1) shown above. As can be seen, the curve is continuous and the sides never become straight.

[Neil Strong]

Bowl Gouge Flute Descriptors - Part 3 of 8

Examples of Parabolic Flutes

When David Ellsworth developed his signature bowl gouge in the early 1980s he and/or Crown used the term parabolic to describe his flute profile. Like most flutes that are called parabolic, it’s not quite a true parabola, but close enough. Here it is with the characteristic continuous curve that runs right up the sides …


493493


Some other bowl gouges that subsequently came along with parabolic or close to parabolic flutes have been Woodcut (left) and Vicmarc (right)…


493494 493496

[Neil Strong]

Bowl Gouge Flute Descriptors - Part 4 of 8

Other Examples of Parabolics

Here are a few more examples of parabolics that I don’t have myself for which I have been able to find clear endview images on the web …


493497
Ashley Harwood

493498
Glenn Lucas (Hamlet)


493499
Robust

Forum members may have images of other examples of bowl gouges with parabolic flutes that I don’t have that they might like to post here with a clear end view of the flute profile, eg Hamlet Masterflute, Robust parabolic and Oneway Mastercut (John Kananis has posted one for the Oneway in another thread and I will add that).

[Neil Strong]

Bowl Gouge Flute Descriptors - Part 5 of 8

The Vs and Us

That brings us down (or back) to the V and U profiles. The U fluted profile is as old as spindle roughing gouges (not they are intended for bowl work), which is semi-circular at the bottom of the flute with straight parallel sides. Here is the ¾” D-way U Fluted BG…


493500


When the straight sides are at an angle to each other the now well established and understood convention is to call it a V flute. The size of the circular section in the bottom of the flute and the angle of the straight sides to one another can vary…



493501


This flute profile came in with making bowl gouges from HSS bar and their profiles were partly influenced by the milling cutters and grinding wheels available and the economics of the profiles that can be readily achieved with those. Most of us that had an early HSS bowl gouge are familiar with the V profile. For example, here is my early P&N V flute profile…


493502


Jerry Glaser, who pioneered the use of HSS gouges in the mid-1960s, and later the high alloy powdered metals, used a V profile as one of his preferred flute designs. Doug Thompson who followed, acknowledges Jerry as his predecessor with his V flute design. Theirs is a more open V that most of us are now familiar with…


493503
Thompson V flute

[Neil Strong]

Bowl Gouge Flute Descriptors - Part 6 of 8

Other Examples in the V Flute Tradition

Among the other excellent (IMO) bowl gouges in the V fluted bowl gouge tradition are the D-way (next image) and Jamieson (the image below that), which to my eye are very similar with both having wider and deeper cut circular sections at the bottom of their V flutes…


493504

493505


Despite some wording to the contrary on their websites, neither gouge is parabolic in any way that I can see, no matter how hard I squint… :~}


493506


This is not a criticism of the excellent bowl gouges from these two woodturning tool designers/makers. As I have said here and elsewhere, they both have 1st rate V fluted bowl gouges, however, I just can’t see a parabolic profile on any of the gouges that I have from them.

Are there any other bowl gouges in the same esteemed V fluted tradition?

[Neil Strong]

Bowl Gouge Flute Descriptors - Part 7 of 8

A Few side by side Comparisons

Here are a few side by side comparisons to highlight the differences between V and parabolic flute profiles…


493507
From left Thompson V, Jamieson V
& Henry Taylor parabolic

493508
Ellsworth sig parabolic on left P&N V on right

493509
P&N V on left & Thompson V on right

493510
Thompson V on left & D-way V on right

[Neil Strong]

Bowl Gouge Flute Descriptors - Part 8 of 8

The Importance of Accurate Descriptors

Back before we could purchase our gouges online we would go to shops or events that had vendor stalls to select our tools. We could inspect them before we bought them.

Nowadays most of us buy our tools online and we are dependent on accurate information on websites to inform our purchasing decisions. Likewise, it’s important that we don’t create confusion in what the established descriptors mean.

I reckon that three simple descriptors is all we need to avoid confusion; U, V & Parabolic. The last being preserved for flutes that have a continuous curve even where they are not a precise parabola. In addition to the catchy and meaningless names given to some, the makers of the parabolics can add wording to that descriptor to explain and extol the features and virtues of their flutes.

Any bowl gouge flutes that have straight sides are either U or V flutes. If it is a V flute, the makers can add any manner of words to that descriptor to explain and extol the features and virtues of their particular flute design (other than parabolic :-).


~~~~~

I welcome any corrections, other perspectives, examples, inputs or critiques.

It is not my intention in this thread to discuss my or your preferences for one flute profile over another or which flute profile might be better suited to a particular grind or use. There have and will be many other threads for that.

Let’s keep this thread to just bowl gouge flute descriptors.

Letting those who are members of other woodturning forums know that I also intend to post this thread elsewhere.

[Neil Strong]

Oneway Mastercut (John Kananis has posted one for the Oneway in another thread and I will add that).

Here is the Oneway Mastercut parabolic flute profile from John...



493511

[Steve Nix]

Thanks for your very informative history and descriptions of the different bowl gouges.

[roger wiegand]

Very interesting, thanks! Do profiles stay the same over time in manufacturing? I have to admit I don't know how such tools are made-- are they ground with an abrasive wheel starting with bar stock? Or is there another method with a more precise cutter to form the flute? If an abrasive wheel, how does the profile of the first gouge cut with a wheel compare to the last? I can imaging the center of the wheel wearing more than the edges, changing the profile.

[Edward Weber]

Thanks, I know that took quite a bit of time and effort to put together.
IMO,
That should be in the site library or at least a sticky in the turners forum.

[roger wiegand]

Or a fleshed out version (eg with fancy artwork) in the AAW magazine!


Thanks, I know that took quite a bit of time and effort to put together.
IMO,
That should be in the site library or at least a sticky in the turners forum.

[Neil Strong]

Do profiles stay the same over time in manufacturing? I have to admit I don't know how such tools are made-- are they ground with an abrasive wheel starting with bar stock? Or is there another method with a more precise cutter to form the flute? If an abrasive wheel, how does the profile of the first gouge cut with a wheel compare to the last? I can imaging the center of the wheel wearing more than the edges, changing the profile.

Roger

With the Henry Taylor Superflutes, which have been around the longest, there has been some changes over time. In the following photos (in order of original, early and later), the flutes profiles remained fairly consistent but the position of the flute in the bar changed later on...


493552

493553

493554



On your manufacturing method question, I also don't know the answer to that. Other forum members may know more on that. I do know that the wording 'milled from bar' was used when gouges were first made from HSS. Grinding and polishing probably followed. That may have changed since the CNC manufacturing came in. The introduction of powdered metals may have also have had an influence on how things are done now.

[Neil Strong]

Thanks for your very informative history and descriptions of the different bowl gouges.

There is of course a lot more to the history of bowl gouge development than their flute profiles.

Steels and grinds are major topics in themselves, but are beyond the scope of this thread.
.

[John Kananis]

What a fantastic post - thank you, Neil for taking the time to put this together.