Bowl Gouge Flute Descriptors

[Neil S]

I’ve used parabolic bowl gouges for a number of years and wanted to purchase another one late last year. I chose to purchase 3 Robust gouges (3/8”, 1/2”, 5/8”). Errantly I assumed all parabolic grinds were essentially the same with 5/8” bar gouges all having 1/2” flutes, etc.

The 5/8” is my ‘go-to’ bowl gouge and I couldn’t figure out why I kept gravitating back to my Crown 5/8” vs the Robust 5/8”, especially finishing cuts etc. A week or so ago I started investigating further and found the Robust 5/8” flute was significantly narrower leaving the bar on each side of the flute significantly thicker. When I compared to an older Henry Taylor 5/8” I found that was also very similar to the Crown.

Interestingly this same relationship of the flute/bar did not carry to the 3/8” and 1/2” Robust gouges, their flutes were wider more like other parabolics I’ve used and much more comfortable to my use. In fact, the Robust 1/2” bar gouge has a flute nearly as wide as the 5/8” bar Robust gouge. The inconsistency within a manufacturer across bar sizes surprised me a lot.

I don’t know for sure, but I think this is the crux of my preference for the 5/8” Crown over Robust. I want to get another 5/8”, but think I’ll wait a little until I’ve used the Robust even more and see if I can force myself to be more comfortable with it, or if I keep going back to the Crown (I like some other attributes of the Robust including it’s flat top and where it comes from).

Attached are some pics I took before I remembered this thread and so didn’t follow @Neil S conventions. I also apologize for the screenshot pic but I’m having difficulty combining pictures

I’ll also add my thanks again to @Neil S for the info contained in this thread AND my support again of his summarizing all of this into an AAW article

Ron

Many thanks for those details.

I've flipped the images of the end-on view of the flutes so that they can be seen in the same orientation as the others flutes in this thread...

​

And, yes, the Robust 5/8" flute profile is definitely different and is quite close to the original Roy Child flute design (Roy's diagram on left), so has very good pedigree! The Woodfast flute (on right) was also quite close to the that original profile, so the the Robust 5/8"is in good company...

​

Ron, I would persist with that Robust 5/8" for a bit longer. Perhaps vary your grind on it to find the sweet spot for it and for you.

As you have pointed out, the flute profile does make a difference to how the bevel grind interacts with the flute and then on how the gouge performs. Much attention is given to bevel grinds as that is what turners can most readily change and flutes tend to be only mentioned in terms of chip ejection. But, flute profiles are the fundamental factor in cutting edge geometry and how we turn with them, which was the primary purpose of this thread, ie. to raise awareness of flute profiles and getting more clarity into the descriptors we use for them.

Of course, experienced turners can turn with almost any flute profile, but they do not always communicate clearly about the way in which those flute profiles change the way they grind and turn with them. That can also apply to tool makers.

On making this thread into an AAW article, that would be a snapshot of the current situation, but hopefully we will see ongoing developments and new offerings, which a thread like this can include with further updates.

 

[Richard Hodsdon]

Ron
You are bound to get slight variances over time with any bowl gouge manufacturer, Have a look at the Sorby 3/8 bowl gouges picture that I posted on this post a while back.
When you look at the method used (or was used by some manufacturers ) that involved grinding the flute with a profiled grinding wheel , this is to be expected. The grinding wheel is ground to a parabolic shape and then this is used to grind out the flute in the HSS blank. Someone has to dress the wheel and keep its shape over time and although they will use a profile gauge to check the shape there are bound to be changes over time as the shape is not hypercritical as say with a jet engine turbine blade. they probably use a Go No go gauge to check the profile , so anywhere in between is acceptable .
.

 

[Ron Solfest]

@Richard Hodsdon - yeah, I agree. But I was surprised at what I consider normal width flute grinds on the 3/8” and 1/2”, and the fact that the 5/8” flute width is not much wider than the 1/2” gouge flute…leaves a lot of metal on both sides of the 5/8” gouge…

 

[Neil S]

Not wanting to get too side-tracked into gouge manufacture, one explanation for the difference between the flutes on the two Robust gouges is perhaps that the same grinder that was used for the 5/8" was also used on the 1/2", but to a lesser depth on the smaller bar.

When I put the two flutes side by side and adjust the image of the 1/2" so that the ruler in the two images appear at about the same scale, the flute on the 1/2" appears like it would slot neatly into the bottom two thirds of the flute on the 5/8" BG, as shown by the white line that I have drawn across the two flutes...

​

The flutes below the two white lines are almost identical when viewed that way. I know of other instances of similar things being done, but in this case I'm only guessing that is what is happening there.

 

[Richard Hodsdon]

@Richard Hodsdon - yeah, I agree. But I was surprised at what I consider normal width flute grinds on the 3/8” and 1/2”, and the fact that the 5/8” flute width is not much wider than the 1/2” gouge flute…leaves a lot of metal on both sides of the 5/8” gouge…

I noticed that, when I was measuring the flute width for the table I sent NeilS in this post was where do yo measures it as the top pf the flute was rounded and ground down below full diameter of the bar. I think NeilS has nailed the reason for the differences in his reply above,

 

[Ron Solfest]

@Neil S - Thank you again for the time and effort you've put into this! I felt I should at least put a little more effort into it than I did so I took some better pictures (albeit still not dead-on as well as they should have been) and pulled out my micrometer and made some measurements to also include.

Some background reference information:
- all gouges (except HT and BB) are sharpened with a Wolverine jig only varying distance from 8" CBN wheel (angle). 5/8" have ~50deg, 1/2" have ~45deg and 3/8" have ~40deg primary bevel sharpening
- HT has been mostly used up and is now sharpened freehand as a bottom-feeder, angle about 60deg
- BB was purchased only to practice freehand sharpening on (you can see I need more practice
- Heals have all been freehand ground off leaving ~3/16" primary bevel

Measurements

Robust

Crown

Sorby

Henry Taylor

Benjamins Best

in mm

3/8"

1/2"

5/8"

1/2"

5/8"

6mm (3/8")

10mm (1/2")

5/8"

1/2"

Bar width

9.9​

13.2​

16.2​

12.3​

15.5​

9.5​

13.0​

15.9​

12.7​

Flute width

7.8​

9.2​

9.9​

8.4​

10.7​

5.6​

8.6​

10.6​

7.4​

Flute base

3.8​

4.7​

6.0​

4.4​

5.3​

3.5​

4.0​

4.9​

6.7​

Flute width %

79%​

70%​

61%​

68%​

69%​

59%​

66%​

67%​

58%​

Base %

38%​

36%​

37%​

36%​

34%​

37%​

31%​

31%​

53%​

My take-away's at this point are:
- Robust flute grinds appear that the same tool could be used to shape all three bar diameters as you suggested
- Sorby 3/8" flute is much wider at it's base, maybe closer to a U flute than a parabolic? this might explain my relative difficulty in sharpening this using the same process as with all of the others
- I should probably shorten up my primary bevel to about half of what I've been using
- and I'll keep trying with the Robust 5/8" but have less expectation that my next 5/8" will be another one...we'll see

Thanks again for your insights, and effort in cataloging and summarizing all of this data

 

[Ron Solfest]

More pics

 

[Ron Solfest]

And a couple more pics

 

[Neil S]

I felt I should at least put a little more effort into it than I did so I took some better pictures (albeit still not dead-on as well as they should have been) and pulled out my micrometer and made some measurements to also include.

@Ron Solfest, many thanks for all of those very helpful additions to your previous post. The more detail we have like this the better informed we will be when acquiring and using our bowl gouges.

On the Sorby, I let my mine go some time back, but if I can remember correctly and also looking at your photos and measurements, and also those in post #77 by @Richard Hodsdon, the Sorby BGs varied quite a bit and also over time. My take on what I can see there is that their flute profile tended to be parabolic but at times wandered closer to being a wide bottomed V flute, where the upper sides came close to being straight. They may have also made a U profile where the upper sides of the flute were parallel to one another, but if they did, we don't have an example of that posted here (yet?).

 

[hughie]

This thread has taken on a life of its own and that a good thing as there is so much info coming to the fore.

I might have a Sorby U shape, have a couple Hamlets and P&N, but it might be awhile before I get to them.

 

[Matt Miller]

Here is a Crown Pro PM gouge measuring .40” outside with a .20” max flute width.

New to turning and without a good understanding of BG sharpening I have not yet had good results with this tool. Stuart Batty emphasizes straight wings so I’ll fix that and try again. It is ground to 55 degrees using the Wolverine with the leg set at about the mid point. I would sure welcome any advice.

 

[Neil S]

Here is a Crown Pro PM gouge measuring .40” outside with a .20” max flute width.

New to turning and without a good understanding of BG sharpening I have not yet had good results with this tool. Stuart Batty emphasizes straight wings so I’ll fix that and try again. It is ground to 55 degrees using the Wolverine with the leg set at about the mid point. I would sure welcome any advice.

Hi Matt

Welcome to the world of woodturning!

As you post is primarily about how to sharpen your Crown PM bowl gouge and this thread is primarily about gouge flute profiles, I'm going to suggest you start a new discussion thread, repeating what you have posted here, and give it a thread title something like 'Help with sharpening my Crown PM bowl gouge' and I'm sure you will get lots of good advice. I have some thoughts myself, which I'll contribute to your new thread.

Leave what you have already posted here as it adds valuable information to what we have on the Crown bowl gouges flutes, which in the case of your gouge is a V flute and quite different to what we already have here from @Ron Solfest of his Crown 1/2" shown in post #87.

Thank you Matt for your contribution and I look forward to see your new thread on sharpening your Crown Pro PM bowl gouge.

 

[Steve Chaplin]

Here is a Crown 1" PM Pro BG. The bar stock is 1.2", so not sure how this equates to 1", probably the funky English method. Not sure if this is the same BG as Neil posted. It has a 40/40 grind on it. I'll leave it to the experts to categorize it.

 

[Neil S]

Here is a Crown 1" PM Pro BG. The bar stock is 1.2", so not sure how this equates to 1", probably the funky English method. Not sure if this is the same BG as Neil posted. It has a 40/40 grind on it. I'll leave it to the experts to categorize it.

View attachment 56473

It's very good to have that end on view included of your Crown 1" PM Pro BG, Steve

IMO, it definitely has a very nice parabolic flute profile. I really really like the look of it.

Here's my Crown PM with an approx 1" (0.97in) bar dimension and more of a U flute, so my 1" is a very different gouge in every way...



In comparison, here is my Crown 7/8", which has more of a parabolic flute, but still not as sweet as yours!

 

[Steve Chaplin]

It's very good to have that end on view included of your Crown 1" PM Pro BG, Steve

IMO, it definitely has a very nice parabolic flute profile. I really really like the look of it.

Here's my Crown PM with an approx 1" (0.97in) bar dimension and more of a U flute, so my 1" is a very different gouge in every way...

View attachment 56481

In comparison, here is my Crown 7/8", which has more of a parabolic flute, but still not as sweet as yours!

View attachment 56482

Neil, do you think the grind has an effect on how the gouge looks end on?
I think it may. A 40/40 style of grind has flat tops to the wings rather than curved like styles done on a vari-grind setup.

 

[Travis Pagel]

Thank you so much for this post!

 

[Neil S]

Neil, do you think the grind has an effect on how the gouge looks end on?

The grind shouldn't make any difference to the flute profile if viewed directly end on as you have photographed it Steve.

Here is an example of a gouge with the grind that came with it, which I didn't like, and a 2nd photo with most of the bevel & wings ground off, as I'm wont to do before regrinding it!

The flute profile remains the same after most of
the bevel & wings have been ground down.
​

So, when viewed end on, the bevel grind doesn't change the flute profile, however, it does work the other way around. The flute profile is an important determinate of how the gouge will grind to form the cutting edge profile and why having agreed flute descriptors is helpful in any discussion on bowl gouge sharpening.