Flute Shape and 40/40 Grind

[Izzy Charo]

Hello, I'm interested in obtaining a couple of new bowl gouges and grinding them to Stuart's 40/40 grind. I have a couple of questions: First, for those who have mastered doing this grind free-hand, and have also tried Ron Brown's jig, do you think that Ron's jig faithfully reproduces the grind? Second, which gouge to buy? I believe Stuart recommends a parabolic or V-shaped flute, with a preference for the parabolic flute... Has anyone done this grind on either a Thompson or Carter and Son V-shaped flute, and were you happy with the result? Thanks for the advice!!
Izzy Charo

[Don Stephan]

With a grinder platform, the 40/40 grind is very straightforward, easy to complete, and easy to evaluate. Yes, I have been sharpening freehand for years and experienced a very long learning curve, in large part due to lack of detailed instructions. Mr. Batty's instructions and demonstrations are very detailed and descriptive. With some practice, you may find you can sharpening freehand as fast or faster than installing the gouge in a jig and preparing to sharpen, making turning a more enjoyable experience and pehaps leaving you willing to sharpen more often.

[Brian Deakin]

Stuart has this video on you tube

https://www.youtube.com/watch?v=fhlMQr7Hk0k&t=258s&ab_channel=DeniseSawyer

Additional notes
(1)Use marker on tool to identify where you have sharpened
(2) Use light pressure

Notes I found someone (not Stuart)posted about their approach to 40.40 grind you may find useful




Start by marking a 40 degree angle to each side of your grinding platform, meaning 40 off the perpendicular center line of your wheel.
Set the gouge on the grinding platform with the flute closed (open?) to the right and align the axis of the gouge with the 40 degree line on the right side of the platform
Keep the flute closed to the right as you move the handle of the gouge from 40 degrees down most of the way to maybe 10 degrees - don't start rotating the gouge until you get down there. (This is what I screw up most often and I wind up with a pointed gouge instead of a rounded nose).
Once you reach about 10 degrees off the perpendicular center line of the stone, roll the gouge open upward as you come down the last 10 degrees. So sweep the handle to bring the gouge to 0 degrees and roll the gouge from closed to the right to open upward.
Bring the grind a little past center but don't try to continue the grind very far to the left.
Now align the gouge on the left hand 40 degree line of the grinding platform, flute clolsed to the left and repeat the operation.
Your two grinding passes should overlap a bit in the center of the grind.

Stuart often makes a pass or two with the flute open upward from 10 or 15 right to the same amount left to blend the final grind.

I have the most trouble when I get to near the perpendicular center line - I have to be quite careful and use a light touch to avoid burning the edge. Not that being ham fisted works well for me anywhere during the grinding process!

I would recommend just practice freehand and use light pressure so you simply remove the marker and hold the tool up to the light and rotate is you see a glimmer of light on the edge you have not fully sharpened
THE TOOLS IS SHARP WHEN YOU CANNOT SEE THE EDGE
A common mistake when learning this grind is spending too long on the tip Focus on the wings first then use light pressure on the tip
Examine the tip before use and check you do not have a birdsbeak at the tip

hope this helps

[roger wiegand]

Very useful thanks! One note, "burning the edge" pretty much isn't an issue with high speed steel. It's really hard to heat it hot enough by grinding to affect the temper.



Stuart has this video on you tube

https://www.youtube.com/watch?v=fhlMQr7Hk0k&t=258s&ab_channel=DeniseSawyer

Additional notes
(1)Use marker on tool to identify where you have sharpened
(2) Use light pressure

Notes I found someone (not Stuart)posted about their approach to 40.40 grind you may find useful




Start by marking a 40 degree angle to each side of your grinding platform, meaning 40 off the perpendicular center line of your wheel.
Set the gouge on the grinding platform with the flute closed (open?) to the right and align the axis of the gouge with the 40 degree line on the right side of the platform
Keep the flute closed to the right as you move the handle of the gouge from 40 degrees down most of the way to maybe 10 degrees - don't start rotating the gouge until you get down there. (This is what I screw up most often and I wind up with a pointed gouge instead of a rounded nose).
Once you reach about 10 degrees off the perpendicular center line of the stone, roll the gouge open upward as you come down the last 10 degrees. So sweep the handle to bring the gouge to 0 degrees and roll the gouge from closed to the right to open upward.
Bring the grind a little past center but don't try to continue the grind very far to the left.
Now align the gouge on the left hand 40 degree line of the grinding platform, flute clolsed to the left and repeat the operation.
Your two grinding passes should overlap a bit in the center of the grind.

Stuart often makes a pass or two with the flute open upward from 10 or 15 right to the same amount left to blend the final grind.

I have the most trouble when I get to near the perpendicular center line - I have to be quite careful and use a light touch to avoid burning the edge. Not that being ham fisted works well for me anywhere during the grinding process!

I would recommend just practice freehand and use light pressure so you simply remove the marker and hold the tool up to the light and rotate is you see a glimmer of light on the edge you have not fully sharpened
THE TOOLS IS SHARP WHEN YOU CANNOT SEE THE EDGE
A common mistake when learning this grind is spending too long on the tip Focus on the wings first then use light pressure on the tip
Examine the tip before use and check you do not have a birdsbeak at the tip

hope this helps

[Izzy Charo]

Thank you for this extremely useful and detailed reply! Lots of great information!

[Reed Gray]

Parabolic flutes work fine. I have mostly Thompson and D Way tools, both of which are kind of an open V flute, and the 40/40 grind works well on them. You do need to pay a bit of attention when rolling from the nose to the wing. You kind of do a quick flip when going through that area. If you spend too much time in that transition area, you can get a 'bird's beak' dip in the bevel. I think I cover that in my sharpening video. The U shaped flutes, more common as BOB (bottom of bowl) gouges do not work for the 40/40 grind. I have viewed a video, I think, about the Ron Brown jig set up, and it is supposed to work. What I didn't like about it is that you need 3 inches protruding from the jig. A problem when your gouge gets short. Dennis Gooding, over on the AAW forum has a method for using the Wolverine jig and a 2 inch protrusion in the Tips and Techniques part of that forum. Since I don't use the Wolverine, it didn't really make sense to me. I just use the platform that I used to make. If you turn a lot, the skills you use for 'free hand' or platform sharpening are the same that you use when turning.

robo hippy

[Brian Deakin]

Sorry

The point I was trying to make is not about burning the edge but creating a bird,s beak dip in the nose on the gouge if you spend to much time or place too much pressure on the tip

other believe I Stuart has said you can get close to a 40..40 grind with Johannes Michelson vector Jig

https://www.youtube.com/watch?v=eleN0SfdeYU&ab_channel=JoHannesMichelsen

[Neil Strong]

I find the true parabolic flutes take the 40/40 grind best for me.

[Jeffrey J Smith]

I've used the jig that Ron Brown sells and found it works well to produce a version of the 40/40 grind. The drawback is that it requires a 3" stickout, making it unusable for those older (shorter) gouges I wanted to 'practice' on without trying to find a way to hold the tool securely. I had bought a couple of gouges from Robust to see how they compare with the D-Way and Thompson tools I've used for many years. The nice thing about them is that they have a flat machined on the top the full length of the tool - from the end of the flute back that allows use of the varigrind when the flute gets extremely short. It also allows the 3" stickout on shorter tools. I do like the Robust gouges - they seem to hold an edge about the same as the D-Way and Thompson tools for the most part, and the profile is closer to a true parabolic shape to my eye. Not sure about the steel composition or the benefits of nitriding, but I like using the tools both with my usual grind and now with the 40/40 version I get with RB's jig.
I've had a couple people that have taken Stuart's classes remark that the grind is very close. Seems to work well for me. It was easy to setup using Ron's instructions.

[tom lucas]

Parabolic flutes work fine. I have mostly Thompson and D Way tools, both of which are kind of an open V flute, and the 40/40 grind works well on them. You do need to pay a bit of attention when rolling from the nose to the wing. You kind of do a quick flip when going through that area. If you spend too much time in that transition area, you can get a 'bird's beak' dip in the bevel. I think I cover that in my sharpening video. The U shaped flutes, more common as BOB (bottom of bowl) gouges do not work for the 40/40 grind. I have viewed a video, I think, about the Ron Brown jig set up, and it is supposed to work. What I didn't like about it is that you need 3 inches protruding from the jig. A problem when your gouge gets short. Dennis Gooding, over on the AAW forum has a method for using the Wolverine jig and a 2 inch protrusion in the Tips and Techniques part of that forum. Since I don't use the Wolverine, it didn't really make sense to me. I just use the platform that I used to make. If you turn a lot, the skills you use for 'free hand' or platform sharpening are the same that you use when turning.

robo hippy


Reed,
I find the AAW website difficult to navigate and find things. Can you point me to the Dennis Gooding article you reference. thanks.

[Reed Gray]

Tom, found it, about 3 pages back.

https://www.aawforum.org/community/threads/40-40-grind-using-the-oneway-varigrind-jig.17005/

The real difference between any gouge grind and jig grinds seems to be that the wings have a much more acute angle when using a jig. You can't roll the tool over enough to the sides to get the stronger/thicker wing angles. I don't think it would be too hard to make a set up where the gouge is seated in a tube, and there is a stop to keep it rotating too far, but still be able to roll it over to the point where you have a thicker wing. Maybe more like the Tormek set up, which is closer than the Wolverine.... Maybe I will invent it some time....

robo hippy

[Brian Deakin]

Best link for Stuart Batty

http://www.dmwoodturners.com/?page_id=642

[tom lucas]

Tom, found it, about 3 pages back.

https://www.aawforum.org/community/threads/40-40-grind-using-the-oneway-varigrind-jig.17005/

The real difference between any gouge grind and jig grinds seems to be that the wings have a much more acute angle when using a jig. You can't roll the tool over enough to the sides to get the stronger/thicker wing angles. I don't think it would be too hard to make a set up where the gouge is seated in a tube, and there is a stop to keep it rotating too far, but still be able to roll it over to the point where you have a thicker wing. Maybe more like the Tormek set up, which is closer than the Wolverine.... Maybe I will invent it some time....

robo hippy

Thanks Reed. I think I'll keep doing my 40/40 manually. Getting good cutting results. So, why change?

[Neil Strong]

I think I'll keep doing my 40/40 manually.

The advantage of a jig is that it should ensure that you get the grind right each and every time, at least until you know that you are getting it right and familiar with how it should perform.

The disadvantage of a jig is the extra time it takes to put it on and off the gouge. Platform sharpening is quicker, if you can get it right first time every time.

I hand sharpened gouges for decades before gouge jigs came along. I much prefer to use jigs now for my bowl gouges other than on the almost straight across grind on SRGs and the 40/40 grind, which are both simple grinds. Other than the 40/40, the grinds that I use on my bowl gouges are more complex and difficult to repeat accurately. Using a jig with CBN wheels gives accuracy and repeatability, but it also saves on valuable steel. I know how much steel is unnecessarily lost through hand sharpening and for me any extra time taken to jig up is worth it. That may not be the case for a production turner.

The area of the gouge that I concentrate on when doing the 40/40 grind with the platform is the bottom inside of the flute nearest the platform. I like it to be parallel to the platform. That area is not so easy to see as only some of it is exposed when the gouges is rolled over. It is also easier to judge with a straight sided flutes and a bit more judgement is required with the continuous flute curve on the parabolics. A good light helps. If you have an aluminium platform a long thin magnet attached to the bottom inside flute can initially help get the required amount of roll over, at least until you are confident you have that right. The proportion of exposed bottom flute to the width of the gouge is the reference I now use. It is 1:3 on some of my gouges. You need to be looking perpendicular to platform when doing that. Depending on your flute profile, the proportions may be different for you.