Twice Turning with 40/40

[James Lee]

I have watched Stuart Batty's method of using a jam chuck to turn the outside of a bowl with a 40/40 bowl gouge without having to use the tailstock. I am committed to using this method of bowl turning. However, I don't understand how this works in regard to a twice turned bowl blank that has warped. Do you finish the inside of the bowl first, and then re-mount it on a jam chuck in order to finish the exterior? Thanks.

 

[Kirk Amidon]

In a similar position. My take would be to mount the bowl with a friction chuck, re-shape the tenon or mortise, rough turn the outside, flip bowl and place into chuck, turn the inside to final. Then do the jam chuck for the last pass on the outside.

Interested in seeing how others would approach this.

 

[Steve Nix]

That’s how I do it

In a similar position. My take would be to mount the bowl with a friction chuck, re-shape the tenon or mortise, rough turn the outside, flip bowl and place into chuck, turn the inside to final. Then do the jam chuck for the last pass on the outside.

Interested in seeing how others would approach this.

 

[Marvin Jones]

I use the 485mm large bowl jaws on a 120 Vicmarc chuck. That's a hair over 19" max, which is close enough to the 20" max of the Powermatic 3520B. I rotate an oval cured bowl until 4 of the rubber stoppers, two on each side of the blank are touching the wood evenly, then snug the dovetail stoppers onto the wood. The other 4 stoppers usually do not touch. Vicmarc says do not turn faster than 600 RPM with these jaws but that is plenty fast enough to true up the tenon or recess with light cuts, I usually turn about 400 RPM. You can use the tailstock for safety. I mount the bowl in the standard jaws for finishing inside and out, except for the bottom of the base. Once finished, I remount the bowl in the large bowl jaws, once trued all eight stoppers grip the bowl and remove the tenon and finish the bottom. I did put double sided tape on the face of the jaws so the finished bowl edge rides on the tape and against the rubber stoppers. I bought two of the Vicmarc 120 chucks, one with standard jaws and keep the bowl jaws in the other.
I'm not a professional nor an expert, this works for me. Some of the other chucks also have pretty close the same type of jaws. This is just one way to skin the cat...

 

[Tim Tucker]

Well, if you are committed to it - I understand. But, what about a hybrid approach to off you more flexibility? I - just last weekend - attended a three-day turning course that was a concentration on bowls, using the 40/40 method and was taught by Ashley Harwood - who uses the Stuart Batty grind, and so on. We made jam chucks - but used them on green wood turned the previous day. Already the warping caused us to need to return the jam chucks. Had the rough turns been left to dry first ... I would think it unlikely that I could get a good fit of a dry, elongated bowl on a round chuck without problems. I am thinking of stressing the wood to the point of breaking, and difficulty in getting the piece balanced.
I much prefer to use a vacuum chuck to remove the foot after the 2nd turn - because I can turn natural edge bowls of almost shape this way. Just a thought ...

 

[Marvin Jones]

I apologize, I misinterpreted the question, please disregard my message.

 

[Gerald Lawrence]

Stuart turns the outside and finishes the inside and then makes the jam chuck to finish the foot. Very interesting to watch and it is thin too. I am just not that adventurous to get that thin and not be able to measure. By the way, the one I saw at SWAT, he forgot to measure the bottom.

 

[James Lee]

I apologize, I misinterpreted the question, please disregard my message.

Marvin, Thanks so much for your post. Even though it didn't quite get at what I was asking, still you offered a lot of great info. I appreciate you taking the time. Jim

 

[Marvin Jones]

Your welcome!

 

[James Lee]

In a similar position. My take would be to mount the bowl with a friction chuck, re-shape the tenon or mortise, rough turn the outside, flip bowl and place into chuck, turn the inside to final. Then do the jam chuck for the last pass on the outside.

Interested in seeing how others would approach this.

Thanks Kirk, I think your approach makes a lot of sense. I have e-mailed Stuart Batty directly to ask him about turning a warped bowl blank also. I'll let you know.

 

[JeffSmith]

Here's my routine for twice turned bowls - and even green to finish most of the time.

When roughing green wood, I typically core from large to small. Before coring, a recess is turned in the face. As the cores come off, the large blank is removed from the chuck and thrown into the boiling pot or set aside to dry. The smaller core is gripped by the recess on the face, a tenon turned and the outside form trued up. Turn and grip by the tenon and pull the next core. Lather, rinse, repeat.

When dry and nicely warped, I use the warped tenon in a chuck (its plenty secure for moderate speeds and light cuts), true up the rim and put a shallow recess in the inside for gripping by a large set of jaws. Turn the bowl around, gripping by the recess, and true up the tenon then work on the outside form. Turn the bowl, grip by the trued tenon and hollow the piece.

In practice, it takes longer to describe than to do - without the drying step... Even though the tenon is warped its typically still a very secure hold - I use smooth dovetail jaws - and haven't lost anything yet after nearly two decades.

 

[Marvin Jones]

Well, if you are committed to it - I understand. But, what about a hybrid approach to off you more flexibility? I - just last weekend - attended a 3 day turning course that was a concentration on bowls, using the 40/40 method and was taught by Ashley Harwood - who uses the Stuart Batty grind and so on. We made jamb chucks - but used them on green wood turned the previous day. Already the warping caused us to need to re-turn the jamb chucks. Had the rough turns been left to dry first....I would think it un-likely that I could get a good fit of a dry, elongated bowl on a round chuck without problems. I am thinking stressing the wood to the point of breakage, and difficulty in getting the piece balanced.
I much prefer to use a vacuum chuck to remove the foot after the 2nd turn - because I can turn natural edge bowls of almost shape this way. Just a though

I haven't watched Ashley a lot but am working on the 40/40 grind. Stuart makes removing wood from a bowl like me peeling a potato...and yes, I need to get out of my routine of just turning green bowls, curing and second turning them. I just watched a video of him turning on a clubs Powermatic, he was talking about a vibration caused by trash being between the headstock and the bed that I will check out tomorrow on mine. I've always wanted to turn a few boxes, never have and it appears I will more than likely need to use different chucking methods to complete those. When I first started turning I turned a few natural edge bowls, goblets and have the perfect opportunity now as I just picked up a trailer load of some of the prettiest black walnut, not huge pieces but really figured just right for natural edge, love the way the white ring follows the edge all the way around. I do have a nice vacuum system set up but rarely use it, mainly when I finish a bowl the edge does not lend itself to be safely held by the rubber stoppers in the big bowl jaws. I once finished an ash bowl so large it would not fit on the big jaws, cleared the bed by a 1/4", vacuum chuck worked great on that one,but rarely turn big bowls any longer, not much of a demand for them.

 

[Tim Tucker]

Marvin-
Stuart Batty has been quoted as saying that the Johannes Michelson grind is almost the same as Stuart's 40/40. Johannes sells a fixture that allows you to jig up your gouge - and get a consistent grind every time. I have been hand grinding the 40/40 lately and using the Johannes Tool fixture. I can't find a difference that is worth noting - other than the consistency favoring the Johannes fixture and me wasting less steel with it than when I hand grind - then re-grind to correct the first attempt.....
I love the challenge of turning big stuff, and when it is a great piece of wood - it is impressive. But, around 14" seems to be the sweet spot for size as most people cannot accommodate anything larger than that in their cabinet if they want to store the bowl. Otherwise...it becomes a "centerpiece"....since they can't put it away anywhere.

 

[robo hippy]

Well, back to the original question. You can't really remount a warped bowl on a jamb chuck the way that Stuart does with his once turned bowls. You do need a center point on a tenon, from the tailstock preferably, since the tenon will warp. You reverse chuck it with some thing firm and probably padded on the inside of the bowl, and the tailstock engaged. The rim of the bowl is not on any firm surface. Then you true up the tenon. I think a lot of turners will then finish turn the outside, or at least true it up, then reverse and turn finish turn the outside, and then finish turn the inside.

I switched to the 40/40 grind some time ago. I never use a swept back gouge any more. The 40/40 and a number of different BOB tools to finish the inside. I do prefer a shear scrape for my finish cut on both inside and outside of the bowl. I have a video up about that.

robo hippy

 

[Doug Freeman]

Stuart Batty’s purpose of the jam chuck is to turn a thin walled bowl with his signature 40/40 grind, without shear scraping etc. The jam chuck stops the thin wall vibration that otherwise prevents a clean cut.

With a warped 2-turn thick wall bowl, get the tenon/shoulder returned. It's very helpful to have a center mark in the tenon from the original turn. I have some friction chucks I use, or sometimes just use jaw tops as the friction source. I don't turn much of the outside of the bowl at this point. The friction chuck is exerting uneven pressure on the ID since it is warped, between this and the chucking process there are times when the OD has runout after chucking. Next cut the top of the rim even, then trim up the OD, but not completely. Just remove ~95% of the warp. This removes excess thickness and stress. I've had plenty of 2 turn bowls where I finish cut the ID or OD, then started working the other side, and the 1st side developed runout from the stress reduction. Next finish the ID. Next fit the bowl to the jam chuck and finish the OD. I have not actually done Stuart's method, but these steps will most accurately follow his method. I just never wanted to mess with the jam chuck.

I've used 3 other methods to reduce wall vibration - 1) hand pressure, 2) friction chuck placed 1/2 way or further up the wall, 3) a steady rest wheel putting pressure on the opposite wall. These work with varying degrees of success, but none of them allow the OD cut to be made with a 40/40 gouge push cut as Stuart does, since the HS or TS is going to be in the way, depending how the bowl is mounted. I'm ok using a pull cut and shear scraping to get there. I've demonstrated to myself I don't have the level of tool control to not have to so some scraping anyway.

 

[hockenbery]

I use the 40/40 on platters where there is no tailstock in the way and I’m single turning dry wood.

With warped dried bowls. The Ellsworth grind is my choice.

I use the center point in the tenon and do a friction drive jam with the slightly opened jaws of the chuck against the inside bottom of the bowl. Resting on the open jaws is usually rock solid. In the rare case where I sense a tiny wobbly i open the jaws a bit more or close them a bit to find a solid no wobble.

I adjust where the bowl rests on the jaws so that the edge of the 2 high points on the rim are centered(= distance to the tool rest set parallel to the ways) and the 2 low point edge centered.

This gives me the largest bowl I can return from the warped bowl. With this centering I will take equal amounts of wood off the endgrain wall and close to no wood off the side grain wall.
The chuck jaws give a solid drive.
1. True the top of the rim ( flatten it ) with push cuts toward the tailstock. This removes most out of balance part.
2. Return the outside wall foot to rim
3. True the tenon to about 2” ( near the perfect circle) my rough out tenons are 2.5” so the dry oval tenon is about 2.5 x 2.25

Mount in the chuck. Test for tuning true - it usually does. If it is off looses the chuck and turn the bowl as quarter turn tighten and check.n. If that didn’t fix it tap the rim lightly with the lathe running with the tool handle if it runs true tighten the chuck a bit.
If that doesn’t fix it I will return the outside.

Then turn the top of the rim
Then turn the inside.

This thread has a demo video of me returning a really warped dried sycamore bowl.

Working with green wood

The August 2015 AAW JOURNAL has great article by David Ellsworth on working with green wood. This is followed by 11 marvelous ways turners turned cracks into features. One of David's themes is that the deck is stacked against newer woodturners successfully working with wet wood. Might be a nice...

www.aawforum.org

 

[Tim Tucker]

THIS is deserving of a video Al!!!

I use the 40/40 on platters where there is no tailstock in the way and I’m single turning dry wood.

With warped dried bowls. The Ellsworth grind is my choice.

I use the center point in the tenon and do a friction drive jam with the slightly opened jaws of the chuck against the inside bottom of the bowl. Resting on the open jaws is usually rock solid. In the rare case where I sense a tiny wobbly i open the jaws a bit more or close them a bit to find a solid no wobble.

I adjust where the bowl rests on the jaws so that the edge of the 2 high points on the rim are centered(= distance to the tool rest set parallel to the ways) and the 2 low point edge centered.

This gives me the largest bowl I can return from the warped bowl. With this centering I will take equal amounts of wood off the endgrain wall and close to no wood off the side grain wall.
The chuck jaws give a solid drive.
1. True the top of the rim ( flatten it ) with push cuts toward the tailstock. This removes most out of balance part.
2. Return the outside wall foot to rim
3. True the tenon to about 2” ( near the perfect circle) my rough out tenons are 2.5” so the dry oval tenon is about 2.5 x 2.25

Mount in the chuck. Test for tuning true - it usually does. If it is off looses the chuck and turn the bowl as quarter turn tighten and check.n. If that didn’t fix it tap the rim lightly with the lathe running with the tool handle if it runs true tighten the chuck a bit.
If that doesn’t fix it I will return the outside.

Then turn the top of the rim
Then turn the inside.

 

[hockenbery]

THIS is deserving of a video Al!!!

There is one. My working with green wood demo. Has 3 parts.
1. Slide show about wood movement
2. Rough turning a green bowl to dry
3. Returning a dried bowl

Working with green wood

The August 2015 AAW JOURNAL has great article by David Ellsworth on working with green wood. This is followed by 11 marvelous ways turners turned cracks into features. One of David's themes is that the deck is stacked against newer woodturners successfully working with wet wood. Might be a nice...

www.aawforum.org

 

[Marvin Jones]

As usual, great info from you guys, the only thing I hear occasionally that scares me is a 2" tenon on a bowl, I will turn a 2 1/2" but prefer a 3" which fits great with the size base I like on my bowls. I have no data or failures that made me want the larger tenons, just a 'me' thing...by the way, my Rikon 1HP grinder came in, haven't bought the CBN wheels yet, building my coins up though. Can't believe the difference the low speed and a little finer grit of the aluminum oxide wheels versus my old tool steel grinder. My chisels are already staying sharper quite a bit longer, maybe because they are not getting as hot when sharpening? I haven't upgraded, still using HSS.

 

[Tim Tucker]

There is one. My working with green wood demo. Has 3 parts.
1. Slide show about wood movement
2. Rough turning a green bowl to dry
3. Returning a dried bowl

Working with green wood

The August 2015 AAW JOURNAL has great article by David Ellsworth on working with green wood. This is followed by 11 marvelous ways turners turned cracks into features. One of David's themes is that the deck is stacked against newer woodturners successfully working with wet wood. Might be a nice...

www.aawforum.org

Somehow...I thought - there must be one THANKS AL!

 

[Steve Chaplin]

When dry and nicely warped, I use the warped tenon in a chuck (its plenty secure for moderate speeds and light cuts), true up the rim and put a shallow recess in the inside for gripping by a large set of jaws. Turn the bowl around, gripping by the recess, and true up the tenon then work on the outside form. Turn the bowl, grip by the trued tenon and hollow the piece.

This is brilliant. I use 40/40 and have tried a lot of methods to re-chuck twice turned bowls. Including jam chucks or disk shaped vacuum chuck plates inside the bowl for support. Also tried truing the tenon chucked that up and then used a bevel rubbing pull cut on the outside. But I prefer using the 40/40 as I turn a lot of spalted wood and the cut is much better. Jeff, your method allows re-turn on the outside with no tailstock and a 40/40. I am stealing this from you for sure!

The Batty method of jam chucking for the final cut I find time consuming. I also would rather do the final pass on the inside of the bowl because that seems to give better results. Maybe I'm doing something wrong or just have not mastered the final on the outside. I turn a lot of thin bowls and use a Oneway Bowl Steady to remove vibration for the final pass on the inside.

 

[James Lee]

Marvin-
Stuart Batty has been quoted as saying that the Johannes Michelson grind is almost the same as Stuart's 40/40. Johannes sells a fixture that allows you to jig up your gouge - and get a consistent grind every time. I have been hand grinding the 40/40 lately and using the Johannes Tool fixture. I can't find a difference that is worth noting - other than the consistency favoring the Johannes fixture and me wasting less steel with it than when I hand grind - then re-grind to correct the first attempt.....
I love the challenge of turning big stuff, and when it is a great piece of wood - it is impressive. But, around 14" seems to be the sweet spot for size as most people cannot accommodate anything larger than that in their cabinet if they want to store the bowl. Otherwise...it becomes a "centerpiece"....since they can't put it away anywhere.

Tim, I have found Ron Brown's jig really helpful regarding the 40/40 grind. I had trouble doing the 40/40 free hand also. Here is a link

View: https://www.youtube.com/watch?v=dcFIZ5Bx4t8

 

[Kirk Amidon]

This has been a great thread to come back to, so many approaches to solving the challenge. Can definitely see trying some different processes, as some may be both faster and provide a better outcome than my approach. Looking forward to trying different methods.

 

[Tim Tucker]

Tim, I have found Ron Brown's jig really helpful regarding the 40/40 grind. I had trouble doing the 40/40 free hand also. Here is a link

View: https://www.youtube.com/watch?v=dcFIZ5Bx4t8

I have the Ron Brown jig. I do not like it. I love the Johannes Michelson set up. The Ron Brown stuff is plastic, and very cheap feeling. Michelson's is machined, all metal - and easier to use than the Ron Brown stuff. And - the Michelson is the grind that Stuart Batty has said is closest to his hand grind.

 

[Doug Freeman]

FYI the tormek gouge jig produces a decent 40/40 grind as well. It is similar to the Vector jig and v- arm. The Vector set up moves the jig pivot off center to each side, increasing the wing bevel angle vs being in the center(like a varigrind). The tormek jig slides to each side. The result is similar, but I’ve not had a Vector ground gouge to measure to know just how similar.

 

[robo hippy]

Any one tried Dennis Gooding's method of using the Wolverine that he posted in the tips and techniques section here? Since I don't use a Wolverine set up, it didn't make a lot of sense to me. I will be trying to figure out how to make one that will work for the 40/40, but it will take a year or so.... The part the gouge fits into needs to be able to rotate independently of the pivot arm....

robo hippy

 

[Dennis J Gooding]

The method that robo hippy refers to is described in my post

"40/40 Grind Using the Oneway Varigrind Jig"​

in the Tips and Tutorials Forum April 09, 2010. It involves about five minutes of filing with a round file to extend the length of the circular slot by about a quarter of an inch to allow a smaller minimum arm angle. This presumes that a 1.75 inch gouge protrusion is used. The Ron Brown approach produces the same result but requires a much larger gouge protrusion, thus considerably reducing the useful lifetime of the gouge.

 

[Timothy White]

The problem with trying to use varigrind to grind to make a 40-40
there is side to side swing but little to no gouge rotation. Robo is right on with his statement that the gouge needs to rotate as it swings. Watch Stewart’s sharpening videos where camera is looking straight down on the gouge and watch the flute rotate as the goug swings.
The Vector grind (Michelsen grind) when using the two offset points allows the flute to rotate a full 360 degrees (180 degrees on each point) while swinging. The 40-40 doesn’t need as much rotation as the Hannes grind but it needs more rotation than Varigrind can provide

 

[Tim Tucker]

Timothy - Yep! If using the Michelson Vector - you do not need to rotate as far to produce "normal" 40/40 wings. I have compared the grind from platform grinding to the Vector - and they are so close that I seriously doubt any significant difference in use can be found.

 

[Dennis J Gooding]

The problem with trying to use varigrind to grind to make a 40-40
there is side to side swing but little to no gouge rotation. Robo is right on with his statement that the gouge needs to rotate as it swings. Watch Stewart’s sharpening videos where camera is looking straight down on the gouge and watch the flute rotate as the goug swings.
The Vector grind (Michelsen grind) when using the two offset points allows the flute to rotate a full 360 degrees (180 degrees on each point) while swinging. The 40-40 doesn’t need as much rotation as the Hannes grind but it needs more rotation than Varigrind can provide

Timothy, I disagree. There IS rotation of the gouge and just the right amount over the course of the swing. At the two extremes of a swing you will note that flutes point in almost opposite directions.

 

[Gerald Lawrence]

I have always used the method Jeff described by using the warped tenon to return the bowl. I may not get the largest possible bowl but rarely have any problems from this method.

 

[Donna Frazier]

In sharpening the 40/40 grind...what ya'll are forgetting to consider is which flute shape the gouge you are trying to grind is. Flute shape don't matter with JoHannes Michaelson grind but it does matter in grinding a 40/40 gouge.

 

[Doug Freeman]

Timothy - Yep! If using the Michelson Vector - you do not need to rotate as far to produce "normal" 40/40 wings. I have compared the grind from platform grinding to the Vector - and they are so close that I seriously doubt any significant difference in use can be found.

How far from centerline are the pivot points for the Vector base arm?

 

[robo hippy]

Well, I have no experience with the Michelson Vector grind set up, but with any V shaped flute, if you spend too much time just to either side of the nose/flutes 5 minutes to either side, you will get that bird's beak.

robo hippy

 

[Tim Tucker]

How far from centerline are the pivot points for the Vector base arm?

Been in Texas all week. Will check when I get back in a couple of days

 

[john lucas]

I calculated the distance using a photo of the vector grind. I know the support bar is 3/4" or .750". So I measured the photo I printed off my computer and interpolated. Later I went to a friends house who had a Vector grind and all of my holes were dead on.

 

[Doug Freeman]

I calculated the distance using a photo of the vector grind. I know the support bar is 3/4" or .750". So I measured the photo I printed off my computer and interpolated. Later I went to a friends house who had a Vector grind and all of my holes were dead on.

Remember the distance off center?

 

[Tim Tucker]

Hey Doug I am home now…. When you say off - center….I can go down to the lathe room and get some measurement in just a few minutes and will post.

 

[Tim Tucker]

@Doug Freeman
Center of grinder shaft to base height is 6-1/2”. Using thr Wolverine gouge holder with a 2” protrusion. I round the bottom of that piece so it pivots in the divots more accurately.Used a stop collarto help me with consistency as seen in the photo. Any other measurements needed please let me know.

 

[Doug Freeman]

@Tim Tucker thanks, that is useful. What I’m also after is the distance of the off-center dimples from the center dimples in the arm base plate. Just turn your tape 90 deg and shoot from directly above.