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Remounting a Twice Turned Bowl

Joined
Aug 14, 2018
Messages
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Location
South Londonderry, VT
Hello All,

I have a several of larger ash bowls, 12+ inches in diameter, that I roughed out last June. I remounted the bowls between the chuck and the tailstock and true up the outside. For some reason I am having a hard time getting the bowl to run true especially out by the rim. Once I think I got it, I mount the bowl in the chuck to do the inside and the bowl is way out of round. The tools are sharp and my tenon is cut clean. I am moving the gouge slowly through the wood, not rushing the cut.

Do I need to mount larger blanks differently? Any suggestions would be greatly appreciated.

Thanks,
-Joe
 
The bowl should run pretty true when you put it in the chuck.
Maybe off a 1/32 or a 1/16.
The inside will be out of round since you mostly cut wood off the outside endgrain sides and take very little wood off the side grain sides. The wall thickness at the end grain ends is a bit more than the thickest wall you can make in the dried bowl.

You can see how this works by going to the returning a dried bowl thread in tutorials and tips..
This thread includes a video of a demo of me returning a dried bowl
http://www.aawforum.org/community/index.php?threads/re-turning-a-dry-bowl.12610/

I rechuck over the slightly opened chuck jaws.
When I do I line up the rim to get the biggest bowl. I almost alway center the grain in the bowl so they warp symmetrically. The two high spots and low spots on the rim are opposite each other. if necessary I shift the bowl where’s it rests against the chuck so that the two high spots are the same distance from the toolrest set parallel to the ways. Then get the two low spots equidistant from the tool rest.
Just needs to be close. Tighten the tailstock

I first cut the rim true this is the most out of balance part. Then true the out side cutting foot to rim. Then true the tenon with clean cuts. I use a spindle gouge.
The bowl will run true if the tenon was cut true. If it’s off a little I will loosen the chuck turn the bowl a little and tighten. It it’s not running tru I tr tapping in the the high spot on the rim and retighten.

If I’m making a thin walled bowl i with final turn the outside after the bowl is in the chuck.
 
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Several things will help but remember this is wood and it compresses differently throughout it's structure. first is to cut your tenon correctly. Don't know what jaws you have but the jaws should grip without opening very far. You want nearly closed so that you have as much jaw as possible touching the wood. Shape your tenon so that the jaws grab the sides and the bottom of the bowl sits on top of the jaws. Stewart Batty has a great video somewhere that explains this very well but I could not find it. Lastly, orient the jaws on the tenon. The best way I've found to describe this is the draw a line on the tenon parallel to the grain. Now draw a line perpendicular to this so it forms an X across the middle. Now orient your chuck so the gap in the jaws touches each line. This way you will have an equal amount of side grain and end grain on each jaw. Ideally this would compress the wood equally on each jaw and perfectly align the bowl. Doesn't always do it but it's as close as it gets.
 
Hi Al,

I am a big fan of your videos and have watched both parts of the twice turned bowl video several times. I have learned a lot from your videos as your methods make sense to me and I use them when turning a bowl. I am wondering if ash is a bit of a pain to turn. I tend to get a lot of bounce on the gouge as I get closer to the rim. I think the constant changing of direction of the grain and the fact that the endgrain is tough as nails adds to the bounce. I don't have this problem when I turn cherry.

Thanks,
 
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Hi John,

I am using #2 dovetail jaws on a Talon chuck (I wonder if I am pushing the limits of the chuck). The diameter of the tenon is about 2 inches. I cut the tenon with a spindle gouge and the tenon sits firmly in the chuck as you described. I need to try orienting the jaws in the X and see if that makes a difference.

Thanks,
 
Another technique on a twice turned bowl is to mount the bowl as centered as possible on the tenon and bring the tail stock in to keep it centered and
turn a recess in the inside of the bowl to allow reverse mounting the bowl on the chuck from the cut recess and then re-cutting a clean tenon or recess on the outside of the bowl on the bottom and remounting on a bowl chuck.

When I rough turn a bowl I always leave a center point indent on the tenon and one on the inside of the bowl this allows remounting the bowl when you are ready to do your second turning after the wood is dry. Certain woods tend to warp a fair amount when they dry, it is critical to have a 10% of wall thickness based on the diameter of the roughed bowl dimension.

Another technique is to rough turn the bowl and leave a center point indent on the inside and outside of the bowl, when ready to turn the bowl for the second time you can use a jamb chuck with a center point on the headstock and bring the tailstock live center up to the indent on the inside of the bowl and recut a tenon on the bowl and remount it with a bowl chuck.

You also need a good sharp tool to true up the out of balance rough turned dry bowl and until you get it close to being true on the inside and outside you will have some vibration which makes it difficult to make your final clean cuts on the bowl. Depending on the wood species you may need to re-sharpen your lathe tools often when you are turning the dry wood bowl.
 
Side grain bowls will generally dry to form an elipse from what was originally circular. This includes the tenon. I always size the tenon to allow turning the tenon back to round using a jam chuck. It doesen't take much, but the bowl, vase, platter, will run true when it's reversed. End grain turnings are somewhat more "well behaved" with regard to drying to retain a circular form. Trying to re-form an eliptical recess is a pain and well-nigh impossible.
 
Hi Al,

I am a big fan of your videos and have watched both parts of the twice turned bowl video several times. I have learned a lot from your videos as your methods make sense to me and I use them when turning a bowl. I am wondering if ash is a bit of a pain to turn. I tend to get a lot of bounce on the gouge as I get closer to the rim. I think the constant changing of direction of the grain and the fact that the endgrain is tough as nails adds to the bounce. I don't have this problem when I turn cherry.

Thanks,
Thanks for the kind words.
The bounce is your problem. You aren’t cutting the bowl round when the gouge bounces you’re following the uneven surface.

When you get bounce stop and get rid of it- feed rate of cut too fast, too much bevel pressure, lathe speed too slow(feed rate related), Dull tool, tool handle not held against your side, cutting over a not round surface,.....

Also the outside wall will be the most oval at the rim
The outside wall near the foot is near round

The ash being harder than cherry just means you need to slow your feed rate, take more cuts of a shallower depth, sharpen the tools more often

When I true the outside of a bowl I work from smooth to rough in short increments 1- 3 inches from foot to rim
Near the foot it is usually easy to get a bevel riding cut. The bevel riding cut feels smooth. As I cut toward the rim I will be cutting a more oval and uneven surface. When the tool feels like it wants to bounce I back the tool toward the foot with light bevel contact. The tool doesn’t cut going backwards but it will feel smooth as it gets over a round area. When it feels smooth push the cut forward slowly - the idea is to cut from the smooth into rough increasing the smooth area. I want cut into the rough area a little to cut the top off the out of round making a transition area between smooth and rough, before the tool starts bouncing in the rough

Each short cut passes over four areas
1 floats over the smooth(tiny depth of cut if any)
2 cuts the transition to smooth
3 cuts a new transition area.
4 get into the rough. - stop

As I work from foot to rim the cut lengths get shorter.
Up near the rim I may be making 8-10 passes over the area before the cut feels smooth.
Once it is all round I make several light cuts from foot to rim improving the curve.

Hope this makes sense
 
I probably cut 90% of the 2nd round on a twice turned bowl mounted in the chuck after truing the tenon. I put a dimple in the tenon center when roughed. Remount with the tail stock locating in the dimple. Use a friction chuck inside the bowl, turn the tenon round, and usually the bowl foot and only the lower 1/4 or less of the OD, then get it in the chuck. The main reason is what you describe - the rim will never be true if I true it then mount in the chuck. I also have a mark on the chuck and make a mark on the bowl to get it back in the chuck in the same orientation since by the time I've completely finished the bowl it will get re-chucked a few times. I follow the same "rules" with tenon shape and location in the jaws as John Lucas described. I don't have any issue with the amount the chuck is open - can be near closed or fully open, hasn't made a difference for me.

Once in the chuck, I "rough" the rim and the outside to ~ round to re-balance, then rough the inside. The rim and OD may go out of true again after the inside cuts release tension. I then work to final shape which can require ID and/or OD cuts, then get finish cuts/sheer scrapes on all surfaces.
 
Hi All,

Problem solved. Al you were right, the bounce was killing me. Once I slowed everything down and took my time, everything went smoothly. I need to print out this thread and keep it on the lathe.

Thank you all for your help.

Looking good! Do more bowls and it will all be in your head memory and muscle memory to pass on to the next new turner.
 
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