Bowl shape questions #2

[Jamie Straw]

OK, this is a different bowl than I posted about yesterday, but has problems I'm trying to avoid. At least it seems to me there are problems. Second turning on this dry piece of apple. The bowl looks like it's "leaning" -- one side longer than the other -- and the thickness of the rim varies by a visually detectible amount. Wondering what I did to cause these.

Here's the rim shot....


The outside shape looks asymmetrical to me:

 

[Charlie Knighton]

when u returned the bowl it was offcenter compared to the first turning.......this also can happen while turning the form the first time if the turning moves in the chuck........so turning it the second time u need to return the tendon to make it round......I always start between centers so I can use the holes to center it .....if you use a faceplate with say 4 inches of waste wood u can avoid this but could increase the chance of cracking.......when u have something like that happen it is an opportunity to wing it......most turners strive for perfection, thus making their turnings the same as others....especially if they use the same finish

 

[Charlie Knighton]

uneven rim thickness.......entered in mixed media completion......did not win, but enjoy the piece......I do not attempt to turn the top of jar......by not turning the top of the blank, the sides can vary in height up to an inch and add to the sense of leaning.....the piece is still in the show for another 2 weeks or I would give you a better picture of rim....I drew the eye to the rim with the yellow rim but not to the difference in thickness to a nonwoodturner

 

[hockenbery]

Jamie,
Many things can cause and contribute.

I turn the outside of the bowl and true the tenon with the dried bowl jamb chucked over the open chuck
I put it in the Chuck and before hollowing I put a thumb on the tool rest and turn the bowl by hand checking that it touches evenly all around. I test it running at low speed. It must run true on the outside to get an even wall.
Adjusting in the Chuck may make it run true if not I will true the outside while in the Chuck.

You may have turned the outside oval.
The outside can be turned and sanded oval.
It warped oval and too much bevel pressure will have a tendency to follow the oval contour instead of cutting the high spots. Any bounce in the tool is likely following the oval outside contour rather than turning off the high spots.
Light cuts light bevel pressure. Cutting foot to rim. It is least warped near the foot. So it urn it round near the foot to begin truing the outside. Once a round surface is formed there each smoothing cut moves from smooth to rough a making the smooth little further toward the rim. Bevel rides nicely on the smooth and then cuts into the rough a little bit.

Same thing with sanding. Too much pressure can create an oval or follow an oval.
softer side grain can be sanded away faster than the harder endgrain. Softer wood in different parts of the bowl can sand away faster than harder wood.

In your bowl the void from the hollow can contribute to the sanding or turning going more deeply with too much pressure on either side of the opening. Plus the wood is likely softer on either side.


Number one be sure the outside of the bowl is round and run it true before hollowing.

Al

 

[Odie]

I think Charlie was hinting at this......but, some people will look at the uneven rim, and consider it artistic, aesthetic and desirable.

Jamie, I realize you just want to know why the uneven rim happened, and you are getting some good advice.....but, you should realize that the observer may not see your bowl as you do. Even though it's not the kind of turning I do, I do see that bowl as very appealing WITH the uneven rim. The natural edge gives the observer a sense of "natural", and the uneven edge contributes to the appeal.....IMHO, of course!

ko

 

[Gerald Lawrence]

I cannot speak for the rim, but as to the outside. It is difficult to tell from the pic as the grain on one side sort of drops or does not match the level of the other side . Then the left side is where part of the rim has the void, So I think part of the out of round I see may be an optical illusion. To verify you can make a template cutout of the profile on one side and match that to the other side.

 

[Jamie Straw]

I turn the outside of the bowl and true the tenon with the dried bowl jamb chucked over the open chuck

I attempted to do this -- still figuring out how to have the rough bowl as centered as possible via jamb chuck. Getting it mounted correctly for this part has been elusive.

It warped oval and too much bevel pressure will have a tendency to follow the oval contour instead of cutting the high spots. Any bounce in the tool is likely following the oval outside contour rather than turning off the high spots.

I can't remember how gently (or not) I turned the outside, having done this final turning 2 weeks ago. I watched your natural-edge video again today, with a new eye because the last time I watched I had attempted half the bowls that I've turned now.

Cutting foot to rim. It is least warped near the foot. So it urn it round near the foot to begin truing the outside. Once a round sirface is formed there each smoothing cut moves from smooth to rough a making the smooth little further toward the rim. Bevel rides nicely on the smooth and then cuts into the rough a little bit.

These details really help, and watching the video. I'm pretty gentle now with the sanding, learning-learning.

I put it in the Chuck and before hollowing I put a thumb on the tool rest and turn the bowl by hand checking that it touches evenly all around. I test it running at low speed. It must run true on the outside to get an even wall.

For natural edge bowls, it seems a huge factor to make this happen is how the blank is cut originally, yes? Aren't they often irregular (higher here than there or everywhere)? Perhaps the next time I go to Mr. Mentor's shop, I'll take 3 or 4 NE blanks and get some hands-on help. Getting late here, not thinking straight. Will re-read tomorrow! Thanks.

 

[Jamie Straw]

I cannot speak for the rim, but as to the outside. It is difficult to tell from the pic as the grain on one side sort of drops or does not match the level of the other side . Then the left side is where part of the rim has the void, So I think part of the out of round I see may be an optical illusion. To verify you can make a template cutout of the profile on one side and match that to the other side.

Great idea Gerald, I'll do that tomorrow. I tried getting an angle on the two sides, not useful.

 

[Jamie Straw]

I think Charlie was hinting at this......but, some people will look at the uneven rim, and consider it artistic, aesthetic and desirable.

Jamie, I realize you just want to know why the uneven rim happened, and you are getting some good advice.....but, you should realize that the observer may not see your bowl as you do. Even though it's not the kind of turning I do, I do see that bowl as very appealing WITH the uneven rim. The natural edge gives the observer a sense of "natural", and the uneven edge contributes to the appeal.....IMHO, of course!

ko

Thanks, Odie, I like this bowl, it came off our ancient apple tree that fell (a small limb for this bowl), and the voids are aesthetic to moi. Mainly, I want to learn from it so I can waste less wood making mistakes down the line. I killed a plum bowl today, foot cracked while it was in the chuck. Might be for the best since the rim on that one wasn't looking great.

 

[Bill Boehme]

Like Odie said, everybody has a different opinion. Plus, the 2-D photos aren't conveying the 3-D issue well enough for me to follow how your words and the pictures match up. So I'll just give my personal thoughts about it. My number one opinion is that a bowl should have either a natural edge or a smooth edge, but half and half just doesn't tug my chain. Also the height to diameter proportion isn't to my liking. Right now it looks like a vase the seems too short.

Instead of using an orthographic view in the photos, try a more natural perspective.

There appears to be ample thickness to make the foot diameter smaller and shorten the height to get rid of the remaining natural edge. Natural features need to "fit" into the overal design and not just happen to be there. Think of Al's natural edge hollowforms as a good example of how those elements flow together in a very pleasing way. The commonly heard joke that says a piece is art if it doesn't hold water shouldn't be taken literally.

 

[Gretch Flo]

Not sure that I'd call this a "natural edge bowl" as well , Bill. It just looks to me like a regular bowl whose rim had defects. The rim doesn't undulate (second picture shows the rim to sit flat).The only "leaning" I think I see is that the the center of the wood is offset from the diameter of the original piece of wood. For example (to make it clearer on what I said) on a hunk of wood that had been cut in half from pith to pith, the inside aspect usually has a lighter color of the sap wood. If you scribe a circle and cut it with the equal amounts of sap wood at each side, then it can be centered ok. If you scribe the circle with no sap wood on one side and normal amount on the other side (say one inch), then you get asymmetry. Make sense??

 

[Bill Boehme]

In rereading your original question, I would like to know how the bowl was mounted. I'm wondering if you turned the exterior jam chucked to true up the tenon (I think that Al mentioned this) and then mounted it in the chuck to turn the interior. If so, that would be one explanation of why the inside and outside aren't concentric.

Also, a possible explanation of a small amount of leaning could be due to the wood itself. Fruitwood, especially plum, but also apple, pear, and peach move much more than average. Even after drying it will move as wood is removed during turning.

 

[hockenbery]

Jamie, I put it in the Chuck and before hollowing I put a thumb on the tool rest and turn the bowl by hand checking that it touches evenly all around. I test it running at low speed. It must run true on the outside to get an even wall.
Adjusting in the Chuck may make it run true if not I will true the outside while in the Chuck.

For natural edge bowls, it seems a huge factor to make this happen is how the blank is cut originally, yes? Aren't they often irregular (higher here than there or everywhere)? Perhaps the next time I go to Mr. Mentor's shop, I'll take 3 or 4 NE blanks and get some hands-on help.

If you want even walls the bowl should run true on the outside before hollowing for both cut rim bowls and NE bowls. Thick walled bowls 1/2" + can be off a 1/16" and no one will notice. If an 1/8" thick bowl is off a 1/16 big difference!

Cutting the NE blank: rip a near round log/limb ( for a symmetric rim bowl)in half parrallel to the bark.
I like blanks 2-4" longer than wide. This accentuates the oval look. I drill a 1/14" hole through the bark top dead center for a spur drive. Once you have a doze symmetric bowls turned you can experiment with the interesting not so round logs.

Natural edge bowls are some of the best bowl gouge training! Once the challenge of the interrupted cut is mastered you have the ability to turn almost anything. It takes a little practice to get competent and a lot of practice to get really good.

David Ellsworth does the best NE bowl demonstration I have seen. It is well worth a trip to Fort Collins see his demo if you have a chance.
http://www.rmwoodturningsymposium.com/presenter2016.htm

 

[MichaelMouse]

My "jam chuck" is one of these. http://i35.photobucket.com/albums/d160/GoodOnesGone/Method-One.jpg A 1" hole fits a 1" pin chuck ( or pin jaws) on the wet piece. When cured, it measures ~1" X 15/16", which makes it easy to drop the 1" Forstner down the hole, guided on the end grain, removing face to make another 1" hole precisely centered on, and in line with the original. Since I use a mortise to hold the outside of the piece, it is a case, once again, of making it as large as it was before curing. It's then used to hold, turning the inside. http://i35.photobucket.com/albums/d160/GoodOnesGone/Method-Two.jpg. http://vid35.photobucket.com/albums/d160/GoodOnesGone/BottomHoldProcess.mp4

All the talk of re-rounding tenons neglects what seems to be your real problem - no shoulder to jam the jaws against. Without that shoulder you can get a tilt, as it seems you have from the picture. With that shoulder, you have the advantage of the mortise while using a tenon. I prefer the greater depth possible on cross-grain pieces made available when using the mortise, and the ease of finishing the outside before reversing to inside.

Interrupted-edge pieces often seem to have unequal thickness because of the differential tilt of the natural edge. Nothing critical. http://i35.photobucket.com/albums/d160/GoodOnesGone/Biggest-Ever.jpg

 

[Jamie Straw]

My number one opinion is that a bowl should have either a natural edge or a smooth edge, but half and half just doesn't tug my chain. Also the height to diameter proportion isn't to my liking. Right now it looks like a vase the seems too short.

I totally agree, Bill, after looking at it yet again. (BTW, I don't consider it natural edge either. In the mention of NE in the earlier post, I was speaking of "in general.") When I greened-turned it months ago, I had no idea what I might do with it, no vision really. Should have taken the rim all the way down. I've done another "vase" out of green cherry that looks to be more balanced; when it comes to 2nd turning in 6 months or so, let's hope my skills are up to snuff. It was challenging even to green turn it, as I've not done much that's steep-ish. On another note, watching your NE video has me really hankering after an Ellsworth grind on a bowl gouge. Going to put that on the Fall list of "to buy" things, and set up a session with the VP in charge of mentoring at our club. IIRC, he is the EG demonstrator from last year.

 

[Jamie Straw]

The only "leaning" I think I see is that the the center of the wood is offset from the diameter of the original piece of wood.

Yep, that's what I see too, Gretch. What my mind has wrestled with is: If I take a bowl that has dried since turned green, jamb chuck it with tailstock poking in original center hole on the foot/nub, and start re-turning it, shouldn't it center? Al gave me several reasons how this objective might get defeated. I have more blanks that are near-stable, so just have to keep practicing. Though I know several people here prefer to just cut to the chase and turn from dry blanks, I simply have a soft spot for green wood.

 

[Jamie Straw]

In rereading your original question, I would like to know how the bowl was mounted. I'm wondering if you turned the exterior jam chucked to true up the tenon (I think that Al mentioned this) and then mounted it in the chuck to turn the interior. If so, that would be one explanation of why the inside and outside aren't concentric.

OK, now it's really getting confusing. Al said "I turn the outside of the bowl and true the tenon with the dried bowl jamb chucked over the open chuck." Your post seems to indicate that's not a good idea? Or is the devil in the details? Here is what I suspect happened:

1. I didn't jamb chuck it properly -- it wasn't centered as well as possible
2. I trued up the tenon OK (hard to screw that up, right?)
3. ...but when I henceforth "trued up" the exterior (bowl still jamb-chucked), I didn't do it a little at a time from the tenon, per Al's description, and the bevel and cut followed whatever asymmetry was there
4. Then I reversed it, installed in the chuck and finished the interior. Have no memory If I checked the rim. Probably did, but perhaps not a good job.

Next time, I'll video myself.

 

[Jamie Straw]

My "jam chuck" is one of these. http://i35.photobucket.com/albums/d160/GoodOnesGone/Method-One.jpg

Michael, while I appreciate your offers of help, I no longer go to Photobucket. Might save you some effort if you know that ahead of time.

 

[Jamie Straw]

All the talk of re-rounding tenons neglects what seems to be your real problem - no shoulder to jam the jaws against.

There's a shoulder after re-turning the tenon. Not sure what leads you to think not.

 

[Jamie Straw]

........so turning it the second time u need to return the tendon to make it round......I always start between centers so I can use the holes to center it

Yes, that's what I've been taught to do also. Still working on it!

 

[MichaelMouse]

There's a shoulder after re-turning the tenon. Not sure what leads you to think not.

The most common cause of tilt where chucked is lack of contact on a shoulder with a tenon or not leveling and contacting the bottom of a mortise. experience.

 

[Bill Boehme]

OK, now it's really getting confusing. Al said "I turn the outside of the bowl and true the tenon with the dried bowl jamb chucked over the open chuck." Your post seems to indicate that's not a good idea? Or is the devil in the details? Here is what I suspect happened:

1. I didn't jamb chuck it properly -- it wasn't centered as well as possible
2. I trued up the tenon OK (hard to screw that up, right?)
3. ...but when I henceforth "trued up" the exterior (bowl still jamb-chucked), I didn't do it a little at a time from the tenon, per Al's description, and the bevel and cut followed whatever asymmetry was there
4. Then I reversed it, installed in the chuck and finished the interior. Have no memory If I checked the rim. Probably did, but perhaps not a good job.

Next time, I'll video myself.

No, I agree 100% with Al, but I probably confused more than helped. What I was attempting to say is if you turned the tenon, shoulder, and exterior shape while jam chucked between centers and then mounted it in the chuck to finish the interior then that would explain why the inside and outside aren't concentric. Once you get the piece in the chuck you really need to true up the exterior again, because there will be some shifting in alignment when going from jam chuck to scroll chuck. If I misunderstood Al then I'll take whatever punishment he sees fit to administer to me.

Michael, while I appreciate your offers of help, I no longer go to Photobucket. Might save you some effort if you know that ahead of time.

Photobucket has changed ... and, not in a good way. Once upon a time it seemed to be a good free site for pictures, but now you get covered with advertising pop-up windows and my McAfee Anit-Virus software give me all sorts of Don't-Go-There warnings..

 

[Jamie Straw]

If I misunderstood Al then I'll take whatever punishment he sees fit to administer to me.

 

[Jamie Straw]

Photobucket has changed ... and, not in a good way. Once upon a time it seemed to be a good free site for pictures, but now you get covered with advertising pop-up windows and my McAfee Anit-Virus software give me all sorts of Don't-Go-There warnings..

Can't help but wonder if it is the reason my spam has multiplied by 100 since I joined awhile back. Also haven't found much help when I've clicked on videos that were suggested to me here. I'm done with PB -- had signed up for it because it was the easiest way to post photos in a different forum, but I don't spend any time there now anyway, too much good stuff here and at Sawmill Creek.

 

[hockenbery]

What I was attempting to say is if you turned the tenon, shoulder, and exterior shape while jam chucked between centers and then mounted it in the chuck to finish the interior then that would explain why the inside and outside aren't concentric. Once you get the piece in the chuck you really need to true up the exterior again, because there will be some shifting in alignment when going from jam chuck to scroll chuck...

We are on the same page ....
Usually a cut rim bowl will run true enough not to need truing on the outside when I put it in the Chuck.
I do check it and sometimes the Chuck hold can be adjusted to make it run true. Once in a while I might return the outside but not often.

Natural edge bowls I always finish turn the outside in the Chuck for two reasons.
1. I hollow it some to release any tension and the walls may move.
2. I'm likely to have a thin wall and it will need to be as true as can be.

 

[MichaelMouse]

I have Adobe flash on a permission required basis, so no popups, just glacially slow access - sometimes - to photobucket. Norton doesn't give warnings, so I'm pretty comfortable. If you feel what you might learn is less important than popups, don't go. However, you might think why a properly formed shoulder and good contact is so important - what counters lift on one side is attempted compression of the other. Flat folks are familiar with shouldering to counter wracking, I'm sure.

Some people neglect the shoulder entirely, just sort of narrowing where they put their jaws. No benefit. Some make a shoulder, even a good one, then don't seat both sides properly. Also no benefit and possible detriment, as they squeeze the tenon to try and regain what the shoulder would have given them. Soft part of the wood may bulge under these circumstances, ruining the formerly good shoulder seat. Most common problem while turning comes when there's a "catch" lifting one point, not countered by pushback on the opposite side. Squeezing without re-seating may follow. Those who look at the several thousand words provided will see that I leave pieces between centers until things are at their lightest and most balanced. Born coward or non-termite, your choice. I don't intend to eat any wood, though I have been known to put wet cherry shavings "between my cheek and gum" rather than go get a drink upstairs. Both ends centered, no need to go outside/inside/outside when removing the material. Matter of fact, proper shouldering and snug -not tight- hold in a round mortise or tenon also ensures centering as good as between points. I recommended a wedged hold in another post. Good alternative if the jaws are shaped properly, because the act of snugging up drives the nose of the jaws into register with the shoulder or bottom of the mortise. Any deviation noted on initial spinup thereafter is going to be dust trapped somewhere, and is easily remedied by cleaning the mortise or tenon.

 

[Dean Center]

Jamie,
I'm going out on a limb. I think what some folks are trying to say is:
If you return the outside of the bowl in the jam chuck, and then turn it around to place in the chuck, the outside won't be true. You have to return the outside while the tenon is in the chuck. I am guessing lots of folks don't do any significant turning of the outside while jamb chucked, but rather wait and do all of the outside while tenon chucked.

Quick tip: I have learned the hard way to remember when I finish the outside of the green blank and the tenon, to put a hole in the center of the tenon with the live center. This gives you a really good starting spot when you go to return the blank. Sometimes I clean off the tail stock mark when I'm cleaning up the tenon of the green blank and end up kicking myself when I can't seem to get it jammed properly 5 months later. If only I'd remembered to slide the tail stock up and make a new dimple.....

 

[Bill Boehme]

We are on the same page ....
Usually a cut rim bowl will run true enough not to need truing on the outside when I put it in the Chuck.
I do check it and sometimes the Chuck hold can be adjusted to make it run true. Once in a while I might return the outside but not often.

I've convinced myself that if I true up the tenon to match the perfect circle diameter of dovetail jaws then there is very little shifting in alignment when going from jam chucking to the scroll chuck.

It's not always feasible to have the tenon at the perfect diameter and in those instances I usually prefer to use Oneway profiled jaws rather than having the dovetail jaws just holding by the corners. In either case I think that there is a greater likelihood for the alignment to shift when going from jam chucking to the chuck jaws.

Jamie,
I'm going out on a limb. I think what some folks are trying to say is:
If you return the outside of the bowl in the jam chuck, and then turn it around to place in the chuck, the outside won't be true. You have to return the outside while the tenon is in the chuck. I am guessing lots of folks don't do any significant turning of the outside while jamb chucked, but rather wait and do all of the outside while tenon chucked. ...

I think that you have summarized things well ... at least, for me it's true that after truing up the tenon I put the bowl in the chuck before I continue. If it is a hollow form then I usually true up the exterior while between centers.

 

[Harold Adams]

The speed of the turn can cause tools to shift in and out as your turn creating an oval shape. When your tool passes over a void it will have a tendency to move inward and then hit the wood and cut and push the tool out as it continues till it hits the void again. Sharpen your tool when going to the final cuts, turn up your speed and light touch.
The asymmetry to me may just be the grain of the wood causing the eye to follow.
I would suggest the your base may be a little big when considering form. I have a couple potter friends that have given me a phenomenal amount of help in seeing correct form. One thing you might consider when you get close to what you think is final form step back and look at the item while it is turning, (this way you can see form without grain interfering with your visual). If it looks a little funny to you then your eye is telling you something is amiss.
Another thought to consider is lift. When looking at the final form where does your eye stop. If you are constantly drawn to the bottom then it may be to large, clunky, or heavy at the bottom. Sometimes when looking at a piece like this where the outside curve stops abruptly where the bowl meets the table, your eye is trying to find the bottom. Imagine the curve continuing through the plane of the table and the bottom of the bowl is ending under the plane of the table. It then needs something to terminate the eye from making this perception. Just a small chamfer at the very bottom can create a vusual stopping point for the eye and give the piece the lift. By stopping the downward motion of the eye it has terminated it look and will continue back up. This will create movement which creates a greater interest in the item. Even a smaller base with a chamfer and/or a line cut in up from the bottom a small bit will do all that.

Keep up the great work.

 

[MichaelMouse]

I've convinced myself that if I true up the tenon to match the perfect circle diameter of dovetail jaws then there is very little shifting in alignment when going from jam chucking to the scroll chuck.

It's not always feasible to have the tenon at the perfect diameter and in those instances I usually prefer to use Oneway profiled jaws rather than having the dovetail jaws just holding by the corners. In either case I think that there is a greater likelihood for the alignment to shift when going from jam chucking to the chuck jaws.



I think that you have summarized things well ... at least, for me it's true that after truing up the tenon I put the bowl in the chuck before I continue. If it is a hollow form then I usually true up the exterior while between centers.

Am I catching this right? You true the tenon but don't bother to true the bottom at the same time? Doing so not only gives you clear tool space to do the bottom, but ensures that the hold and the exterior will remain true to one another if you reverse and chuck it properly.

One other thought about "holding by the corners." You are wedging up against the shoulder or into the mortise when you use dovetail holds. Four wedges or eight "points" ought to do just fine, with the friction of the jaw fronts all you need to ensure no free spin. Makes the four corners a mere backup. Owning four sets for the Nova chuck, it is ALWAYS feasible to have a tenon/mortise of proper diameter, by changing either jaws or tenon size. Plan ahead is always good advice.

 

[Bill Boehme]

One other thought about "holding by the corners." You are wedging up against the shoulder or into the mortise when you use dovetail holds. Four wedges or eight "points" ought to do just fine ....

If wood were a homogeneous material that would be the case, but it isn't. In many situations for something simple like a bowl it's usually close enough, but I mainly turn things that require a couple reversals and maintaining precise alignment is critical. See my 14.5" diameter basket illusion which is just over 1/4" thick before beading ... After beading you can see light through it ... too much misalignment and it becomes a hoop or funnel.

 

[hockenbery]

Am I catching this right? You true the tenon but don't bother to true the bottom at the same time? Doing so not only gives you clear tool space to do the bottom, but ensures that the hold and the exterior will remain true to one another if you reverse and chuck it properly.

Most times for a cut rim bowl the Chuck runs true enough so I turn the whole outside.
Howeve if I am doing a thin wall I turn the outside after it is mounted in the Chuck.
An advantage of the side ground gouge is that a bevel riding cut can be started close to the Chuck.

Natural edge bowls I turn the outside when it is in the Chuck, I remove some interior wood first. Then true the outside so if tension wood movement that takes place will be turned round on outside before hollowing.

Turning the bottom near the Chuck is a two part process. Using the side ground gouge makes it much easier than using other tools: a pull cut can start within about an inch of the Chuck and a shear cut can cut to just shy of the Chuck. I also usually have a secondary tenon with a notch so I can follow the curve of the bowl.
Second part is I reverse jamb Chuck to finish turn the bottom. Most natural edge bowls I finish with a round footless bottom these are quite stable and functional. If I do a foot is usually about the size of a quarter. If the wood has not moved too much I can blend the new surface I'm turning with the previous surface. If the wood has moved which it usually does I will be able to blend one side and then have part of a transition ring to blend in with sanding. Most times 220 will remove the transition ridge because it is so small.