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Wood balance question

Don C Davis

Don C Davis

Joined
Feb 15, 2018
Messages
256
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Location
Canton, GA
I like turning natural edge bowls a lot--so I've got a question for you folks about them. I frequently have a natural edge piece that just won't seem to balance for me. Often I have the outside shaping done, and have turned the piece over and am holding it on a chuck with the jaws gripping a mortise in expansion mode.

I then go to hollowing the bowl--at this point a large portion of the overall mass of the original blank has been reduced and still I get vibration as if the piece is off balance a good bit, the last few bowls like these I made, I did the work and got the piece turned around and mounted onto the chuck and then returned to the piece the next day and began, or began to complete, the hollowing--and my tool wood hit only a certain part of the inside of the bowl, making it seem like I needed to completely re-round the inside of the bowl, when I completed a cut with my gouge, there would be grooves on only one side of the inside of the bowl in spots--this wood is white oak that is about 1 to 1.5 years old--been sitting inside my heated and cooled shop this whole time--it reads 11% moisture on my moisture meter--so I'm wondering if this wood is still wet enough that it is just moving overnight causing me these issues.

Any feedback/information is appreciated...
 
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I suspect you are still getting wood movement due to stress in the wood. I don't use mortise for natural edge I always use a tenon. I don't think that is your problem unless you aren't cutting the mortise correctly. The bottom of the mortise should be flat and the jaws should bottom out in it.
 
If the wood is still green when you are turning it, once you have shaped the bowl and reverse mounted and hollowing the form it will begin to dry quickly and it will warp if you come back a day later and begin turning it again. You should try to complete your green wood turning the same day. Depending on the wood species it is either drying and warping in 24 hours or the rough turning has released some tension in the wood grain that can cause the rough turned hollow form to relax and warp.
 
Well guys, with white oak at 11% is that still 'wet' enough to cause these issues? I'm thinking that's what it is but I'd just like some of you wiser folks to tell me!
 
John, what difference would it make with a tenon instead of a mortise? I just don't know and as always am trying to learn......
 
I would say you are getting movement as the wood dries. I never start a bowl and then "go back to it". If I can't start a bowl and turn the whole thing, inside and out then I don't start it. Where I live a dry bowl will be around 6 or 7% mc, 11 or 12% mc is not what I would consider a green bowl but you could still be getting movement with it setting a day between turning.
 
Moisture meters will only read the surface and a blank large enough for a bowl will likely be of a higher moisture content inside. The only way to do it is to rough turn it green to oversized uniform wall thickness and then coat the end grain with something like angkor seal and weigh it. During the first days weigh it and record the weight at regular intervals and you will see a gradual decrease in the weight. As time passes increase the time interval and then after about 6 months the weight will begin to stabilize. During the rough turn be sure to have a centerpoint on your tenon or mortise so the you have a center point to true up the mounting. I f using a tenon go over size in the rough turn since it will shrink to oval whereas the mortise shrinkage will not be a problem.
 
Jack and Don, thanks for the input--Jack, that's good information, and going forward I will complete turning one of these in one go.

Don, I do keep a center point inside and out, and as I stated I typically use mortises.

Thanks for the input folks.
 
Natural Edge bowls are one of my favorite things to turn.

1. As several mentioned, try to turn the bowl in one session. If you have to leave it for more than a couple minutes, mist it with water and wrap it with several plastic bags to keep it from loosing moisture. I turn most NE bowls from dead wet wood and sand them off the lathe several days later when they have dried.

2. Consider using a tenon next time. I much prefer a tenon for NE bowls. Most designs I like can not accommodate a recess in the bottom.

3. After I put the bowl in the chuck to hollow it I use the tailstock for support and hollow a little bit leaving a thick wall. This is to relieve tension if it is present and the walls may move a bit. I then true and finish turn the outside.
This corrects any misalignment in the chuck and it corrects any movement from releasing tension.
You can see this process in the demo video below.

4. What is the humidity in your shop now? Find your humidity and temperature on this chart.
34583DD7-120F-4425-BE8F-8C296522E8D8.jpeg
If your shop is 70 degrees and 60% humidity then 11% is as dry as your bowl will get - so no movement from drying.
If your shop is 50 degrees and 30% humidity the bowl will dry to 6.3% - it will move from drying.

5. This demo is a crotch bowl but the turning process is the same half log NE bowls.
The wood is live oak.
Watch the hollowing process
Fast forward to 26:15 to see the tenon refined for the dovetail jaws.
Fast forward to 29:35 to see the steps described in 3 above

View: https://www.youtube.com/watch?v=8jVoI12Kfug&feature=youtube_gdata
 
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The biggest difference between a tenon and mortise is how you want the foot to look. I always reverse turn the piece and shape the foot the way I want. If I use a tenon it's easier to remove it, or include the foot into it. With a mortise you have a much larger area and I usually prefer my foot to be smaller.
 
john lucas said:
The biggest difference between a tenon and mortise is how you want the foot to look. I always reverse turn the piece and shape the foot the way I want. If I use a tenon it's easier to remove it, or include the foot into it. With a mortise you have a much larger area and I usually prefer my foot to be smaller.
Click to expand...
The large mortise can be eliminated by sizing for a smaller expanding jaws.
 
Check out page 46 of the December issue American Woodturner
Jerry Kermode does some of the sweetest NE bowls you will ever see.
He and Deborah are super nice people with an interesting story to go with wonderful bowls

On the way you will see articles by frequent forum contributors: @john lucas @Mike Peace
Be sure to look at John’s angels page 52
 
Don C Davis said:
Well guys, with white oak at 11% is that still 'wet' enough to cause these issues? I'm thinking that's what it is but I'd just like some of you wiser folks to tell me!
Click to expand...

Don......I don't do many NE bowls, but I can tell you surely that a bowl with 11% MC is capable of warping.

-----odie-----
 
The thing with wood is that it is never stable, and will always move. I have been turning a number of boxes lately to prepare for a demo and another video.... No matter how long the wood has been in the shop, or whether it is kiln dried or air dried, or 1 1/2 inch diameter or 6 inch diameter, I ALWAYS rough turn them first, then let them sit for a month or 6 before I finish turn them. If your bowl blank was rough turned and sat in the shop for a year or two, I would never let it sit over night because it will still move. You can have a blank that measures 11% MC on the outside and it can be 15% on the inside. Wood will also 'adjust' to having mass removed.

robo hippy
 
Turning NE bowls involves a lot of interrupted cuts. Interrupted cuts are one of the most challenging techniques to master in woodturning.

Once you can get a clean cut on the interrupted surface that you can sand off the lathe you have achieved something to be proud of. And you can probably turn anything you can imagine.
 
NE bowls have taught me just how much things change when you reverse a bowl blank and put it in the chuck. When you see one side of your bowl's rim 30-50% thicker than the other, it's impressive, depressing, but very educational. I've learned to always make sure the jaws are clean and the tenon well cut, but there's still some some change in alignment when I reverse.

This problem also highlights the only drawback I find with my Powermatic A--it's really hard to return the outside of the reversed bowl with that the big square headstock in the way. Any tips on that, John?
 
hockenbery said:
Turning NE bowls involves a lot of interrupted cuts. Interrupted cuts are one of the most challenging techniques to master in woodturning.

Once you can get a clean cut on the interrupted surface that you can sand off the lathe you have achieved something to be proud of. And you can probably turn anything you can imagine.
Click to expand...
That is absolutely true you can not ride the bevel on air.
 
Well, actually you do rub the bevel. Thing is you only rub it when it is in the wood...... This is the situation where 'the bevel should rub the wood, but the wood should not know it'. Most of us push into the bevel too hard....

robo hippy
 
Within the last 2 months I have turned several natural edge bowls out of red and white oak and since I work down to 1/8" thick or less I experience movement during the final cuts so I will shear scrape and sand as I progress. The form shown in the photo below is red oak end grain and full round ot the log including the pith and that tilt you see happened as I was finishing the stem. The item measures about 10" diameter x 10" high x 1/8" wall thickness and though it has the form of a goblet I choose to call it a pedestal bowl. The blank came from a live standing tree cut in the first part of October and of coarse the sap was not running so the bark is tite plus there are some traces of lichen still on the bark. 8071PedBowl.jpg
 
robo hippy said:
Well, actually you do rub the bevel. Thing is you only rub it when it is in the wood...... This is the situation where 'the bevel should rub the wood, but the wood should not know it'. Most of us push into the bevel too hard....

robo hippy
Click to expand...
You do have to guide the tool into the cut in a nice continuous motion to keep from getting steps or ridges so I normally put a white paper on the lathe bed to help me see the edge I am cutting.
 
Dean Center said:
I find with my Powermatic A--it's really hard to return the outside of the reversed bowl with that the big square headstock in the way. Any tips on that
Click to expand...

It does get a little close.
The demo video of the NE crotch is done on a powermatic b.

On this bowl I have a short false tenon so jaws have a flat tomrest on and the notch at its edge lets me judge the curve. A ONEWAY Stronghold give some distance
I use a pull cut which gets a bevel about a 1/2” from the false tenon. I can later shear scrape this 1/2”

Side view at at 33:27 into the video. Taking light cuts.
9EDF5CE0-8C78-4CB9-8038-F99A2EF89645.jpeg

Top view at 33:40 into the video
91D1C397-BCAA-466A-9728-A2718A56F8B1.jpeg
 
I do NE bowls a lot and if I leave it for a while like dinner or overnight I cover it with a plastic bag. I have rubber bands to seal the bags behind the chuck. If you want them to not be warped leave them thick and let them dry in a bag then turn them again. On some large bowls I turn them three times. Knots and burl wood doesn't have the same weight as straight grain and it will cause an out balance situation. Just the shape will sometimes cause a NE bowl to be out of balance. Keeping the bowl a constant thickness weather dry or wet will help to keep it from cracking. Sometimes it cracks anyway.
 
hockenbery said:
It does get a little close.
The demo video of the NE crotch is done on a powermatic b.

On this bowl I have a short false tenon so jaws have a flat tomrest on and the notch at its edge lets me judge the curve. A ONEWAY Stronghold give some distance
I use a pull cut which gets a bevel about a 1/2” from the false tenon. I can later shear scrape this 1/2”

Side view at at 33:27 into the video. Taking light cuts.
View attachment 27304

Top view at 33:40 into the video
View attachment 27305
Click to expand...
On just about any bowl I use a wood worm screw to hold it (in the case of a NE bowl I use chisels or what ever works the make a flat) then bring up the live center and proceed to do most of the work on the bottom including the tenon. By the way what is a false tenon.
 
Emiliano Achaval said:
Not in Hawaii, LOL
Click to expand...

Ha,ha......:D

About 95% of the time I do my own seasoning, and I never get less than 12% MC here in Montana. I get many KD blanks and seasoned blanks from outside sources that meter 12%, or less than that. Even a KD blank that initially has 12% MC, will normally lose a small amount of weight during the seasoning process, after roughing. Curious, Emiliano......what MC do your bowls reach there in Hawaii?

-----odie-----
 
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Don Wattenhofer said:
On just about any bowl I use a wood worm screw to hold it (in the case of a NE bowl I use chisels or what ever works the make a flat) then bring up the live center and proceed to do most of the work on the bottom including the tenon. By the way what is a false tenon.
Click to expand...

Your NE oak goblet is marvelous. When I do them, I hollow first then use a light for thickness turning the outside. What is your process?

I use worm screws on band sawn disc because the bandsaw cuts determined the grain pattern.
It is a quick fast solid mount.

On all other bowls I use spur drive and tailstock. Because for the few bowls I do the grain pattern control is a feature I want.

With a spur drive I reposition the tailstock center to line up the grain or rim heights in NE bowls so I don’t need meticulous saw cuts. I can also select a position for roughing the balancesthe weight the shift to one that balances the grain. I do spend some time choosing the center of the blank for the spur drive ab in rare instances I can reposition the spur.

What I call a false tenon is a flat shoulder around the tenon that makes a flat top to meet the tops to chuck jaws.
I also make a notch where the bowl’s curve meets it. This notch lets me see the curve better and I can flow the curve from the rim to the notch and visualize it continuing through the mounting wood that will be turned away with the final rechucking.
 
hockenbery said:
Your NE oak goblet is marvelous. When I do them, I hollow first then use a light for thickness turning the outside. What is your process?

I use worm screws on band sawn disc because the bandsaw cuts determined the grain pattern.
It is a quick fast solid mount.

On all other bowls I use spur drive and tailstock. Because for the few bowls I do the grain pattern control is a feature I want.

With a spur drive I reposition the tailstock center to line up the grain or rim heights in NE bowls so I don’t need meticulous saw cuts. I can also select a position for roughing the balancesthe weight the shift to one that balances the grain. I do spend some time choosing the center of the blank for the spur drive ab in rare instances I can reposition the spur.

What I call a false tenon is a flat shoulder around the tenon that makes a flat top to meet the tops to chuck jaws.
I also make a notch where the bowl’s curve meets it. This notch lets me see the curve better and I can flow the curve from the rim to the notch and visualize it continuing through the mounting wood that will be turned away with the final rechucking.
Click to expand...
Yup you got it! When doing the end grain formes I always do the inside first then put a light on the inside and cut back on the shop lighting. The trick to getting a consistent translucent wall thickness is to measure the wall with a caliper to get an idea of what amount of light is coming through for a given thickness but you also have to contend with the difference between sap wood, heart wood and the changing moisture content. The photo below is a simple half log NE that I initially held with the wood worm.
What you are saying about using the spur drive is some thing I also do, but it just illustrates that you should keep your options open depending what the project is.
8066Bowl.JPG
 
The oaks are high-movement woods as they dry, so even in a single turning session you can see distortion. I personally like the distortion in my oak bowls.

One thing I don’t believe anyone mentioned above is to hollow to final thickness in steps and only return to a previously cut section to lightly blend with the next. Leave the bulk of the wood in the bowl and only remove it as you work down after thicknessing the rim. When you hollow from rim to bottom from the center out, you are lacking support which can cause vibration out at the rim.
 
Owen Lowe said:
The oaks are high-movement woods as they dry, so even in a single turning session you can see distortion. I personally like the distortion in my oak bowls.

One thing I don’t believe anyone mentioned above is to hollow to final thickness in steps and only return to a previously cut section to lightly blend with the next. Leave the bulk of the wood in the bowl and only remove it as you work down after thicknessing the rim. When you hollow from rim to bottom from the center out, you are lacking support which can cause vibration out at the rim.
Click to expand...
I think I did mention that technique how ever you have stated the process and the necessity for it much better. The end grain pieces I always hollow first then start the outside in steps as you stated. The side grain pieces I do the out side first then the inside in steps. If you look back on this thread to the 2 oak pieces that I posted you can see the distortion which I think adds another interesting feature.
 
Robbo pretty much stated my thoughts. It really does not matter if the bowl is NE or not it will move and if you plan to come back the next day you had best leave enough thickness or you have a problem. As was stated wood move irregardless of moisture content at. Finishing .
 
The only way to stop wood movement is to maintain it in at constant level of humidity or completely encapsulate it in a finish like epoxy that is impervious to the surrounding atmosphere. I know that where I am located the summers are humid and all wood items in the house take on moisture and expand then in the winter even though the ground outside is covered with hard water (thats ice) the air inside the house becomes dryer and all the wood in the house shrinks.
 
Lots of good info everyone--thanks so much--I have gotten tired much faster since the hospital tried to kill me, and find myself frequently wanting to do half a bowl now, and the other half the next day--I will quit that!! I have made many NE bowls that have a wall thickness of around 3/16" and I like them--a few do show a little movement after a month or two sitting around the house. I got a bunch of Mango blanks about a year ago, and unlike other fruit woods I have dealt with it was durn hard--I made all of them into NE pieces and they haven't moved any noticeable amount---I finished all these pieces with my own mix of walnut oil, carnuba and bees waxes, with a complete coating of carnuba wax for final put on with high friction and a buffer--made a nice shiny durable finish.
 
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