What caused this crack?

[Jamie Straw]

I think this may be the second time a bowl has cracked like this. It's a relatively small Black Locust bowl, green turned last week, end grain (plus a little extra) coated with Artisan wood sealer. Bowl is 7.5" diameter, 3/4" rim, tenon is 2". The raised area between tenon and bowl was set aside for the foot and is 2-3/4" diameter. Perhaps I shouldn't have done that? Something else I might have done wrong? or is it just one of those things? At this point, it's not very deep; after I took the picture, I coated the entire bottom with sealer hoping I can save the bowl. Or should I pop it back on the lathe and turn away that whole area?

 

[hockenbery]

It's a guess but Two things may contribute.
The sapwood may be moving a bit more than the heartwood.
You may have a bottom that is a lot thicker than the walls of the bowl.

I usually turn the bottom of the bowl a little thinner to account for the tenon.
The bottom won't warp much. The tenon and foot are 3/4" if your bottom is 3/4" that is twice as thick as the rest of the bowl. If the bottom is a 3/8" - 1/2" thick then the difference is a lot less and

The sealer might slow the drying enough to prevent additional cracking.

 

[Josh Stevens]

I recently had a few crack the same way and I also think it was because of the sapwood (that's where all the cracks were) and I always try to make the base a little thinner as well.
I've gotten away with leaving sapwood in some timbers but from now on I'm going to turn it all out when I'm roughing out wet wood.

 

[Bill Boehme]

I would wick a little thin CA in the crack and then plan on turning off all or most of the sapwood when you do the final turning. Sapwood has more moisture and is slightly softer than the heartwood. Here is a brief overview: http://northernwoodlands.org/articles/article/what_is_the_difference_between_sapwood_and_heartwood
Also, from Wagner moisture meters: http://northernwoodlands.org/articles/article/what_is_the_difference_between_sapwood_and_heartwood

Sometimes wood just cracks because it wants (or has) to. Your bowl geometry looks like might have a bell shape maybe taller than wide. That geometry might be more prone to cracking than a shallow shape.

 

[diverjoe]

Jamie, I think that the shape of the bowl may have contributed to the crack. From the photo, the sides seem to be fairly straight up and down. that shape does not lend itself to much movement.
Joe

 

[robo hippy]

Well, that is a shrinkage crack. Most probably cause is the thickness, and the sap wood probably contributes to that as well. For twice turned bowls, I would seal that part. Filling with CA glue would help keep it from getting worse. I don't use sealer, but the plastic stretch film over it might help, or put it bottom down in wet shavings.

robo hippy

 

[Jamie Straw]

I recently had a few crack the same way and I also think it was because of the sapwood (that's where all the cracks were) and I always try to make the base a little thinner as well.
I've gotten away with leaving sapwood in some timbers but from now on I'm going to turn it all out when I'm roughing out wet wood.

Agree with turning the base a little thinner, one of our demonstrators schooled us on that a few months ago. For whatever reason, I didn't think that through when I turned this bowl. Seems like sometimes I can't think about all of the things that are important. Like the other day, when I was cutting the only crotch piece from a walnut log procured last week. Thinking hard about the mechanics of doing that with my little Craftsman electric chainsaw without killing it or me, then proceeded to cut the crotch along the wrong plane.

 

[Jamie Straw]

I would wick a little thin CA in the crack and then plan on turning off all or most of the sapwood when you do the final turning. Sapwood has more moisture and is slightly softer than the heartwood. Here is a brief overview: http://northernwoodlands.org/articles/article/what_is_the_difference_between_sapwood_and_heartwood
Also, from Wagner moisture meters: http://northernwoodlands.org/articles/article/what_is_the_difference_between_sapwood_and_heartwood

Sometimes wood just cracks because it wants (or has) to. Your bowl geometry looks like might have a bell shape maybe taller than wide. That geometry might be more prone to cracking than a shallow shape.

Thanks for the links, Bill, will check them out. Will see if I can sneak some CA in (scratch off the wood sealer first). Any vote for remounting and perhaps turning off the tenon and making the green foot a tenon, or is that just asking for other troubles? Yes, it is a bell shape, perhaps not a good (or esthetic) choice. It just possessed me at the lathe. Need to go back to predetermining the shape instead of "going with the flow."

 

[Jamie Straw]

Well, that is a shrinkage crack. Most probably cause is the thickness, and the sap wood probably contributes to that as well. For twice turned bowls, I would seal that part. Filling with CA glue would help keep it from getting worse. I don't use sealer, but the plastic stretch film over it might help, or put it bottom down in wet shavings.

robo hippy

I've gotten really paranoid about wet shavings due to persistent mold problems. Almost guaranteed in maple, don't know about something like Black Locust. I do have some stretch film, might try that. Thx.

 

[Jamie Straw]

It's a guess but Two things may contribute.
The sapwood may be moving a bit more than the heartwood.
You may have a bottom that is a lot thicker than the walls of the bowl.

I usually turn the bottom of the bowl a little thinner to account for the tenon.
The bottom won't warp much. The tenon and foot are 3/4" if your bottom is 3/4" that is twice as thick as the rest of the bowl. If the bottom is a 3/8" - 1/2" thick then the difference is a lot less and

The sealer might slow the drying enough to prevent additional cracking.

Yep, nail-on-head, should have turned the bottom thinner. QUESTION, something I've been wondering about -- when you rough-turn a bowl, are you planning the foot right then and there, leaving a green-turned foot, or just having a tenon (with a centering nub) and cutting the foot when second-turning the bowl? All my earlier bowls (or bowl attempts), I've not concerned myself with the foot. Something of a mystery why, all of a sudden, I decided to include the foot in the green turning.

 

[Mike Johnson]

Another option is turning a hollow recess in the bottom of the piece and using the outer surface of your chuck to
secure the piece on the lathe. This might allow you to remove all of the crack from the piece, just so long as you
have enough wood in the inside bottom to turn smooth after the wood cures out. This method also speeds up the process
of finishing the bottom of the piece since you don't have to remove the tenon after you have the piece turned & sanded.
When I turn some green wood I will turn a tenon on the inside of the bowl and turn a hollow recess on bottom of the bowl.
When I remount the bowl for the second turning I mount it on the inside tenon and then true up the bottom hollow recess,
and then remount the bowl on the hollow recess and finish removing the tenon in the bottom of the bowl. This also allows me
to finish the bottom of the bowl and turn accent rings and sand it before mounting for the final turning of the bowl. This method
also works well for turning plates and platters.

 

[Bill Boehme]

Yes, it is a bell shape, perhaps not a good (or esthetic) choice. It just possessed me at the lathe. Need to go back to predetermining the shape instead of "going with the flow."

When I was a newbie the instant gratification of making something usually led to "letting the wood speak to me" or going with the flow, as you put it. Sometimes it was an excuse arising out of a bad catch more than any real communication going on between me and the wood. Also, too often the shape of the block of wood and my cheapness to get the most out t of it were the two main design drivers. Fine for frugality, but not for aesthetics. Also, my turningis created using that approach had "beginner" written all overt hem.

However, sometimes you come across a special piece of wood that really does speak you and has a voice in the final design. Even then, start with a design for the final shape rather than just poking the wood with a sharp instrument and enjoying the flow of wet shavings.

I think that my turningis advanced to the next level when I started with a plan for the end result and then found a suitable piece of wood. I prefer simpler forms serve as the canvas to showcase the wood itself or for my own embellishments if the wood is plain.

You could remove some material from the bottom if you think it's too thick there, but then you'll lose the center reference point. That's not a show stopper, but it might require more fiddling around when you true up the tenon after the bowl is dry. The foot can fit inside the tenon and can be as short as you wish.

 

[Bill Boehme]

I prefer Anchorseal when drying pieces. I hate shavings because they're too unpredictable. Stretch wrap is good if used for a brief period, but no more than a few days. Otherwise, mold is guaranteed to happen.

 

[hockenbery]

Yep, nail-on-head, should have turned the bottom thinner. QUESTION, something I've been wondering about -- when you rough-turn a bowl, are you planning the foot right then and there, leaving a green-turned foot, or just having a tenon (with a centering nub)

I have made a lot of bowls, so I have a fair idea of what the bowl will look like in size, shape, and grain pattern as I cut blank. I still go through these steps below to get the shape and grain pattern. I try to listen to the wood when it is still a log.

When I rough turn a bowl for a cut rim bowl:
I rough turn the blank round with a crude bowl shape
Line up the grain by shifting the tail center and turn round again
I set the rim with a cut to establish the corner of the rim.
I turn what I call a notion of the foot
I then try to connect the foot to the rim with a pleasing curve.

If I don't like my attempt at a pleasing curve I can:
Change the curve with the same foot and rim
Make the bowl shorter by moving the foot up
Make the bowl shorter by moving the rim down
Make the bowl smaller diameter but cuttin the rim inward
Or combinations of the above

Currently I do sort of an ogee for the foot and my tenon will be in the center of it.
My rule of thumb for foot diameter of a functional bowl is about 1/3 of the rim diameter
The smallest bowl I do is 10" diameter.

I need To Turn the notion of the foot to be able to visualize the curve of the bowl.
Centering the grain and gettin the curve make returning the bowl is fairly easy.

Sometimes I find a surprise in the roughing that makes me change my mind about what to make from the blank.

Al

 

[Jamie Straw]

or put it bottom down in wet shavings

Otherwise, mold is guaranteed to happen

I've gotten really paranoid about wet shavings due to persistent mold problems

Case in point: Last night, I completed the outside of a walnut bowl, not enough time to do the inside, so I bagged it in shavings. When I took it out of the bag this morning, mold had already spotted the bowl. I turned another 1/8" or so off the outside before I reversed it to turn out the inside. That's life in rural Puget Sound. My shop is on the edge of forested land au naturel. No telling what the spore count is in there.

 

[john lucas]

I'm with others I quit using shavings in the bag 20 years ago. I also had mold problems. A paper sack essentially does the same things as shaving which is to hold a little bit of the moisture while still letting it evaporate. Plastic bags stop water loss totally but cause mold so I only use those for over night storage. Well that's not totally true. I have dried really difficult wood by turning a plastic bags inside out every day. That particular piece had lots of knots in it. It tooks months to dry that way but not a single crack.
Back to the bottom thickness. The bottom wood barely moves compared to the sides so you can leave it almost to final thickness. What I usually do is to leave the bottom with tenon and/or foot the same thickness as the walls when roughing. The walls will move a lot and course have to be turned to get the bowl back to round. You will have to remove very little wood from the bottom area so if you left it thin your probably OK. There certainly isn't anything wrong with using anchor seal on all end grain areas after roughing. I do that as well as put the wood in a box or paper sack to slow down the drying. I don't turn as many bowls as Al so I'm always guessing how much the wood will move and whether it will crack so I"m probably over precautious.

 

[robo hippy]

Dry shavings.... Another method for slow dry is from Christian Burshard who puts madrone in a paper bag, then puts that in a plastic bag. Change out the paper bag every day. Bags can be reused when dry again. Too much work for production, but fine for small batch runs. I don't think I have ever twice turned a bowl...

robo hippy

 

[Jamie Straw]

Al, thanks for the details in your last post, I missed it yesterday. I have a pile of bowl blanks to practice on.

 

[Bill Boehme]

Dry shavings.... Another method for slow dry is from Christian Burshard who puts madrone in a paper bag, then puts that in a plastic bag. Change out the paper bag every day. Bags can be reused when dry again. Too much work for production, but fine for small batch runs. I don't think I have ever twice turned a bowl...

robo hippy

Sounds like a lot of effort even for my casual turning especially when I can just slap some Anchorseal on the wood and be done with it. If madrone grew in Texas I might have a different view. Fortunately, we have well-mannered mesquite that can be turned to completion without the extra drying step.

 

[Mark Hepburn]

Plus, it makes good brisket. I know, that's I know, that's heresy.

 

[Hugh]

I vote to finish turn the bowl. The bottom is still thick enough to get a finished bowl out of it. Black Locust is very hard when dry. Now it may be part dry......cut OK, but may move a little bit when it dries. Might be dry enough to sand if finished turned now. So....finish turn it, the dry the finished bowl in a paper bag or dry shavings or a towel.......dry slowly....keep it away from air movement. You might have to do a bit of hand sanding after the finished bowl completely dries.
Hugh

 

[Gerald Lawrence]

Ok now I had been wonder why everyone was down on bagging in chips. I have had very good results with it. I only leave in chips for about 2 weeks, but I take out of the bag and weigh at least 4 times a week. Now what I realized tonight is that my shop is airconditioned and that changes the game. Even when I am not in the shop the central is on but set at 90. When I go in from a 95 outside with humidity way up and the shop feels nice and cool. At least that is my theory.

 

[Bill Boehme]

Plus, it makes good brisket. I know, that's I know, that's hErnest.

You'll burn at the "steak" for that ... but not with mesquite.

 

[Jamie Straw]

Sounds like a lot of effort even for my casual turning especially when I can just slap some Anchorseal on the wood and be done with it. If madrone grew in Texas I might have a different view. Fortunately, we have well-mannered mesquite that can be turned to completion without the extra drying step.

Did you miss the part where he said "I don't think I have ever twice turned a bowl..."? Hah hah. Ya gotta love artsy, warped bowls to turn green madrone, and it is fabulous when done well. Some day I'm going to get down to Eugene and pick up a few pointers.

 

[hockenbery]

Ok now I had been wonder why everyone was down on bagging in chips. I have had very good results with it. I only leave in chips for about 2 weeks, but I take out of the bag and weigh at least 4 times a week. Now what I realized tonight is that my shop is airconditioned and that changes the game. Even when I am not in the shop the central is on but set at 90. When I go in from a 95 outside with humidity way up and the shop feels nice and cool. At least that is my theory.

I frequently got mold with chips so I don't use them.
Chips seem to work well in many shops and climates.
Chips come at the right price and there are lots of them so if they work great.

Paper bags work well for me.
Paper bags come at the right price too and the are lots of them.

 

[robo hippy]

Promises, promises Jamie..... I am up in Seattle in October or November, and will be at the Oregon Woodturning Symposium in March, and of course, home most of the time...

robo hippy

 

[Jamie Straw]

Promises, promises Jamie..... I am up in Seattle in October or November, and will be at the Oregon Woodturning Symposium in March, and of course, home most of the time...

robo hippy

Just a short ferry ride from Seattle to Bainbridge Island. Great restaurants and breweries right here on the island. Hubby and I will treat if you can make it over. So, Albany's only 4.5 hrs away, I can make that drive in one swell foop. Will put the symposium on my calendar and in my budget. Always nice to get away in March, it's really dreary here! Hope that area is busy enough to have lots of hotel choices.

 

[robo hippy]

Thanks for the invite, but probably won't make it. I may have a play date with Eric Lofstrum, but have to be back in Eugene for the Duck football game that weekend.... I quit drinking years ago, unfortunately I loved beer, and that was when all the micro breweries started coming out.... Saved me some extra pounds probably... Albany has a couple of motels in walking distance, I think one is a Holiday Inn. It is at the local Fairgrounds, so plenty of motels. Last one, it was sunny every day, frost in the morning, and about 60 in the afternoon... Probably monsoon this year.

robo hippy

 

[Jamie Straw]

Last one, it was sunny every day, frost in the morning, and about 60 in the afternoon...

Oh, brother, I'll hope for a repeat of that! Lucky you, visit with Eric, his demo last month was excellent.

 

[KellyDunn]

Jamie, You gotta work out what works for you. As a full time production turner i am with Bill. Coat the outside with something like anchorseal or sealtight 60 and let it do what ever its going to. You also need to slowly find what thickness you need for any given wood. Some can be thin. Some have to be thick cause they go to town and a dry bowl is so warped you cant get it round again. But thats turning piles of bowls to find out. Now I am gonna lay this out. I live in a wet part of Hawaii. Air drying just does not work on my main woods. Getting under 16% moisture is tough as nails. I know the cheap fridge kiln has been talked about I do think on a thread of yours. It works. And get a cheap moisture meter perhaps on ebay. I have the mini ligno.
Bill is down in Texas where the summers are very hot and dry. Folks in Colorado or other very dry states do not have the problem you and I have. We cant get it dry. They cant stop it drying to fast.
That said. Even a cracked bowl can work for you. Perfection does not exist. Unless that crack becomes a perfect idea for you to work on. My 2c.
I dont check in here much. But I find you are sure not afraid to ask questions. Good on ya.

 

[Mike Johnson]

A crack is natures way of doing some work for you so you can add some inlay and color to the piece.
You can catch a crack early and try to stop it, or you can let the wood do what it wants and then work with what it provides.
Adding some inlay and color to a piece can really add the "WOW" factor if done right.
Even with your bottom crack you could end up drilling the entire bottom out and gluing a different colored wood for the bottom.
Or you could cut the bottom off and sand it flat and glue a new piece of wood on the bottom.
You can cut the bottom at any angle and sand flat to any angle to add some character to the piece.
I like to use colored pieces of Corian on the bottom of some of these types of bowls and vases.
It comes in a variety of colors and is easy to laminate and glue to wood.

 

[Gerald Lawrence]

Jamie I had not thought of this and my wife would kill me if I did this. You could put the turned bowl in a bag and take inside to a conditioned space (heated or cooled). Would even out moisture loss and help to dry faster.

 

[Jamie Straw]

Jamie I had not thought of this and my wife would kill me if I did this. You could put the turned bowl in a bag and take inside to a conditioned space (heated or cooled). Would even out moisture loss and help to dry faster.

Great idea, Gerald (and my hubby would not protest), but after trimming the foot off, adding some CA and re-Anchorsealing, it cracked in a different place, so it's been euthanized.

 

[Mike Johnson]

A moment of silence........ good thing wood grows on trees.

 

[hockenbery]

Jamie I had not thought of this and my wife would kill me if I did this. You could put the turned bowl in a bag and take inside to a conditioned space (heated or cooled). Would even out moisture loss and help to dry faster.

We have a room in the shop where we run a dehumidifier. With RH at 45% - 50% the paper bag technique works well. The one down side of the paper bag technique is high maintenance for the first 5-7 days exchanging the damp bags for dry ones.
The paper bag drying is a great technique for low volume but not good for working with more than a few bowls at a time.