Consistent cracking around tenon while drying once turned bowls

[Nick Allen]

 

[Nick Allen]

Hey folks, I’m new here and joined since most technical questions on the internet seem to get the most helpful responses here!

I’m also new to turning! I’ve turned three green slippery elm bowls that were 15% moisture initially. I sealed the end grain with tite-bond 2 and let them dry for a couple weeks in brown paper bags with shavings.

All three developed the cracking along the tenon as you see here. Sometimes there would be two parallel cracks on each side of the tenon. No cracks elsewhere.

I’m sealing the cracks with CA glue and giving them a couple more weeks before checking the moisture again and trying to turn them (carefully of course); however, I’ve got a lot more elm stock and don’t want to repeat this mistake.

Some ideas that I plan to address:
1. Hollowing out a little deeper into the bottom of the bowl so the bottom (with tenon) isn’t so thick
2. Using anchor seal instead of glue while drying
3. Got a one way Wolverine with varigrind jig to make my cutting edges sharper and more consistent in shape
4. Slowing down and taking less aggressive cuts since I’m still getting some dramatic tear outs when moving too fast (wondering if that’s the primary culprit).
5. Buying a new chuck. The one I have now is the nova 50mm 2 inch JS50N. I don’t think it’s big enough for the 8+ inch bowls I’m turning and the “tooth” at the shoulder almost always results in the bruising marks you can see there.
6. Continue to focus on a properly fitting tenon. I’ve spent a lot of time on this and think this isn’t the issue, but what do I know?

I also don’t think the wood is drying “too fast” since I’m in Rochester, Minnesota and not a desert.

Anyhow, if you all have any thoughts on how I can avoid this... I would GREATLY appreciate it!

 

[Brian Gustin]

Think your problem is the pith - You need to cut out the pith (center of log) before cutting bowl blanks - with the pith in the middle (Can see it in middle of your bowl curve) the pith does not shrink as much as the outer heartwood and sapwood , so as the rest of the wood tries to shrink, it will crack to allow for trying to wrap around the pith. So, best thing to do is when cutting your logs rip them down the middle, preferably cutting either side of the pith , then turn your bowls ASAP - you don't want to let them dry before turning , or they will likely crack anyways - turn your rough bowl to a thickness that is about 1/10th of the diameter (somewhere around 1/2 inch for a 5 inch diameter bowl, 1 inch for a 10 inch bowl, etc) and try to keep an EVEN thickness all the way through (and don't forget to count the tenon as part of the thickness, though don't turn bottom too thin either) THEN bag the roughed bowl with shavings and let it dry a while.. a better way to check for dryness of your roughed bowls, weigh them in grams of weight, record the weight, then weigh again in a couple weeks - when it stops losing weight (and might gain some) check weight more often until you get a few days where it never changes, then your wood has probably stabilized, and you tend to get better results finishing the bowl then...

 

[hockenbery]

Hollowing out a little deeper into the bottom of the bowl so the bottom (with tenon) isn’t so thick

Generally I like to get the bottom with the tenon about the same thickness as the rim wall or just a little thicker

Buying a new chuck. The one I have now is the nova 50mm 2 inch JS50N. I don’t think it’s big enough for the 8+ inch bowls

a 2” diameter tenon is a good size for that bowl

i do my drying in paper bags very successful.
also if the pith is in the side wall - that will definitely cause the radial cracks.
leaving the pith in requires a thinly turned wall. Once turned.


You might consider looking at the thread on working with green wood.
it is mostly taken from a demo. Slides on wood properties and how it moves, video - turning a bowl for draining, video - mounting and 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

 

[Nick Allen]

Think your problem is the pith - You need to cut out the pith (center of log) before cutting bowl blanks - with the pith in the middle (Can see it in middle of your bowl curve) the pith does not shrink as much as the outer heartwood and sapwood , so as the rest of the wood tries to shrink, it will crack to allow for trying to wrap around the pith. So, best thing to do is when cutting your logs rip them down the middle, preferably cutting either side of the pith , then turn your bowls ASAP - you don't want to let them dry before turning , or they will likely crack anyways - turn your rough bowl to a thickness that is about 1/10th of the diameter (somewhere around 1/2 inch for a 5 inch diameter bowl, 1 inch for a 10 inch bowl, etc) and try to keep an EVEN thickness all the way through (and don't forget to count the tenon as part of the thickness, though don't turn bottom too thin either) THEN bag the roughed bowl with shavings and let it dry a while.. a better way to check for dryness of your roughed bowls, weigh them in grams of weight, record the weight, then weigh again in a couple weeks - when it stops losing weight (and might gain some) check weight more often until you get a few days where it never changes, then your wood has probably stabilized, and you tend to get better results finishing the bowl then...

Thank you Brian! I remember now wondering how it would turn out with the pith... one other bowl has the pith in it too... one doesn’t though (picture). That one has the same parallel cracks near the tenon (now filled with CA). Does that change your thoughts at all?

Regarding your comment about turning as soon as you’ve portioned the logs... if I don’t have the time to do that... is sealing the end grain with glue until I can get to it a reasonable stop-gap measure?

And I’m going to have to find either a lot more free time or a lot more patience before I can do serial weights... sigh. Some day!

 

[Brian Gustin]

Thank you Brian! I remember now wondering how it would turn out with the pith... one other bowl has the pith in it too... one doesn’t though (picture). That one has the same parallel cracks near the tenon (now filled with CA). Does that change your thoughts at all?

Regarding your comment about turning as soon as you’ve portioned the logs... if I don’t have the time to do that... is sealing the end grain with glue until I can get to it a reasonable stop-gap measure?

And I’m going to have to find either a lot more free time or a lot more patience before I can do serial weights... sigh. Some day!

1) Not really - As mentioned, the other problem with cracking , generally, is if you are trying to let things dry before turning - as Hockenberry said, things will turn out better if you can get the wood to a consistent thickness for the most even drying (and it does help to seal end grain in any case) - Because the wood is not an even thickness, it dries unevenly - the wood that dries is shrinking, the wood (deeper inside) that hasn't shrank as much is going to make the outer wood crack to relieve the drying stresses.

2) Yes, In fact, try and keep logs as complete as possible until ready to both portion them and rough turn them within the same few days' time and that way you only will need to cut off maybe 3 or 4 inches from ends of logs to cut away the checking But, sealing them helps much - If you can, I'd suggest getting yourself a can of anchorseal which is basically an emulsified wax coating that you paint on (although I have also had success with plain PURE linseed oil - not boiled linseed.. I happened to have several ANCIENT quarts of it that came from my granddad's farm) Ive found it works even better if you can seal the entire portioned blank (all the way around except for bark if it is still firmly attached) - the goal is to stop/reduce/limit the drying as much as possible until you can rough out the bowl to an even thickness..

3) get a little kitchen scale (cheapie from amazon) that reads gram weights, soon as I rough a bowl, I note measurement and weight in grams just before packing it away in a box full of the shavings that came off it (I write weight on tenon, then a quick note of date, size & species of wood, and weight on the box flap - can be as many bowls as you can fit in a box) and the weighting thing only takes a matter of seconds.. then just wait the (anywhere from 3 months to 18 months depending on size & thickness) time to let things slowly dry a bit - I usually wait at least 3 months before going through a box of packed bowls, then check them for cracks/ defects. etc. tossing those that are obviously firewood (cracked tenons are often fatal to the project) and weigh them out once again.. if any seem to be still "heavy" (seat of the pants call) I might re-pack those, but the rest I set out in a cool dark place to let them finish drying.. then every once in a while on a whim I might check a few weights (and again just write weight on tenon and date checked)

Finally, if you are AAW member at all (even associate/trial member) check out this month's may issue of FUNdamentals (AAW publication) because there's a couple of good articles on bowl blank prep and log cutting in there too..

 

[Nick Allen]

also if the pith is in the side wall - that will definitely cause the radial cracks.
leaving the pith in requires a thinly turned wall. Once turned.

I did not know the once turned, thin walled rule for piths! And I looked up radial cracks... learned that you can’t see them and they often arise when the pith isn’t bisected first thing... now I wonder if all my stock is harboring invisible radial cracks!!

thank you so much for the feedback and resource!!

 

[Nick Allen]

Error

 

[Nick Allen]

1) Not really - As mentioned, the other problem with cracking , generally, is if you are trying to let things dry before turning - as Hockenberry said, things will turn out better if you can get the wood to a consistent thickness for the most even drying (and it does help to seal end grain in any case) - Because the wood is not an even thickness, it dries unevenly - the wood that dries is shrinking, the wood (deeper inside) that hasn't shrank as much is going to make the outer wood crack to relieve the drying stresses.

2) Yes, In fact, try and keep logs as complete as possible until ready to both portion them and rough turn them within the same few days' time and that way you only will need to cut off maybe 3 or 4 inches from ends of logs to cut away the checking But, sealing them helps much - If you can, I'd suggest getting yourself a can of anchorseal which is basically an emulsified wax coating that you paint on (although I have also had success with plain PURE linseed oil - not boiled linseed.. I happened to have several ANCIENT quarts of it that came from my granddad's farm) Ive found it works even better if you can seal the entire portioned blank (all the way around except for bark if it is still firmly attached) - the goal is to stop/reduce/limit the drying as much as possible until you can rough out the bowl to an even thickness..

3) get a little kitchen scale (cheapie from amazon) that reads gram weights, soon as I rough a bowl, I note measurement and weight in grams just before packing it away in a box full of the shavings that came off it (I write weight on tenon, then a quick note of date, size & species of wood, and weight on the box flap - can be as many bowls as you can fit in a box) and the weighting thing only takes a matter of seconds.. then just wait the (anywhere from 3 months to 18 months depending on size & thickness) time to let things slowly dry a bit - I usually wait at least 3 months before going through a box of packed bowls, then check them for cracks/ defects. etc. tossing those that are obviously firewood (cracked tenons are often fatal to the project) and weigh them out once again.. if any seem to be still "heavy" (seat of the pants call) I might re-pack those, but the rest I set out in a cool dark place to let them finish drying.. then every once in a while on a whim I might check a few weights (and again just write weight on tenon and date checked)

Finally, if you are AAW member at all (even associate/trial member) check out this month's may issue of FUNdamentals (AAW publication) because there's a couple of good articles on bowl blank prep and log cutting in there too..

Awesome, thank you so much! I’m wondering if waiting a couple weeks to chain saw the logs is the issue... and wondering if all the elm stock is now garbage because it’s harboring invisible radial cracks... I did cut off the checked ends (generally 3-4 inches on each side) ... but maybe waiting too long and not bisecting the pith right away has doomed it all!

 

[Brian Gustin]

Awesome, thank you so much! I’m wondering if waiting a couple weeks to chain saw the logs is the issue... and wondering if all the elm stock is now garbage because it’s harboring invisible radial cracks... I did cut off the checked ends (generally 3-4 inches on each side) ... but maybe waiting too long and not bisecting the pith right away has doomed it all!

Nah -I would not condemn the whole pile because of possible radial cracks that haven't been seen yet... just be aware you need to look for them.. if you already cut them down to blank portions, your best bet is to try and cut any you possibly can to cut away the pith, I think Really a lot depends on log / blank size - if you have room to cut away pith and/or re-cut the blanks (perhaps smaller bowls? platters? worst case, rip them to spindle stock?) then you might be able to save a lot of it. However when you do go to turn the blanks into bowls, that would be the time to inspect the piece for cracking and defects (and even when I put my tenons into the jaw chuck, if I do not yet have bowl interior or bottom finished, I will always bring up tail stock at least to "just kissing" the piece, until I absolutely have to move it away - so if the tenon lets loose, it isn't as likely to go flying.. and usually for me when a tenon has let loose, it has been just shortly after I chucked it into the jaws.. although I have had a couple come off that had cracks like in your first photo.. only had to happen twice before I decided I would either cut away the tenon and make a new one (or possibly a mortise), or it went to the firewood pile..

 

[Don Wattenhofer]

A few observations:
1 the pictures you posted look like red oak from the color, the rays radiating from the pith and the black tannic acid stains. The tannin probably stained your fingers black also.
2. If the wood started out at 15% moisture it would already be full of surface checks so you can not depend on a moisture meter which can not read very far beneath the surface.
3. You need to study how wood shrinks as it dries due to radial and tangential shrinkage rates so you can understand why the cracks occur..
4. If you have not already done so join the local AAW chapter.
4. The wall thickness needs to be uniform and in the case of a once turned bowls probably no more than 1/4" therefor once turned is maybe not the best project for a beginner.

 

[hockenbery]

did not know the once turned, thin walled rule for piths! And I looked up radial cracks... learned that you can’t see them and they often arise when the pith isn’t bisected first thing... now I wonder if all my stock is harboring invisible radial cracks!!

Its a guideline more than a rule.
In most woods the tangential shrinkage around the growth rings is about 2x the radial shrinkage from the center to the bark.
this means each ring wants to shrink more that the wood it surrounds will shrink
in a thin walled vessel the pith can push out into a bump to relieve the stress like the old collapsible camp cup.

cutting logs through the pith let the growth ring half’s shrink without having to crack

one wood in particular, Norfolk Island Pine, is almost always turned endgrain from a log section. This let the ring of knots characteristic of NIP be presented as a feature in the turned piece. this wood can be turned with the pith with high success because the ratio of tangential to radial shrinkage is about 1.5 instead of around 2 for most woods. NIP is also one of the few woods that has a hollow pith.

 

[Don Wattenhofer]

cutting logs through the pith let the growth ring half’s shrink without having to crack

That is a very deceptive comment or should I say guideline, a half round is still subject to checking due to the same forces of shrinkage, that is why you need to rough turn to a uniform wall thickness just like a saw mill rough cuts into flat boards. The end grain areas should be coated with some thing like Anker Seal to slow down the rapid end grain moisture loss that causes the end grain checking.

 

[hockenbery]

That is a very deceptive comment or should I say guideline, a half round is still subject to checking due to the same forces of shrinkage, that is why you need to rough turn to a uniform wall thickness just like a saw mill rough cuts into flat boards. The end grain areas should be coated with some thing like Anker Seal to slow down the rapid end grain moisture loss that causes the end grain checking.

I think you meant well - sealing Endgrain is important.
“deceptive” is a bit harsh.


the slides I suggested do present both the sealing and cutting through the pith.
the diagram shows how the growth rings shrink in the half log to make a peak on the sawn face.

 

[robo hippy]

I prefer to keep my logs whole and cut off sections as I need them. A bit less waste that way. Like Al says, I do keep them off the ground, out of direct sun and wind. I have a heavy vynal tarp under and over the top. I do get to buy whole logs and my guy has a flat trailer that makes it simple to roll them off the edge. If you want to keep one end on the ground, that does work, and some times you get spalting. The end on wet or damp ground will not crack at all. If it is on dry ground, that is as bad as direct exposure, even if sealed because the drier dirt will suck out any end grain moisture. It is another art form to learn what works best for each different wood you get....

robo hippy

 

[Don Wattenhofer]

I think you meant well - sealing Endgrain is important.
“deceptive” is a bit harsh.


the slides I suggested do present both the sealing and cutting through the pith.
the diagram shows how the growth rings shrink in the half log to make a peak on the sawn face.

View attachment 38728

Just because you have a drawing that shows the shrinkage of a half log with out any checks does not mean that it will happen that way in real life. I have gotten wood via the wood raffle at meetings in half log pieces all slathered with anchor seal on the ends with radial checks that had been kept to long without turning so I stand by my previous post.

 

[hockenbery]

Just because you have a drawing that shows the shrinkage of a half log with out any checks does not mean that it will happen that way in real life. I have gotten wood via the wood raffle at meetings in half log pieces all slathered with anchor seal on the ends with radial checks that had been kept to long without turning so I stand by my previous post.

what you said was correct. What I presented was correct as well
both agree.....

Read the text in slide.

end checking is going to happen about 100% of the time Even with anchor seal.

it rarely goes deeper than 2” so cutting a half round 4” longer than the desired blank pretty much guarantees being able to cut a check free blank A few weeks or months later.

the question was about radial crack
the next slide has more about end checking

 

[robo hippy]

End checking can begin as soon as the chainsaw goes through it.... Same with major cracks. I have noticed that with some of the maples, they have a shine to them if you turn it fresh, but if you let it sit for a month, it can be very dull....

robo hippy