Cracking while turning

[Shaun Tyler]

I’m still fairly new to turning but I came across some big maple logs so I’ve just started on my first large bowl. It’s about 16” by 5” deep. The logs were fairly green but were split in the spring and have been stored outside in a covered lean-to. I turned the outside one afternoon and did the inside the next day. The problem I had was with cracks developing on the outside while I was hogging out the innards. They don’t appear to be very deep so I’m hoping they will get turned away when I do the second turning but I’d like to know why. They showed up on both of the end grain faces and there are quite a number of them. After first noticing them I started checking every time I stopped the lathe and would hit the new ones with a bit of CA glue to try to stop them from getting worse and that seemed to work. I was a lot more aggressive than I have been with other bowls I’ve done and I probably didn’t sharpen as often as I should have so I’m wondering if they are “stress cracks” from the wood flexing??? But the bowl is still about an inch and a half thick so I would have thought it pretty stable. Can anybody shed some light on what’s going on? Thanks.

 

[hockenbery]

Can anybody shed some light on what’s going on?

My best guess is you are getting end checks from the wood drying.
Spritzing the bowl with a plant mister every 5-10 minutes will slow the moisture loss and reduce or eliminate the end checking.

The deck is stacked a bit against new turners. I turn a similar size NE bowl in 30-45 minutes - The wood doesn’t have much time to dry. I still mist the endgrain. But I’ve been turning a long time and had terrific teachers.

At this point in your development be safe. Don’t try to race outside your safety zone
If you keep practicing and have good technique you’ll do the roughing faster every time.

You have likely noticed it takes about 4 times longer to turn a 16” bowl than it does to turn a 12” bowl.

I take a shaving 1/2-3/4” wide when roughing with sharp tools.

 

[robo hippy]

Well, kind of like Al said, time can make a big difference, especially with a warmer day, and as near as I can tell, wood that has been stored for a while is more prone to cracking than wood with the spring sap running. For some reason, I have found that dead standing trees are also subject to quick cracking. You can put some stretch film around the outside of the bowl while turning the inside. The spray bottle can help too, but with years of experience, it doesn't take long enough for me when roughing and doing finish cuts. I would expect the cracks in the wood to grow rather than shrink.... Just the way cracks work. Once they start, they always get bigger...

robo hippy

 

[john lucas]

Any. Time you stop turning cover the woid with plastic. It starts drying on the outside abd shrinking. The inside is still wet and not shrinking. So cover it even if you stop for lunch or go to the bathroom. Certainly cover it if you stop for the night.
The other problem is the cracks might already be there just not visible due to the wood sitting. When I cut wood off of a log I cut a 1/2" slice and try to break it. Any cracks and it will break. I keep cutting off slices until I get one that doesn't break. Then I cut my bowl blank.

 

[Dave Landers]

Wood dries from the outside. When you cut away the outside you expose more wet inside and it'll start drying right away. Drying causes movement (shrinkage) and that stress causes cracks. Heat from pushing too hard on the gouge (or sanding aggressively) can contribute, but mostly it's just drying-stress. So, like @hockenbery said, time is a factor. Even a lunch break can be detrimental.
Until you get to the point that you can safely and confidently get your time down, there are a few things you can do...
Turn smaller pieces - most of us wanted to turn something large in the beginning because it just looks fun/cool/etc - but it doesn't really contribute to success....
Get a spray bottle and keep the wood wet. It's not a magic bullet, but can help.
If you have to take a break, wet the wood and cover it with plastic wrap or a plastic bag. Again, not certain but can help.
Of course, depending on your climate and the wood you're using, you may come back after break to find mold starting. So wear protection for your lungs.

 

[John K Jordan]

I’m still fairly new to turning but I came across some big maple logs so I’ve just started on my first large bowl. It’s about 16” by 5” deep. The logs were fairly green but were split in the spring and have been stored outside in a covered lean-to. I turned the outside one afternoon and did the inside the next day. The problem I had was with cracks developing on the outside while I was hogging out the innards. They don’t appear to be very deep so I’m hoping they will get turned away when I do the second turning but I’d like to know why. They showed up on both of the end grain faces and there are quite a number of them. After first noticing them I started checking every time I stopped the lathe and would hit the new ones with a bit of CA glue to try to stop them from getting worse and that seemed to work. I was a lot more aggressive than I have been with other bowls I’ve done and I probably didn’t sharpen as often as I should have so I’m wondering if they are “stress cracks” from the wood flexing??? But the bowl is still about an inch and a half thick so I would have thought it pretty stable. Can anybody shed some light on what’s going on? Thanks.

Shaun,

Wet wood of almost any species is extremely susceptible to cracking (the type you describe is typically called "checking") due to the way wood shrinks as it dries. Checking on the end grain is almost always due to the wood shrinking as the moisture escapes, and it starts on the end grain since the water can escape much faster from the pores open to the end grain than it can on the original round sides of the chunk cut from the tree.

The existing checks may or may not turn away, depending a lot of factors such as how deep you cut. They may LOOK like they are gone but still be there - such "hidden" cracks and checks can come back to haunt you!

There are several things you can do when turning green (wet) wood in a situation like yours.

• One is when you stop for the day, cover the bowl in plastic until the next morning. Some recommend to spritz the wood first with water before wrapping in plastic. (Protect the lathe bed, etc from the water spray)
• Another is to apply a heavy coat of wood sealer to at least the end grain the minute you stop turning. I use Anchorseal but other things work. This will be turned away the next day and won't hurt anything. I would still probably cover the wood with plastic.
• Turn smaller pieces until you get fast at it. Green wood is the easiest wood to turn and done quickly. Typically, bowl turners will turn green wood to a thick wall thickness, enough to allow for the inevitable warping as the wood shrinks when it dries. Then the "roughed out" bowl is dried completely before final turning. That's a whole other topic. I've let the roughed bowls dry anywhere from a few months or longer. I don't turn many bowls but the last I've done I roughed them out years ago. (I tend to go through a phase where I rough out a bunch, then put them up to dry until sometimes much later.)

A student wanted to turn a bowl and I hadn't made one for a LONG time
so I did this one just to see if I could still remember how! Roughed out in 2005.


If you start with smaller pieces and learn to rough to either to a thick wall or turn to final thickness in a few hours, you shouldn't have the cracking problem. Wood turned thin is far less likely to get end-grain checks.
Then after some practice with smaller bowls, ramp up to larger.

Note that if you have more chunks outside and they are relatively short, they may all eventually develop end checks and cracks before you can get to them, even if the ends are sealed. (I always seal end grain on chunks.) You may be in a cooler climate than many of us which may make things easier.

BTW, if you have the choice when cutting the tree, there are some things you can do to protect yourself and one thing that will guarantee disaster.

• Disaster: cut the chunks short and either seal the ends or don't, they will turn into firewood eventually. Splitting them down the pith helps a lot with the deep cracks from the differential shrinkage between the tangential and radial directions but may not stop it. (Some species are better that others)
• If possible, cut the tree in the middle of the winter when the sap is down - this leaves much less moisture in the wood and inhibits the fungal stain that plagues lighter-colored wood in warm weather.
• To help, keep the wood in the shade and off the ground (unless you want to start a "spalting farm". Protect from the sun but don't cover with a tarp except perhaps for short periods.
• Another thing you can do to delay/prevent end checks is spray them with water every day.
• Rule of thumb from the experts: never take more wood that you can turn within a week. This is hard since good, free wood is SO tempting! I've been at turners places where they had

The late great famous John Jordan from TN (not me) was an expert at turning green wood. His work was incredible. If the log was good, he said he always got the whole log, uncut, even if he had to pay for delivery. He put it off the ground and out of the sun. When ready to turn something, he chainsawed 6" off the end and threw it away. Then he examined the end, decided, and cut a blank. He then went inside and turned it immediately, all in one sitting (er, rather, "standing"!) He did a lot of hollow forms from green wood and had learned how to work fast. Once I watched him complete one in maybe 45 minutes. (Turned the outside first to get the form, then hollowed the inside to a fairly thin wall - again, a thin wall rarely cracks.)

I may have forgotten some things but I'm sure someone else will cover them.

One more thing - the more you know about wood, wood structure, and how wood dries and how it shrinks, the better decisions you can make. For this there is one book I recommend: "Understanding Wood" by R. Bruce Hoadley. I bought it on Amazon (bought several copies so I can loan one to students who want to know everything!)

Here's another bowl I did at the same time as the one above, also walnut,
turned from another rough-turned bowl, this one quite thin.


For the most satisfying woodturning experience, consider getting a bandsaw someday, one that will cut at least 12" high. I cut up green wood and make 100s of blanks and let them dry, sometimes for years before turning. Dry wood is harder to turn but doesn't crack, doesn't significantly warp. (I always use 1/2" x 3tpi blades for woodturning)

I'll let a rectangular blank dry and shrink as it will, then cut it round for a bowl blank.
For very large blanks where the log section won't fit on my bandsaw, I'll cut it with the
sawmill behind the barn or with a chainsaw, let it dry, then cut to size.


I suspect someone else will have more and better advice about your situation. 99 percent of my turning is not bowls and from dry wood!

If you are interested, here's a video I did a few years ago on how I make useful blanks from log sections, perhaps smaller sections that you want. However, there is much joy in turning smaller things! (once you develop the skills) Although big bowls may sell well if that's your goal, most people prefer smaller and functional things, especially if they don't have a lot of space.

View: https://youtu.be/4Rbdas-jtD0


A few blanks I cut one day from some green wood, all sealed and
ready to move to the drying shelves. (I track the drying by
weighing some typical blanks from the batch and drying until
the weight stabilizes.)


JKJ

 

[Shaun Tyler]

Thanks for the input. There are a lot of pointers here that I’ll have to keep in mind. Given the one year per inch rule of thumb it never occurred to me that things could be drying that quickly on the lathe. Being new I know I’m slow but I could certainly get the roughing done a lot faster. Even when I’m roughing bowls I’m always practicing different things and aiming for perfection (yet to be achieved). And I still struggle trying to commit to a final shape so I spend a lot longer at it than necessary. I guess I’ve been lucky up until now not to have run into this before. I still find it curious though that there were no cracks when I started again in the morning and that they only showed up as I was hollowing it out. But I guess that’s all part of the differential drying issue.

 

[hockenbery]

still find it curious though that there were no cracks when I started again in the morning and that they only showed up as I was hollowing it out.

The endgrain can dry fast once you start to hollow.
Think of the grain as a bunch of straws.
On a 16” bowl those straws that go to endgrain are 16” long before you hollow it so the water stays in the straws more or less.
When you cut 1.5” wall those endgrain straws are 1.5” long the spinning wood shoots the water out of those straws.
So the endgrain dries.

 

[Richard Coers]

Did you have the end grain coated while they sat outside? If not, they didn't have a chance of not cracking. There is a great chance that the cracks were already there for sitting too long, or the wood was filled with drying stresses and they just opened up when exposed to air.

 

[John K Jordan]

Given the one year per inch rule of thumb it never occurred to me that things could be drying that quickly on the lathe.

Something to know is that "rule of thumb" is mostly erroneous AND it doesn't even apply here. The so-called "rule" is for flat boards and is supposed to predict the time to EMC, not the local shrinkage due to loss of water at the end grain. And the "rule" is actually different for different species and can be different for different trees of the same species and even different parts of the same tree. Flat boards have only side grain down the length with end grain at the ends. I have a sawmill here and can say if I stack MOST species of lumber to dry and don't seal the ends, all the ends will start checking immediately and the checks will eventually result in cracks and splits. It can't help it, it don't have no choice!

The rule really falls apart with wood thicker than 1-2 inches. I've got some fairly large blanks that took years to dry, measured by the weight method. Some species are FAR slower at drying than others, much depends on the pores, whether they are small or large or are plugged with tyloses, the coarseness of the grain, the hardness of the wood, the ambient temperature and relative humidity, the amount of air movement, and probably the phase of the moon and the sign of the zodiac.

And for the speed of end-grain checking, I've seen wood visibly check while I was looking at it just after felling the tree. Cut a bunch of persimmon the other day and put it in a covered truck bed. All had some end grain cracks/checking by the time I got it home and could start applying sealer. If we had sealed after each chainsaw cut, it might have been better but might have made a mess in the guys pristine truck bed. (In this case, it was no problem, there was plenty of wood on the ends to cut away cracks on the bandsaw.)

JKJ

 

[Alan Weinberg]

There’s also the superficial cracking I sometimes see when sanding. Maybe this is due to the heat of sanding. I’m not sure how to prevent this, maybe sanding at a lower speed and misting?

 

[hockenbery]

Maybe this is due to the heat of sanding. I’m not sure how to prevent this, maybe sanding at a lower speed and misting?

I sand most often when the wood is dry. Then as long as the sanding disc is shooting a stream of dust there shouldn’t be much heat because the paper is cutting. When the stream goes away the paper is dull and not cutting so friction will cause heat buildup.

Damp wood will clog paper quickly making it dull. If I do sand wet wood I use abranet. It takes longer to clog, stays sharp for a long time, and can be cleaned by soaking it in water and tapping the abranet against a tool rest to clear the clogs.

When I do HFs and NE bowls with one turning. I let them dry - takes 3-4 days- then sand off the lathe using a 90 degree drill with Velcro discs. No heat checks.

 

[Dave Bunge]

Like Al, I tend to use Abranet when I want to sand wet wood. I find that compressed air is very effective for cleaning it when it gets clogged, faster and more thorough (at least for me) than tapping it against something.

 

[Alan Weinberg]

I tend to use Abranet when I want to sand wet wood.

Why not use it all the time? Cost? Thanks to both of you.

 

[Marc Banka]

Good suggestions here, mostly.

First, if I might share my method for making bowls beginning with a tree.
I can’t take down a tree, but I can be there when the felling is done.
I get the logs onto the truck and cover each in plastic bags. Once home cut each into square blanks. Put each in plastic bags.
Once they are all milled, rough turn to bowls, anchor seal and store. The idea being that cracks start right after the saw cut, not if they are cut off from airflow. This allows you to use more wood with far less waste due to damage.
It certainly makes for a busy week, but the results will speak for themselves.

The wood should not be exposed to air unless actively working with it, or till rough turned and sealed. Whether it’s wet wood or second turning, never leave it exposed to air unless working on it, actively. Leaving it on the lathe overnight is fine. Wrap the piece, including the chuck in a plastic bag. Make it snug, secure it around the spindle.

If one does these things, the piece will be exactly as it was at the previous session.

The complaint I have about the suggestions made that I absolutely object to is the notion that you need to go faster. That speed is some goal to which we should aspire. Why is it that turners here boast about their speed? What does it do for you? Yes, you wouldn’t need to worry about wood drying on the lathe, not that that’s a big issue. I suppose it’s important if one makes their living at this, is a “production turner”, whatever that is. I wonder how many here are in that camp.

 

[Dave Landers]

The complaint I have about the suggestions made that I absolutely object to is the notion that you need to go faster. That speed is some goal to which we should aspire. Why is it that turners here boast about their speed? What does it do for you? Yes, you wouldn’t need to worry about wood drying on the lathe, not that that’s a big issue. I suppose it’s important if one makes their living at this, is a “production turner”, whatever that is. I wonder how many here are in that camp.

I don't think it's boasting, at least not for me. For me it's an observation - more like "huh, that used to take a lot longer (or be more difficult, or feel less awkward, etc)... maybe I've learned something along the way."

 

[hockenbery]

The complaint I have about the suggestions made that I absolutely object to is the notion that you need to go faster

I don’t think any turners I know have a goal of speed. Speed is just something that happens.
I believe speed is an advantage when working with wet wood.

Everything done well takes as long as it takes

I had a 13 year old student who asked if he could do Napkin rings again next class. He said he did four in the class today. Took him 40 minutes to do the first, 25 minutes to do the second, 20 minutes to do the third, and 15 minutes to do the fourth. He thought he would like to make 6 the next class.
I told him he could turn napkin rings but instead of making 6 as a goal, make 1 good one, then make another good one…
He got it! I think he made 8 great ones.

 

[Marc Banka]

“I turn a similar size NE bowl in 30-45 minutes“
“Don’t try to race outside your safety zone”
“If you keep practicing and have good technique you’ll do the roughing faster every time.”
“Well, kind of like Al said, time can make a big difference, especially with a warmer day”
“Until you get to the point that you can safely and confidently get your time down”

I stand corrected on the boasting comment.

Still, the comments above, while not stating that one must be quick surely suggest that it’s a goal. Why is turning a NE bowl in 30 minutes good? Why does one need to rough faster? Why is racing good, whether within or outside one’s safety zone?

I agree that with skill, practice, study, a thousand or more issues to master, the time spent on an identical task will be less than when one first started the journey. That’s true of any endeavor. But speed should never be the goal. It’s only the natural byproduct of one’s hard study.

Skill is the goal. Less time just happens as a result.

 

[hockenbery]

Skill is the goal. Less time just happens as a result.

Exactly!

It’s just what happens when I let the tools do the work.

 

[Brian Gustin]

Why is turning a NE bowl in 30 minutes good?

With the caveat that most NE bowls are also being turned green - Because the wood moves as it dries, so you DO need to get start to finish fairly quickly if you wish to minimize sanding & tool marks as well as uneven thicknesses...

my first couple NE bowls took me a couple hours to complete, and both left a lot of sanding and extra work to get them anywhere near to looking "completed" because I was taking too long to turn them and they warped on the lathe as they began to dry (later bowls I tried spritzing with water as I turned, which only helped a very little - they still warped out of shape and made finish cuts much harder) It was not until I started getting "into the swing of it" and was able to get NE bowls done much more quickly (and I also learned along the way how to nibble down the inside to finish thickness a bit at a time as I went deeper) that I was producing much better results with quicker pace of turning from start to finish. I typically can do a 6 to 8 inch NE bowl in 45 minutes or less, now that I've gotten the sharp tools and practice at getting my form (outside shape) much more quickly and smoothly, and often have a nice NE bowl that requires next to no sanding after it has dried (Still haven't achieved one that did not need some sanding touch up, but that's an ultimate goal..)

 

[Don Stephan]

Shaun

You might consider joining a wood turning group and ask to work with a recognized mentor as you turn a couple bowls. There is no substitute for good one on one support.