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