Stopping Cracking Wood While Turning Green?

[Eric Jacobson]

What am I doing wrong?

Sometimes I turn green bowls or pepper grinders. I'll be turning and everything looks fine when suddenly I look closer and I see about 20 or more little hairline cracks. (shown in the Hickory and Pao Ferro pictures below)

I live in Georgia and I turn outside, sometimes in the sun, sometimes in the shade. Does this have anything to do with it? Is the wood drying out too quickly? Or is it happening when I sand using the 2" velcro discs on my drill?

How can I prevent this and is there anything I can do once it happens?

[Bruce Pratt]

Eric,

You may be overheating the wood when sanding. Try reducing the rpm or pressure against the wood.

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Bruce

[Nathan Hawkes]

Well, a lot of things could be causing the cracks. I turn almost exclusively green wood, and have experienced most of what you're talking about. Depending on the time of day, I get direct sun on the lathe; if I forget and leave the door open, I may get checks. The pics suggest more of an overheating problem from what I can see. I've had the same problems if I try and sand something that is "too wet", and usually let things dry in a place with no direct light, and not too much, but not too little airflow. In other words, not in front of a fan or in the wind. Let the sanding discs do the work without having to mash them into the wood; if you're having to push hard, its either time to change the disc, or start with a coarser grit and work up to it. Just my $0.02.

Edit: I meant to add that I also use a drill, 2500-2750 depending on which one I'm using, and shopmade foam mandrels with 1" thick blue upholstery foam glued to MDF discs with 1/4" threaded adapters so that I can avoid having to pull the discs off for each grit change. I have 1 for each grit, and can change the grit just as easily as pulling off & reapplying a new disc. On the surface of the foam I used contact cement to glue very thin upholstery leather so that I could stick and velcro industrial type (small short hooks) to the surface. I had a hard time getting the velcro to stick without the leather. The very flexible foam makes it so much easier to get into the curves.

[Bernie Weishapl]

Sanding heat could cause that problem you show or drying to quickly outside in the sun. I never use green wood when doing pepper mills as they move or crack when green.

[Steve Schlumpf]

Eric - anything you do that speeds up the drying time will cause cracks.

Having the wood in direct sunlight, allowing the wood to dry while on the lathe, heat caused from sanding - any one of those situations will cause checking! About the only thing you can do at this point is to CA every crack - or if you have it turned thin enough - start applying your final finish so that it soaks into the wood and helps to bond it together.

[Allen Neighbors]

Eric, I live in Texas where it's hot and dry in the summer, and I turn a lot of green wood - and to keep it from cracking on the lathe, once I get the outside turned, I keep it wet while I turn the inside. I have an old 409 bottle that I keep filled with water and soap mixture. The suds just help it to not dry quite as fast.

[Jim Terrill]

Eric, I live in Texas where it's hot and dry in the summer, and I turn a lot of green wood - and to keep it from cracking on the lathe, once I get the outside turned, I keep it wet while I turn the inside. I have an old 409 bottle that I keep filled with water and soap mixture. The suds just help it to not dry quite as fast.

Do you have any issues with the surfactant messing with your oil finishes?

[Allen Neighbors]

Do you have any issues with the surfactant messing with your oil finishes?

No. I use Ivory Concentrated Dish Washing Detergent. It's clear, so there's not discoloration; and it isn't affecting the sanding, other than making the dust smell better, and the oil finishes go on just like bare, unsoaped wood.

[Eric Jacobson]

Allen, that's a great idea. I will try it the soap and water method. Do you keep the wood wet 100% of the time?

Two things I noticed after thinking about my recent habits more:


Does the CA accelerator spray cause an outbreak of these cracks? I tried to CA the first several cracks and it seemed like after I sprayed the CA accelerator , a ton more cracks formed within seconds.
The other new thing I've been doing, that may be causing the increased cracking is to wet the wood to raise the grain before sanding. I saw this in a video. Sand to about 180 grit. Wet the wood with a wet cloth. Let it dry. Then sand with 220 and 320. That is what I did prior to both these crack incidents. Maybe it's just a coincidence.

[Allen Neighbors]

Sorry, I couldn't get back faster, Eric. Yes. When I'm turning the inside, I keep the outside wet with the soapy water, until I get the inside finish turned. If it starts to dry out in spots, I spray it again. It works for me in this part of West Texas.

[Rob Holcomb]

I'm confused. I thought when turning green wood, you turned down to a rough thickness that wouldn't be too thick to dry, and then when dry, you finished the turning and sanded. I am getting some green wood in the near future to try this. Are you supposed to sand the roughed out piece before allowing it to dry?

[Donny Lawson]

I was not taught about sanding roughed out bowls.It would be a waste of time to sand a bowl that is in the roughed out stage.Just hollow it out and seal the end grain,let dry for about an hour or so and put in a bag with some shavings,seal the bag shut and forget about it for about 8-10 months.Then it would be time to start on another one.
Donny

[Allen Neighbors]

I'm confused. I thought when turning green wood, you turned down to a rough thickness that wouldn't be too thick to dry, and then when dry, you finished the turning and sanded. I am getting some green wood in the near future to try this. Are you supposed to sand the roughed out piece before allowing it to dry?

Rob, most everyone turns green wood into roughouts, and then dry them before finish turning and sanding... no sanding on roughouts.:)

Some of us turn some green woods to finished thickness, and then sand them to finish... wait for them to dry, then sand again with the last couple of grits because of the raised grain, and then finish.:)

And some of us turn green woods to finished thickness, then wet sand, and spin "dry" and finish them. I've got several pieces... and most of them move a little -- some of them move a lot -- while finish drying.:eek:

Hope this helps solve the confusion. :D

[Richard Madison]

some green woods to finished thickness, and then sand them to finish... wait for them to dry, then sand again with the last couple of grits because of the raised grain, and then finish.

But which woods are which Allen?

[Rob Holcomb]

Yes, that explains things better to me. Thank you. I'm getting a few pieces of a Cherry log tomorrow. I will turn down to a roughed out stage and then dry one with shaving and paper bag, and another with DNA I think, just to see the differences in drying time. I call my new lathe "the time killer" right now. I'm making a blanket chest for my little nephew and after I glue up a panel, it's over to the lathe to practice more while I wait. I'm spending more and more time at the lathe as each week goes by. I was warned about it's addictive qualities lol

[Richard Coers]

I might add another thought to the cracking. Are you turning close to the sawn edge, or do you remove a couple of inches of the blank before turning? The reason I ask, is that some of those cracks may have been in the blank from sitting around. Then you see the cracks when you turn it. Just another thought. Cherry is not going to be an easy wood to experiment with. Any fruit wood will crack very easily.

[Eric Jacobson]

Richard, these are cracks that were not previously in the blank. In fact, one time I turned some green walnut and finished it all the way through to buffing and waxing...then I ran inside (into air conditioning) to show Melissa. She took the freshly made bowl from my hands, held it, and said, "what's that noise?". It sounded like a bowl of Rice Krispys. I took the bowl from her and looked closely. I could actually see cracks popping open on the bowl...

[Richard Madison]

Eric, There are a couple of posts in another thread describing this same phenomenon when a piece was moved quickly to an area of much lower humidity.

[Allen Neighbors]

But which woods are which Allen?

Some woods that I finish turn green: Mesquite, Black Walnut, Bois d'Arc, Sycamore, American Elm.... there are a few more, but I just can't think of them at the moment. Some woods are really bad about raising the grain during the drying process, some are not so bad... you just have to try one to see what happens.

Oak grain will raise big time, when drying, but I still turn it to finish sometimes, when I'm wanting to see some weird warpage... just have to resand and apply finish off the lathe... (I hate to do that, too.)

[Richard Madison]

Thanks Allen. Oak has always been a challenge for me but have managed to get a few decent pieces from oak. Love the results when successful. Mesquite is easy of course, mixed results with Bois d'Arc. I seem to have the best success rate by keeping it in log form with the ends VERY well sealed to keep it as wet as possible until time to cut and rough a blank.