Wood cracking, how to prevent - Woodworking Talk - Woodworkers Forum

 
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post #1 of 20 Old 11-25-2008, 11:10 AM Thread Starter
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Wood cracking, how to prevent

Hello, new turner here with some questions:

I have turned three pieces so far, of oak that I found as a deadfall in the forest. The pieces tend to crack within hours of being taken inside the house. The pieces started out about a foot long and 3" in diameter, ending up as a candlestick shape about 1-1/2" in diameter. I am working on an old Shopsmith which I rebuilt.

What can I do to prevent cracking? Should I pick up green wood or wood that has been down for some time? Should I let it dry out under cover for a few months before turning?

After turning, should I leave it covered outside to protect it from the dry, heated house air?

Is oak a difficult wood to turn? It is available in my area and I like the look of it. It is also very sturdy.

If I stain or put tung oil on the piece after turning, will that reduce cracking?

It looks like the actual turning is the less difficult part, more difficult is to get the wood to stay stable and not crack after turning.
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post #2 of 20 Old 12-02-2008, 12:19 AM
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I have been turning for about a year and a half, and only in the last 6 months have I really been experimenting with unprepared (not store bought wood). I have not been very successful with woods that I just found lying around. I have tryed with cherry, plum, and cedar. For me it all cracked, the piece of cherry started cracking on the lathe the plum was finished and in the house then cracked. Here lately I have had luck with woods that either I cut myself or get shortly after someone else cuts it. I am still learning, trial and error,, mostly error.

I have turned White Oak before and have some pieces in my shop right now a friend of mine wants some pens from, it does turn farely well.
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post #3 of 20 Old 12-02-2008, 05:57 AM
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Oak is very bad about cracking/splitting. I like to work with solid wood vs plywood but have a problem with oak.

Even with store bought wood it will often crack and shrink when brought inside. I am sitting here looking at a mosaic drawer front that is on my computer desk. Some months after I had made it and brought into the house the wood shrank and has left a visible crack down a glue path from top to bottom.

Other times I have had solid wood split.

My problem here is that my oak sits in a not conditioned environment in my garage until I use it. Then it comes into the inside air conditioning and dries out.

I think that if I brought it inside for 2 or 3 months before using it may stabilize.

G
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post #4 of 20 Old 12-02-2008, 09:39 AM
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Do some searching on the internet about turning green wood. You will find a lot of information to consider. some of it good and some of it pure speculation.
Here's what happens. When a tree is cut it is full of water. As it starts to dry it drys faster by the water leaving the ends and the outside drys first. When wood drys it shrinks. so the outside is drying and shrinking and the inside is drying slower and staying about the same size. Imagine two circles one inside the other. The outside one is getting smaller and the inside one is staying the same. Something has to give so the wood cracks.
Wood takes about a year per inch to dry so a tree that has been down for a few years is still very green on the inside. In fact I read the other day that wood that is down will tend to stabilize after a while and take much longer than a year per inch to dry.
How do you deal with this. Well you have to either turn it thin so it can dry and warp without cracking or you have to slow down the drying time. It gets to be complicated about how to deal with this because every project is different. To start off with split the wood through the heart so you've brocken the circle. This lets the wood move a little and lessens the chance of checking. Then seal the end grain with a sealer. I use either wax or Anchorseal end grain sealer. This only slows down the loss of water but won't stop it from checking if it drys too fast.
to get around this I try to harvest the wood. I saw it into 2x2, 3x3, 4x4 etc and seal the ends. Then I put it up off the ground to dry. It will take a year or more but if you do this often enough you will always have some dry wood to deal with. Thing like candlesticks or lamps that are fairly thick have to be completely dry or they will crack when you take them inside where it's really dry and warm. To do boxes I take the 3x3 blanks and cut them down to 4 or 5 inches depending on the length of the box and then put them in the microwave. I heat them up until they are warm and let it cool and do that again. It may take a dozen or more heatings to dry and it still may split but I've had pretty good luck with wood that has been sitting for a while before being subjected to the microwave.
Short candlesticks might also be dryed in the microwave. The reason this works is the microwave heats from the inside out and equalizes the drying stresses. It can smell up the microwave so be careful or buy a cheap one for the shop.
To turn large lamps I hollow out the inside so the sides of the lamp are only 3/8" or less. this lets it dry more evenly although it will warp depending on how the grain runs through the piece and if there is a knot in the piece. it still might check at the knot.
To turn bowls as soon as possible I rough out the bowl so the walls are about 10 percent as thick as the bowl is large. I seal all endgrain areas and then put the bowl in a paper sack or box to restrict the air movement. You want even wall thicknesses all the way around, even the bottom. I let this dry until it stops losing weight and then re-turn it for the final product. It takes about 6 months for the average bowl.
to turn a bowl to completion in one sitting I turn it so the sides and foot are all about 3/8" or less. If it takes a while to turn the bowl I spray the outside with water to keep the whole piece drying at the same rate. When I finish the inside I lightly hit the whole piece with a hair dryier to dry the surface. Then I sand the bowl and put it in a paper sack to dry for a few days. It will warp so when I pull it out I sand the foot flat and it's ready to go.
OK that was a long winded scenario of how to deal with green wood and I just touched the surface. Read all you can. Or you can do what I did early in my turning career and that is to glue up dry wood to get the sizes you need. There are some excellent books on segmented turning and since you have a shopsmith you have all you need to do that. I started with a shopsmith. Order Malcolm Tibbets book on segmented turning and you will learn all you need to know to do accurate pieces.
Amazon.com: The Art of Segmented Wood Turning: A Step-by-Step Guide: Malcolm Tibbetts: Books
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post #5 of 20 Old 12-02-2008, 10:01 AM
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split oak

I agree with George .I have fooled with oak now for a couple of yrs now and have basicly gave up on oak.Wet oak is just to dang temperamentalLove dry and seasoned oak.To answer your question about wet wood.As soon as you get this wood,you want to trim the ends off if they are already splitting,you want to trim it down past any splitting,but if it has already split all the way thru on a 6" log,then it firewood(sorry)after you trim the piece then you want to seal the ends with an end sealer.I use anchor seal,but there are are other optons,a plain ole cheap latex paint will work,just not quite as good as anchor seal.Then store your wood off the ground.If you turn the wood right away then you want to seal the endgrain of the piece.If I read your post right,these are small logs,then you are probably not cutting out the pith and this will cause spliting ,checking and all kinds of nasty things to happen.Here is a great web site you can go to for more info,as I am running out of room here.
.Wood turning lathe tips:techniques: woodturning instruction
Good luck
Ken

Last edited by The woodsman; 12-02-2008 at 10:03 AM.
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post #6 of 20 Old 12-02-2008, 10:06 AM
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split Oak

As for applying a finish after turning,that won't help in the splitting or warping.
Ken

Last edited by The woodsman; 12-04-2008 at 09:15 AM.
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post #7 of 20 Old 12-02-2008, 11:05 AM
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While I am not a turner, I did stay in a Holiday Inn Express last night. What if you put the wood in a dehumidifier for a few days and dried it out before turning. It seems it would keep it from splitting. We have a small one we use to dry fruit.

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post #8 of 20 Old 12-02-2008, 11:45 AM
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I think a dehumidifier might help but you still have to control the rate of moisture loss. There is a lot of information about drying wood if you do searches for wood drying kilns. People use old refrigerators and my best friend uses a dehumidifier in a large shed to dry his 4" thick blanks for his rocking horses. I think Russ puts the wood in the shed and lets it sit for several months before turning on the Dehumidifier. It's an enclosed shed so the dehumidifer also heats the room. This is wood that has been cut to 4" by 12" wide so it loses moister differently than round wood.
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post #9 of 20 Old 12-04-2008, 12:44 AM
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I only use wood that I obtain myself. I have made friends with a few different guys that cut down trees for a living. I give them a call and they give me all the wood I could handle. I would really suggest doing this. Then I take the wood home and cut it all up into smaller pieces. Then I paint it with wax and put it in a bag with a date on it. I store it in my basement where it is nice and cool. Now the waiting game begins. I personally don't like to wait a lot so I sometimes turn stuff that isn't ready to be turned. If I do turn something that is still really wet I make sure to do it in one sitting and after it is finishes I throw it in a bag and everyday take it out of the bag for a while. The moisture will seep out slower. Don't leave it in too long or mold will grow. I haven't turned out so I don't know what its like. I have turned a couple different types of eucalyptus which is a hard wood and cracks a ton. This method has worked pretty well so far.

Alex

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post #10 of 20 Old 12-04-2008, 09:18 AM
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I did forget to mention that I have turned a fair amount of Oak and do find it harder to save than some woods. Not as hard as most fruit woods but worse than hardwoods like Walnut. Basically any there is a learning curve with just about any wood but what I mentioned above is the best I've come up with so far.
Most of my early failures were either the lip or the foot area. Most lip failures were because the lip was thicker than the rest of the bowl or I cut it too close to the pith. The bottom areas were mostly because I left a tenon that was too large. I now coat the entire tenon with anchorseal and make the bottom of the bowl thinner. The bottom doesn't distort as much as the sides so you can leave it thinner because you will be removing less wood when you true everything up.
If I'm turning a green bowl to completion If at all possible I do it in one quick session. If I have to stop for any reason I put a plastic bag over it. sometimes while I am turning the inside I will spray the outside with water to keep the whole bowl drying evenly.
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post #11 of 20 Old 04-28-2011, 12:37 PM
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Wood Cracking

I'm new to woodworking and new to this forum. I appreciate the posts I've seen on this subject. I'd also like to add my observations (from my limited experience).

I found a log -- already fallen -- in the woods. The two ends were cut across the grain -- saw cut in the standard way. Once I got it home, I cut it diagonally, in half. After 3 months, the two pieces, about equal length (2.5 ft each), have not cracked on the end with the diagonal cut. They have cracked on the ends cut across the grain. My thinking is letting the log dry with both ends cut on a diagonal might take a while, but cracking should be limited. Anyone else have experience/knowledge of this?
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post #12 of 20 Old 04-28-2011, 01:42 PM
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I would only add that using a 3" diameter you are having to leave the pith. If you can get a larger log (maybe 8") and split out sections away from the pith you should have less cracking/splitting. Seal the end grain while it dries.
If you have someone near you that sells firewood they may be an excellent (cheap) source as they typically spilt their wood at least a year before to allow it to dry before selling it.
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post #13 of 20 Old 01-15-2012, 06:09 AM
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Lightbulb Ways to fix cracks

When the wood cracks come up with a unique way to fill the crack. We use key shavings (brass) and super glue while turning the projects. Also we use stone grindings torquise, and other things. it gives the project some unique features and it fun to see how it turns out
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post #14 of 20 Old 01-15-2012, 07:15 AM
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Cutting out the pith does seem to help but only buys you a little more time. The wood species and where and how it's stored has much more to do with it. Covering the wood to keep it out of the weather seems to be the best solution for reasonably short term storage. I'll let you know, I have an entire truck load of fresh cut oak sitting in the driveway right now with a tarp over it. I hope to turn at least one piece by the end of January but I'm so busy it may sit there for awhile.
I have so much I'll probably leave some of it as a test and not do anything else to it and see how long it takes to start to crack. I guarantee if I left it uncovered it would already show small cracks on the end and it's only been about 2 1/2 weeks.
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post #15 of 20 Old 01-15-2012, 11:51 AM
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Myself being too impatient and new to the game, i have been mostly green wood projects and dealing with the cracks. Basically asked the question not too long ago. Donít really have any words of wisdom. Turn a vase last night out of oak. It was a fairly wet piece with some larger knots, and the pith, so pretty but I know I will be lucky to save it. Put it in a zip lock when I came in thinking the water would disperse evenly I would take it out once a day for an hour or so and put it back in the bag. Bottom is already black this am so I will forget this idea. Now its bagged and tapped so only the exterior is covered and the interior is free to dry as it pleases...Read about that some time ago but basically another test. But I have been wondering about a vacuum seal bag and a water soluble sealer-finish. Thought being a wet turned piece is placed in a bag with the sealant and placed under a vacuum. As I have seen air bubbles come out of end grain and mess with my finish on pieces, I would think under a vacuum air will pulled out and some of the water. When the bag is opened the sealer will be sucked in. If anyone is familiar with rock chip repair on windshield, somewhat of the same idea. I know its not the most practical idea besides the fact just because a tree has water in it this doesnít mean that the water is going to mix with a water based sealer or finish. Not to mention depending on what type of tree and time of year it was cut down it could have lots of sugars in it as well. I donít even know what to think the rolls sugars will play. I will give it a try in way or another before to long. As of now water based poly is the only thing I can think of using at this time but I really donít care for it much. Perhaps someone else has an idea of another material to use.
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post #16 of 20 Old 01-15-2012, 12:41 PM
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just read in another post-question, that I am not the only one who has the vacuum bag idea...
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post #17 of 20 Old 01-15-2012, 01:21 PM
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I recently started to turn a green cherry bowl and could not finish it until the next day so I wrapped it all up in plastic. The next day the jaws had started to rust. If you have to cover it do not cover the jaws if possible.
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post #18 of 20 Old 01-15-2012, 01:35 PM
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Wood is Yellow Poplar harvested after hurricane Irene. Have completed and given away six or eight bowls since harvesting.

Found wood end sealed with latex paint checking stored in my woodshed. Needing a component for lamp am working on rough turned little hollow bead which will be a lamp base. Put in paper bag for week now sitting corner of my shop for week or more. Roughed out bowl been sitting in the shop for couple months. Have another half dozen roughed out bowls not touched since do not know when.

You can see latex paint did not stop end checking. Majority of end sealers only slow down drying process not stop it. Even with shelter and out of the weather wood will continue to dry. Cut your blanks (bowl or spindle) longer than you need.

Wood thickness, species, open - close grain wood and time of year cut all affect drying process. Find out what works in your area and do it.
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post #19 of 20 Old 01-15-2012, 01:45 PM
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Quote:
Originally Posted by Hwood View Post
Myself being too impatient and new to the game, i have been mostly green wood projects and dealing with the cracks. Basically asked the question not too long ago. Donít really have any words of wisdom. Turn a vase last night out of oak. It was a fairly wet piece with some larger knots, and the pith, so pretty but I know I will be lucky to save it. Put it in a zip lock when I came in thinking the water would disperse evenly I would take it out once a day for an hour or so and put it back in the bag. Bottom is already black this am so I will forget this idea. Now its bagged and tapped so only the exterior is covered and the interior is free to dry as it pleases...Read about that some time ago but basically another test. But I have been wondering about a vacuum seal bag and a water soluble sealer-finish. Thought being a wet turned piece is placed in a bag with the sealant and placed under a vacuum. As I have seen air bubbles come out of end grain and mess with my finish on pieces, I would think under a vacuum air will pulled out and some of the water. When the bag is opened the sealer will be sucked in. If anyone is familiar with rock chip repair on windshield, somewhat of the same idea. I know its not the most practical idea besides the fact just because a tree has water in it this doesnít mean that the water is going to mix with a water based sealer or finish. Not to mention depending on what type of tree and time of year it was cut down it could have lots of sugars in it as well. I donít even know what to think the rolls sugars will play. I will give it a try in way or another before to long. As of now water based poly is the only thing I can think of using at this time but I really donít care for it much. Perhaps someone else has an idea of another material to use.
the best way to dry is with denatured alcohol here is a google search on this. I know it work's .or go to a tunrning web site. Ohttp://www.google.com/#sclient=psy-a...iw=978&bih=561
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post #20 of 20 Old 01-15-2012, 05:11 PM
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Wood stabilizer keeps green wood from cracking, checking and splitting during the drying process. Would rather see you kill a $20 bill on this stuff over DNA or boiling blanks. Simply because can brush it on your rough blank. Soaking probably a better op, but feel that is as much busy work as boiling and soaking in DNA.

I have read details, feel manufacturer gives an honest description of what product will, and will not do. No, will not be buying the stuff.

Pentacryl™
http://www.preservation-solutions.com/pentacryl-wood-stabilizer.php

Click on “Pentracryl reduces turned bowl losses to less than 1%
Click on “View Label.” Wood fortifier for spalted wood, maybe

Polycryl™
http://www.preservation-solutions.com/product.php?category_id=1000&product_id=1006

Make sure click on “VIEW LABEL.”
Polycryl will fortify semi punky wood not extremely punky wood. Softer the wood better Polycryl penetration. Polycryl will not penetrate hard wood.

Not aware of any product that will strengthen punky wood. Some of the home brews made with thinner will penetrate punky wood but never harden it. Does not matter if using capillary action or vacuum. Simple explanation: Due to cell collapse, thinner can penetrate punky wood not finish mixed with it. When Lacquer or poly finish materials dry they strengthen spalted wood, if cannot get in punky wood not much use.
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