Wood movement on second turning

[Marty Tippin]

Trying to figure out if I'm not waiting long enough for my roughed-out bowls to dry or if the amount of wood movement I'm seeing is normal and to be expected.

My process so far has been to rough out to about 1" wall thickness, 24 hour soak in DNA, coat the outside with Anchor Seal and leave the bowls to sit for 4 to 5 weeks in my not-air-conditioned shop. Humidity has been pretty high in the shop all summer, but temps have been in the low 80's.

First bowl was a piece of box elder with some really nice figure, about 12" diameter. I turned it to a thickness of maybe 1/4" or so and by the time I got the bottom of the bowl fairly smooth and ready to start sanding, the rim had warped by maybe 1/4" or so. I tried (foolishly) to get it back to round again and ended up with one wall way to thin.

Second bowl just worked on tonight was a piece of cherry, also about 12" diameter and turned to 1/4" or so thickness. Not as much movement as the box elder, but still it's pretty wobbly as I'm trying to power sand the interior. Things go downhill from there as I struggle to get all the tool marks out of the interior and have to fight the wobble.

Normal? Am I just in too much of a rush? Should I just take up knitting instead?

[John Thorson]

All bowls move a little (some a lot) in the second turning due to stress locked in the wood as it dried down. Things get worse if the wood is not dry due to additional warping forces added by the rapid dry-down of the thin walled finished bowl. I've had bowls out in the shop that were 10% by moisture meter go up instead of down in moisture during the humid summer months so your shop storage is working against you at the moment. Moisture meters have gotten very inexpensive and they take all of the guesswork out of what is causing the warping during the second turning. It could be the wood but it is probably moisture.

[Roger Chandler]

Marty........the only sure way to know how much moisture is still in a piece is with a moisture meter.......or do what I do and that is weigh the piece frequently. I have a digital scale accurate to within 1/10th ounce, and up to 55 lbs...... and when I rough out, I do anchorseal and then put in a bag, seal shut with folding edges over and stapling the bag shut.

I weigh the entire thing and write the date and weight on the bag.........after a couple of weeks, I begin weighing and recording the weight on the bag every few days........until after 3 readings it is not losing any more weight [evaporating moisture away] and when it has stopped losing weight, I know it is safe to put it back on the lathe, and do finish cuts, sand and finish...........my luck so far with this has been pretty good........no cracks with maple, walnut and box elder maple.

Give that a try........see if it does not help with stability. Good luck! BTW, I got my scale from Amazon.com for about $28.......not bad!

[Steve Schlumpf]

Marty - in my opinion there are a number of things happening here that may be frustrating when trying to finish turn a bowl.

First off, once I DNA a turning, I let it flash dry, then wrap it in brown paper (grocery bag) such that the outside is totally covered and the inside of the bowl is exposed to the air. The purpose of this is to control how fast the bowl dries. You want the interior of the bowl to dry first as it will compress (shrink) and you want to delay the drying of the exterior of the blank to give the interior a chance to dry first. Dry too fast on both surfaces and you will get cracks. By covering with brown paper on the outside only, it creates a micro-climate and allows the inside to dry first, then the outside. Basically you are controlling the rate and the direction the wood dries. By sealing the outside with Anchor Seal you have effectively prevented that portion of the blank from drying.

Finish turning a semi-dry blank will result in a lot of warping because the newly exposed wood (usually the outside) will dry and the blank will flex accordingly. Also, don't discount the grain of the blank moving once stress has been removed. Meaning that as you turn a blank thinner, the wood will warp according to the grain structure.

So, how do you overcome all this? Well, when you rough out a bowl be sure to keep the walls of the blank an even thickness so that the blank will dry evenly. Wrapping in brown paper helps to slow down the drying process on the exterior of the blank for me but you may find something that works even better for you.

Only other thing I can suggest when turning wood that is not 100% dry is to turn and then finish sand the piece in sections. Basically remove about 2" of the interior of the bowl, sand, then move on to the next 2" of the bowl. Once you finish sand a section - Never - go back to it because it will have warped by then. Just keep hollowing in sections and you should be good to go.

Good luck!

[Reed Gray]

Well, as some one who likes warped bowls, I am pretty sure the wood was still pretty wet. One way to tell without the moisture meter is to feel it. If it is cool to the touch, and this is very noticeable, then it is pretty wet. All bowls will warp a bit as you finish turn them. When spinning, it flexes a bit differently along end grain than it does along side grain. This won't cause it to go out of round 1/4 inch though. Generally, it is more like 1/16 inch or maybe a tiny bit more. Let it dry till you think it is dry enough, then give it another month or so. General air drying for board stock is 1 year per inch of thickness, and then bring it into the dry shop for another 6 months. The DNA soaking does seem to speed that up, but I don't use it, as I said, I prefer warped.....

robo hippy

[Grant Wilkinson]

Ask 10 turners and you will get 11 answers. For me, a few weeks is not enough. My rough turns are in my basement in bags and in Ottawa, ON, they need several months before they are finished losing weight. My method - as I was taught - is to rough turn to a wall thickness of 10%, seal only the end grain, then wrap in newspaper and put into a brown bag. So far, I've had excellent results. I goofed once and sealed the whole bowl, not just the end grain and the bowl split. As I understand it, we are trying to get the moisture to come out uniformly. Since it wants to come out of the end grain faster than the side grain naturally, we coat the end grain to slow the moisture loss out of it to equal the moisture loss on the side grain. I would humbly suggest that if you sealed the entire bowl, you retained the disproportionate side grain/end grain moisture loss. You just slowed them both down.

Having said all that, I'm with Reed, I turn most of mine once and thin and let them potato chip. :-)

[Marty Tippin]

I would humbly suggest that if you sealed the entire bowl, you retained the disproportionate side grain/end grain moisture loss. You just slowed them both down.

I didn't -- only the outside of the bowl, as I understood that leaving the inside "raw" lets it dry faster and helps prevent cracking. Whether to use anchor seal on the outside or to wrap it in paper I suppose is still up for discussion. Anchor seal is quick and easy to apply; paper is a pain to deal with.

Thinking maybe I'll get a moisture meter - it seems I can never have enough gadgets... ;-)

[Wally Dickerman]

As an old timer I'll give you the old timers method of checking for moisture. Put the bowl against your cheek. If it feels cold it's still wet.

[Lee Watermann]

All,
I turn green to 1/4 or less all the time. I immediately put a cross brace inside opposite the pith and they will stay round. The pith on, each side, will rise a little bit. I let it dry and it will take about two weeks checked by weight. I then jamb chuck and true up the bottom and turn it around to true up the lip. You don't have to touch the bow sides at all. When installing the brace round all corners and it would be good to put a piece of leather, or something, to cushion the ends as the bowl will try to warp and it could dent the sides. I have never cracked a bowl doing this but sure have turning them thick. The bowl will stay absolutely round if you brace it right away.

I tried to upload a picture but it failed.

Cheers,
Lee

[Ken Glass]

Marty,
I most always rough turned the thickness to 1/10th of diameter. I use, or should say used, a method very similar to Rogers, and used Brown paper as Steve does, and rarely had problems. I always weighed my turnings after wrapping and waited until the piece stopped losing weight for at least 4 days straight and then finished turned it to thickness. The shop humidity probably does help thing either.

[Marty Tippin]

So I bought an inexpensive moisture meter on Amazon and used it last night to check several of my DNA-treated bowl blanks, plus just about every other chunk of wood I have laying around.

The box elder bowl that I mentioned in my original post that moved so much shows about 18% moisture; all of my other blanks that have been drying for 3 weeks or more were at 16-17%. The cherry bowl that moved a little during second turning was also at around 16%.

Other hardwood lumber (kiln dried, I think) was at 10% and a few raw logs from a recently cut maple tree showed 25% or more at the ends (treated with anchor seal) and 50% or more on the sides when I poked through the bark. So the readings seem reasonable, though the meter claims an accuracy of +/- 3%.

So for those of you who use a moisture meter, what moisture content do you find your dried bowl blanks have when you do your second turning?

[John Keeton]

I don't do a lot of "re-turns", but I do use a lot of air dried wood. I am comfortable with 12%. Most of my pieces involve multiple pieces that fit together.

[Fred Belknap]

Along the same line, I Anchorseal the outside of most of my bowls and am wondering how much the wax effects the reading of a pin type moisture meter? I like to check moisture in the tenon to keep from punching holes inside the bowl.

[John Thorson]

I like to be under 12%, the bowl still moves too much in the final turning for my liking when its 12 or over. This may be a factor of my shop climate when doing the final turning. The shop is very dry in the winter with the heat on here in Minnesota. I seldom get a bowl to dry down to under 10% out in the shop.

As far as the Anchorseal goes I get the same reading on the inside (unsealed) and the outside when on the drying shelf. With a "10% of the diameter" wall thickness there will be enough wood turned away from the bottom inside to never show a mark, I don't test in the side wall of the bowl to avoid a mark though.

[James Roberts]

I usually rough down to 10% of planned final diameter then pack the blank in wet shavings and double-wrap in brown paper. I write the type of wood and date I roughed it on the outside and toss it on a shelf and forget about it for 5-6 months or so. I've only lost a few to serious cracking and of the few that did crack I was able to use the crack as a design feature, filling with turquoise, coffee grounds etc. I have a moisture meter and I am generally happy when my pieces are around 10% or so. I also run a dehumidifier in my basement but that may or may not help the process and at any rate the relative humidity in the shop will probably be different than upstairs in the house or whatever place the finished piece ends up. Wood moves, it's all part of the game we play.