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Forum topic by ldl posted 03-07-2013 12:16 AM 850 views 0 times favorited 16 replies Add to Favorites Watch
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ldl

1135 posts in 1017 days


03-07-2013 12:16 AM

Last month I turned a couple of green bowls from pecan to an approx 3/4” to 1” thickness. For the last couple of days I have been trying to turn them down to about 1/4” to 3/8” wall thickness. This is my first attempt to turn thin sided dry bowls and I have cracked both of them. One I got a catch and the bowl split in half. I glued it back together and semi-finished turning it being real careful and taking light passes. The other one I also got a catch and it cracked but not into. I drilled into the side to insert wooden dowels. This wasn’t very successful and as I was trying to finish turning it it cracked again so I glued the cracks again and will probably just try to sand this one to finish it. Really now just trying to finish turning them for the experience.

I know you can’t see what I was doing and it is hard to give advice this way. I was using a half round scraper with a 15deg edge both times I had the catches. The first bowl was a natural edge bowl and the second a reg bowl.

Kinda thinking it may be the pecan wood but I have two first here. The pecan wood and turning to a thin wall thickness.

Any pointers, methods or advice would be greatly appreciated.

-- Dewayne in Bainbridge, Ga. - - No one can make you mad. Only you decide when you get mad - -


16 replies so far

View bobasaurus's profile

bobasaurus

1252 posts in 1836 days


#1 posted 03-07-2013 02:09 AM

Maybe let the green rough turnings dry for longer, at a slower rate. Put them in a paper bag filled with wet shavings to make it really slow.

-- Allen, Colorado

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ldl

1135 posts in 1017 days


#2 posted 03-07-2013 02:38 AM

Is it possible to dry to fast?

-- Dewayne in Bainbridge, Ga. - - No one can make you mad. Only you decide when you get mad - -

View CaptainPathology's profile

CaptainPathology

9 posts in 560 days


#3 posted 03-07-2013 03:08 AM

I’ve turned lots of bowls, and I’ve had much better turning with a large (maybe oversize would be a better word) bowl gouge with an extra long handle (added myself) than any other tool. The bowl gouge is very forgiving, and the extra long handle adds lots for stability. I have used a scraper on very thin walls, for very light touchup at very high speed. Come to think of it, I used a scraper extensively on my latest hackberry bowl, wet-turned to final 1/8”, also using high speed. That was a homemade side-scraper, light cuts, high speed, tool rest as close as I could get it, watching thickness with a lamp shining from behind.

-- Dave, Lexington, KY

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CaptainPathology

9 posts in 560 days


#4 posted 03-07-2013 03:16 AM

Re: Possible to dry fast: I’ve occasionally turned wet to final thickness, you just end up with a warped final turning. Lots of sites recommend denatured alcohol (they refer to it as “DNA”, rather confusing to a biologist like myself), but I’ve never used it. I hope to try it some time.

-- Dave, Lexington, KY

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TheDane

3770 posts in 2315 days


#5 posted 03-07-2013 03:21 AM

Dewayne … Pecan is a good wood to turn, so I don’t think that is the problem.

When I am using a scraper, I set the tool rest slightly above center as close to the work as possible, and hold the tool with the cutting tip angled down slightly. That reduces the chance of getting a catch.

How ‘wet’ was the wood, and how did you dry it? I have bowls I turned wet last September that are still sitting in grocery bags stuffed wit shavings. I figure they’ll be dry enough to turn in the next couple of months.

—Gerry

-- Gerry -- "I don't plan to ever really grow up ... I'm just going to learn how to act in public!"

View bobasaurus's profile

bobasaurus

1252 posts in 1836 days


#6 posted 03-07-2013 03:22 AM

Drying is usually an exercise in patience. There are people who use dehumidifiers/kilns/ovens etc to dry bowls… never used these techniques since they speed drying which often leads to cracking. I think there are even liquid products that supposedly migrate into the wood and replace the moisture with stabilizers that harden.

-- Allen, Colorado

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TheDane

3770 posts in 2315 days


#7 posted 03-07-2013 03:44 AM

I know a turner that soaks rough-turned bowls in denatured alcohol from 12 to 24 hours, then lets them dry in a bag for a week or two. He buys the DNA from an auto paint supply and keeps it in a 5 gallon pail outside his shop.

—Gerry

-- Gerry -- "I don't plan to ever really grow up ... I'm just going to learn how to act in public!"

View MonteCristo's profile

MonteCristo

2097 posts in 840 days


#8 posted 03-07-2013 03:48 AM

I rough turned a lot of green deodar cedar a while back and had a lot of the rough turnings crack while drying. Same deal with some alder. It seems to me that especially if the wood comes from a crotch or other place where stress will abound, it’s safer to dry the wood as slowly as possible. Least haste, most speed as the old Pommie saying goes.

-- Dwight - "Free legal advice available - contact Dewey, Cheetam & Howe""

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NGK

93 posts in 563 days


#9 posted 03-07-2013 04:13 AM

Here in the Midwest (or Cornbelt states) the average outdoor humidity dries wood to about 15-16 percent poisture. This is known as EMC (equilibrium moisture content) and varies from region to region worldwide.

Therefore, our air-dried wood is at best 15 percent moisture, and is often more most than that. A chunk (blank) from a freshly dropped tree might be as high as 60-80 percent moisture. Moist wood, when mounted on a lathe cuts very easily. It’s a sheer joy to watch it peel off the lathe in tremendously long ribbons (once it’s perfectly round).

A prudent turner will leave the wall thickness about 10 percent of the diameter of the intended bowl. One inche thick for a 10-inch bowl. Rough-turn it to the approximate shape of the final bow. If this is a two-day operation, keep the piece covered with plastic, even spraying it with water if you take a 30-minute break on a hot, dry day. Otherwise cracks will develop, and they can develop quickly.

After rough-turning, place the “partially finished” bowl in a brown Kraft grocery bag with moist shavings (as others have mentioned) for approximately 6 months. Put it in a cook, draft-free area like a basement woodworking shop. If necessary, weigh it periodically—it’s dry when it stops losing weight. At that time re-mount it on the lathe and refine it to final shape; then sand it and finish it as soon as possible. A good finish will prevent future changes in environmental moisture from affecting it seriously.

View ldl's profile

ldl

1135 posts in 1017 days


#10 posted 03-07-2013 02:10 PM

A lot of good advice that is really appreciated.

Sorry I mistakenly said I dried these in a paper bag but I got them mixed up. These two I dried in the microwave. I just yesterday bought a set of digital scales to weight my bowls with. I hadn’t weighted these yet so I don’t know what the weight or moisture content was. They were very dry though probably because of the microwave. I have 3 more of the pecan bowls in paper bags but I didn’t put any shavings in with them. They have been in the bags for about 2 wks. Since I now have the scales I think I am going to take them down and weight them and mark the bag. All these bowl blanks came from the same tree I got a little over a month ago. Would drying in microwave make any diff here.

I sharpened my scraper to 15deg. Opinions on that angle appreciated. I am just really getting serious about learning to sharpen tools and some angles I’m not sure of yet.

Dave I am a semi-beginning turner. I have turned in the past but only spindle types. I am now trying to turn bowls and also larger bowls and these are the first I have tried to turn thin so I am on a steep learning curve. The largest gouges I have are 1/2” bowl gouges and am beginning to get used to making the turn with them. I really think part of my problem is being to stiff with the tools specially when I am getting close to the finish. I have noticed I really hold them tight, specially the scraper, to try to sneak up on the top edge. Sitting here thinking about how i did things I rem that there was a slight hesitation when I would bring the scraper accross the rest. I think I need to go back and put a radius on the underside edge of the bevel so the sharp edge doesn’t catch on the rest. Anybody do this?

Gerry I think you might have part of it there about setting the rest a little above center. I have been setting mine at or slightly below center. I need to make a curved rest to get inside and closer to the bowl side. I made 2 other rest but they were straight also just shorter. I have read about the DNA and wanted to try it just haven’t got around to it yet. I think I might need to lay off natural edge bowls till I can get better at turning them thin. To much turning air with the thin wood. I have been turning all bowls to about 1”+- and natural edge has been fine but when I try to thin them out I catch a lot.

Dwight I have turned a good bit of cedar lately but it has all been air dried for 2-3 yrs and haven’t had any cracking trouble so far. Knock on wood, Haaa Haaa

I am really trying to learn and thanks for all the comments. I think I also need to just get on with turning and practice, practice, practice. Any other comments would be greatly appreciated.

They have a turning club in Tallahassee Fl which is about 50mls from me but circumstances prevent me from joining with them.

-- Dewayne in Bainbridge, Ga. - - No one can make you mad. Only you decide when you get mad - -

View Wildwood's profile (online now)

Wildwood

1034 posts in 786 days


#11 posted 03-07-2013 03:07 PM

Dewayne, all my scrapers have a bevel angle of 70 degrees. I sharpen with bench grinder & Wolverine platform, and touch up with Veritas Scraper Burnisher. I measure bevel angle on my all turning tool using two protractors that rotate around a small bolt & nut in middle. You can make your own burnisher, and sharpening with a belt sander okay too. Protracter cost me about $.50 to make several years ago.

http://www.ossmann.com/protractor/conventional-protractor.pdf

If scroll down to three part scraper article thing will find lot of good information.
http://www.docgreenwoodturner.com/articles.html

I use my straight tool rest, and have no problem sticking part of it inside a bowl.

-- Bill

View Bluepine38's profile

Bluepine38

2876 posts in 1737 days


#12 posted 03-07-2013 03:44 PM

Sounds like you are on the right trail, as a beginning turner, a few decades back, I did not have much trouble, but when I returned to turning a few years ago, the darned tools tended to catch the wood, then after a few
days of practice the catches tended to diminish, surprising what a lot of practice does to your ability. Captain
Pathology mentioned putting a long handle on his turning tool, this practice tends to help us more mature
fellows handle and hold the tools better, and I recommend that you try this also. I tend to like to dry the wet
bowls in a barrel of sawdust, moving then around in the sawdust every week, for at least 6 weeks. For some
reason, I am no longer in a hurry to get the bowls finished and just like to take my time. Hope you find the
solutions to your catches and have fun in the workshop. It tends to keep us off street corners and out of
trouble as well as keeping us from being too annoying to whatever friends we happen to have.

-- As ever, Gus-the 75 yr young apprentice carpenter

View ldl's profile

ldl

1135 posts in 1017 days


#13 posted 03-09-2013 01:43 AM

Thanks Wildwood for the article link. I have found at least one thing I am doing wrong. I would use almost the whole sharp side when coming up the side. Article says use no more than 3/8” of the scraper when turning. I plan to go back and reread it several times. It is interesting reading.

By the way the protractor PDF didn’t werk. It went to the file but nothing on it.

-- Dewayne in Bainbridge, Ga. - - No one can make you mad. Only you decide when you get mad - -

View MonteCristo's profile

MonteCristo

2097 posts in 840 days


#14 posted 03-09-2013 04:08 AM

Hi Dewayne The deodar that gave me a hard time is not native to North America. See (http://en.wikipedia.org/wiki/Cedrus_deodara).

I have had much better luck with Western Red Cedar and what we call Yellow Cedar, neither of which are actually true cedars. The deodar has a really nice heartwood/sapwood contrast, but it seems to be a hard one to dry.

-- Dwight - "Free legal advice available - contact Dewey, Cheetam & Howe""

View Wildwood's profile (online now)

Wildwood

1034 posts in 786 days


#15 posted 03-09-2013 12:24 PM

I should have said two plastic protractors, each costing twenty five cents. Got idea for making my angle finder from Wood Magazine’s tip section several years ago. So use plastic not paper!

Have sites online can print off a protractor recommend buying plastic ones. Once glue to boards, print will blur with use.

-- Bill

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