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Forum topic by RussellAP posted 02-23-2013 09:50 PM 2923 views 0 times favorited 18 replies Add to Favorites Watch
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RussellAP

3059 posts in 1754 days


02-23-2013 09:50 PM

I’ve been trying the microwave method of drying my bowls. I’ve done some things wrong and I’d like to share my experience and what I’ve learned from them.

When you turn a wet bowl you quickly give up on the idea that it will be anything close to smooth, so the tendency is to leave the tenon on so you can come back after you dry the bowl in the microwave and sand it on the lathe. The problem is that the tenon makes a natural microwave problem worse and that is that the grain will want to pull together to make an oval and if you leave the tenon on, it warps the bowl. In fact I think that if you leave any thickness one the bowl it will warp in the microwave.

So I’m going to try to turn the bowl out completely with no tenon and then just see if it helps the oval problem.

I’d like some discussion from some folks who’ve tried this method and what you did to overcome it.

-- A positive attitude will take you much further than positive thinking ever will.


18 replies so far

View Wildwood's profile

Wildwood

1888 posts in 1603 days


#1 posted 02-23-2013 10:26 PM

When rough turn a bowl strives for an even thickness. If used a tenon to hold the bowl will reverse bowl and turn away tenon before setting aside to dry. The recess I create will allow remounting the bowl in chuck later. Key word to remember is even thickness!
No, this does not stop a bowl from going oval. Thickness of a rough turned bowl will help you make a bowl round again during final turning.

If turn too thin bowl can oval severely and not much you can do. Not to worry all part of the plan you designed it that way.

JMHO, microwaving, soaking in soapy water, alcohol, and boiling just busy work. Feel same way about green wood stabilizers and completely sealing rough turned bowls in green wood sealers.

Yes, rough turned bowls can take several months to dry sufficiently to rough turn. If want to work smarter than harder, build box kiln with light bulb, small fan and vent. So folk use old kitchen appliances (dish washers, refrigerators plastic beer coolers) but any box with racks will do. Get fancy an add an auto timer controlling lights and fan. There is a learning curve on using home kilns, guess that is why do not have one.

-- Bill

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RussellAP

3059 posts in 1754 days


#2 posted 02-23-2013 10:42 PM

I may just do that Bill. My wife already suggested I buy my own microwave.

-- A positive attitude will take you much further than positive thinking ever will.

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TheDane

4997 posts in 3131 days


#3 posted 02-24-2013 12:21 AM

Russell—Try putting the bowl in a plastic bag, set the microwave on high, set it for 5 minutes, then stop it when the bag shows moisture on the inside.

That will tell you how long you should run the microwave.

Remove the bowl from the plastic bag, let it cool, then cook it (no plastic bag) for the number of minutes/seconds you observed before.

Remove from the microwave and let it cool, then repeat until you get to the right moisture content.

Guys in my group rough turn the bowl to about twice the desired thickness before drying in the microwave.

—Gerry

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

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REO

889 posts in 1542 days


#4 posted 02-24-2013 02:48 AM

It can be curbed but the deformation is more about the grain than the thickness. It cam be more pronounced if it is thicker but it will always distort. the amount of the soft summer grain compared to the harder winter growth makes the difference. There is more water compared to wood fiber in the soft areas that can be removed. as the water leaves the wood has to contract if it cant it will check or crack. that is why most of the bowl turners try to avoid including the center of the tree and turn a lengthwise blank instead of a transverse section of the tree. the center or pith of the tree, because it grew slowly and has a high ratio of hard to soft growth rings when compared to the mature tree will consistently cause trouble as the item dries. if you want to speed up your completion rate turn dry material. it isn’t quite as forgiving but it can be turned just as fast. it will finish faster because you don’t have to wait for it to dry.

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RussellAP

3059 posts in 1754 days


#5 posted 02-24-2013 02:50 AM

Reo, do you know anyone that sells dry stock?

-- A positive attitude will take you much further than positive thinking ever will.

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wooddaddy

13 posts in 1901 days


#6 posted 02-24-2013 02:54 AM

Russell, I’ve nuked bowls with and without tenons with good success but I believe the recess works better because it is closer to the overall thickness. The rule of thumb is ten percent of the bowl diameter is the wall thickness. If you multiply the diameter by 10 you’ll get close enough. Ten times ten,(10×10=100)or 1 inch. So a 10” bowl should have a wall thickness of 1” before drying. Timer settings need to be adjusted depending on size of the bowl. A good rule of thumb is to feel the temperature of the bowl when you take it out. You want the wood fairly warm but not hot. I do not use a bag because you want to get rid of the moisture. If you don’t overheat the wood there is no need for the bag. I begin with weighing the bowl and keep track of moisture loss each time. Take the bowl out immediately at end of cycle and allow to completely cool. This may take up to 1 hr. if it is a large, 14”-18”, bowl. As the moisture leaves the difference in weight will lessen because the wood is drying and stabilizing. When you began seeing only a few tenths of an ounce loss between cycles, it is stabilized enough to finish turning. I plan on buying a moisture meter to more acurately measure the moisture content. I had a wedding gift to make and successfully turned a 14” walnut bowl from wet to finish in two days. If you have a real job and can’t keep at it during the day, this process could take three days. I’m fortunate to have a wife who doesn’t work and gets a kick out of helping me with the process. I’m still perfecting my method but the key is don’t overheat and allow to cool completely before the next cycle. Good luck

-- Floyd, PA

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RussellAP

3059 posts in 1754 days


#7 posted 02-24-2013 02:58 AM

Floyd, I’m pretty sure I’m not overheating the wood, it’s warm, but not hot. The wood tends to constrict the grain closer together and that is where it warps. I don’t see any way around this as a turned product dries.
I don’t mind turning a dry blank, but I can’t really cut my own with my HF BS. I’d need a way of cutting blanks out of logs and that’s too expensive for right now.
I have some really beautiful maple in my driveway waiting for some way to cut it to size now. I don’t think my electric chain saw is up to it.

-- A positive attitude will take you much further than positive thinking ever will.

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Jimbo4

1432 posts in 2231 days


#8 posted 02-24-2013 03:40 AM

I used the microwave ONCE ! :o] – was told NEVER do that again !

-- BOVILEXIA: The urge to moo at cows from a moving vehicle.

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REO

889 posts in 1542 days


#9 posted 02-24-2013 03:58 AM

what sized blanks do you want? I do play bowls for kids from reclaimed Ash. they are four layers of 5/8” material. the bowl finishes out at 5 inches dia. I lam a batch and then use a 5” one tooth hole saw to hawg them out and then do the outside with a foot. the chuck will hold the dry stock better as well.
http://www.youtube.com/watch?v=Z1sf00vxB3M&feature=player_detailpage

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RussellAP

3059 posts in 1754 days


#10 posted 02-24-2013 05:04 AM

I’d like to see a place that sells dry blanks like the wet ones, same dimensions.

-- A positive attitude will take you much further than positive thinking ever will.

View Wildwood's profile

Wildwood

1888 posts in 1603 days


#11 posted 02-24-2013 12:57 PM

Do not know of any wood vendors catering to turners that will guarantee MC of the wood they sell.

I have given away some air dried rough turned blanks at times. No longer do that! If belong to a turning club may find people to swap wood with.

There are folks that rough out bowls and sell them, many may not advertise online.

http://www.roughoutbowls.com/rough_out_bowls.shtml

-- Bill

View Rob's profile

Rob

229 posts in 2455 days


#12 posted 02-24-2013 01:39 PM

I’ve turned many bowls from wet wood and I use the denatured alcohol followed by wrapping the bowl in newspaper until dry method. My tenons and the bowl to some degree are always warped. I don’t know of any method that won’t cause some distortion to the bowl and tenon. I just use a homemade donut chuck (I made several sizes out of 3/4 plywood) to mount the bowl and turn the tenon round again so it will seat properly in a conventional chuck and then finish turning the bowl.

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Wildwood

1888 posts in 1603 days


#13 posted 02-24-2013 03:12 PM

[IMG]http://i1338.photobucket.com/albums/o695/wildwood5/IMG_1197_zps1aee0bf7.jpg[/IMG]

[IMG]http://i1338.photobucket.com/albums/o695/wildwood5/IMG_1198_zpsa0631fb6.jpg[/IMG]

I do not always add shavings when placing roughed out blanks in paper bag. I live in zone 5 the worst for supporting stain and mold growth.

Wood is Poplar and comes from storm damage tree. Many of these have been finished turned and in new homes. Just posting to see if I can post pictures. Would like to learn to inbed photis in a post without linking but that is for another day.

-- Bill

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REO

889 posts in 1542 days


#14 posted 02-25-2013 02:01 AM

rus you didn’t mention a size. If you are saying that you want single piece dry blanks in sizes for bowls your best bet is a dead standing tree where the bark is off and then it may still contain moisture. processors aren’t going to run the risk of trying to dry it down in such a sixe because they would tie up the kiln for other items. you cant just leave a hunk in the back of the kiln till it dries out. there is a process and it varies from charge to charge and species to species. glue some up!

View needmorewood's profile

needmorewood

2 posts in 1035 days


#15 posted 02-16-2014 01:36 AM

Hi guys I’m new here was just reading about drying green bowls. And I was just wondering if anyone has ever tried vacuum drying?

showing 1 through 15 of 18 replies

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