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Turning big bowls; several questions

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Forum topic by pmayer posted 06-28-2017 05:43 AM 1390 views 0 times favorited 15 replies Add to Favorites Watch
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pmayer

987 posts in 2903 days


06-28-2017 05:43 AM

I’m in the process of roughing out some 20” +/- sugar maple bowls, and I wanted to get some advice from experts who have experience with this. I’m turning them in two steps; first I’ll rough them out, then let them dry, then finish turning them when they are dry. My questions:

- I’ve always heard the rule to leave the wall thickness 10% of the overall diameter of the bowl. Typically I’ve turned 10-12” bowls and this rule has worked fine. Would you really leave these walls 2” thick? That’s what I’ve been doing on the first couple, but I want to be sure because that is going to make for a long dry time and a lot of work to finish turning 2” of dry sugar maple.

- For large bowls like this, is it better to mount the chuck onto a mortise or a tenon? I’ve turned a 5.5” mortise into the base for the first couple, which has worked great for rough turning but my question is more on the re-turn after the blanks are dried and distorted. Which one will work better?

- With such a large bowl, would you mount it to do the second turn, would first mount using a jam chuck and re-shape the mortise or tenon so that the chuck grabs evenly?

- Any advice for faster drying on big bowls like this? I’ve just wrapped them in rosin paper and stuffed some shavings in there (which some people say isn’t necessary but I still do just cuz I guess).

Thanks for your input!

Cheers,

Paul

-- PaulMayer, http://www.vernswoodgoods.com


15 replies so far

View DocSavage45's profile

DocSavage45

8375 posts in 2680 days


#1 posted 06-28-2017 06:24 AM

Not an area i’m Knowledgeable. Have a lathe and I will be following this thread.

-- Cau Haus Designs, Thomas J. Tieffenbacher

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Wildwood

2186 posts in 1972 days


#2 posted 06-28-2017 09:54 AM

I shoot for uniform thickness my bottoms little thicher. Have never roughed a bowl more than 1” thick. JMHO, mortise or tenon depends upon design and personal preference. If mortise working for you go for it.

Don’t always use or recommend shavings or paper bags due time of the year and where I live. Live in an area where wood highly prone to mold, mildew, & stain. If wood really wet have used paper bags & shavings for week or two. Then remove and allow to air dry.

Not sure what rosin paper all about so will not comment.

If have facebook account, man says can dry 1” bowls submerging in silica gel pretty quick in video on another thread. Read another article by man that outlined his procedure also linked there.

Big proponet of simple air drying but silica gel packets or submerging roughs in silca gel helps speed things up migh be worth a look. I am too cheap to try it!

-- Bill

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pmayer

987 posts in 2903 days


#3 posted 06-28-2017 10:40 AM

Thanks, Bill. Yes, the wood is extremely wet. The tree was cut down less than a week ago, and the blanks that I have turned so far were spraying water the entire time they were spinning. I was soaked!

Rosin paper is commonly used as a flooring underlayment. It’s probably not ideal for drying bowls because it has some moisture resistance, but these bowls won’t fit inside of any paper bags that I have. Interesting that you don’t always use paper bags. I figured that this would lead to cracking, but I’ve never tried it.

-- PaulMayer, http://www.vernswoodgoods.com

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Lazyman

1504 posts in 1225 days


#4 posted 06-28-2017 01:08 PM

I’m certainly no expert and have not turned anything even close to that large but in my limited experience, a tenon is more likely to break off than a mortise, especially if it cracks after drying. Might not matter as much on something that big but just something to consider. Also, with a mortise, you don’t have to remount the bowl backwards after final finishing to remove the tenon so it might save a step as well. You would need a pretty big chuck to hold a 20” bowl for tenon removal.

-- Nathan, TX -- Hire the lazy man. He may not do as much work but that's because he will find a better way.

View LeeMills's profile

LeeMills

460 posts in 1139 days


#5 posted 06-28-2017 02:24 PM

No experience with that size but just my thoughts.
I would leave 10% thickness. Mike Mahoney in his video turns large ones and leaves the about 2”. Just on my experience with very wet smaller ones… warpage may be the bigger factor when returning. I’ve had two that could not be trued up due to warping. My guess is that as wet as they are if you leave only one inch there may not be a way to get it round again without greatly reducing the height (which is what I had to do).
I would heed Grumbines advise and make the bottom a little thinner (maybe 1.5”) since it is side grain and will dry slower.

Mortise or tenon. At that size it may not be too important. I have seen lots of pic with smaller tenons which sheared off from the stress. With a 2” there is three times the amount of wood to break away using a recess compared to a tenon. You can calculate the area for a larger base, it may be about the same.
I would go with a recess with 1.5” of wood surrounding. Often I use both. First with a recess only cutting a “dado” for the jaws and leave the center intact. On remount you can true to a larger recess or true for a tenon.

On remount I doubt that you would be able to use a jam chuck due to warping. I always use a friction chuck which is fast and easy. Guessing that IF you can do it you would need about a 24” jam chuck?

As to drying I would coat with anchorseal, especially the exterior. I would probably even add the stretch film on the exterior to force the drying from the interior.

-- We cannot solve our problems with the same thinking we used when we created them. Albert Einstein

View Wildwood's profile

Wildwood

2186 posts in 1972 days


#6 posted 06-28-2017 03:39 PM

There is no right or wrong way approach to drying bowl blanks basically learn as you go proposition. Based upon where you live, average relative humidity and current weather & temperatures in your area.

I have used carboard boxes with shavings if turning a lot of really wet roughs bowls temporaly. Have put more than one bowl in the box.

If dealing with your situation might end seal and store some bowl blanks after spliting for later turning. After a month or two won’t get as much water flying off as you turn them as you turn and actually dry faster. That is how get away from bags, boxes, and shavings. Simply rough out and set aside to air dry.

After seeing that short video on “wood turners around the globe,” on face book thought about that silica gel or desicant pack thread to replace shavings. Might be the ticket for me based upon where I live. Have has bowls blanks go moldy stored in bags with shavings.

Guy on facebook video said can dry a 1” thick bowl in 24 hours completely submerged! Silica gel absorbs the moisture from wood but doesn’t stop wood movement. I too cheap to buy enough silica gel to try it so think free packets better op even if takes longer.

Mortise or tenon let design or style decide for you which to use!

-- Bill

View OSU55's profile

OSU55

1425 posts in 1827 days


#7 posted 06-28-2017 03:47 PM

You can get thick brown paper, I think 36” wide, in a roll at Lowes and probably other bbs. What I use for stuff too big for a bag. I would get it out of the resin paper take too long to dry. Dont use anchor seal, take forever to dry. May take 6 mo to dry at 2”.

Bigger bowls will need more removed after drying, so yes, follow the 10%, 2”. Mortise or tenon – in part depends on how you finish. I finish on the lathe, and sanding and finishing is easier with a tenon, more access to the bottom, provided your lathe has the swing to use a friction chuck to clean up the dry tenon. Never had a strength issue with a prperly sized tenon.

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Wildwood

2186 posts in 1972 days


#8 posted 06-28-2017 03:49 PM

Folks drying wood simply a water removal process and evaporation from gentle air circulation is your friend. Coating outside or end grain on a bowl blank rough will leave you with wet wood. Forcing the drying process normally leads to cracks!

We had a bowl turner build a kiln with lots of hot lights and couldn’t understand why his bowl blanks cracked. Then could not understand why no one want to buy them after filled those cracks!

A homemade light bulb small fan kiln will increase number of bowls without drying defects and shorten drying times. Just don’t over heat wet wood! Yes, they use heat in commercial kilns but they are drying boards not bowl blanks!

-- Bill

View pmayer's profile

pmayer

987 posts in 2903 days


#9 posted 06-28-2017 04:06 PM

Wow, lots of great input here! Thanks, guys! Very glad that I asked.

-- PaulMayer, http://www.vernswoodgoods.com

View TheDane's profile

TheDane

5332 posts in 3501 days


#10 posted 06-28-2017 04:37 PM

For larger bowls, I use those lawn & leaf bags the big boxes sell … they are a heavy paper bag and I have good luck with them. Just throw in some shavings, put the rough-turned bowl in, add more shavings and roll the top of the bag. I weigh it and write the weight on the bag … rinse and repeat every month or so until it stops losing weight.

I have found that tenons are easier to re-true when re-mounting to finish turn (assuming you left a center mark on the tenon). I have a faceplate with a wooden block covered in leather that I use as a friction drive, with the live center in the tenon center mark. I true up the tenon (it is pretty much always warped), then reverse and re-mount in a scroll chuck. The only time I tried to re-true a mortise, I wound up with a mortise that was too big for any my jaw sets.

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

View DocSavage45's profile

DocSavage45

8375 posts in 2680 days


#11 posted 06-28-2017 05:48 PM

Paul,

I’m glad I’m following this thread. Watching is definitely different than getting soaked from a wet wood blank. I was under the wrong impression that it might be easier to turn wood when recently cut. And totally unaware of the influence of drying times. LOL! Thanks to all who have shared their experience!

-- Cau Haus Designs, Thomas J. Tieffenbacher

View bigJohninvegas's profile

bigJohninvegas

383 posts in 1300 days


#12 posted 06-28-2017 05:57 PM

Leaving it a little thick will slow the dry time, but give you more to work with if it warps really bad. As far as it being to big for a paper bag. You can try loose wrapping it with news paper, or butcher paper maybe. I would still try to add some shavings to it.
Have you ever tried turning it green? I really enjoy green wood turning.

-- John

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pmayer

987 posts in 2903 days


#13 posted 06-28-2017 06:36 PM

Wow, lots of great input here! Thanks, guys! Very glad that I asked.

Doc, it’s much easier to turn green, and more fun IMO. If you want the final project to remain round, however, you want to stop turning at a certain point and leave the walls thick enough so that when the bowl dries and you finish turning it there is sufficient wall thickness to allow you to return it to round without blowing out a wall.

John, yes, I love turning green. These are about as green as it gets. A lot of times I take the bowl all the way while it is still green, and then I get a distorted shape. Sometimes I don’t mind that, but I’m hoping to keep these round if possible.

-- PaulMayer, http://www.vernswoodgoods.com

View lew's profile

lew

11846 posts in 3593 days


#14 posted 06-28-2017 08:52 PM

Here’s something I’m going to try-

http://www.ronkent.com/techniques.php

http://www.ronkent.com/oaq.php

https://www.woodcraft.com/blog_entries/soap-in-your-bowl

https://youtu.be/5YM-Iw1KMmc

-- Lew- Time traveler. Purveyor of the Universe's finest custom rolling pins.

View RonGreenbush's profile

RonGreenbush

3 posts in 460 days


#15 posted 06-29-2017 02:07 PM

I turn twice. Rough it out, let it dry and finish turn it. I have turned many 16” bowls…that is as big as my lathe can handle. I always follow the 10% rule and maybe a little more depending on the species of wood. I also leave a touch more in the bottom as someone else posted. I weigh my rough turned bowls monthly keeping track of the weights. Some of my rough turned bowls (1 1/2+ inches) are still losing weight after 2+ years (mostly maple). Some are dry in 6 months (red elm). I coat my bigger bowls with a product from https://www.woodturnerscatalog.com/. https://www.woodturnerscatalog.com/p/45/4032/Artisan-Woodsealer?term=drying+wood. I have had good success with this, coating the outside, rim and an inch or two on the interior. The bigger bowls need patience to dry.

-- Ron, Greenbush

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