When do you decide to finish turn a roughed bowl......?

[Odie]

Howdy folks......

My usual habit is to weigh all roughed bowls once a month. As a general rule, I feel free to finish turn bowls when the weight remains within 5 grams for three weighings. That seems to work pretty well for me, but I have a number of bowls that just keep losing weight month-by-month.

I'm not sure if I can get away with finish turning, unless the bowl definitely "stabilizes". An added consideration is I'm one who pretty much specializes in "thin wall" bowls......1/8th to 3/16th inch, or so. When the bowl meets the three-weighing rule I've established for myself, it appears as though I'm not getting any cracking over time. (Many of my bowls are given away, or sold.....so, I'm not able to monitor all of them......but, from what I do know, my rule seems to work well.)

I have given the weighing log for a couple of my roughed bowls below. (all weights are in grams) Do any of you feel comfortable in finish turning these bowls? At what point, and why?.....if you do. Take into consideration that they are intended to be thin wall. I'm sure there would likely be no problems if I finished turned them 1/4", or thicker.

Note: You can definitely see that during the winter months, it's cooler in my shop......and the rate of moisture loss reflects that.

Thanks for any insight, input......

otis of cologne

========================================

#541 8x8x3 Red Oak (moisture meter= 26%)

Roughed 8/22/07

8/22.....860g
9/9.......785g
10/4......720g
11/13....680g
12/1......665g
1/5.......650g
2/4.......650g
3/1.......635g
4/4.......625g
5/16.....615g
6/10.....610g
7/12.....605g

=========================================

#546 3x8x8 Claro Walnut (moisture meter= 24%)

Roughed 9/20/07

9/20.....955g
10/4.....940g
11/13...905g
12/1....890g
1/5......875g
2/4......865g
3/1......855g
4/4......835g
5/16....815g
6/10....800g
7/12....770g

===================================

#566 4x10x10 figured Maple (moisture meter= 14%)

Roughed 11/28/07

11/28.....1340g
12/1.......1335g
1/5.........1330g
2/4.........1335g
3/1.........1325g
4/4.........1320g
5/16.......1310g
6/10.......1305g
7/12.......1285g



.

 

[john lucas]

I have a very rough time getting back to rough turned bowls. I always have more than I need. I used to weight them and use the not losing weight thing to decide when to return them. Almost all were dry withing 6 months or less. I checked the other day and many of my bowls are a year old or more so now I just rough turn when I can, put a date on them and when I'm ready to return I just grab one of the older ones.

 

[Odie]

I have a very rough time getting back to rough turned bowls. I always have more than I need. I used to weight them and use the not losing weight thing to decide when to return them. Almost all were dry withing 6 months or less. I checked the other day and many of my bowls are a year old or more so now I just rough turn when I can, put a date on them and when I'm ready to return I just grab one of the older ones.

I appreciate the input, John.......but, this really wasn't what I was looking for. With the cost of the green bowl blanks I purchase, I just can't afford to have hundreds of drying bowls at a time in order to keep my shop moving along. I'm pretty picky about what I purchase, and don't want to bother with a multitude of bowls that are destined for mediocrity......so, I usually have to pay more to get what I want. I necessarily have to pay particular attention to the details, since my interests are "thin wall". I do, however, have about forty bowls in progress at this time.

What I'm looking for is a formula that works for others for determining when roughed bowl blanks are, or might be ready during the weighing process, with the stipulation that the intended purpose is an ultimately "thin wall" finished bowl. For roughed bowls that continually see weight loss, month-by-month, is it possible to determine if any particular weight can yield acceptable results.....?

It's a given that weight "stabilization" will give what I want.....but, is there any other method, formula, reasoning, that works? I suppose that, with some species, a determination of the percent moisture content might......but, how would one know which and how much?.....or, is each piece of wood truly an "individual"?

Thanks anyway, but I'm looking to steer the input on point.

otis of cologne

 

[Frank Drew]

Otis of Cologne,

I went by feel (how heavy it felt), but I also would wait a good while before attempting to return a roughed out bowl (minimum 6-8 months for smaller bowls, more like a year for larger ones.)

 

[Malcolm Smith]

I appreciate the input, John.......but, this really wasn't what I was looking for. With the cost of the green bowl blanks I purchase, I just can't afford to have hundreds of drying bowls at a time in order to keep my shop moving along. I'm pretty picky about what I purchase, and don't want to bother with a multitude of bowls that are destined for mediocrity......so, I usually have to pay more to get what I want. I necessarily have to pay particular attention to the details, since my interests are "thin wall". I do, however, have about forty bowls in progress at this time.

What I'm looking for is a formula that works for others for determining when roughed bowl blanks are, or might be ready during the weighing process, with the stipulation that the intended purpose is an ultimately "thin wall" finished bowl. For roughed bowls that continually see weight loss, month-by-month, is it possible to determine if any particular weight can yield acceptable results.....?

It's a given that weight "stabilization" will give what I want.....but, is there any other method, formula, reasoning, that works? I suppose that, with some species, a determination of the percent moisture content might......but, how would one know which and how much?.....or, is each piece of wood truly an "individual"?

Thanks anyway, but I'm looking to steer the input on point.

otis of cologne

I don't know that there is an easier way than weighing the bowls and would think that as they end up 'very thin walled' it would be especially important that they be completely dried out and stable. I notice in the weights in a previous post that the final weight is not the same as the next to final weight etc. Comparing the list with weight lists that I keep, It seems to me that it is not clear that they are fully dried. I re-turn when I have two or three weighings that match or are extremely close to matching. This could be affected by there being large changes in temperature or humidity in your shop. I store the bowls where this does not occur.

There are sensoring systems that measure moisture but require that the wood me probed which leaves holes. Also, unless one is turning common woods, the list of correction factors given by the manufacturer doesn't list the wood.

A very accurate suitable scale is one I have that is designed for weighing refridgerant bottles.

Malcolm Smith.

 

[MichaelMouse]

First, get a good humidity gauge. Your weight will vary with the RH, so knowing that you can't be any dryer than X% at Y RH might help you make the decision to zap if you want to turn that blank. A trip to the micro can help give your fibers a bit of a set which will help stability even as it regains moisture.

I suppose a guy might use the relative density figures and do some math to determine a rough moisture measure, but weight is the definitive measure. Just balance it with the best possible based on the RH.

Thin turnings are more likely to distort from tension released when turning than with subsequent moisture change, in my experience. Makes a bowl steady a great purchase. I would take the springs off, were I you, so that the steady is rigid. That way you can get uniform thickness and with outside, inside, outside inside touch-ups, the best circularity in spite of newly released tension.

 

[Bill Pottorf]

Purchasing WET TIMBER?

With the cost of the green bowl blanks I purchase, I just can't afford to have hundreds of drying bowls at a time in order to keep my shop moving along. I'm pretty picky about what I purchase, and don't want to bother with a multitude of bowls that are destined for mediocrity......so, I usually have to pay more to get what I want. I necessarily have to pay particular attention to the details, since my interests are "thin wall". I do, however, have about forty bowls in progress at this time.

Otis of Cologne,
Why are you purchasing wet green wood for roughing out? Why are you not harvesting from local sources for free? I guess that most store bought blanks are wet as well and must be roughed out and dried.

As for a roughing out rule of thumb, if you use the 10% rule of thickness to the diameter of the bowl blank, it generally takes about 1 year per inch of thickness for drying. After this amount of time, the wood is sufficiently dry for final turning.

 

[Odie]

OK, men......I know I was on a little fishing excursion, here.....

I guess I was hoping for some "magical" new insight to the drying process, but it appears as if my methods are probably not going to be revised as a result.

A couple of comments:

MM: Yes, you are absolutely right about the internal stresses in the bowl. Those need to be dealt with as the bowl is on the lathe for final turning. I was pretty much thinking along the lines of how continued moisture release, over time, will effect the finished bowl......and how I might judge that using the information I have.

Where might I get a RH gauge, cheap?.....I believe I'd like to get one of those.

The springs on my bowl steady are added in such a way that I have the option of using them, or not. Sometimes, I don't.....but, I feel there are times where they have proved very useful.

Bill: I purchase bowl blanks because there is a very limited source of local woods.....and no hardwoods to speak of, that is, unless it comes from a private source. Even there, the availability isn't as good as we'd all like to see! When I purchase bowl blanks, I usually (not always!) get what I want and pay for. I may gripe a complain about spending as much as $70-80 for some of my bowl blanks, but the finished result is worth it to me.

Thank you for all your comments. I really do appreciate that very much. If there is anyone with additional information to share......bring it on! I'm sure I'm not the only one who has an interest in this subject.

otis of cologne

 

[Richard Baker]

Odie,
Nothing to add. So why write? Dunno. IMHO you are already doing it the best possible way for your purposes. From the data listed, none of those three pieces has completely equilibrated with the surroundings. Agree with what MM said re. stress created/released during final turning.

 

[Mjonesrdg]

RH Gauge

Odie,

An "RH Gauge" is also called a "Hygrometer". A weather instrument that can be found at hardware and department stores. Woodcraft has hygrometers sold separately for less than $10.00 and combined with thermometer/barometer/shop clock for a few bucks more.

Also, having a 'constant', such as "bone dry" could help. You can only achieve this by baking/weighing/baking/weighing until the weight remains constant, immediately weighed out of the oven. (do this with scrap) Allow the piece to acclimate over a period of time until there is constancy in increased weight. Then do the math. The percentage weight gain will be the relative H20.

One other thing that might help. You can find historical RH values (seasonal too,) for your area on Wunderground's web site.

Mike

 

[n7bsn]

Odie,

An "RH Gauge" is also called a "Hygrometer". A weather instrument that can be found at hardware and department stores. Woodcraft has hygrometers sold separately for less than $10.00 and combined with thermometer/barometer/shop clock for a few bucks more.
...
Mike

Yup, that's what's in my shop, that way I know the time, temp and RH
Nice BIG 15 inch face, bought from Amazon on one of their sales

Ralph

 

[MichaelMouse]

Yup, that's what's in my shop, that way I know the time, temp and RH
Nice BIG 15 inch face, bought from Amazon on one of their sales

Word has it they even make more expensive models that people turn bases and frames for!

I'm digital, because that's cheapest, but upstairs is an analog I can read to the "good enough" without my glasses.

 

[rsser]

FWIW my approach is to rough turn, measure the moisture with a meter at the inside tenon and write it and the date between the pin marks, then periodically re-measure. When the number stops dropping it's ready to go.

 

[Dave Roller]

What I'm looking for is a formula that works for others for determining when roughed bowl blanks are, or might be ready during the weighing process, with the stipulation that the intended purpose is an ultimately "thin wall" finished bowl. For roughed bowls that continually see weight loss, month-by-month, is it possible to determine if any particular weight can yield acceptable results.....?

I measure across grain. When that stabilizes, I turn.

 

[Angelo]

Thin Walls

How thin is thin? If you are turning end grain or face grain turn as thin as possible (1/16" or 3/16") when it is green and accept the distortion?

If you want flat rimmed, face grain bowls, then you need to rough turn 'em to a wall thickness that is +/- 10% of the diameter. So a 12" bowl would have a wall thickness of +/-1.25".

If we accept the old timers rule of thumb for air drying (1 year per 1" of thickness plus a year) The a 12" bowl with a 1.25" wall thickness will take 2.25 years to reach 6% moisture content.

In reality I find that they are ready in 4 to 6 months depending on how wet they were in the first place.

BTW I use the paper bag with shavings method to dry the rough turned bowls.

A

 

[Odie]

What I'm looking for is a formula that works for others for determining when roughed bowl blanks are, or might be ready during the weighing process, with the stipulation that the intended purpose is an ultimately "thin wall" finished bowl. For roughed bowls that continually see weight loss, month-by-month, is it possible to determine if any particular weight can yield acceptable results.....?

I measure across grain. When that stabilizes, I turn.

Now, that is an interesting concept.

I think I may try verifying that by cross-referencing with weight readings.....and see what turns up.

Thanks.....

otis of cologne

 

[MichaelMouse]

Now, that is an interesting concept.

I think I may try verifying that by cross-referencing with weight readings.....and see what turns up.

That's already been done by professionals on hundreds of samples. Look at Ch 03 of the Wood Handbook on that FPL site again, or the informative pdf here for formulae and explanation. http://www.fpl.fs.fed.us/documnts/usda/ah188/chapter01.pdf


Noting that pits are holes and stomata are holes, but pits are not stomata. :cool2:

 

[Dave Roller]

That's already been done by professionals on hundreds of samples. Look at Ch 03 of the Wood Handbook on that FPL site again, or the informative pdf here for formulae and explanation. http://www.fpl.fs.fed.us/documnts/usda/ah188/chapter01.pdf


Noting that pits are holes and stomata are holes, but pits are not stomata. :cool2:

MM, if it's no longer shrinking across grain, for a woodturner's purpose shouldn't it be considered "dry?"

 

[MichaelMouse]

MM, if it's no longer shrinking across grain, for a woodturner's purpose shouldn't it be considered "dry?"

Good enough for me. I look at how much the recess has shrunk on my stuff and use it as sort of a rough ready. When the eighth inch across the grain is gone, it's good to weigh, and normally good to go. Can't really rely on the top end, because it's more affected by the grain orientation.

 

[Ron Warman]

When do you decide to finish a rough bowl

This may not answer your question but this is what I do now. I turn to 1/8" or less because I pierce my work and it has to be thin. I use green wood only, no exotics. I turn the outside to shape first and mount the wood in my chuck and true up the outside again. When I hollow the inside I go to my desired thickness in steps of about 1/2" at a time. When I reach the 1/8" I sand this area and go for the next 1/2" segment until I am at the bottom. I have made several vesels like this and they do go oval but none have cracked and with the piercing the oval shape is not too noticeable. When you turn this thin the wood is almost as dry as it will get and I apply my sanding sealer before I remove the piece. I adopted this because when I roughed out a piece it was too hard for me to blend the segments together. I am no expert and this may not work for what you do. If I paid $80.00 for wood I would be afraid to turn it.

Ron

 

[Mike Gould]

I know it's not super accurate. But what I do is air dry after a rough turn until I "think" it has been long enough. Then I touch the blank to my cheek. If it feels cool then it is probably still wet. And needs more time. If warm/dry it usually is "good to go". No scales/science/etc. needed.

---Mike---

 

[Malcolm Smith]

This may not answer your question but this is what I do now. I turn to 1/8" or less because I pierce my work and it has to be thin. I use green wood only, no exotics. I turn the outside to shape first and mount the wood in my chuck and true up the outside again. When I hollow the inside I go to my desired thickness in steps of about 1/2" at a time. When I reach the 1/8" I sand this area and go for the next 1/2" segment until I am at the bottom. I have made several vesels like this and they do go oval but none have cracked and with the piercing the oval shape is not too noticeable. When you turn this thin the wood is almost as dry as it will get and I apply my sanding sealer before I remove the piece. I adopted this because when I roughed out a piece it was too hard for me to blend the segments together. I am no expert and this may not work for what you do. If I paid $80.00 for wood I would be afraid to turn it.

Ron

Interesting. Different procedures suit different end results. I don't personally like the oval form and if what results is an egg shaped form, that seems particularly dissapointing. If you are carving, punching etc, I would guess that the oval form can be made a feature of the turning.

As for 80 dollar wood, I don't sell my work and therefore would rather turn fewer pieces that are more interesting because of the woods I employ. A lot of bowls that are being turned today could be turned out of most any wood as the character of the wood is not a major feature of the turning, in fact, some of them are painted.

Malcolm Smith.

 

[MichaelMouse]

I know it's not super accurate. But what I do is air dry after a rough turn until I "think" it has been long enough. Then I touch the blank to my cheek. If it feels cool then it is probably still wet. And needs more time. If warm/dry it usually is "good to go". No scales/science/etc. needed.

Remember mom touching her lips to your forehead to see if you were feverish? Apparently they're more sensitive to temperature difference than your cheeks. You were talking about your face, right?

Females' are supposedly more sensitive than males' lips, too.

 

[Gretch Flo]

sensitive lips

Remember mom touching her lips to your forehead to see if you were feverish? Apparently they're more sensitive to temperature difference than your cheeks. You were talking about your face, right?

Females' are supposedly more sensitive than males' lips, too.

Saw Jimmy Clewes at turning demo tell which grip of sandpaper he picked up by brushing against lips. I (female) can't saw I have mastered that the few times I have tried when my piece of sand paper had the number torn off, Gretch