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Cutting Bowl Blanks: How far from the pith should you be? (Read 1,601 times)
 
Chris Gunsolley
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Cutting Bowl Blanks: How far from the pith should you be?
May 22nd, 2016 at 1:23pm
 
This question is for those of you whom have experience in cutting their own bowl blanks from logs:

When cutting bowl blanks from a log, in your experience, how far away from the pith do you need to be in order to minimize the chance of your blank cracking?

I realize that the obvious answer to this question is "as far as possible," but I'm trying to maximize the size of my bowls. I'm hoping to borrow from your experiences and gain insight into whether there's some threshold in the sense that, as long as you are this far away from the pith, you should generally be safe.

What is your rule of thumb, if you are trying to maximize the bowl size, whilst avoiding cracks?

I also realize that size may matter. Most of the logs I am working with are 6 to 12 inches in diameter. Perhaps the optimal distance is a certain percentage of the diameter of the log?

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« Last Edit: May 22nd, 2016 at 1:25pm by Chris Gunsolley »  
 
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Re: Cutting Bowl Blanks: How far from the pith should you be?
Reply #1 - May 22nd, 2016 at 3:17pm
 
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Chris Gunsolley
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Re: Cutting Bowl Blanks: How far from the pith should you be?
Reply #2 - May 22nd, 2016 at 3:56pm
 
Ron Sardo wrote on May 22nd, 2016 at 3:17pm:
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Thanks for the videos, but I can find those on my own. I was hoping to have a discussion about it, which is why I started a topic in a forum...
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Re: Cutting Bowl Blanks: How far from the pith should you be?
Reply #3 - May 22nd, 2016 at 5:07pm
 
Chris Gunsolley wrote on May 22nd, 2016 at 3:56pm:
Thanks for the videos

The links are not videos
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David Hill
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Re: Cutting Bowl Blanks: How far from the pith should you be?
Reply #4 - May 22nd, 2016 at 7:11pm
 
Chris-  Discussion it is-----those links are good stuff, I'd found them initially when I started out.  My quick answer---as far as you're comfortable---most of that will come with experience.
I work with Mesquite mostly and don't worry about pith since it's such a stable wood & if it did crack, well that's why I learned inlays. About the only trees I can think of that we may have in common are some of the Oaks, Sycamore, Hickory, Hackberry, Walnut, Elm and Osage and maybe Pecan.
Those are some of the other trees that I use around here and I do try to stay away from the pith on some since they tend to "move" more.  I don't generally worry about the moisture levels since most of my wood has been stacked outside for a while before I cut it into blanks & if it warps, so be it--makes a more unique item.
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Re: Cutting Bowl Blanks: How far from the pith should you be?
Reply #5 - May 22nd, 2016 at 7:39pm
 
Chris Gunsolley wrote on May 22nd, 2016 at 1:23pm:
What is your rule of thumb, if you are trying to maximize the bowl size, whilst avoiding cracks?

I also realize that size may matter. Most of the logs I am working with are 6 to 12 inches in diameter. Perhaps the optimal distance is a certain percentage of the diameter of the log?


Species of wood matters
location & weather matter
MC of the wood matters
All variable must be taken into account.
When working with wood (a natural product) nothing is fixed. Every piece of timber is different.
Every piece must be scrutinized individually. The distance from the pith can change drastically within the same log, inches apart.
As much as I would like to give an easy, one size fits all answer, I can't.
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Re: Cutting Bowl Blanks: How far from the pith should you be?
Reply #6 - May 22nd, 2016 at 8:04pm
 
At minimum, 1" for me when chainsawing blanks.  By the time I true up the face I may be 1 1/4" from the pith, sometimes slightly more.

Not sure what you are hoping to read that is not in the TPT, unless you don't like the content there.
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Re: Cutting Bowl Blanks: How far from the pith should you be?
Reply #7 - May 23rd, 2016 at 12:39am
 
Ed Weber wrote on May 22nd, 2016 at 7:39pm:
Species of wood matters


+1 (and everything else Ed said.)

Sad And time matters. And sun exposure. And whether checking or cracking has started. And...

I had some white ash logs sit out for a week or more with little checking, no cracking. Cut to 1inch either side of the pith, sealed, dried beautifully, turns awesome, no worries.

I have some jacaranda I basically cut right on the pith, no margin - dried without a single check or crack.

That peppertree I made a few bowls from - ugh. I cut the same way as the ash, and sealed right away, no cracks when stored properly. Within a couple weeks, end checking, internal grain splitting - nothing I could do about it. However, it has improved my skills in "void filling". Smiley

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« Last Edit: May 23rd, 2016 at 12:43am by Bill Rockwood »  
 
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Chris Gunsolley
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Re: Cutting Bowl Blanks: How far from the pith should you be?
Reply #8 - May 23rd, 2016 at 9:43am
 
Ron Sardo wrote on May 22nd, 2016 at 3:17pm:
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Really great material all around. I actually have the one by Todd Hoyer printed and put in sheet protectors for reference in my shop. The videos are nice as well. Finally, the pictures in the piece by Bill Grumbine on cutting logs into blanks tap more directly into my question here and suggest that he stayed about an inch or even more away from the pith on that particular log.

Thanks, Ron.
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Chris Gunsolley
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Re: Cutting Bowl Blanks: How far from the pith should you be?
Reply #9 - May 23rd, 2016 at 10:09am
 
David Hill wrote on May 22nd, 2016 at 7:11pm:
Chris- Discussion it is-----those links are good stuff, I'd found them initially when I started out. My quick answer---as far as you're comfortable---most of that will come with experience.
I work with Mesquite mostly and don't worry about pith since it's such a stable wood & if it did crack, well that's why I learned inlays. About the only trees I can think of that we may have in common are some of the Oaks, Sycamore, Hickory, Hackberry, Walnut, Elm and Osage and maybe Pecan.
Those are some of the other trees that I use around here and I do try to stay away from the pith on some since they tend to "move" more. I don't generally worry about the moisture levels since most of my wood has been stacked outside for a while before I cut it into blanks & if it warps, so be it--makes a more unique item.


David, I'm starting to get a feel for this "as long as you feel comfortable" reference, and I think it primarily has to do with two things: status of the wood condition and diameter. I think I'd want to be further from the pith, for example, if I already see small cracks at it and/or the wood is of a larger diameter. 1" close to the pith on a 16" log is probably comparable to 1/2" close to the pith on an 8" log. (Unfortunately, this is a point I've never heard anyone make, anywhere.) You could also judge by the growth rings. I assume you'd want to be away from the curves that show a tighter radius near the pith side. Let me know if you think this sounds about right...

Also, I'm very interested in this comment you made about stable woods. Are you saying that one may get away with either being close to the pith, or including the pith, on a piece made from some Oaks, Sycamore, Hickory, Hackberry, Walnut, Elm and Osage and maybe Pecan (due to their stability)? By this, the more stable the wood, the closer you could be to the pith. If so, are there any more wood types you'd add to that list?

I like your comment about not worrying about the piece warping, because I'm very eager to finish off some bowls, and I just started turning a couple weeks ago, so everything I read tells me that I need to wait 5-6 months now until my rough-turned bowls are ready for me to finish. Talk about patience, I'm obsessed right now, come on! I think what I'll do in the mean time is design some bowls to warp on purpose, whereby the warpage would actually be an asset as you mention, and amass those in addition to the rough turned ones that are in waiting. That way, I'll be able to actually 'finish' some bowls right now. I finished two, and they turned out very nicely, but I was too close to the pith on those. I think as long as I'm away from the pith, they should warp but not crack, so at least they'll survive...
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« Last Edit: May 23rd, 2016 at 10:25am by Chris Gunsolley »  
 
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Re: Cutting Bowl Blanks: How far from the pith should you be?
Reply #10 - May 23rd, 2016 at 10:15am
 
Well, how far away is like drying, every piece is different, so it is more art than science as the exact same method will work some times and not others. Only real rule I try to apply here is to make sure you turn away any cracks, and then a little bit extra because some times they extend past what you can see. Cracks always get bigger.

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Re: Cutting Bowl Blanks: How far from the pith should you be?
Reply #11 - May 23rd, 2016 at 10:21am
 
Don Stephan wrote on May 22nd, 2016 at 8:04pm:
At minimum, 1" for me when chainsawing blanks. By the time I true up the face I may be 1 1/4" from the pith, sometimes slightly more.

Not sure what you are hoping to read that is not in the TPT, unless you don't like the content there.


Those numbers you just gave me are exactly what I was hoping for, so thanks, Don. And, that's a good point that you're going to be taking off yet more when you true up the face. That makes me less concerned about being off just a little when I attempt to cut the blank out.

The content in the TPT is excellent, and some of it I actually keep in my bundle of documents that I treat as a 'bible' for my turning. The pieces by Todd Hoyer and Bill Grumbine, for example. As good as those are, none of them attribute an actual number--a general rule--as to how far to stay away from the pith. With this reply, you did, so thank you for that. I know you should stay away from it to minimize the chance of your blank cracking, but what I want to know is more specific: When you go to cut that log, do you have a particular distance in mind?
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« Last Edit: May 23rd, 2016 at 10:27am by Chris Gunsolley »  
 
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Chris Gunsolley
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Re: Cutting Bowl Blanks: How far from the pith should you be?
Reply #12 - May 23rd, 2016 at 10:36am
 
Ed Weber wrote on May 22nd, 2016 at 7:39pm:
Chris Gunsolley wrote on May 22nd, 2016 at 1:23pm:
What is your rule of thumb, if you are trying to maximize the bowl size, whilst avoiding cracks?

I also realize that size may matter. Most of the logs I am working with are 6 to 12 inches in diameter. Perhaps the optimal distance is a certain percentage of the diameter of the log?


Species of wood matters
location & weather matter
MC of the wood matters
All variable must be taken into account.
When working with wood (a natural product) nothing is fixed. Every piece of timber is different.
Every piece must be scrutinized individually. The distance from the pith can change drastically within the same log, inches apart.
As much as I would like to give an easy, one size fits all answer, I can't.


These are all very good points, and things I'll have to learn to account for through experience. I fully expect there to be a number of influences on making this judgment, so it helps that you've named a few so that I can start considering them in combination. Since local climate matters, I suppose the way I could accelerate that learning is by talking to turners whom cut their own blanks in my area. (Anyone near Appleton, Wisconsin?)

That's a really interesting insight here when you say that the distance you need to be away from the pith can change within the same log, only inches apart. So, if you could imagine this happening, as you progress from one part of the log to the next, what changes in the wood/growth rings might make you decide that you need to be further away from the pith further down? I realize this could be a little tricky to answer, so, would it be if the growth rings suddenly adopt a tighter radius, for example?
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Re: Cutting Bowl Blanks: How far from the pith should you be?
Reply #13 - May 23rd, 2016 at 10:42am
 
Chris Gunsolley wrote on May 22nd, 2016 at 1:23pm:
I'm trying to maximize the size of my bowls


I think the biggest mistake beginners make is trying to maximize every bit of a log or a bowl blank into as big a bowl as possible. Some of the results I've seen are less then aesthetic.

Sometimes I cut a blank into thirds instead in half to get three blanks, I then trim off the pith.

Other times I leave 3"-4" of the center while cutting the two sides. I then cut out the pith and have two sides for spindles or boxes.

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IMO all you need is to practice, cut a log then turn the results. Move on to the next log and make some changes that will better suit you, and so on and so on. After a while you will gain experience as to what works best for you.

The one thing I have never done while cutting up a log for turning was measure how far I was to the pith. Its not rocket science, its woodturning.
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« Last Edit: May 23rd, 2016 at 10:53am by Ron Sardo »  

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Chris Gunsolley
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Re: Cutting Bowl Blanks: How far from the pith should you be?
Reply #14 - May 23rd, 2016 at 10:48am
 
Bill Rockwood wrote on May 23rd, 2016 at 12:39am:
Ed Weber wrote on May 22nd, 2016 at 7:39pm:
Species of wood matters


+1 (and everything else Ed said.)

Sad And time matters. And sun exposure. And whether checking or cracking has started. And...

I had some white ash logs sit out for a week or more with little checking, no cracking. Cut to 1inch either side of the pith, sealed, dried beautifully, turns awesome, no worries.

I have some jacaranda I basically cut right on the pith, no margin - dried without a single check or crack.

That peppertree I made a few bowls from - ugh. I cut the same way as the ash, and sealed right away, no cracks when stored properly. Within a couple weeks, end checking, internal grain splitting - nothing I could do about it. However, it has improved my skills in "void filling". Smiley



Well, I suppose one lesson here is don't expect to be able to accurately predict what will happen with each blank. All of this really has me thinking about wood stability. The link at Multimedia File Viewing and Clickable Links are available for Registered Members only!!  You need to Login or Register made me realize that the rate of change as the wood dries, which depends on its density, can actually be measured, and the woods thereby ranked in terms of stability. Here are some of their results, which are generally consistent with some of the woods David listed as being particularly stable:

Most stable woods (of those measured):

1) Walnut
2) Merbau
3) Ash
4) Cherry
5) Birch
6) Oak
7) Maple
8) Beech
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