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Problem with tear-out on inside of bowl (Read 598 times)
 
David Muehlbauer
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Problem with tear-out on inside of bowl
May 6th, 2016 at 11:07am
 
I am new to woodturning - about 9 months since I retired. Over the past few months I have been doing segmented bowls. I've generally had pretty good success, but my most recent bowl (#6) has some serious tear-out on the inside edges of the segments. There are no problems on the outside of the bowl. The bowl is Birch with Padauk accents. My tools and techniques have been consistent, so I am wondering if it is just the nature of this type of wood, or if there is some other explanation.
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« Last Edit: May 6th, 2016 at 11:09am by David Muehlbauer »  
 
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Ed Weber
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Re: Problem with tear-out on inside of bowl
Reply #1 - May 6th, 2016 at 2:33pm
 
Short answer is inconsistent grain direction.
The vertical segments really need to run in the same direction as the rest of the grain.
The Birch is most likely not as hard as the Padauk, along with the directional change of the grain can cause issues.
You may have experienced some bumping or skipping when turning the inside. cutting with the grain the abruptly cutting across then back, can cause the tool to catch the un-supported fibers of the softer wood and give you the tear-out.
This is one possible cause
Here are a couple of examples
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Walt
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Re: Problem with tear-out on inside of bowl
Reply #2 - May 9th, 2016 at 11:57am
 
I agree with Ed and would add that the tool sharpness and the length of the segment/species of wood can also be a cause.
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John Cepko
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Re: Problem with tear-out on inside of bowl
Reply #3 - May 13th, 2016 at 7:27pm
 
Walt wrote on May 9th, 2016 at 11:57am:
I agree with Ed and would add that the tool sharpness and the length of the segment/species of wood can also be a cause.




Smaller/shorter being better?
Or longer pieces with fewer joints?
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Ron Sardo
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Re: Problem with tear-out on inside of bowl
Reply #4 - May 14th, 2016 at 10:36am
 
John Cepko wrote on May 13th, 2016 at 7:27pm:
Smaller/shorter being better?
Or longer pieces with fewer joints?


I think the design is more important than if the segment is longer or shorter or the amount of joints in a ring. Its just something you need to take your time with.

Sharp tools and way you approach the wood with the tool is also a consideration. Learning to shear cut (not scrap) with a heavy tool that doesn't bounce will go a long way.

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Re: Problem with tear-out on inside of bowl
Reply #5 - May 14th, 2016 at 10:44am
 
John Cepko wrote on May 13th, 2016 at 7:27pm:
Smaller/shorter being better?
Or longer pieces with fewer joints?


John, I'm not sure I know what you're asking.
I wouldn't tell anyone to change their design, I would keep the existing design and change the grain direction of the wood. This alone may not eliminate the problem, only lessen them.

One issue is transitioning from hard to soft wood (regardless of grain direction)
Second issue is grain direction itself. Cutting easily with the grain and the sullenly cutting across grain can be abrupt. It may cause the tool to skip over the hard section and dig back in when it gets to softer wood. This can be amplified by the wood species being used.
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Walt
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Re: Problem with tear-out on inside of bowl
Reply #6 - May 14th, 2016 at 2:14pm
 
What I meant by shorter segments is, as with a solid piece, as you are cutting against the grain it tends to break rather than cut.  Sharp tools present in a sear cut angle will have better results.  Grain orientation is also important and should always be the same.  Having cross grain direction can later cause seam failures.
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