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Stem Warpage (Read 806 times)
 
Glen Nicholson
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Stem Warpage
Dec 7th, 2017 at 6:29pm
 
I have a long-stemmed ash goblet that the stem has warped. I believed this wood was dry but later determined it was at around 12%, which is high for this location at this time of the year.

I tried stem but the kettle I have has a thermostat that shuts the thing off just when it really starts going. Tried holding it over a boiling pot of water but that is inefficient.   

I want to include this piece in a show I have coming up this Sunday. Help!! Shocked
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Bill Godber
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Re: Stem Warpage
Reply #1 - Dec 7th, 2017 at 7:24pm
 
I've had good results with a wet towel and a hot steam iron on the cupped side of warped boards but never on a long stemmed goblet. it might be worth a try.
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Don Stephan
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Re: Stem Warpage
Reply #2 - Dec 7th, 2017 at 8:41pm
 
I have no idea how ash would respond but you could try a 30 second burst in a workshop microwave.  If its not too hot to handle after 30 sec you could try a second blast, but a long blast may set the wood on fire.  A chuck of walnut had a red hot core and smoked up my microwave like no tomorrow.

Exposing the stem to steam will push some moisture into the wood, perhaps interfering with application of finish and curing before Sunday show.
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Glen Nicholson
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Re: Stem Warpage
Reply #3 - Dec 8th, 2017 at 2:55pm
 
Thanks guys.  Thumbs Up
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Tony Allwright
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Re: Stem Warpage
Reply #4 - Dec 13th, 2017 at 4:16am
 
Its heat rather than steam per se that softens the wood and allows it to be bent. I have used a hot air gun and this works OK. Try it on a  test piece similar diameter to the goblet stem. You only really get one go at the bending. Once the wood has been heated and them cooled, reheating does not allow for much bending.
Tony
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Ed Weber
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Re: Stem Warpage
Reply #5 - Dec 13th, 2017 at 10:19am
 
Tony Allwright wrote on Dec 13th, 2017 at 4:16am:
Its heat rather than steam per se that softens the wood and allows it to be bent.


When trying to bend wood, your are trying to have wood that can absorb compression and tension forces without failure.
The steam carries the heat along with moisture (obviously), this slightly raises the MC of the wood and also eliminates the risk of scorching. The steam temperature is roughly similar to the temperature where the lignin (organic polymer that stiffens wood) starts to soften.
When the lignin softens, the wood looses some rigidity, combine this with a higher moisture content (think green wood) and the wood is much more acceptable to bending (compression on one side, tension on the other)
Using dry heat can also cause brashness. Heating to too high a temperature for too long can weaken the wood. This is almost impossible to regulate with a heat gun.
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Don Stephan
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Re: Stem Warpage
Reply #6 - Dec 14th, 2017 at 8:36am
 
Thanks for the discussion Ed, can't recall ever seeing such a full picture re bending wood.
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Ed Weber
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Re: Stem Warpage
Reply #7 - Dec 14th, 2017 at 9:51am
 
Wood will always bend easier and further the first time.
Re-bending is more difficult but with correcting a warp or slight curvature in something as small as a goblet stem it should be able to be done.
For small items (like a goblet stem) I have used a tool that was intended to train bonsai branches. It can placed on the affected area. Apply steam and increase clamping pressure and allow to set/cool.
Example
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Ron Sardo
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Re: Stem Warpage
Reply #8 - Dec 14th, 2017 at 11:02am
 
DIY Luthiers (those that make string instruments such as guitars) use dry heat to bend the sides on an instrument. I've seen, but never tried a simple setup something like this.

Of course pros use a more sophisticated setup with heating blankets and thermostats

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I've also witnessed a single 300w bulb inserted into a pipe to bend rosettes (the design around the hole of an acoustic guitar

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Good luck and let us know how it works out.
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Ed Weber
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Re: Stem Warpage
Reply #9 - Dec 14th, 2017 at 11:27am
 
You touched on the main point Ron, which is IMO control.
Thermal blankets and even light bulbs have a known amount of heat output, constant and uniform (in most cases).
Also when using irons and heated forms, often the wood is saturated or soaked in water beforehand. Pre-soaking softens the wood fibers, (like soaking reed for baskets) the dry heat softens the lignin and allows for easier bending.
Dry bending can be scary and is dependent to a great degree on the wood species. being used.
This is why, unless you are skilled in the science/art of bending, I don't suggest using a heat gun.

For those interested, here is an article on bending wood. Although it's directed at luthiers, the principals are the same. Multimedia File Viewing and Clickable Links are available for Registered Members only!!  You need to Login or Register
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Ron Sardo
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Re: Stem Warpage
Reply #10 - Dec 14th, 2017 at 12:09pm
 
Good article, I just started to look for that same page and linking it as well but you beat me to it. Smiley Thanks
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Glenn Jacobs
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Re: Stem Warpage
Reply #11 - Dec 14th, 2017 at 1:24pm
 
When I was building canoes, we used a steam generator. Tea kettle and plastic pipe to hold the ribs.

Glenn J.
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Ed Weber
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Re: Stem Warpage
Reply #12 - Dec 14th, 2017 at 1:30pm
 
Ron Sardo wrote on Dec 14th, 2017 at 12:09pm:
Good article, I just started to look for that same page and linking it as well but you beat me to it. Smiley Thanks


I really like the Multimedia File Viewing and Clickable Links are available for Registered Members only!!  You need to Login or Register
If you're a luthier (or not) they have a wide variety of unique and specialized woodworking tools.
I originally looked there when the were one of the advertisers here.
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Tony Allwright
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Re: Stem Warpage
Reply #13 - Jan 2nd, 2018 at 4:23am
 
Glen
Did you manage to straighten the stem on the goblet and if so what technique did you use.
Tony
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Len Mullin
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Re: Stem Warpage
Reply #14 - Jan 4th, 2018 at 9:25pm
 
Glen Nicholson wrote on Dec 7th, 2017 at 6:29pm:
I have a long-stemmed ash goblet that the stem has warped. I believed this wood was dry but later determined it was at around 12%, which is high for this location at this time of the year.

I tried stem but the kettle I have has a thermostat that shuts the thing off just when it really starts going. Tried holding it over a boiling pot of water but that is inefficient.

I want to include this piece in a show I have coming up this Sunday. Help!! Shocked



Glen, what location are you talking about? Where your from, isn't showing in your avatar like most other member's are. And it's not shown on your profile page, it's very bewildering when a member puts an "around here" in their posting, and then not let anyone know where here actually is. There's no need for you to post where your from, but it sure would be nice to know.
Len
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