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I often got cracks in my projects (Read 897 times)
 
Ed Weber
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Re: I often got cracks in my projects
Reply #15 - Jun 27th, 2017 at 8:44am
 
Ralph Schipper wrote on Jun 21st, 2017 at 8:15am:
Yeah I've read that it's not a good idea to microwave the bowl at full trotle all at once.
you need to do that a few short times, when you microwave it when theres is no moist anymore then you get burn marks.


When you're try to accelerate the drying time of wood, heat can help. Heat helps the transfer rate in which the moisture moves to the surface and also speeds up evaporation.
That said, with a microwave oven, you want heat the water (moisture in the wood) NOT boil it. Using a MW on too high of a power setting will boil the moisture trapped inside the wood.
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robo_hippy
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Re: I often got cracks in my projects
Reply #16 - Jun 27th, 2017 at 10:11am
 
Drying is an art. Every piece and species of wood is different. General rule is drying too fast the wood cracks. Dry too slow, and the wood molds. Sudden changes in temperature and humidity and the wood cracks. Some times wood just cracks. Cracks can also happen from sanding, usually with dull abrasives at high speed and with a lot of pressure, looks like spider web pattern on the end grain. I don't force dry the wood. Mostly because it takes extra time that could be spend turning more pieces.

So, for bowls, there are two choices, green turn to final thickness, or twice turn: rough out, dry, then return. With green turning, my favorite, turn down to about 1/4 inch thick, round over the rims, wrap the rim in stretch film (woods like maple which have a lot of sugar in them will tend to mold under the film, but are generally easier to dry without cracks). Put in a cool dry spot in the shop on the concrete floor is best. Dry enough to easily sand out in about a week. You will need very slow speeds or the spindle lock to sand them out though, over about 15 rpm, and you can't keep abrasives on the wood.

Twice turning, rough turn to about 10% rule (about 10 inch diameter to about 1 inch thick), round over rims, seal at least the end grain, and off to a cool spot in the shop to dry, 6 months to a year. There are light bulb kilns that will speed up the process, but again that is extra time. Some woods like madrone which warp insanely need to be once turned only or boiled after you rough turn it, then seal and dry. The micro wave does work, but again, that time factor.

With box blanks, I ALWAYS rough turn them, even from kiln dried stock. From KD stock, let sit a month or so to 'adjust' to having the mass removed. From green stock, I let them dry a year or so.

Other than that, "10,000 more times" and you may have better luck.

robo hippy
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Arlin Eastman
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Re: I often got cracks in my projects
Reply #17 - Jul 9th, 2017 at 4:31pm
 
A few things I have thought about reading this again is this.

1. You can get cracks afterwards if while sanding you get it to hot and it will crack. or
2. If a person is to aggressive with the tool and heats up the wood it will crack also.

So it could be one of these also.
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robo_hippy
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Re: I often got cracks in my projects
Reply #18 - Jul 14th, 2017 at 12:19pm
 
Hmm, I have gotten the micro checks from hand sanding before. Don't think I ever got any thing hot enough to crack from cutting with my gouges or scrapers though... Most of the time I am turning green wood, so the water would bleed off most of the heat...

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robert baccus
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Re: I often got cracks in my projects
Reply #19 - Jul 22nd, 2017 at 10:12pm
 
A drying of a walnut bowl in my bride's microwave almost bought me a divorce.  Dam good dogfight anyway.
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