What's a good level for workshop humidity?

I've recently aquired a de-humidifier in an attempt to stop my tools and machines going rusty during the winter - what's a good relative humidity level to aim for so I don't make the air too dry for all the wood in the workshop? Many thanks Tony
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Actually if you can control the wide sudden temperature changes it may help. My tools are always subject to humidity in between 25 and 100% and do not have rust problems. That plus TopCote.
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40 to 60 percent.
David
Tony B wrote:

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The perfect humidity is exactly the same as the environment your project is going into when complete. 40% to 50% is considered good for the hmans in the house.
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As Leon has so perspicaciously stated, it is not so much the relative humidity as it is the relationship of the highs to the lows, and the swiftness with which they occur.
What will really rust your tools is a cold front, precipitously followed by a warm front (that happens to be carrying a lot of moisture, as is their nature.)
Unfortunately, the reverse is also true.
If you simply allow your tools to live at the ambient air temperature, and only bring them up to working temperature in a gentle way - you will be fine.
Wood does not react as quickly to temperature/moisture changes as cast iron, so they will be just fine ( and prolly achieve closer to the ideal mc ) if left alone.
Regards, Tom.
"People funny. Life a funny thing." Sonny Liston
Thomas J.Watson - Cabinetmaker (ret.) tjwatson1ATcomcastDOTnet (real email) http://home.comcast.net/~tjwatson1
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In my shop, er, studio, the temp ranges from 60F to 75F and the RH from 50 to 70.
Right now, the temp is 65 with a RH of 60. At the peak of summer, the temp might reach 75 for a short while and if I didn't run the dehumidifier it'd reach around 90, but I keep it at about 60. Obviously right now the dehumidifier isn't running. My furnace is a condensing type, that does a good job of further wringing out already dry air.
Check out "Understanding Wood" by Hoadley for a discussion on temperature, relative humidity and grains of moisture in the air.
What this means is that if the water content of the air is unchanged, the RH will rise and fall opposite the temperature. The temp rises, the RH falls. The temp falls the RH rises. Of course if the temp is unchanging, if the RH rises there's more moisture in the air, if it falls, less. But that's obvious.
Probably more than you asked for.
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Tony,bare iron/steel won't rust below 50% RH.
Jerry
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Well, lots of answers. The room at school is 45% which is about 8% MC.
What wasn't mentioned is that dehumidifiers ice up so fast under about 50 degrees F that they're essentially worthless.

level
workshop?
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