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I have never had a problem with humidity. I have a Martin 000-28 I bought new in 1974 and it has spent winters in VA, OH, PA, IN, DE and MD and it is still crack free. That said, I think it is nice to know approximate RH and I keep an electronic hygrometer/thermometer around, but thought it would be helpful to have something I can glance at as I enter the shop to see how things look. Saw one of these years ago and found a few on the innerwebs. I spent a couple hours on this fun project. I picked wood that lives in my 40% RH shop, and this is how much it bent after 15 minutes in a 130° oven. I still have to do a little relative calibration and make a couple of marks.

Ed

Love it! Did you use spruce for the indicator? I would like to make one too.

There are 2 strips glued together. One has grain running the length of the indicator, and one running across the width. The long grain is a piece of spruce (from a 2X4?) and the cross grain is from a piece of ash from a guitar I did. Wood expands and contracts across its width, but not its length, so the ash gets "wider" and "narrower" as it takes on and gives off water which forces the indicator to bend. The strips are about 1/8" thick and 1/2" wide. Science at work

Ed

Very neat! It's interesting you'd post this.

I'm having low humidity problems in my shop at the moment, even though I'm running a very large capacity evaporative humidifier, in addition to the whole house humidifier on the furnace. My digital hygrometer is pretty old and not holding calibration anymore. It was reading 40%, ( I Try to keep the shop 45-50) but I'm getting nose bleeds. I used a professional psychrometer, (my husband is retired HVAC) and found it was way off, 12% off. So, I bought a German made, synthetic hair hygrometer that's +/- 3%, but can be further calbrated.

I've added another humidifier.

I took the little guy outside, and when I brought it back in you could actually watch the end of the indicator move as it adjusted. The longer the arm, the more sensitive it is, and I might make one that is 18" rather than the 10" on this one

My guitar are becoming pretty good hygrometer needles. I'm running an April Aire inline furnace humidifier but right now it's 25% inside. Interesting, the necks are curling indifferent directions. I keep little humidifiers in the sound holes in the winter. Wondering if I'm OVER humidifying? Mexi-Martin is the worst with the laminated sawdust fingerboard (HPL) with a multi-layer laminated neck. The belly is flat as a rail. The 14th fret is sky high with a huge back bow. Had this last winter too. Very frustrating

Kbore wrote:My guitar are becoming pretty good hygrometer needles. I'm running an April Aire inline furnace humidifier but right now it's 25% inside. Interesting, the necks are curling indifferent directions. I keep little humidifiers in the sound holes in the winter. Wondering if I'm OVER humidifying? Mexi-Martin is the worst with the laminated sawdust fingerboard (HPL) with a multi-layer laminated neck. The belly is flat as a rail. The 14th fret is sky high with a huge back bow. Had this last winter too. Very frustrating

You need a hygrometer to find your humidity level. My husband installed an April air on our first floor furnace. If you have a high efficiency furnace, remember that they don't run often and when they do, they satisfy the thermostat quickly. We have 2, 2-stage furnaces and they rarely kick into the higher setting. Even with the april air set at 50%, my first floor air is dry. This is why i keep my guitars that aren't in the shop, in their cases with an Oasis humidifier, to create a microclimate for them.