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  #1  
Old 01-19-2021, 12:38 PM
kmanuele kmanuele is offline
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Default humidity, bridge install

I have a few guitars in process, with unfinished bodies built this summer waiting on the shelf. I have noted the doming on the top no longer matches the build profile (25' radius). That is, the top radius has increased, which I speculate is due to drop in humidity in winter.

The shop is heated, about 65F, and humidity now measures about 35% which isn't too bad. Humidity will probably go lower as we get into colder weather.

The bridge undersides were pre-profiled to 25' (which was probably a mistake), so they no longer match the bodies.

The underside of the bridges can always be re-profile to match, of course, but am hesitant with the change in doming.

I am wondering how small builders maintain component humidity, if not humidifying the whole shop. Can I put sponge-type humidifiers in the bodies, with no cases? Should I?

Is this a non-issue, and I should just reprofile the bridges and move on?

Maybe complicating factor: One of these guitars will be going to NYC, which has much higher average humidity levels than out here on the west coast.

Thanks for any advice.
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Old 01-19-2021, 12:58 PM
charles Tauber charles Tauber is offline
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As wood dries, it shrinks. The shortest distance between two points is a straight line. Arched surfaces shrink and flatten as they dry, which is what you have observed.

What was the humidity level in the summer when the body and its components were assembled? If the humidity level drops below that, you run the increasing risk of having components crack, same as is true for finished instruments.

I glue flat bridges to domed tops. I've done it that way for four decades with good results. Arguments can be made for both contouring the bottom of bridges to match top arches and for gluing un-contoured bridges. You chose which you think is better. Objectively substantiating your choice is more difficult.

In climates that see considerable variation in seasonal indoor humidity levels - typically colder climates that heat indoor air - if one is to make guitars year-round, humidity control is required. It doesn't have to be complicated or expensive, necessarily, but is required. It can be as simple as a walk-in closet with a de-humidifier, or, if you don't have a lot of materials to control, a large box heated with a light bulb. Floor model humidifiers will keep humidity levels up in the winter months. I don't think putting sponges inside an unfinished guitar surrounded by dry air will be very effective. All of the wooden parts will expand and contract in response to humidity changes.

My current shop is a two-car garage. I heat it in the winter with a small space heater and humidify it with a standard floor-model humidifier. The humidifier consumes about a bucket of water per day, less if I keep the temperature a little cooler. In the summer, I dehumidify using a standard floor-model de-humidifier. I can easily keep the humidity constant year-round at 40%. Parts of the year require neither humidifying nor dehumidifying.
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Old 01-19-2021, 01:16 PM
John Arnold John Arnold is offline
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Quote:
I glue flat bridges to domed tops. I've done it that way for four decades with good results.
As do I, though I do use a larger radius than 25 foot.
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Old 01-20-2021, 07:21 PM
kmanuele kmanuele is offline
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Default humidity, bridge install

Quote:
Originally Posted by charles Tauber View Post
What was the humidity level in the summer when the body and its components were assembled?

I glue flat bridges to domed tops. I've done it that way for four decades with good results.

My current shop is a two-car garage. I heat it in the winter with a small space heater and humidify it with a standard floor-model humidifier. The humidifier consumes about a bucket of water per day, less if I keep the temperature a little cooler. In the summer, I dehumidify using a standard floor-model de-humidifier. I can easily keep the humidity constant year-round at 40%. Parts of the year require neither humidifying nor dehumidifying.
Thanks for this, and lots of food for thought here.

Re: flat bridge glued onto dome. Interesting concept. Maybe I am worried too much re: built-in glue joint stresses? The gap I am seeing is quite small (~0.015", worse case body), and will easily close with minimal clamp pressure and no profiling of bridge.

My garage is my shop too, with space heaters but no AC. Don't recall what humidity was (yes, I should know :-(), but it can run in the high 40s, mid 50s, in summer.

I guess I'm investing in a humidifier :-) Will see if a dehumidifier is needed later this year. The house has AC, so that is an option for storage in summer.

Thanks again;

Kevin
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