Official Luthiers Forum!

. . . and boredom had truly set in. This thing actually works!

Is it calibrated....???

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A person who has never made a mistake has never made anything!!!

60% RH as in the picture. more luck than by design. Straight down is 50%, no real surprise there as the indicator strip was glued at that humidity. It can't possibly me any more inaccurate than my digital Hygrometer, which has now gone way off. Given that we are building instruments and the importance of the effects of humidity on wood I suspect this is one of those simple tools that has real life practical purpose.
Still somewhat in the testing stage though.

hey, fill us in on that!
how'd you make it?

Now I really am bored.





The crucial bit is the wooden blade (indicator). That consists of cross grain (end grain) strips glued to a piece of long grain - the bi-metallic strip idea.
Blade length is 390 mm. End grain strips of mahogany cut from 80mm wide material ( 5 in total) all glued in sequence to a strip of Walnut. The Walnut is 1.5 mm, the Mahogany end grain is 2.5 mm's. Blade depth is 15 mm.
I'm quite sure other types of wood will also be suitable.
Having cut the strips make sure they are stable at a certain Humidity level eg. 50%. It's best to check this with a sling psychrometer - an accurate thermometer, decent vacuum cleaner and the tables will take care of that.
I used fast setting Epoxy. largely because water based glue may well have distorted the indicator. Just a thin coating of Epoxy on both the end grain and long grain pieces. You don't want to seal the wood so that it doesn't take on moisture. Clamp them all flat and once dry the indicator should come out straight, providing the humidity has not changed.
No finish on the indicator. That would just slow down it's reaction time.
I'm still testing the accuracy of these simple wooden hygrometers. Early signs show promise. When the indicator has noticeably moved I've checked it against the Sling Psychrometer and they seem to agree. There also seems to be consistency between the two.
They don't really need to be accurate over a wide Humidity range but they do need to be accurate over the range we consider 'safe' or appropriate for making instruments. I'm happy to build within a range of 10%, between 45 and 55 % RH. Hopefully I can use the wooden Hygrometer as a simple go, no go indicator.

brilliant. thanks.
good thing about that is you don't need reading glasses to see it.
nothing wrong with boring anyway.