Hygrometer

[newt]

Here is something that is a novelty and has a practical application and can made from the scrap box, the overall dimensions are 400mm *120mm. The indicator shaft is a length of long grain in this case cherry and some sapele end grain. The end grain is about 2.5 mm thick and the long grain 1.5 which tapers of to about 1mm towards the tip (nothing critical). The width of the indicator is 20mm. The sapele is 3 slices off a 100mm wide board, I cut them about 4 mm thick. The 3 pieces of end grain are placed on their edge for about 6 hours in the room you intend to have the device, this is so when completed the indicator will be roughly in the middle. The 3 pieces of end grain are glued to some cherry stock using epoxy (no water based glue) and lightly clamped. When cured the indicator can be machined to the dimensions. The indicator is fixed at the top, I used a brass fitting but anything will do. As the humidity reduces the end grain contracts and bends the indicator one way, and vice versa. It is surprisingly sensitive.

The first pic shows the indicator at a humidity of 30% and the second at 55% (based against my digital hygrometer). I was surprised how quick the indicator responded to changes, there is of course no finish on the indicator.

 

[Paul Chapman]

A stunning piece of work, Pete =D> Many thanks for bringing it to yesterday's bash so that we could see it.

Cheers :wink:

Paul

 

[MikeG.]

Lovely!

What a great idea!! The bi-metallic strip is the principal of many thermostats etc, but to apply the same idea to timber and use it as a hygrometer.....well, brilliant!

Was this your idea, Pete?

 

[newt]

I forgot to mention that I made up several indicators and treated them with danish oil which reduced their sensitivity. Wainlock dod made one of these and we had a chat about the dynamics when I recently visited him in Scotland. I have this one in my living room and before the central heating came on it was in the centre, now with the heat on its spends most of the time off the board. However when my wife put on the extractor fan for cooking it moves back the other way past the centre.

 

[paulm]

You can't really see so well in the pictures, but the attention to detail is well up to Pete's usual amazing standards :shock:

What it shows so well is how quickly untreated timber responds to levels of moisture, or lack of it, in a room, and how much potential for movement there is in timber.

The indicator was literally repositioning itself from one side to the other of the hygrometer when placed in different rooms yesterday and only took 10 minutes or so to respond.

Very interesting to see, and also to admire for the detailing and thought put into the design and construction =D>

Thanks for bringing it along yesterday Pete.

Cheers, Paul

 

[Chris Knight]

Nice job Pete! A great way of demonstrating the importance of catering for wood movement too!

 

[newt]

Mike I made one a long time ago but it was not successful, Dod inspired me to make this one. One thing it does show is the strength of wood when subjected to moisture, the indicator does require some force to bent by hand, no wonder wood cracks and moves, bit scary really. Also on my first attempts I used to much epoxey and it filled up a lot of the end grain and did not work to well.

 

[Waka]

I can vouch that its a nicely crafted piece. Pete you should also show some of the other pieces you made.

 

[Jake]

Brilliant - and handsome with it.

 

[ProShop]

Excellent, love it


=D> =D> =D>
=D> =D> =D>

 

[motownmartin]

Superb

I suppose these would have to be made in a controlled enviroment for accuracy, they would make an excellent christmas present and provide hours of fun watching it move in different rooms

 

[newt]

Martin the end grain pieces are placed on their edge in the room that that you intend to have it for about six hours. Then they are stuck to the long grain with epoxy, and clamped with the end grain down on a flat surface. I have found that this gives a fairly central position when operated in that room. I built mine for the living room when the heating was off which showed about 45 to 50 % on the digital hygometer. As you can see with the heating on it spends most of the time to the right about 30% with this cold dry snap. In the warmer wetter weather (still with the heating on ) it sits on the right dot which is about 40%.

 

[motownmartin]

Martin the end grain pieces are placed on their edge in the room that that you intend to have it for about six hours. Then they are stuck to the long grain with epoxy, and clamped with the end grain down on a flat surface. I have found that this gives a fairly central position when operated in that room. I built mine for the living room when the heating was off which showed about 45 to 50 % on the digital hygometer. As you can see with the heating on it spends most of the time to the right about 30% with this cold dry snap. In the warmer wetter weather (still with the heating on ) it sits on the right dot which is about 40%.

Thanks for the info Pete.

 

[woodbloke]

I'm making three of these at the moment. The timber thats across the grain is English Cherry, and the long grain is Oak, Elm and Mahogany...it'll be interesting to see which one is the most sensitive - Rob

 

[Paul Chapman]

Be interested to see how you get on preparing the wood for the moving bit that thickness (or should that be thinness ).

Cheers :ho2

Paul

 

[woodbloke]

Be interested to see how you get on preparing the wood for the moving bit that thickness (or should that be thinness ).

Cheers :ho2

Paul

...I spoke yesterday at length to the man wot knows :wink: :lol: - Rob

 

[Ironballs]

Very well designed and finished and a superb idea. I'm impressed. Can we have a sweep on which wood will move most Woodbloke, I reckon it will be elm, oak, mahogany (elm moving the most)

 

[MIGNAL]

I've been meaning to build a wood hygrometer for years, just never got round to doing it.
That is a very attractive instrument and it has inspired me to finally cut some strips of wood!
What will be of interest is just how accurate and consistenly it measures the changes in humidity. I suspect that it will react a little slower than a digital hygrometer but once calibrated I've got a feeling it will be fairly accurate.
I have both a digital hygrometer and a sling Psychrometer that I use to check the accuracy of the digital unit. Unfortunately not all digital hygrometers are accurate despite what is written on the blurb. They also lose their accuracy over time.

 

[newt]

I have to say I was very surprised at the sensitivity of the instrument and the speed of response. The other impressive aspect is the shear strength of the wood movement, it takes quite a bit to bend it by hand. I am starting to research the possibility of using the wood movement to power a perpetual clock. I made up 4 samples of the indicator and gave the end grain a couple of coats of danish it reduced the sensitivity a little but not much. Also there appears to be an optimum thickness for the end grain, to thin and there is not enough strength, to thick and the sensitivity suffers.

 

[Wanlock Dod]

Nice hygrometer Pete,

It's certainly better to have one which is normalised to a particular set of conditions. My own one, assembled whilst at equilibrium with an unheated garage in a dampish part of the world (<70% humidity in there is really quite dry), is basically useless indoors (where I have it) because it is sufficiently bent that changes in its position are hard to distinguish.

Cheers,

Dod