Has anyone checked the shrinkulator?

[Phil Thien]

This is the online shrinkulator:
http://www.woodbin.com/calcs/shrinkulator.htm

It is a calculator that predicts wood movement with changes in moisture.

I'm wondering if anyone here has ever actually performed any of their measurements of furniture inside their homes stretching over differing seasons?

My house is climate controlled. In the winter we have forced air heat which dries the home to moisture levels seen in the finest wood-drying kilns.

In summer the air conditioner does a pretty decent job at dehumidification, but I imagine the difference between the two seasons is still maybe a good forty or more points where humidity is involved.

I've never actually checked measurements of panel widths or anything, from summer to winter. I probably should because I'm curious.

But has anyone else? Have you measured solid wood table tops (for example) from season to season, and do the changes in width correlate to what would be expected from the shrinkulator?

Just curious.

[keith micinski]

I am keeping an eye on this table. Breadboard end extreme movement? (http://www.sawmillcreek.org/showthread.php?212304-Breadboard-end-extreme-movement&highlight=)

I was shocked to see this much movement in it and am interested to see what happens this spring. I built this in late winter and was actually expecting to see it go the other way if anything.

[Kevin Jenness]

Yes, the shrinkulator agrees with reality.

[Bob Lang]

The Shrinkulator, and the data tables it is based on, are worst case scenarios and in my opinion tend to overstate the amount of wood movement. Wood movement is a very real thing, and should be a concern but every board is an individual that isn't likely to match what the shrinkulator predicts. In my experience actual movement is about half (or less) of what is predicted.

Bob Lang

[Kent A Bathurst]

I'm with Bob -

Half seems about right, but when there is no design or functional impact, I go with the calc numbers. For example, the top on hall table. Back end of top is fixed, and it expands to the front - no harm in whatever expansion, so I build it accordingly.

On, say, the breadboard ends that are the topic of the included thread, I go halvsies. But - I try to adjust for where I am in the seasonal cycle. My preference is to have the end offset at both extremes - a bit too long in the summer, a bit too short in the winter - just ballpark it, really.

[Steve Baumgartner]

My 42" wide cherry table top moves about 1/8-3/16 on both ends of the breadboard from winter to summer. I believe this is less than the shrinkulator predicts but easily enough to have torn it apart if I hadn't allowed for movement.

The shrinkulator is for bare wood; it does not account for any finish coatings. Since finishes slow the migration of moisture between the wood and air, a finished piece will usually have a smaller annual cycle than an uncoated board. But with the possible exception of total encapsulation in epoxy, no finish completely blocks moisture. The wood will move!

The science behind the shrinkulator is quite well-developed (read Hoadley's book if you want more detail than you can digest!), but wood is a natural material so no two pieces are quite the same. The values used are averages over a large number of samples (I do not believe they are worst case as Bob stated).

[Jamie Buxton]

The key input to the calculation -- either by Sagulator, or by some other means -- is the humidity faced by your piece of furniture. The trick is that humidity varies all over the US, so you need to know it in your shop and in your house. One tool is a data logger which records humidity, like this one: http://www.lascarelectronics.com/temperaturedatalogger.php?datalogger=102 . I bought two -- one for house and one for the shop. I'm about 7 months into logging values for an entire year.