6 inch is not what it seems…
July 13, 2008
Today - after yesterday’s 4 hours of grass strimming in the garden of our holiday cottage - I didn’t feel like any serious physical labor so I decided to work out a design for the roof rafters for the shed. After some fiddling about with a pencil and a paper I was fed up. What now? I remembered I downloaded Google SketchUp a while ago. I hadn’t given it much attention but maybe it could do the job. And impressed I was!! Within a couple of minutes I cooked up this really professional looking and functional design with all relevant measurements to saw the rafter template.
But then… I found out that a 6”x2” piece of timber is not really 6” by 2”. I thought I’d use a website with an inches to mm converter and just use the converted values. In which 6” is 152mm. Wrong!!!! It appears that a 6” piece of timber is actually 145mm. Where did those 7mm go? Well, a 6”x2” is only 6” by 2” until it gets treated (sawn, planed) and then it gets its actual size of 145mm x 45mm. Confusing!!
Luckily Google’s SketchUp tool is UK measurement quirkiness proof and I had the changes made fairly quickly. The design shows: the roof pitch (38 degrees), the location of the bird’s mouth within the rafter, the location of the 4”x2” on the joist which will slide into the bird’s mouth and all relevant size to precisely layout the rafters.
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