Japanese woodworking marking, measuring and laying out

The main purpose of this post is to show off some gorgeous pictures of sumitsubo, the Japanese carpenters ink markers, equivalent to European chalk lines.

I’ll also give a brief overview of the measurement system and the different way carpenters mark out their timbers.

Whilst Japan went metric in 1924 carpenters the world over tend to hang on to old units and so in Japan they still use the shaku as the base measurement. One shaku is 303mm or 11.93 inches so about a foot. This is subdivided into 10 and 10 again to give sun, bu, rim and mo. The carpenters square marked in sun looks close enough to an English square marked in inches to cause confusion. Houses have standard room sizes based on the size of tatami mats, though tatami mats vary slightly in size from region to region.

 Now to marking out using the sumitsubo, European carpenters and joiners start marking timber by creating a single straight true face on their work and everything else is marked and measured in reference to that. Japanese do not work from faces they work from a centre line. So instead of snapping a line down the edge of a large log they snap an ink line down the centre and mark everything out from this. The sumitsubo is loaded with ink the line drawn out and pulled taught then snapped leaving a true line down an uneven surface. The joints at the end of each timber are then marked out equally either side of the centre line. I don’t have a photo of a centre line goin on but here is Hannes using a sumitsubo to snap a line for European style hewing.

 And here is Ueki-san marking a joint for me. Rather than pencils they use a special marker made from bamboo dipped into the ink in the sumitsubo, it leaves a very thin crisp and waterproof line.

After a chouna the sumitsubo were the things I coveted most in Japan, they were simply beautiful objects, much loved, continually used and highly patinated. I will be making myself one but it will probably take years to get into the state of the old ones I loved.

3 Responses to Japanese woodworking marking, measuring and laying out

  1. Brian September 3, 2010 at 8:52 pm #

    What gorgeous tools they still use in japan. Over here our traditional tools are all but gone. So if you can turn up a treasure at a car boot sale its worth hanging onto. Nice posts from japan im glad I found your blog :)Brian(:

  2. JRC September 5, 2010 at 2:44 am #

    The Japanese square is really a marvellous instrument. It can be bent without losing squareness, so you can bend down, say, the long arm to get the short one really square to the work. The traditional squares (metric or otherwise) include scales multiplied by the square root of two (which allows you to figure out diagonal braces or estimate the largest square timber that can be hewn for a round log). Another scale is multiplied by pi; you can thus estimate circumference from diameter or vice-versa. I just bought a (sadly) westernized one from Lee Valley. The price was right, however.I was aware of the Japanese india-ink marking method (and the bamboo line makers) but hadn't a clue as to their use. Thanks for the post; very informative. I may use Japanese layout on my next frame construction.

  3. John Richards March 4, 2014 at 11:54 am #

    I too was looking at the Japanese square, it seems to be just perfect for my ageing hands as my roofing square is becoming too cumbersome and heavy… I frequently drop the thing so is now not so square.
    I’ve searched online for here in uk (computer skills not that good) but so far unable to find a supplier other than “LeeValley in Canada”where postage is more than the square!, So I was wondering if you knew of a supplier here that I may acquire one.


    John Richards