Using a Sumisashi and Sumitsubo

by Mathieu

Upon request of several readers we will have a closer look at how you can use some of the Japanese layout tools I discussed in the previous post.

Snapping Lines with a Sumitsubo

Make sure your sumitsubo is prepared well and ready to go. See this post.

Since we snap center lines we have to mark the center first.

Mark the center by measuring and placing a tick mark.

mark center

Note how I use 100mm at the edge to increase accuracy. The lens of this camera creates a false perspective. It appears that the stick is less then 60mm but in fact it is exactly 60.


Set a marking/scribing gauge to distance approximately half the width of the piece. (about 1mm larger) Mark from either side and you will find the center exactly in between both marks. Very fast, convenient and accurate.

scribing center

Pin the line either to the end grain or on the surface. I prefer the end grain and early wood since it doesn’t leave a hole on the surface and the pin is easier to remove. When removing the pin after snapping twist it while pulling to avoid bending the metal pin.

pin line

You can rotate the pin to get your line spot on your mark. And make sure you tie the line to the metal pin with a halfknot.

half knot

After unrolling you can either grab the line before you place the other end on the mark or place the line down while creating tension on the line, the reel is now locked with your thumb or by the palm of your hand.


In order to make sure you snap a straight line without any curvature you have to hold your head still. Put down the line on the mark, make sure you have the right amount of tension and tap the line in front of you. This creates a tick mark. Now without moving your head you lift the line straight up and snap it aiming for the tick you just made.

The centerline is then marked with a Z-type mark.

Voila, two hundred and fifty eight words later we have…  a line.


Good or Bad

When holding the sashigane to make marks hold it with one hand and bend it slightly to lay it flat on the surface. The friction between the thickened corner and the blade should be enough to keep it in place.

good sashigane practice

good sashigane practice

This might take some practice but avoid using your fingers to hold the blade while marking a line. Sometimes you have to but in general this is considered bad practice.

bad, bad, bad

bad, bad, bad

Laying Out a Mortice

If you align the bottom side of the long blade with your centerline (CL) and mark along the top you have drawn a line that should be exactly 15mm (the width of the square) away and parallel to the CL. Often a mortice is located directly upon the CL. Let’s say your tenon is 90mm wide (which is common) you have placed the long blade with the bottom along the CL and the crossing CL at the 45mm mark. This way you can draw two sides of the mortice at once.

mortice layout step 1

Without moving the square you have placed a tick mark at 90mm.

mortice layout step 2

Use this tick to mark the other short side of the mortice holding the square to the edge of the timber.

mortice layout step 3

Only one side of the mortice remains to be marked and often I flip the square to draw this line since then the short blade has a longer bearing surface on the timber which aids a bit in accuracy.

mortice layout step 4

Mark the mortice and mark the depth if necessary. Eventually you add about 2mm of clearance to avoid that the tenon will bottom out. I Wouldn’t write 122mm, it is something you just know while cutting out the mortice.

mortice layout step 5

All the above takes about 7 to 8 seconds.

Secret Tricks

For what I am about to tell you the guardians of secretive craftsmanship might come and hunt me down. I couldn’t care less and in these times of global industrialism I will do anything that contributes to the continuation of this ancient craft. The last thing we need today is secrecy.

Take a fine file and make a mark on your sashigane at 28mm. You can now quickly use this to mark the offset of the pegholes of your tenons. Seconds saved, consistency guaranteed.

file mark

Invest in a reel of superfine braided dyneema fishing line and replace your sumitsubo inkline with this stuff. They don’t soak up too much ink thus leave a clearer and fine line. They are super strong and last a long time.

Cut back the top on the tip of your sumisashi, it will make it write in both directions which works great when doing layout on round logs.

cut tip

And remember, when laying out always think in function of the centerline!

This post has been a new experience for me and is written in a truly internet-like, how-to, step-by-step-guide way. I hope it will be useful to some. It seems a bit superficial but maybe that is just me being old fashioned. The next step up from here is video tutorials. Cold shivers down my spine when I only think of it. I don’t know I could ever go there, I am sorry. Pictures and text will have to suffice.