Tameshigiri means test cutting. We cut to hone our cutting technique and also to develop a sense of maai [distance] as in Kendo. Tameshigiri never develops into a progressively more “realistc” targets and it does not exist as a show of strength. Tameshigiri is a way to test and show that your cutting technique is correct. By looking at the kiriguchi [cut face] of what you have cut, you can learn certain things about the way you cut and refine it depending on what you see there.
Cutting exercises we often do is to cut un-anchored bailing twine and light bamboo. Bamboo is good because you can see more of the dynamics of your cutting technique in the pieces left behind. Bailing twine has a different value to cut, if the cut is not right, the sword will either pull the bailing twine down or brush it aside. Even though it is a small light target, it is actually quite difficult to cut. This exercise shows the spirit of tamehsigiri very well. Its definitely not about showing that you can cut through a 1m thick roll of tatami or whatever. One roll of tatami or about 10~15cm of hay is about the equivalent of a person’s thigh, so if you can cut through this cleanly, that’s all you really need to take out your enemy. A child can cut through one roll of tatami easily, so the point is not to prove that you can cut through it, it is to prove to yourself how well you can cut through it.
Tameshigiri is not about powering through big targets
Having physical strength is not important, having good technique is important, and cutting small targets can be more difficult than cutting big targets as well
Mugai Ryu dojos generally do Tameshigiri because Mugai Ryu is often described as "cutting Iai" as opposed to the more ritualistic approach and philosophy of some Iaido ryuha. The Mugai Ryu philosophy is that when executing the kata, you should be cutting exactly as if you really are cutting your enemy. This is important, and doing Tamehsigiri teaches you just how much [or how little] power you need and if your cutting technique is effective or not. having a shinken in your hands is also a great reminder to keep your thumb tucked in and to always have respect for the sword, even if you are usually using an iaito.
Examine your kiri-guchi to refine your cutting technique
By cutting light targets such as bamboo garden stakes or unanchored bailing twine, you can concentrate on your technique, and by examining the kiriguchi of the bamboo and the marks on your blade, you can tell if you are cutting well or not. Generally a good sword shouldn't have too many marks on the blade even after cutting dry bamboo. If the marking is excessive it means that either your cutting technique is not good or that your sword is not good.
The pictures below show what to look for in the kiriguchi of your target. The first picture shows a cut that is far too shallow and as such couldn’t even cut through a 1cm thick piece of bamboo! The second picture shows a cut that hasn’t got the necessary Ki behind it and is indecisive and weak. This doesn’t mean about physical strength. the last picture shows a much better cut, it is straight and clean with good angle. Cutting thicker rolls is the same, you are looking for clean straight cuts with a 45~50 degree angle. If you are cutting twine, the proof is just by a clean cut, not wrapping around your blade or being brushed aside.