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Yumi Care - Rise Height

After a new yumi is made and strung the bow maker generally leaves it strung 4 to 8 weeks before sending the yumi out to a customer. Some new yumi need a longer settling period beyond the 8 weeks. This could be six months or longer. The purpose of keeping the yumi strung for this period is to allow the yumi to settle in its curves and overall balance. In addition, if needed during this time, the bow maker can make corrections to the yumi's shape. An archer with a new yumi needs to give attentive care to the yumi’s maturing and settling process. Yumi care instruction given by a yumi maker can vary from yumi to yumi and between yumi makers. Each yumi maker knows what their yumi need.

Generally, the archers first concern with a new yumi should be that the unstrung rise height (see diagram below) of his/her yumi becomes established and continues to remain at 15 to 20 centimeters (6-8 inches) when the yumi is left unstung for three days or more. The yumi should be left strung until it settles to this standard.
Once a yumi settles into the standard the archer can take four preliminary shots a day without holding at kai. After these first shots the yumi should be left strung and four similar shots can be taken in each of the next few days. In the next week slowly increase the number of shots and the length of kai. After this period take no more than 20 shots per class period for three months.

Shooting a yumi too soon in regular practice without allowing the yumi to settle or not doing the preliminary shooting with no kai could damage the yumi and prematurely lessen its strength. In the preliminary shooting phase always listen attentively for any irregular sounds coming from the yumi as it is opened or released. Stop the shot and examine the yumi immediately if an irregular sound is heard. A yumi drawn and released without a ya is called dry shooting. This should not be done as it can cause damage to the yumi.

After a yumi becomes settled in it's rise height with regular use and care, the rise height could regularly recover to a height of 13-17 centimeters. This height will vary yumi to yumi. The amount of use and weather conditions are determining factors. In this phase of the yumi's life do not leave your yumi strung after use if the recovery height stays below 17 centimeters.

Humid weather can cause a yumi's rise height to increase above its standard limit. This means that even after a yumi seems settled it can still go out of balance above the rise height limit if not watched and attended to. A yumi not in regular use and left unstrung for weeks or months can unexpectedly develop a higher than acceptable rise height. If this occurs follow the rise height instruction and preliminary shooting for a new yumi.

With a new or settled strung yumi the measured distance from the rattan (yazurido) just above the leather grip across to the tsuru needs to be checked frequently and corrected to the proper distance of 14 to 15 centimeters. In nearly all yumi the distance of 14 centimeters (5.5”) is the minimum. If less than this minimum, the archer’s yumi hand or wrist can be hit upon release. It should be remembered that the “rattan to tsuru” distance is relative to the distance of the tsuru off the lower part of the upper plate (kamisekita) of the yumi. The standard for this distance is 4-7 mm. The two distances at the kamisekita and the lower yazurido always are considered together when the tsuru is adjusted and can vary from yumi to yumi and the choice of the archer as to the sound of the tsuru (tsurune) at hanare.

Always be vigilant in the care of your yumi.