Yumi - cross sections and shape?
I suppose it would be possible to make a simple two-laminate and adjust the thickness untill the correct bend appeared - but it would be very helpful to have a set of cross sections with measurements along the limbs to get the correct proportions. And, I suppose there is at least some width-profile to these bows, even though they seem to be a fairly parallell in width.
If there is a source of information on this, I would be very greatful if you would share it. My bamboo laminates are telling me that they want to become a "proper" bow :wink:
Recently I came across a video about a traditional Japanese bowyer, it?s done by the German ARTE channel, I can?t remember the title, but a guy of the PALEOPLANET has posted it: maybe it?s in the PALEOPLANET- composite bow- section.
The REFLEXBOGEN- BUCH is published in the TRADITIONELL BOGENSCHIESSEN- VERLAG.
Ackording to my knowledge you could find it as a google book too?
Michael
I am afraid I have been a bit quick at pressing the "new topic"-button. In fact, Jack, you have been so generous to provide a nice set of dimentions in an earlier post. I have quoted them beneath here.
jack farrell wrote:
You will have to forgive me if you found yourself ignored. Not my intention. Accept these dimensions as rough working measurements, the bamboo varies. On an 89", 226 cm long bow, above the grip the back bamboo 1/8' thick, 1-1/8" wide, the belly 1" and 1/8 thick, the core 9/32"thick. Overall thickness above the grip around 11/16".
Tapers to 1" wide at the back, 15/16" at the belly, the backing thinning slightly, the core thinning to 3/16", the belly bamboo narrowing but the thickness remaining at 1/8" overall thickness about 1/2 " below the nockpiece, which is 6-3/8 exposed and as i remember is notched slightly under the rattan binding.
The lower tip above the nockpiece 15/16" wide on the backing which has thinned out, though the belly bamboo has not, core is now 5/32 and the overall thickness to 1/2" also. Lower nockpiece 4-1/2 exposed, 5/16 more buried underneath the lash.
The grip, which is a folded hard paper mass is 3-1/4, centered 32-3/4 from the botton tip.
The backing runs the full length, but the belly slat and part of the core is notched to let in the nockpieces, of some super exotic material, possibly Ippe wood. Signed above the lower nockpiece, "Itoisi" die burned in kangi.
The back shows 7 nodes, the belly 5 (exposed) This is a must! -j-
I also found a post by Kyudohund, which I thought was giving some interesting constructional information:
Kyudohund wrote:
To the reflex above the grip: its normal and even necessary this reflex gets lower after first bracing and drawing. Before shooting this hight must not be more than 25cm and not less than 12,5cm. If its higher and you shoot with the technique used in Kyudo, it can happen the bow throw off the string and the bow can be demaged. If too low, the Yumi is week and has to rest unbraced in a humid climate (f.e. bathroom), until the reflex gets more again (can last a bit).
the Yumi is built like the bamboo is grown, that means the bamboo is used in the same direction (lower tip = ground, upper tip = sky). Usual the back-bamboo has 7 nodes and the belly-bamboo 6, so back and belly divide in half the distance from node to node, the best solution for the durability of the bow.
Peter
Does the limb width and thickness taper in straight lines? To me it looks like the bend is somewhat concentrated to the middle of each limb, which seems to tell me that there probably is some variable tapering of the limbs. I bet there is not much tapering, so it would not take many measurements along the limbs though.
I wonder what rules the masters use for dimentioning their bows. I bet they don't use callipers and sketches, hehe. With such an intact tradition, it would be very interesting to understand what the constructional ideas and rules are. There is probably little risk of this tradition to die out yet, but it would be a shame if this information was not written down and saved for later times.
Neither a yumi- bow nor a hornbow is a greater challenge than to make a selfbow. Every kind of bow is made along the same principles. A lot of people are able to do a somewhat shooting bow, but it takes a lot of experience to make a real bow.
Michael
here is a sketch of the upper and lower tips of my yon-sun-nobi Yumi (227cm), 19,2kg at 97cm drawlength.
i will measure it for you, but need little time, because i?m very busy at time.
hope this will help
Peter
Would you consider cherry as a good alternative for the tips, or should it have density closer to oak?
I will patientely await limb measurements :) Again, ATARN shows it's muscles 8)
the other is an eye-catcher. for japanese people its too a kind of decoration. i saw yellow, red, brown and black wood being used for this.
so far
Peter
here they are:
bow length (ntn) 227cm, drawweight 19kg at 95cm drawlength;
i measured (mm) every 15cm starting from lower tipend (not nock)
point (cm)/ width / thickness (outside) / thickness (body, inside)
1 (15) / 23,8 / 12,6 / 5,6
2 (30) / 24,0 / 13,5 / 5,8
3 (45) / 25,2 / 14,8 / 6,2
4 (60) / 26,5 / 15,3 / 6,8
5 (75) / 27,3 / 16,2 / 7,6
6 (90) -> here is the "To"-winding directly above the grip, cannot measure
7 (105) / 27,9 / 16,6 / 7,6
8 (120) / 27,5 / 16,0 / 7,2
9 (135) / 27,4 / 15,8 / 7,0
10 (150) / 27,1 / 14,9 / 6,4
11 (165) / 26,9 / 14,4 / 6,1
12 (180) / 26,0 / 13,7 / 5,9
13 (195) / 25,1 / 13,6 / 5,6
14 (210) / 23,4 / 12,6 / 5,3
the standard yumi has a crossection back 27mm and belly 18mm, sides shaped round (the crossection looks like a flattend halfcircle). more important is the thickness-measurement of the body inside, because the back- and bellybamboo is never grown exactly straight.
notice: in opposite of a hornbow, correcting the shape of a ready glued rawbow (Fujibanashi, width >30mm) can only be done taking away material from the sides of the bow, never from back or belly!
a Fujibanashi should have a nearly halfecircled reflexed C-shape, little flattened in the middlepart of the upper and the first half, below the grip, of the lower limb.
the upper end of the grip is directly at the 3rd node of the belly-bamboo, from lower tip, which has in total 6 nodes. the thickest part of a Yumi is ~5cm above the grip.
bracing a Fujibanashi is very difficult; in Japan 3 men are doing this together! bracehight 15 - 16cm. brace it with a steel string with covered loops, not to damage the nocks. the bow should have an acceptable shape -> recurve at the upper end, less recurve at the lower end and above the grip. at a ready shaped Yumi the form is controlled as follows: take the lower end, put the upper end on the floor in front of you and hold the lower tip towards your navel. then turn it that you see the bow from the side; if it looks like the middle, almost straight, part is parallel to the string -> ok. take the bow the other way round: should look like the middle part is in one line with the lower tip.
and now, what Jack mentioned, when you hold the bow i discribed first, let it swing free in your hand; you now see the string in relation to the bow: the string shall optical "touch" the right side of the bow between the 2nd-3rd and 5th node from upper end. this is called "Iriki".
the Fujibanashi should stay 1 month braced before shaping. bind the string down on the bow at the upper limb, where the wooden part ends, to center it. all shaping is done on the braced bow. first flatten the sides with a file and then take a scrapeblade (right name?). never start to scrape where is a node on back or belly. step by step, only one hand full of shavings, then controll as discribed above. inbetween put away the binding from the tip and pull the bow controlling the shape (perhaps in front of a mirror). -> the bow shall bend over the whole length equal. bind the string ............etc.
there is the too possibility to correct the shape cold, or by heat. but this is another story :wink:
i hope this helps and wish you good look for your work, which, i am sure, will be well!
Peter
found some fotos from my Shigeto. it has a good shape. the right picture shows you the "Iriki" - but its extreme, shouldn?t be so much; the string should be bit closer to the right side of the bow.