Author Topic: Yumi fabrication process  (Read 13839 times)

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Offline Prarie Bowyer

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Yumi fabrication process
« on: December 02, 2014, 07:31:15 pm »
Doing research and finding it hard to find the details.  Found this handy and thought I'd post for others.

http://ecoecoman.com/kyudo/item/yumi_seisaku_01.html

Then there is the YouTube videos of Jaap k.

And the guy who smokes his bellies for months.

https://m.youtube.com/watch?v=yX6DFD1_aZk


Offline Prarie Bowyer

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Re: Yumi fabrication process
« Reply #1 on: December 02, 2014, 07:45:21 pm »
Wonder which is more effective the long smoke or the belly burned core?

Also are the rinds tapered or is the core tapered?

Is there a taper in width towards the tip?

Is the nock like a belly underlay or does it butt up to the belly boo?

Offline dylanholderman

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Re: Yumi fabrication process
« Reply #2 on: December 02, 2014, 08:12:57 pm »
there is also a good build along over on paleoplanet, let me see if i can get a link to work. ???

http://paleoplanet69529.yuku.com/topic/55920/Rope-and-wedge-bowmaking-buildalong#.VH5WeNJDuSp

oh hey it did cool ;D

Offline Prarie Bowyer

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Re: Yumi fabrication process
« Reply #3 on: December 02, 2014, 09:24:51 pm »
there is also a good build along over on paleoplanet, let me see if i can get a link to work. ???

http://paleoplanet69529.yuku.com/topic/55920/Rope-and-wedge-bowmaking-buildalong#.VH5WeNJDuSp

oh hey it did cool ;D

Awesome!  Exactly the sort of thing I was looking for!

Offline Prarie Bowyer

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Re: Yumi fabrication process
« Reply #4 on: December 02, 2014, 09:45:38 pm »
http://paleoplanet69529.yuku.com/reply/502492/A-bevy-of-bamboo-composites#reply-502492

More of his work.    Hmmmmmm.  Till now I'm strictly a PA guy.   Wonder if he is on here?

Offline SteveT.

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Re: Yumi fabrication process
« Reply #5 on: December 04, 2014, 06:10:09 pm »
Hi Prairie Bowyer: I'm the guy who did the works on Paleoplanet. Making a yumi is quite difficult, but please go ahead and try to build one as you'll learn a lot from the experience I'm sure. Something very important to keep in mind is the spacing of the nodes on the back and belly bamboo plate. I measure them when I cut them in the grove and set these apart, as they are specific to this bow. Next I would make the laminated core as it is way better for performance than just a plain wooden core. The core is then thickness tapered and this determines the draw wt. of the bow. After you glue the bow you can do some tapering of the tips , but that's about it.  Setting the curves during glue-up is critical ,in where they are located and how much to impart. Do some dry runs before, to get practiced. I make the hybrid now, as it is much more stable and user friendly. If I can be of more help please ask. You can see more photos of these bows at   bowsforpros.com
I hope this helps a bit in your project.  Steve Thomson.

Offline SteveT.

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Re: Yumi fabrication process
« Reply #6 on: December 04, 2014, 06:19:42 pm »
Sorry. I forgot to tell you that there is one more submission on paloeplanet in the composite bow forum, called "yumi-esque hybrid"  which you will find interesting and could be of help to you. Could be 5 or 6 pages back. Please let us know how things work out. Take care.

Offline Prarie Bowyer

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Re: Yumi fabrication process
« Reply #7 on: December 04, 2014, 07:21:15 pm »
Wow cool!

I was going to buy another bag of 25 bamboo slats.  I kinda don't like the look of the true yumis but I love the hybrids.  But it looks like yumis are strong performers?


What about the thickness in the middle in the grip area?  Bamboo is all knife edged thickness from end to end?

Could a person get the same effect with bike tire tubes as the wedges?  I've done it on a smaller scale for splicing and repairing arrows.

I was planning to try the following for my first one.
Try to find two rinds that are close to each other in terms of node spacing.  I'm guessing in the bag of 25 there will be several from the same stalk. 

Cut both to 68". 
Use verticle grain carbonized boo flooring for the core.  Make it 3/4-5/8" wide with a "z"splice in the middle.  Possibly burn it a tad.  Then taper it to a slightly narrower tip. 
Then glue on hard wood squares along the edges of the bamboo core so they follow the narrowing at the tips.

When that is dry plane it flat then thickness grind in my taper of 1/4" from center to tip leaving a level section at the grip.  Taper both sides?

The core will be pretty much finished at this point. 
Lay that on my bamboo rinds with registration marks to align the parts and trace around it.
Saw out both rinds then saw, plane and belt sand to thickness using a small block plane to clean up the edges from wavers and saw marks.

 Cook the belly with a heat gun.

Scrape grooves in all with a large tooth hacksaw blade.  I like daap weld wood plastic resin for boo laminations.  Wrap the glued pieces in Cling wrap and slide them around as needed for alignment.

Wrap in skinny bike tubes with a small gap between wrappings so I can monitor.  Try to get my bends in for the recurves and possibly some reflex at the center.  Just a little for the first one.

Into the hot box.

After unwrapping clean up with a small Block plane and file.  Tiller it by planeing  the edges.

I'm intrigued by the knocks on the belly so I may try that.  Saw the rind off the belly at the tips and clean up with plane and sanding block.

Make a mullberry knock that is also a Grumley knock?  Possibly just the regular.  Match the contours and glue with TB3.

Cut the pin nocks, sand and finish the bow.
Dye it black and then use a few coats of either lacquer or shellac and wax.
Wrap the cane arrow pass, leather grip etc.   
go shooting.


Offline SteveT.

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Re: Yumi fabrication process
« Reply #9 on: December 05, 2014, 12:30:32 am »
There are a lot of things that I have no experience with, regarding the materials and method you suggest of putting the pieces together. I was trained a certain way ,and that is what I try to stay true to. I'm not saying that what you propose will not work. The hybrid I make is 72 inches long, and that would be able to take a 33 " draw.Making yours at 68" would be too short to get the curves in proportion needed to get that shape. I do bow making classes , and could show you how to build the bow and I have bamboo for sale which would be appropriate for these bows. Perhaps consider that as an option to get you started. See the contact page on the website I referred to , and contact me privately. Getting a bow and learning how to do it for a reasonable cost is a good deal if interested.

mikekeswick

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Re: Yumi fabrication process
« Reply #10 on: December 05, 2014, 03:03:56 am »
These are tricky things to make. Good luck and i'd take Steve up on his offer. :)

Offline Prarie Bowyer

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Re: Yumi fabrication process
« Reply #11 on: December 05, 2014, 01:06:06 pm »
Well .. I'm going to try it first.  Ok to the length.  Though I did do a much Shorter Boo back and belly recurve previously.

I'm not seeing why logically the rubber tubes would not = the wedges method.  Unless there is something beyond friction locking the bow in that shap while glue dries. 

Question: Some of the Originals are made using Deer hid based hide glue.  Have you ever tried to make these with TB3?

Note on length taken.  I love the look of them.  How are you finishing them.  Laquer?


Offline DC

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Re: Yumi fabrication process
« Reply #12 on: December 05, 2014, 01:18:56 pm »
I've watched a few of those yumi making videos and the way they pound in those wedges I bet you would need over 300 psi to equal it with a hose(OK that's a WAG). But still, I'm amazed that there is any glue left in the joint. Plus they can localize the pressure if they want. Remember one wedge can tear apart a hickory log and they must use 50 or more.

Offline SteveT.

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Re: Yumi fabrication process
« Reply #13 on: December 05, 2014, 05:37:10 pm »
Prairie Bowyer: In Japan, the really high end yumis still are made with hide glue. The issue with hide glue is that it will gel and set, before you can get everything done with putting the bow together and setting the curves. So they use a steam hood , which keeps the glue fluid and moist until the bow is complete. Hide glue is also prone to high humidity, which is why they laquer the bows to seal them. I like to use G2 epoxy from Lee Valley ,which gives me more than an hour of open time. Usually it takes me 1 hour to glue and wrap and set curves before putting into the hot box. You could try the rubber band method , but I don't believe the wedges will be held tight enough to set the curves. I have not used it myself.  With the rope, I set the tension when wrapping and then tighten the wedges to create a nice even pressure along the bow , and this will allow me to set the curves and hold the shape I want. Always check to make sure the bow is not twisted some way, as you cannot correct it much after the glue sets.
  As for finishes, I use leather dyes to stain the bow and then several coats of polyurethane to protect the limbs. I've been doing this for 12 yrs. now and am still learning and trying different things, but the rope and wedges is still what I use for all my bows because it works well for me. So try some thing different and see how it works for you. That's what bowmaking is all about. Let us know how things go.
Steve T.

Offline Prarie Bowyer

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Re: Yumi fabrication process
« Reply #14 on: December 06, 2014, 10:56:24 am »
Will do.

what little I've done with the rubber band method is with out wedges.  Wrap them tight and no  need for wedges.