all bamboo created equal?

[Gordon]

I’ve made 3 bamboo backed bows and have noticed differences in how the bows reacted to reflex. The first bow was made with a bamboo slat that was given to me by a friend. The belly was quarter sawn high-elevation yew and I glued in about 3” of reflex. After thousands of shots, the bow still holds about 2” of reflex and when I unstring it, it returns to its pre-braced profile almost immediately. The second and third bow were backed with moso bamboo slates that I purchased from a company in California that specializes in bamboo materials. I used lemonwood for the belly of one and low-elevation edge-grained yew for the belly of the other. All three bows have a crowned belly, a similar design and the same amount of reflex glued in. But unlike the first, the other two bows lost most of their reflex during tillering and break-in and it takes them several minutes to return to their pre-braced profile after a shooting session.

Are there variances in bamboo materials that could explain the differences between these bows, or is it more likely some aspect of the belly material or design?

[Far East Archer]

Hey Gordan,
I know some bamboo vary in their characteristics, but usually not by much.
From what I have heard, lemonwood is strong in compression, but takes set.
I'm guessing that the bamboo overpowered the belly? Maybe flatter bellies
would have taken less set?

Alex

[Badger]

Gordon, this is a very interesting and worthwhile topic you brought up. I have built many boo backed bows that have actually incresed in reflex as I removed belly wood, as well as experiencing the same things you have. This is telling me that the backing is pulling the belly back into shape so we really don't know for sure what condition the belly wood is in. I tend to leave my boo backings thicker than most and the thicker you leave the boo the more it will tend to pull the belly wood back. It doesn't neccessarily help the performance but it looks better unbraced. There is a method of tillering you can use that will closely and accurately monitor the condition of the belly wood. It is really amazing how much performance you can pick up if the belly wood is still in pristine condition when you finish a bow. The process can be a little time consuming but I think worth it and I also find it fun and exhilerationg once you get started.
      Once you are past the floor tillering stage and ready to first brace the bow you will take a weight measuremnet at say 20" of draw, I take it a step further and use a weight measurement as well as a chrono speed measurement. You want to have the tiller pretyy much right on when you start this and the projected weight of the bow pretty close to target weight even though at this point it may never have been drawn past about say 40# for a 60# bow. The 20" mark has become your benchmark and you know the bow weight and chrono speed at 20". Now proceed to draw your bow to 21". Recheck bow weight at 20" and go back to your chrono and shoot an arrow at 20". If there is no change in the speed or weight you should go to 22" and then 23" rechecking the condition of the bow at 20" after each additional 1" of draw has been gained. If it becomes neccessary to shave off some wood to readjust tiller or lower weight then re-establish a new benchmark ay your present maximum draw length and proceed as before. Anytime you notice that there has been a slight drop in performance caused by simply adding 1" of draw to your bow you will know the belly wood is starting to compress. At this point you will have to make a decision, either get more limb involved in bending or possibly lower the projected  draw weight for the bow. It is surprising how many bow we build that are underbuilt and we don't realize it. Usually just underbuilt in the main bending areas. Once you do this a couple of times it almost becoes second nature. Steve

[Gordon]

It is worth noting that the backing was quite a bit thicker on my first try. I wonder if that explains the difference.

Badger, that is an interesting way to tiller and it makes perfect sense when you think about it.

[Far East Archer]

Badger,
That is quite interesting, too bad I don't have a chrono yet
About the bamboo, I didn't realize this until you mentioned it.

Maybe 2006 I made a hickory bow backed with bamboo.
The bow was glued up with zero reflex and the backing was super thick, maybe 1/4".
It came out around 11/8" wide, 60" long and 85#@26"...no set at all. This was in
our humid summer too, maybe 90% RH. Later the bow broke from de lamination on the top limb.
What surprised me though was that when I removed the backing the hickory belly almost immediately
took 2 inches of set.

Next bow I made was also bamboo backed hickory but this time, after reading that bamboo
should be made thinner for less dense woods I thinned it up to maybe 1/8" or less.
The bow came out 11/2" wide, 62" long and 64#@26". It had 2.5 inches of set after shooting it in.
I have removed the backing on this one and plan on redesigning it, maybe this time I will leave the
backing thick and see if I get similar results as the first bow.

Also, this first bow was the fastest bow I made and in a test shoot, I drew the arrow 20"
(couldn't pull further at the time) and I got 203 yards, +/- a yard with a 690 grain ramin arrow.
hmm interesting stuff....

Alex

[Gordon]

What surprised me though was that when I removed the backing the hickory belly almost immediately
took 2 inches of set.

That is very interesting. Clearly the backing was holding the bow in reflex despite the belly compression. I wonder if this resulted in any net gain in performance?

[Slivershooter]

I found a big difference in the performance of my BBO’s when I switched from Maso to Tonkin Boo (not Tonkin Cane, I am unable to find any cane).  I got my last batch from Mike at Dryad Bows.  It was a little more expensive but the quality and service are excellent.

[Jesse]

I have not noticed a difference in different kinds of bamboo but that doesnt mean there isnt one. One thing for sure I noticed is that on a design with glued reflex the thickness of the backing is not all that matters. The thickness of the belly is also important. If the belly is thick you have to use a lot of force to glue in the reflex and it makes a higher tension glue joint. Its my opinion that with a highly stressed glue joint the profile is more likely to change when tillering than with a glue up that is closer to finished dimensions.   Jesse

[Rich Saffold]

Gordon, you also used by far the best wood on your first bow, and I believe belly wood is more important than the backing. Light bamboo can over power lemonwood made with the same design I use for good ipe, yew etc.

I recently made a r/d longbow with  old cuban lemonwood , and I glued it up with more deflex than reflex with the tips barely even with the grip. It's holding its set and performs better than I anticipated. It also has a rather deep core..

Most of my faster bows have very thick backings on them as well, some are nearly 50%, and this is why I am a fan of using dense ipe on these since most woods can't produce nearly the same bow for the same mass and poundage, yes the ipe bows are usually the lighter ones..

I know folks rave about "tonkin" this and so on, but I cut a lot of different bamboos where I live including tonkin and I find what I use on the belly matters more than the backing..The design of the backing matters, and the bamboo  has to be in great shape .

Often like Steve mentioned my bows will increase in reflex, and sometimes I'm trapping the back of the bamboo to limit its strength and keep the belly from compressing..

Rich

[Gordon]

Thank you Rich, your explanation was very insightful. I think I need to pay more attention to the belly material. The yew I used for my latest bow was somewhat marginal in that I would never have used it for a selfbow. It turned out okay and I got a nice shooting bow out of it, but it took more set than I like. That said, I'm not crazy about turning prime yew wood into laminations.

[Rich Saffold]

Gordon, I firmly agree and I don't like turning pristine osage, yew, or most others into belly woods or lams. Plus If I find the pipe straight cut ipe board it becomes a selfbow. But I have made many bows from average woods mentioned and turned them into much faster bows than anticipated when these pieces would never have  made a bow in the first place..

I also tend to evaluate bamboos more by the piece quality like I evaluate our woods, and don't place an emphasis on one species over another. I have seen the best of all species and the worst.That being said probably the fastest bow I ever made under 40#'s was juniper backed with the lightest piece of bamboo I ever cut..

Even the two bows you made which took a  little set..are still very fine performers and you probably got as much performance as possible out of them..

Rich

[Gordon]

Rich,

On what criteria do you evaluate a particular piece of bamboo?

[Rich Saffold]

Gordon, I don't have a specific check list, but I do cull my bamboo accordingly:

Quality-Cracking, or mold on bamboo which I purchased indicates too much dryness or moisture after harvesting. Bamboo suffers from these, and often long distance shipping, or storage in a house where the heaters going full speed in winter will damage it as well. For those who buy bamboo the denser or "tonkin" bamboos will handle these conditions better. Black bamboo is very dense and handles adversity well, but no bamboo is bullet proof, or even close.

Straightness- Especially applies to smaller diameter bamboos since flattening can make the node sections too thin to handle the tension strain.

Density, If I cut it, how light did it get compared to other poles from the same yard.  Lightness isn't necessarily a detriment, and it means I just use more of it which I like doing..Sometimes the very dense bamboos you have to make sure you don't use too much, and have to trap it more than you want so the belly wood doesn't collapse.

If it's a purchased bamboo and it feels too light compared to what the species normally feels like and it has a "dead" feeling or tone when tapping it on a hard floor. It will be used on a very light bow if at all..

Rich

[Gordon]

What thickness do you prefer your prepared backing to be? Assuming you have a belly wood that can handle the compression.

[Badger]

  Gordon, I make mine anywhere from 1/8 up to a 1/4" thick, I worry more about how thick the belly is, real easy to get the belly wood to thin. On long narrow bows I usually leave it an average of about 3/16" thick.