Bamboo bellied bows

[RyanY]

When one makes a laminated bow with bamboo on the belly, how do you determine your tapers? I’m interested currently because someone on the bowyer subreddit asked about a bamboo backed and bellied ELB style bow. I thought that would be a great idea and am interested myself but I’m not sure how to go about these types of bows.

I also have some bamboo backing strips that I could sacrifice for the belly and am wondering if heat treating the strip is much different than heat treating a normal bow?

[Mad Max]

NOT a BLE
But

James Parker does it a lot.
You have to try different taper rates until you get what you want and the belly boo needs to be heat treated.
His bamboo is a good bit thicker than your normal bamboo backed bows and is tapered too.
You should talk to him at the classic.

I went to his house for a week and we made a few, I had to promise not to give out information.
The thickness and taper you can see with the bow in hand so I'm keeping my promise.

[Hamish]

For a bamboo belly ELB you would need to make the  belly out of narrow sections of boo so they are glued together so they look like quarter sawn timber on the end grain. I would flatten the back, then remove all excess boo from the inside, to insure that the slats are primarily made up of power fibres. Heat treat the belly before you glue it up into a slat. This method was used in many bows in the pre fibreglass era.

Tiller the bow as you would with any other wood laminated ELB.

If you wanted to make a bow with a raw boo on the belly it wouldn't technically be an elb, rather a flatbow(even if narrow) but it is doable.

Like Max said, you're going to need to estimate what sort of taper you need for the cores(unless someone chimes in with what they personally have used).

Check out meadowlark adventure gear on youtube. He has plenty of videos on how he pretillers the bamboo backing and belly slats by eye. eg. Howard Hill American longbow with back and belly.

[RyanY]

Mark, I’ll definitely ask James next year. I doubt I’ll build one of these in the next year.

Hamish, is there a reason you can’t do the bamboo on the belly as you would in other bows like R/D bows? Seems like it’s totally possible to do.

[Hamish]

Yep, it is doable. Plenty of guys have made them, it's just that technically the bow wouldn't be an ELB because of the belly shape. It would still be a good bow because boo on the back and belly can handle a narrow, deep limb.  The problem arises if you overshoot the intended weight, with the glue up/taper depth as you would only be able to tiller the stave on the edges. This can lead to limb instability in a narrow, deep bow design.

Meadowlark Adv is really good at showing you what options you can do with boo on the belly.

[superdav95]

I’ve made a number of narrow pyramid style longbows and recurves with hickory as the core.  I’ve also done boo core also that worked quite well.  I have not done this with elb.  As far as thicknesses that I’ve played around with I don’t have an issue sharing what I’ve used and experimenting found. 

For my 64-66” long bows with flipped tips dimensions are about 1 1/4- 1 1/2” wide tapered out towards tip of 3/8” or less.  The core wood was around just a hair under 1/4” thick with slight taper thickness out to tips.  It narrows as a typical pyramid.  With below thickness tapers it yielded around a 50-55lbs bow at 28”.

The tapers for the top boo strip are as follows. 

At the handle.  .125” for about 2-4” then tapers down to .110 into the fades then tapers again to .095” out to the tips. 

For the bottom strip.  (Belly lam is thinner)

Very thin at the ramp where fade is 0.90” thick and also pre bent with heat.  Then tapered from .110” out to 0.95” at the tips. 

Thes strips on belly are heat treated fairly dark.  The backing strips are only mildly heated to rid excess moisture then reground flat to the taper desired.  I also stagger the nodes strategically so that the nodes on the back and belly evenly staggered.  I do not sand down my nodes on the backing.  I have at times sanded down the belly ones with success but prefer to leave them intact.  Tillering these bows are tricky though if you want to keep the nodes intact.  Side tiller scrape only.  Some of my fastest bows were these builds.  Some surprising speeds out of these.  They take a bit to get tapers right but worth it.  If you search my previous posts last year you’ll see a few of these built.   My tapers have vary a little bit these worked well for me.   Not sure how that would translate into a elb and so maybe hamish suggestion would be the way to go.  Anyway figured I’d post my taper stats if interested.   

I’ve made short bows with this method too with no core wood at all and just used boo back and belly lam with tapers.  These bows turned out very well too.  Heat treated belly lams helps in these also.