Boo Backed Ipe Tri-Lam: Core wood?

[bvalentine002]

I'm working on a design for a Boo Backed Ipe bow and I've decided that I'd like to get the mass weight down and help reduce the potential for handshock by making it a tri-lam bow.

My thought is 1/8" boo backing, 1/8" core, and 1/4" ipe belly. I want it to be 68" length, 60#-ish @ 31". I'm going to make it with about 3" of reflex and 1/2" of deflex.

Here's my question: I have Walnut, Red Elm, and Cedar (the light, weak stuff from Home Depot). Which of these would you recommend for the core wood?

I like the idea of the cedar (it worked GREAT between glass), but I'm worried about it being crushed or shearing by not holding the Resorcinol well.

Thoughts?
Thanks,
Brett

[4runr]

If I were doing it, and I may be wrong technicaly(sp) speaking, I would use the Ipe as the center lam and the Red elm on the belly. I think the color contrast would look better this way. However the Ipe, in my opinion, would not need to be 1/4 inch thick. That is some strong stuff.

I'm sure someone with some real knowledge will come along and blow my opinions out of the water!!  lol...

[Jeremy]

4runr, he'd want the denser wood on the belly.  It'll hold up much better in compression than the others.

I'd put the walnut in the center, but that's just b/c I love the stuff.  The elm would work well, but I'd stay away from the cheap cedar from the Depot.  Not to say it wouldn't work, but I'd be worried about shearing.  Crushing shouldn't be an issue - it's in the neutral zone of the limb.

I'd pretaper the 1/8" core down to near nothing at the tips before glue up.  Otherwise you'll end up with very little belly wood left in the outer thrid of the limbs - been there, done it twice!
If you go with 1/4" ipe belly you'll end up with a skinny bow... should look cool and be a screamer!

My $.02... you're gonna post pics, right?  We love pics!    :D

[4runr]

Jeremy, that's why I like it here. I can learn stuff from folks who've been there done that!!
I've done HBI's but no tri-lams.

[bvalentine002]

I'm going to make it 1 and 3/8" wide-ish at the fades with a straight taper to 3/8"-ish tips. This way I can avoid tapering the middle lam. It's basically a pyramid design...easy as heck to tiller.

Seems to me that Red Elm is marginally heavier than Walnut but does it have a higher Mod. of Elasticity? I suppose it would depend on the specific pieces of wood.

Anyone else have a preference between Red Elm and Walnut for a mid lam?
TIA,
-Brett

[Doug S]

I like the walnut for the middle. FYI OL Adcock has a few good things to say about walnut on his site.

[Buck Buckley]

Brett all I do is boo backed bows, my opinoin would be to put the walnut in the middle taper it 3/8 to 3/16 on the tip and then keep your Ipe on the belly about 1/8" Thick. Good luck with your build Buck.

[Jeremy]

Brett, to get the bow bending the way it should at those dimensions you're going to have to remove too much of the ipe in the outer third to avoid most of the bend being near the handle.  For a true pyramid bow (ie no belly taper) you'd need to be much wider at the fades.

My last trilam was a r/d, boo backed, 1/8" walnut center lam and 1/4" osage belly.  1-3/8" at the fades, a hair over 3/8" at the tips. 66" NTN and 55# @29".  There's almost no osage left at the tips.
 
Here's another, same dimensions, same problem with nearly no belly wood left at the tips
 

With those dimensions you're best bet would be to pretaper the walnut, or go much thinner with it.

[4runr]

Dang, Jeremy. You're just overflowin with talent. You make some gorgeous knives and that bow layin on the quiver is just plain purty. I like that profile.

[mmgrode]

If you are planning on an r/d design and depending on what type of form you are using I would taper the center lam. It will give you smoother curves on a torges type form(what I use). Even for a straight profile it would be good to taper the middle lam to ease in tillering and shaping. Cheers, Matt

[bvalentine002]

I'm really wondering about the need to taper the mid-lam...

I recently finished a Boo backed Jatoba, similar dimensions, and it came out great (and I mean almost great enough for me to say I have reached my stopping point). It had quite a bit of bend near the fades, but that helps me keep the string angle below 90 degrees (keep in mind: 31+" draw).

I had to do almost zero tapering of the Jatoba. The stack height (for lack of a better way of describing it) at the edge of the bamboo (not measured at the center) is contstant along the full length.

Measured at the center of the limb, the bamboo tapers by default in thickness because of the convexed back.

The consensus seems to be Walnut. I'll go with that.

Jeremy, what do you mean "much thinner with it"? Is 1/8 too thick? If I take it much thinner, the core lam doesn't add much to the design!

Thanks,
Brett

[Jeremy]

Brett, at that width with 1/4" thick ipe you don't need much in the way of a core lam.      Good ipe is some dense stuff!

As far as needing to taper (tiller) the bow... remember that as you add reflex you stiffen the limb.  That lets you get away with thinner tips, reducing weight and handshock and increasing performance.  Take a look at the two bows I posted above.  The last 6-8" out toward the tips in both bows is not bending at all.  Wood near the fades is barely bending (as it should be for a r/d bow)  Most of the work is being done by the middle third of the limb.  Both bows probably could benefit by getting the outer limb working a little more, reducing the mass and the stress on the limb that is working.  Measuring the running taper on both bows came out to just over 0.006" per running inch.  That ends up being just over 5/32" taper over the length of the limb (fade to tip) and gets rid of nearly all of the 1/4" belly lam.

Think of most of the glass lam bows out there today.  They are all about the dimensions you're thinking of (OK except the length    )  OL will tell you the highest performing longbows all have one thing in common - stiff tips.  They do this by adding reflex and some more taper - thus stiffening the tips and reducing their mass at the same time = better performance.  One of the fastest r/d glass lams I've shot had .004" per running inch taper.  It wasn't an extreme r/d and the tips were still stiff.  It doesn't take much to keep tips stiff.

I'd probably plan on making a narrower bow and keep it deep cored.  Depending, of course, on how your piece of ipe is.  The nice dense stuff works well with a narrow deep limb... so I hear      I got to shoot a real nice one that was only 1" wide at the fades!

[bvalentine002]

Jeremy,
Thanks for getting back to me.

My thought on the 1/4" of Ipe was to allow me to tiller it on the belly if needed. I may only end up with 1/8", but I don't want to start with 1/8 becuase I can't add any!

I'll admit, the main reason I'm hesitant to taper the walnut is because I have no easy means of doing so accurately.

Hummmm. I'm going to have to mull this all over for a while.

More thoughts?
-Brett

BTW Jeremy, did you ever use the Rosewood I traded you for? I'd like to see how that turned out.

[Richard Saffold]

Brett,Don't make it a tri-lam. It should shoot sweet  with just ipe and bamboo. I have been making them for years, and while I also make tri-lams and selfbows, there isn't any reason for the bow to be harsh or heavy in the hand..

Usually the tips end up too large or the outer limb sections are too wide for the density of the ipe. And this is the cause of many problems with ipe. Too much wood left on the bow..Examples

My last 70" 80#@32" draw ipe boo elb style longbow weighs 17oz 3/4" wide thru the grip, and is as fast as my 5 year old 68" ipe/boo r/d which recently tested out at 195fps with a 30" draw its around 64-66#'s at this draw length..

Hope this helps
Rich

[Jeremy]

I could never get that stuff not to feel oily.  I tried acetone, alcohol, dish soap... nothing seemed to work.  Don't know if I'd trust it in a limb.  It warped pretty bad after drying out, so I hope your floor is still OK!!

There's no need to be extremely accutate when tapering the middle lam.  Do you have a handplane? A No 4 would work well, but a block plane would do the job.  Being careful with a belt sander would be quick.  Even a stanley sureform would do the job quickly on walnut.  It's easier than planing down the boo...

Rich, 3/4" wide!  Dang!  That's the narrowest one I've heard of, but really goes to show that the really dense woods do great with a narrow, deep limb.  Any pictures?

[4runr]

Pics of that would be awesome Rich. I'm set to tiller my second attempt at a HBI. I could use some visual aid!!

[Richard Saffold]

My kids do the pics.and website for me, and they are gone, but I have several of my favorite ipe/boo  designs on my website   www.richardsbowyery.com  Isn't a sales pitch since I have a normal job, and primarily   sell my bows to keep them from building up in the shop!

[3wolvesrunning]

I have had two tri-lam failures using Home Depot cedar.  Walnut would be a far better choice for a middle lam.  I am about to try Ipe and Hickory in a reflexed longbow.  It should prove interesting. BOL on your project.  Keep us posted

[D. Johnston]

My last 70" 80#@32" draw ipe boo elb style longbow weighs 17oz 3/4" wide thru the grip, and is as fast as my 5 year old 68" ipe/boo r/d which recently tested out at 195fps with a 30" draw its around 64-66#'s at this draw length..

Rich, How wide are the tips on these bows? 80 lbs. and 17 oz. THATS INCREDIBLE! What is the rest of the profile of the limb? Nice post.

[Richard Saffold]

I keep the limb profiles slightly concave outside the grip/fades to the tips which run between 1/4" and 3/8th's wide at the nock.. With ipe sometimes having twice the density of many woods backed with bamboo dimensions need to be around half the width to be on scale. Often these bows aren't made thin enough and they end up heavy and sluggish, and the bowyer blames the wood which is a cop-out for not having the experience to realize what he is working with..

The Amazon Natives called ipe "pau D arcos" meaning wood for bows..and for good reason..

The other day I got to see perhaps the only ipe tree in our area..I was drooling hard!   :eek:  Now I have to figure out how much to bribe the folks who own it to get a branch for a selfbow.. Making ipe selfbows is fine from boards and they can be very fast, but getting a stave would be as much fun as I could legally have!