Questions about re-curve bow building

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Questions about re-curve bow building

Postby rdahunter » Thu Jan 15, 2015 1:58 am

These may be simple questions to a lot of you and may have been answered in the past. I apologize if they are repeats but I haven't found the answers after a couple hours of reading. I have tried to make re-curve bows on several occasions with a goal of a 50-60lb bow @ 28 inch draw.

Through trial and studying the error, I have found that the most suitable wood for limb laminations that I currently posses is hard maple, and any combo of Cherry, Walnut, White Oak, Cedar, or Maple for the riser.

As for design, I used a wooden batten bent into an oval to fair some curves together. Surprisingly, I came up with a design similar to the one in Greywolf's build along. I plan to use bo-tuff on the belly and back, hard maple for the core, and a combo as I mentioned earlier for the riser. The 1/2 length of my form following the curves is 33 inches, and in a straight line from tip to center of riser is 29 inches. The riser is finished out to 1 5/8" wide.

With my Goal in mind the questions that have are as follows-
1- What thickness bo-tuff should I order?
2- What thickness should the core lams be and how many?
3- If Ea 40 is heated prior to mixing does it thin out? does it affect pot life?
4- Where in the world do you find firehose? (bike inner tubes only allow for about 26 psi unless fully encapsulated)
5- Should the wood for core lams be quartersawn or plainsawn? Does it even matter?
6- Is there a minimum rule of thumb for grain run out on limb lams?
7- Is White Oak or Walnut suitable for limb wood?
8- Can I rip bo-tuff to 1 5/8" on table saw? Or am I better off planing riser and cutting limb lams to 1 1/2"?
9- Does bo-tuff add poundage to bow or just hold everything together? If so, how much added weight per laminate?

I'm sure I can come up with other questions but I think if these are answered ill be able to send you guys a nice picture in a couple months when I get home from work. Thanks!
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Re: Questions about re-curve bow building

Postby KsBow » Thu Jan 15, 2015 6:00 pm

I'd love to help you...but alas.. I'm one of the primitive dudes on here. I don't use any glass. Someone will come to your rescue. Welcome aboard the site. Really good folks on here. :campfire:
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Re: Questions about re-curve bow building

Postby Jumpster » Thu Jan 15, 2015 11:26 pm

Welcome to Tradrag!

Before I begin, a disclaimer...

I've only done a couple of bows so far, and I have had 1 fail on me already (A "Dark Angel" design by Greywolf - poor girl). However, since no-one else has responded just yet, let me give you my two-cents worth of info...

First off, I frequently refer to this Bow Draw Weight Chart from Bingham Project's web-site for reference.

Additionally, I also check out (for reference) Sam Harper's place as well as among others. Lot's of good information out there...

Now, in reference to your questions; let me give you my suggestions:

1 and 2) Bo-tuff thickness? Me personally, I go with the .050 and/or .040 black glass variety. Why? Because according to the draw weight chart above - which is just a reference - I would need .254" thick limb for a 55# bow. I use .040 in front (shooter side) and .050 on back (target side) which reduces my laminated wood thickness to .164". I then use a core lamination of .090" with a second lamination .075" to make up the difference (.050" + .040" + .090 + .075 = .255"). I use a lam-grinder similar to Sam's above to grind them down. As for the glass with or without scrim? I go with the cheapest. I'm still learning and, well, mistakes will be made.

3) Heating EA-40 does thin it out a bit; makes it easier to spread - more fluid like. However, does this affect the pot life? I have NO idea. I've not kept EA-40 around long enough for it to go bad. The one Dark Angel I lost was not due to glue failure neither; except that my "know it all" attitude, preparation and experience (or lack thereof) doomed it to failure from the beginning.

4) Fire hose? I got my first batch of fire hose from the local fire department. I asked for, and received, an old hose that they had deemed as "un-serviceable". They were willing to give it to me because it was just sitting on their shelves taking up space. However, "un-serviceable" it was! I would try to fill it with air and it would promptly lose pressure. Tiny micro-air-bubbles would seep out through the length of the hose. I even tried the "pulling an inner-tube" through approach to make it work. Under 40# psi, my end-caps would blow off. I have a couple of holes in my walls from my attempts at that. Ultimately, I ended up buying a fire hose with end-caps from Bingham's.

5 and 6) Since about 80% of the limbs strength comes from the bo-tuff glass that you use, I'm under the impression that there isn't a noticable difference in the different types of wood cuts and grain run-offs. However, please refer to the disclaimer above; I am still a beginner and may be mistaken on this point. However, with the exception of the Dark Angel failure, I've not personally had an issue with a glass laminated bow.

7) The Traditional Bowyer's Bible would seem to suggest that BOTH woods are suitable for limbs. In fact, I'm about to begin a project using Walnut and/or Cherry for limbs myself.

8) For this one, I would suggest not trying to grind the glass down; at least not before the glue-up. I'm not sure but you may be able to buy them the proper size. Anyway, if not, I would suggest making the limb using 2 pieces of wood minimum (both 1 3/4") to match the glass and sand the entire limb down to the 1 5/8" you appear to require. This can easily be accomplished with a center-line drawn on the limb for reference.

9) This one's a bit harder to explain. Why? Because in part, it just holds the limbs together but more than that, the glass adds a bit of strength to the limb. Recall that about 80% of the limb's strength comes from the glass used. Thus, the remaining approximate 20% of limb strength rests on the wood laminations being used. I can't prove the 80% strength of glass any more than I can prove the 20% of wood; however, I have personally resolved in trying to "force" the glass to bear the weight I "require" by going with the heaviest glass configuration I can come up with. Therefore, in my calculations, the glass measurements come first. Only after I've decided on the glass thicknesses to be used (based on availability and price - with heavier glass on target side of bow) do I begin to consider the thicknesses of the wood laminations inside.

I hope that this helps you, at least some, in your endeavors!


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Re: Questions about re-curve bow building

Postby rdahunter » Fri Jan 16, 2015 9:23 pm


Thank you for taking the time for your response. Your good advice coincides with what I have read on the forums here and the huntches that I had. I just ordered all four "Trad Bowyers Bibles" today and will have lots of time to read them before my next attempt at building. As for the firehose, I must have missed it on the website and will look again. I also wouldnt have thought to use two different thickness of Bo tuff, so thanks for that too.
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Re: Questions about re-curve bow building

Postby Greywolf » Sat Jan 24, 2015 8:22 pm

Aloha, I'd also like to welcome you to Tradrag.

You have a lot of good questions.

This is what I do.......... and with this opinion and $6.00 you can buy a cup of Starbucks coffee, so take it at face value. AND, I'm Not taking away from what Jumpster wrote, every bowyer experiences different things during his or her builds. We share what we have experienced, there isn't one "better than the other" just personal preference.

All of my formulas have a base of .050 glass (with or with out scrim is totally up to you). Scrim adds more strength across the limb. but I've never used it (unless it was on sale, then I might have,I'd have to check my Journal)
I base my longbows on a limb thickness of .265 at 62" NTN for #50@28 longbow (.260 for 60 inch)
***I also don't use Tapers now either. that is another topic***
My lams are divided 50-50 55-65 center core is .055 to .065 again this is my formula and I use Red Elm for my lams and Bamboo as my core. There are a couple of things that will change weight, tip width for one, will increase the weight. So in your Bowyers Journal take meticules notes, write everything good bad or indifferent in the journal, a mistake just might lead to something great. ****One of my Takedown limb had "ACS" issue. Adcock cross section, also known as bowed limbs in the cross section due to a messed up sanding drum.
O.L. Adcock patented the idea later and look how famous his bows are LOL Oh well !!!

#3, I'll have to defer to Dumpster on the EA- 40, I used it one time on the 3-4th bow I did, had a limb failure and I have never used it again.

#4, Fire hose is a one time purchase I got mine through Binghams, same with the end caps and it's still good as gold today as the day I bought it. But I did also get some fire hose from the maintenance guy from a housing unit I was working on, guess they got to be changed every 5 yrs Code Rules or something, it looked great to me. I got 2 more end caps from Binghams so I have a long set and a short one for take down limbs only,both longbow and recurve.

When I started making my own lams, I tired to get as straight a possible growth patterns in the wood, I tried to cut the wood so the the "V" pattern was centered in the limb, I did notice that I did experience some "Built in Limb twist" if the grain pattern ran off the side of the limb. But I'm not 100% for sure if the test was me and my nocks I cut, but it was the way I corrected them.
I noticed that Binghams has for the most part has straight grain in the center of the lam, so I just do it that way too. I figger why take the chance?

#7. Any wood can be used as limb laminations, it's elasticity is the key. Cedar for instance requires a thicker limb to achieve desired draw weight. just have to do one and see how it comes out and record everything in the Journal.

I rip my glass on the table saw, a few times they have sent me 2 inch glass in .050 all because they didn't have it in 1 3/4 or 1 1/2 sizes when I called, I rip mine with the blade 3/16th above the glass so it cuts cleanly with minimal splintering just go slow and also you will have to replace the fence with a piece of wood, as the glass will slide under the rip fence, there is a small gap big enough for the gas to slide under. A piece of wood and 2 C clamps will do the trick

#9 Not really, the "Total Stack" is how the desired poundage is achieved, How ever multi layers of laminated piece of wood is stronger than a solid piece of wood. it adds strength to the entire piece but doesn't add "weight" like your thinking. Conventional wisdom is .003 thickness makes one pound difference plus or minus the total stack thickness.

Ok, some is the same, some isn't. Try one and see, then try another. iI's what works best for is the best way for you.

Post pictures, we all love pictures.

Aloha Nui Loa
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Re: Questions about re-curve bow building

Postby rdahunter » Mon Mar 23, 2015 9:06 pm

Jumpster and Greywolf,
Thanks for the reply. I've been home busy making a bow and believe or not have had success. You may not know it but you helped me build this bow from scratch to finish. I wanted to personally tell you thank you for all your help! Greywolf, your build along with Dark Angel gave me insight enough to successfully build a bow, now I just have to learn to shoot it. Ha. Pic is prior to finishing. I put a nice satin sheen on her. Funny thing, I've built furniture, boats, display cases, cabinets, and all kinds of stuff from wood/fiberglass, but nothing has proven more difficult than a bow.Thanks again for the information and wisdom that you are sharing with everyone, it means a great deal to me.
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