Recurve Build #4, 65" I-Beam

 My last recurve build was my first attempt to build a longer version of the Bingham Projects, Inc. one-piece recurve (normally 60" max).  The result was a very nice shooting bow with a draw cycle that I find preferable, thanks to a longer limb.  One issue I had was with the pull weight coming out a bit too heavy for my calculations (based on Bingham's tables).  From talking to other builders, it appears that it is very difficult to alter any design without throwing the weight tables off.  So I decided to give it another try with a .010" thinner limb to see if the weight would drop into the mid to upper 40lb range.

With this build, I wanted to use a piece of exotic Kingwood that I picked up locally. I also wanted to try some Bubinga on the limbs, which KennyM supplied perfectly. Working with the Kingwood was quite an experience.  It was so hard that sometimes I felt like I was working with a rock.  It took a lot to get it sanded,  but it came out really smooth when it was done.

Here are the stats for this bow:

• target stats: 65", 46# @28", 2" wide limbs
• achieved stats: 65", 50# @28", (55# @30"), 203 fps with a 378gr arrow
• .040"  ULS black glass for the back
• .043"  ULS clear glass for the belly
• .070"  Bubinga parallel lam for back 
• .090"  Bubinga tapered lams for belly (taper: .001/1") (visible thru glass)
• .243" total stack height: 
• limb core wood: Bubinga
• riser: 2 x 3 x 26" Kingwood with Bubinga i-beam

I have detailed builds on some of my other build blogs, so this one is just finished pictures.  These pictures are taken in the morning sun, so they are not the best.

(click any image for a larger view)

The tips are layers of Bubinga and black phenolic.

The Bubinga looks quite red in the sun, compared to the Kingwood. The sight window shelf is cut past center. This riser wood is plenty strong.

Rather than building the i-beam and then cutting it to insert black layers for detail, this time I put some strips of black phenolic into the Bubinga layer before sandwiching it with Kingwood.  I wanted to see how it would come out when the sight window was cut out.  I just wish the 2 black lines had been centered better.  I will have to compensate for that next time.

The Kingwood has great figure and contrasts the black glass nicely.

The front of the bow is lined with a layer of Bubinga and Kingwood.

In a certain light angle, the clear glass makes the heel piece almost look like it's floating on the bow.

The Finish is about 20 layers of Minwax Wipe-On Poly, gloss.  I usually use a satin sheen, but I thought this wood deserved to show off a little. After all, it was not inexpensive.

A piece, cut from the back of the riser to create curves and then glued to the belly to help form the grip, contained a layer of black phenolic. I decided to leave a small sliver on the heel of the grip, for some detail..  This piece also carries the center beam line, made of Bubinga, thru the grip area. This is the only place on the bow where the i-beam layers are visible.

The clear glass on the belly shows the curvy Bubinga limb laminates that KennyM sent me.

Conclusions:
  I still like this design and it is a great shooting bow.  I need to work on the design a bit more.  The weight only dropped about 3# for a .010 change in limb thickness.  That is simply not enough change compared to the original design.  I think I will make the fade-outs (where the riser tapers into the limbs)increase a bit slower. Perhaps they get thick too quickly and therefore stiffen the limbs a bit too much.  I will have to look into that.  I also tend to create rather fat grips, since I like that feel.  I slimmed this one down a bit from the last attempt, but I need to try to create a slimmer grip still. Otherwise, I am quite happy with this design.

In the future, I think I will attempt to alter the bow press, by adding 2 wedges, to create a bow where the glass covers the entire back of the bow, similar to what I did with my 2nd recurve build.

I just found out that I probably should have used a .002/1" taper, so I will use that on the next bow and see if that makes the draw weight closer to what I expected it to be.