planning my bow while waiting for the materials.

[Sempertiger]

Well, I ordered the bamboo backing and glue for my bow. I'm not planning on hunting with it, but want to start shooting "hunting weight" bows so I can if the opportunity/desire ever arrives. According to Alaska State Law, there are two weight requirements. 40 lbs for smaller big game, and 50lbs for the larger big game. I don't want to play with these rules, so I want to build a bow that is between 55 and 65lbs at 28" but will probably be closer to 55. I plan on tillering it to 65 and trying it out, slowly dropping weight until it feels right. I'm planning on making it out of Merbau, since I have it, backed with bamboo. The problem is that I have several ideas and I'm not sure which way to go. All of them will be shot off the hand. I've gotten used to shooting off my gloveless hand and feel a connection with the arrow that I feel robbed of when shooting with a glove, or off a shelf.


Idea 1. Make a standard flat bow, 68" long in a pyramid design. 12-14" riser section that is between an inch and a inch and a half wide, quickly tapering out to 2 inches, then down to roughly half inch or less at the tips. I might consider reflexing this at glue up to 3 inches. Easiest.

Idea 2. Same as above in a reflex deflex thinking about an inch or two of deflex followed by 3 or so inches of reflex. I'm not really sure what is an appropriate amount of each... Advice is more than welcome!! A bit more challenging.

Idea 3. 64" bow in either a similar to above "pyramid" design, or holding the 2 inch width to mid limp then taper. Either way, I would static re curve the tips and reinforce with merbau, deer antler or a combination of both. If I go this way, I'm also debating on if I want to bring the backing all the way to the tips, or end it in a sinew wrap just before the curve starts. I'm also considering a bit of deflex in the early/mid limb section. Though my materials may change, I do want to build this bow some day, but not sure if my skills are where they need to be for this challenge, now.

[bubby]

your going to be limited in width buy the boo, i'm not familliar with Merbau but if it's anything close to epe go 1 1/4" wide out to about a foot from the tip's and taper to 1/2" tips, how many bows have you built as the skill's involved with various design's can be challenging for a newbie, Bub

[Sempertiger]

the bamboo I have coming is 2" wide but I'm not certain if it needs to be narrowed at all to ensure it's thick enough to contribute structurally. I've made two bows, however, I learn extremely fast and thrive under pressure, especially, that from a good challenge. My only hesitation with going for the recurve at this early stage in my experience is getting more materials if I manage to break it. I figure that I can fix any mistakes, as long as I catch them before a break. I just want to start shooting a bow that I made, instead of the hickory stick i picked up off sleezbay for under $50.

as far as the characteristics of Merbau, Here is a list of it's characteristics compared to several other common bow woods.

Common Name(s): Merbau, Kwila, Ipil
 
Average Dried Weight: 52 lbs/ft3 (825 kg/m3)
 
Basic Specific Gravity: .68
 
Hardness: 1,710 lbf (7,620 N)
 
Rupture Strength: 20,700 lbf/in2 (142,400 kPa)
 
Elastic Strength: 2,465,000 lbf/in2 (17,000 MPa)
 
Crushing Strength: 10,600 lbf/in2 (73.1 MPa)
 



Common Name(s): Osage Orange, Horse Apple, Hedge Apple
 
Average Dried Weight: 59 lbs/ft3 (935 kg/m3)
 
Basic Specific Gravity: .76
 
Hardness: 2,760 lbf (12,280 N)
 
Rupture Strength: 19,300 lbf/in2 (133,300 kPa)
 
Elastic Strength: 1,677,000 lbf/in2 (11,600 MPa)
 
Crushing Strength: 9,380 lbf/in2 (64.7 MPa)

 

Common Name(s): Black Locust, Robinia, False Acacia
 
Average Dried Weight: 51 lbs/ft3 (825 kg/m3)
 
Basic Specific Gravity: .66
 
Hardness: 1,700 lbf (7,560 N)
 
Rupture Strength: 19,400 lbf/in2 (133,790 kPa)
 
Elastic Strength: 2,050,000 lbf/in2 (14,140 MPa)
 
Crushing Strength: 10,200 lbf/in2 (70.3 MPa)




Common Name(s): Ipe, Brazilian Walnut
 
Average Dried Weight: 73 lbs/ft3 (1,175 kg/m3)
 
Basic Specific Gravity: .91
 
Hardness: 3,680 lbf (16,370 N)
 
Rupture Strength: 26,190 lbf/in2 (180,600 kPa)
 
Elastic Strength: 3,167,000 lbf/in2 (21,840 MPa)
 
Crushing Strength: 13,510 lbf/in2 (93.1 MPa)
 
 

[DarkSoul]

I can see several problems with the plans you listed:

"I plan on tillering it to 65 and trying it out, slowly dropping weight until it feels right."

Don't do that, please. A bow must be designed with a drawweight in mind. Width for a 50# bow will be significantly less than for a 65# bow. Once tillered and pulled to 65#, the wood will be stressed (and thus 'damaged' to a certain extend) for a 65# bow. Dropping the bow to 50#, will affect performance. A bow pulled to 65# and then scraped down to 50#, will shoot slower than a bow that has never been pulled beyond the 50# limit. Never pull a bow past its intended drawweight.


Next issue. I don't like merbau. I've never used it in bows, nor have I seen any bows made from merbau/kwila. I've handles a lot of it, though. So I know what it looks and feels like. I would urge you to try a simple bend test. Possibly with a backing of boo glued down to it, if possible. See if it fails in tension or compression, if it gets chrysals or takes a lot of set. My intuition tells me the wood is course grained, with short fibers and large pores. All disadvantages for bowwood. I just feel it does not like to bend...but prove me wrong, please

Third issue. Glueing in three inches of reflex is a lot. The bow needs to be wide, to avoid the bow 'flipping over' when you try to brace it for the first time. I prefer two inches of reflex myself. That is way easier on the tillering string, yet is still sufficient for bows.

Have you laminated before? It's a fun, but not so easy process. Preparing the lams and clamping the whole set together is not easy, when you do it for the first time. It get even more complicated when you want to make a nice reflex/deflex or recurved design. Not trying to scareyou off now, just want to avoid you from being disappointed when the first try at laminates does not provide you with an actual shooting bow you made yourself.

Jorik

[Sempertiger]

Jorik,

This is exactly why i posted my Ideas before I started building. You've given me alot to think about.

the bow I built my daughter is made of merbau, backed with three layers of linen cloth, but it only pulls 15lbs at 20" and is overbuilt, for her safety in mind. It looks like I need to build a bend test jig and see how merbau works.

I haven't laminated wood for bows before, but I have for gunstocks. I imagine the process can be just as, if not a bit more, difficult. As long as my glue has enough working time, I should be fine. off the top of my head, I think it's 30 minutes or so. Since it's a single layer, I should be fine.

The more I think about it, I might just go with a bit of reflex and limit my variables to glue up. That way I'm familiar with the tillering process, and have the highest chance of success for my first hunting weight bow.

[Pat B]

When you reduce the boo to the suggested 1/8" at the crown at the fades you will only have about 1 3/8" to maybe 1 1/2" width. Your belly and/or core can be a little wider than that with a trapped cross section.
  What You want to do it flatten the belly side of the boo, trace out your bow shape on the belly side of the boo and cut it out. Then thin the boo so it is 1/8" at the fared at the crown of the bow. Now flatten the belly side making sure the tips are no more than 1/8" and they can be as thin as 1/16".

[Sempertiger]

ok, I built my jig and formed 4 pieces of merbau so that the grain and rings were orientated the same way the bow would be built. I completed the process as described in the "standard bend test" in TBB V1.
my results were:
1/4"set at 3" and 32lbs, breaking at 3 3/4" at 37.5 lbs (average for all 4 pieces (weight and measurments were all within a very small amount))

Thoughts?

JS

[DarkSoul]

I don't know about the figures, but what does the break look like? A clean break, failed at tension, chrysals visible...?

Laminating two layers is probably very doable for you  Flatten the lams (spend a LOT of time on this step), and clamp with inner tubes. Then use a few clamp to get the blank in a mild (Perry) reflex.

[Sempertiger]

they all appear to have broken under tension, and don't see any chrysals. they appear to be clean breaks, but they didn't break straight across the grain, they appear to have lifted a bit of grain on the back, then followed the grain 5-6 inches then broke clean for the last 1/8 inch One of them came apart, almost like it was a deck of cards, un shuffling. Oh, they did break how I expected. they didn't break and then it was done. They exploded, sending the two pieces flying quite fast.

[Sempertiger]

I got my boo today... since my relative humidity is high here, average of 80%, i'm going to give it some time to adjust. in the mean time, since i have 3 pieces of Merbau with straight grain, I'm going to see if I can put together a heavier linen backed version of what I made for my daughter. I'm shooting for 55lbs and see how it works. If my math is right, i should make the bow 1.83" wide for that wood, but I'll overbuild it a bit for safety and go with 2". If it doesn't work, I'll pick something else up to use as a belly wood for my stick of bamboo. I'm thinking that It might be time to start with a more "traditional" piece of wood as a more complicated design. I don't want to spend a bunch of time making a bow that wont work because my wood is junk. The linen backed bow is easy, I should have it shooting Wednesday night, if it'll work.

JS