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Aabow: Actually A Bow.


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#1 KaneTheMediocre

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Posted 15 August 2010 - 05:58 PM

Edit: It has been brought to my attention that this post is super-broken. And it's not the current version anyways, see Aabow writeup

Now there's also a nerfhaven version of those instructions:
http://nerfhaven.com...43

The Aabow.
Posted Image


The Aabow was born after I made the Autobow
http://nerfhaven.com...showtopic=19632
and wished that I had a version for decent range and a hopper. So, I made a pneumatic version with a slightly modified (mostly shortened) snap head.

Posted Image

To make a bow, a cross of some sort is needed to hold the bow arms perpendicular to the plunger. The standard PVC cross is unfortunately not up to the job. The autobow, which uses fairly light tension to fire streamlines mechanically, has broken 2 crosses so far, so the tension I'd want for a SNAPoid needs something special. The first Aabow used a 1 1/4" T as the basis to make a sturdy homemade cross. I didn't like how bulky it was, or how it felt as a handle when I used the bow, so I changed to a different method. But, the T style allows a 5/8" hole (for CPVC) to be drilled through instead of a 1/2" hole (for PEX), so the T potentially has an airflow advantage. So, I'll tell you how to do both.

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The T has 1 1/4"--> 1" bushings, where inner tube stop was removed, such that a 1" PVC pipe can fit straight through the T. In order to drill a 5/8" or 1/2" hole through the T, opposite the middle port of the T. In order to ger this straight, you will need a 1 1/4" --> 1/2" coupler. Put some Sch80 pipe in there, and a 1/2" hole can be drilled centered and straight, using the sch80 to guide the drill. Longer drills / segments of sch80 will work better, but even a short segment helps enormously. Centering a 5/8" hole is much more difficult. I did it by wrapping duct tape on the stem of the 5/8" spade, up to the ID of the sch80 (about 1/2"), so that the spade shaft was guided by the sch80 just like the 1/2" drill.


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The more compact version reinforces the standard 1/2" cross with steel EMT conduit, which nests inside thinwall PVC. Put short thinwall stubs in the arm ports f your cross (Glue them if you're into that kind of thing), and stick some EMT through the thinwall and cross. Make sure that your piece of EMT is long enough for 1.5" or so to stick out of each side, as this is what the CPVC arms mount to. Then use a sch80 stub in the plunger / output port (they are indistinguishable at this point) to guide a 1/2" drill through the EMT conduit. Clean it up as best you can, then put a short piece of PEX through the hole, and use hot glue to seal around the PEX on one side. If you can do the same on the other side without ruining the port (This will be your coupler), do it, but I found it easier to just stuff hot-glue and wads of paper towel in the EMT on each side instead.

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For ergonomics, I like to use a plunger rod guide that keeps the plunger rod from cocking sideways, and also allows me to put a T on the back of the guide for use as a handle. This requires a slotted piece of sch80, which I used a mill to create. I braced the sch80 against a bar of aluminum to prevent it from bending during the slotting process. The bar needs to be on the correct side for the direction of cutting and the rotation of the endmill bit to properly keep the sch80 straight.

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The string goes through the slot, and through a hole in the plunger rod. To allow the string to push and rub on the plunger rod without slicing it, I used a ~2" long steel tube, 3/16" OD, ~1/8" ID. I got a 6' long stick of the stuff from mcmaster, and I use it on all of my bows, although early on I had to drill a hole through a piece of solid steel to do this (not fun). Anyways, the string goes through the steel tube, and a piece of straw is used on each side to shield the string from the ends of the tube. Then, the whole assemblage is covered in E-tape to make a nice padded finger-grip. Although the E-tape usually overlaps onto the bare string, the string should still be able to slide back and forth through the tube assemblage.

The bow arms are made of 3/4" CPVC, which nests outside the EMT. The CPVC varies from easily sliding over EMT, to being ruinously difficult to press over it. Make sure that you use CPVC from the same batch for both arms, or one arm may bend much more than the other:

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Cut V-notches into the CPVC, and put it over the EMT, with the notched on the outside. Then, use a knot on the end of the string to catch it on the V-notch, and wrap a couple of times around the CPVC before putting the final end through the V-notch slot. The V-notch slot should be coplanar with the rest of the bow, such that the string is already pointed in the right direction, and doesnt need to bend around a CPVC edge to get through the plunger and to the other bow arm. Do this on both sides. You can vary the tension without taking the bow apart by changing the number of wraps on the bow ends, although this also changes the neutral point of the bow (the spot where the string would rest if there was nothing in it's way). A neutral point at about the middle of the plunger is ideal for performance, but if you want it to look more like a bow and arrow you can tighten the bow such that it's at the back of the plunger. The relationship between tension, neutral points, and string length depends on the length of the bow arms, so you may need to change this a few times to dial in the tension/shape that you want.

Posted Image

Finally, put a T on the back of the plunger guide. This acts as a handle, which makes it easier to hold the bow when it's drawn, and easier to hold the bow steady when it's being fired. Hopper clips are highly recommended for bows, so you should slap one on.

And here's a pic from my bow family reunion:

Posted Image

Ranges depend on bow tension. I usually keep mine firing about 80-90', but if you want it to do 120' or 60', you can do it with exactly the same method.

Edited by KaneTheMediocre, 18 January 2015 - 01:04 PM.

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#2 jaybo1996

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Posted 15 August 2010 - 06:12 PM

Thank you very much for the write up, but there must be an easier way to build the cross, perhaps use steel crosses, and PVC reducers?

Edited by jaybo1996, 15 August 2010 - 06:13 PM.

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#3 KaneTheMediocre

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Posted 15 August 2010 - 06:21 PM

Thank you very much for the write up, but there must be an easier way to build the cross, perhaps use steel crosses, and PVC reducers?


I haven't found a steel cross for sale at any hardware stores I've looked at. Larger crosses don't have notably thicker walls, and the reducers add too much dead length to the bow. I'll update the writeup when I find something that I like more, as I don't enjoy the process of making the cross at all.

Update: Mcmaster sells a steel cross 45005K174, but it's expensive ($19.25). Still, I'll order one with my next mcmaster batch, and see how it goes

Edited by KaneTheMediocre, 15 August 2010 - 07:33 PM.

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#4 Niteshot

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Posted 15 August 2010 - 06:22 PM

Sexy bow.
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For the love of fuck. The next person who announces that they are using something in their signature, ever, is banned. I fucking hate you.

#5 Carbon

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Posted 15 August 2010 - 08:37 PM

Nice seeing a writeup on how you made yours...I was majorly exhausted when you explained it to me, and I missed a lot of details. So, I ended up building my bow differently than yours...thought I'd list the difference for discussion of building.

I used a version of your tee method, and haven't had any problems thus far. The big difference is that I used 3/4" sched 40 for the arms, so things sized differently. I slit a piece of 1" sched 40 lengthwise, and slid it onto the 3/4" arms with the help of a hammer. That then fit into the 1.25" tee, with some small chunks of 1.25" slid into the ends of the tee. Because my arms were bigger, I was able to drill a bigger airway: I used a 7/8" hole straight through the tee and arms so I could use a 1/2" PVC barrel stub. I drilled the first hole on the drill press through the tee, using the molding seam to center it up. I then used that hole as a guide to drill through the arms.

I haven't found the sheath for the plunger rod to really be necessary. I actually ended up with better range after I took it off, but that was in all likelihood due to the abysmal slot I cut in the PVC. At any rate, no sheath = less friction, and I've had no problems with the shaft going crooked.

I gotta say again, nice job on these. They're really simple, and really fun. I'm looking forward to the next war with all these bows...
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#6 Lion

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Posted 15 August 2010 - 08:46 PM

How about just using the steel EMT conduit for the bow's arms rather then using it to reinforce them?
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#7 Ryan201821

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Posted 15 August 2010 - 09:19 PM

How about just using the steel EMT conduit for the bow's arms rather then using it to reinforce them?

LOL, really? Last time I check EMT doesn't bend too well.
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#8 KaneTheMediocre

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Posted 15 August 2010 - 09:22 PM

Nice seeing a writeup on how you made yours...I was majorly exhausted when you explained it to me, and I missed a lot of details. So, I ended up building my bow differently than yours...thought I'd list the difference for discussion of building.

I used a version of your tee method, and haven't had any problems thus far. The big difference is that I used 3/4" sched 40 for the arms, so things sized differently. I slit a piece of 1" sched 40 lengthwise, and slid it onto the 3/4" arms with the help of a hammer. That then fit into the 1.25" tee, with some small chunks of 1.25" slid into the ends of the tee. Because my arms were bigger, I was able to drill a bigger airway: I used a 7/8" hole straight through the tee and arms so I could use a 1/2" PVC barrel stub. I drilled the first hole on the drill press through the tee, using the molding seam to center it up. I then used that hole as a guide to drill through the arms.

I haven't found the sheath for the plunger rod to really be necessary. I actually ended up with better range after I took it off, but that was in all likelihood due to the abysmal slot I cut in the PVC. At any rate, no sheath = less friction, and I've had no problems with the shaft going crooked.

I gotta say again, nice job on these. They're really simple, and really fun. I'm looking forward to the next war with all these bows...


The plunger rod sheath definitely adds some friction, even if it's well made. The main reason I use it is because it allows me to put a T-handle on the back of the bow.

As for the arms, whenever I read of someone doing something of this nature, they always use PVC, not CPVC. Still, CPVC just seems to be more elastic to me. I look forward to a side-by-side comparison.


How about just using the steel EMT conduit for the bow's arms rather then using it to reinforce them?


I don't see the EMT conduit having that nice elastic twang.

Edited by KaneTheMediocre, 15 August 2010 - 09:25 PM.

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#9 Carbon

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Posted 15 August 2010 - 10:01 PM

Still, CPVC just seems to be more elastic to me. I look forward to a side-by-side comparison.

Definitely agree. The PVC arms seem to creak more, and also retain more of a curve when I unstring them. CPVC arms draw smoothly, and go back to straight when unstrung. I'll be curious to see how they perform after a day of use.
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#10 Demon Lord

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Posted 15 August 2010 - 10:26 PM

How about just using the steel EMT conduit for the bow's arms rather then using it to reinforce them?

LOL, really? Last time I check EMT doesn't bend too well.

EMT bends quite well, it just doesn't snap back well.
This just cleared up a bunch of questions I had regarding how this thing was built. Now to build my own.

Edited by Demon Lord, 15 August 2010 - 10:26 PM.

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Don't worry so much about what other people will allow. Throw your own wars and kick your friends' asses until they all want one.

#11 Lion

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Posted 16 August 2010 - 01:04 AM

Don't you think having a higher draw weight would cause it to preform better? Rather then having the elastic effect.

Edited by Lion, 16 August 2010 - 01:05 AM.

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#12 Zorns Lemma

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Posted 16 August 2010 - 04:11 AM

Don't you think having a higher draw weight would cause it to preform better? Rather then having the elastic effect.


Think of it this way: if it takes 80 lbs to pull back, but then is permanently bent in that fashion, will the bow fire?

Of course if it only takes 10 lbs to pull back, you'll only get 10 lbs back. Trying to theoretically find the best material commonly available (i.e. buying actual bow arms is not really an option here) is a lot more effort than building a bunch of bows and using them side-by-side.

But you don't need complex stress/strain analysis and elasticity calculations to know that EMT conduit is possibly the worst option available. It permanently deforms at such a low amount of deflection that you'd probably need 20' bow wingspan to get 8" of draw.
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#13 Lion

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Posted 16 August 2010 - 04:46 AM

Don't you think having a higher draw weight would cause it to preform better? Rather then having the elastic effect.


Think of it this way: if it takes 80 lbs to pull back, but then is permanently bent in that fashion, will the bow fire?

Of course if it only takes 10 lbs to pull back, you'll only get 10 lbs back. Trying to theoretically find the best material commonly available (i.e. buying actual bow arms is not really an option here) is a lot more effort than building a bunch of bows and using them side-by-side.

But you don't need complex stress/strain analysis and elasticity calculations to know that EMT conduit is possibly the worst option available. It permanently deforms at such a low amount of deflection that you'd probably need 20' bow wingspan to get 8" of draw.


Then how about finding some wood rods, I feel like you've missed the point of my suggestion.

Edited by Lion, 16 August 2010 - 04:47 AM.

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#14 Zorns Lemma

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Posted 16 August 2010 - 04:52 AM

Then how about finding some wood rods, I feel like you've missed the point of my suggestion.


The point of your suggestion was "harder to pull back = better" right? If that is the case then it is wrong, because as I outline, it is not the only factor. There are a lot of cases where "harder to pull back = worse."
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#15 Lion

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Posted 16 August 2010 - 05:04 AM

Then how about finding some wood rods, I feel like you've missed the point of my suggestion.


The point of your suggestion was "harder to pull back = better" right? If that is the case then it is wrong, because as I outline, it is not the only factor. There are a lot of cases where "harder to pull back = worse."




Oh my bad, I completely forgot that "harder to pull back = worse" is the reason real bows only have a draw of 10 lbs. Other then saying that EMT will bend and not flex back you gave no reason to suggest another material could not be substituted for the PVC arms with your only argument being "harder to pull back = worse".
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#16 Carbon

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Posted 16 August 2010 - 07:05 AM

Other then saying that EMT will bend and not flex back you gave no reason to suggest another material could not be substituted for the PVC arms with your only argument being "harder to pull back = worse".

Read it again. Zorn's point was that there are three things to consider:

1. Weight of pull. How hard does it resist deformation?
2. Elasticity. Does it snap back to shape once deformed, or does it crack/stay bent? Also, is it elastic at a length usable for a bow?
3. Ease of purchase. Can you actually buy the stuff?

There's nothing wrong with using another material for the bow arms. Seriously, go for it. PVC just currently satisfies all three requirements very well, and better than EMT. Metal arms work, of course, they just need to be something like spring steel that returns to shape.

Edited by Carbon, 16 August 2010 - 07:09 AM.

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#17 jaybo1996

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Posted 16 August 2010 - 08:25 AM

Since archery is a subject I've been intrigued with since I was 4, I thought I should make it aware to you guys, you can buy Bow arms, seperate from the main handle, that's why most modern day bows can twist apart, and break down into 3 parts. Also, looking for materials, try fiber glass, generally coated with Carbon Fiber, Or the clasic wooden bow limbs, I still think that a thick enough dowel would make this thing much deadlier.

I would like to just point out, that Lions point is correct. More draw wieght, if the bow is reinforced enough, is better. Also, Incase no-one thought of this, there is a reason that most bow arms are rectangles, not rod shaped, Aside from holding energy better, they alow you to easily reinforce the front and back of the bow separatly, depending on what the material must do, the back material must be compressive, and hold energy well, in other words, springy. The front material must have a high enough tensil strength not to rip, but not compress as well, hence stopping the bow from snapping on the return.

Edited by jaybo1996, 16 August 2010 - 08:26 AM.

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#18 Lion

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Posted 16 August 2010 - 12:24 PM

Read it again. Zorn's point was that there are three things to consider:

1. Weight of pull. How hard does it resist deformation?
2. Elasticity. Does it snap back to shape once deformed, or does it crack/stay bent? Also, is it elastic at a length usable for a bow?
3. Ease of purchase. Can you actually buy the stuff?


You must have missed my immediate reply to "EMT doesn't spring back"


Then how about finding some wood rods


Of course I can foresee a few problems with one or two wood rods as the bow, but suggestion was simply ment to over come the need to have to do a lot of reinforcing + added power.
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#19 Carbon

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Posted 16 August 2010 - 12:53 PM

This one?

Don't you think having a higher draw weight would cause it to preform better? Rather then having the elastic effect.


A higher draw definitely increases performance, but won't help if the arms don't spring back....it really can't be separated from the springiness of the material.

EDIT: Ah, my own reading comprehension fail, finally saw what you meant in your previous post with using wooden rods. Wood sheathed in PVC would probably work, and give better structural integrity (as in, not having to worry about exploding wood as much). But to me, I see it as diminishing returns.

Edited by Carbon, 16 August 2010 - 01:35 PM.

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#20 Buffdaddy

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Posted 16 August 2010 - 02:08 PM

I have to agree with Bob, at least in terms of overdoing this. If we start engineering these too much, banhammer is going to land. In the meantime, stuff like this is a great addition to Nerf, and props to you guys for experimenting with these.

Let's just make sure to keep the SNAP mindset for these - stuff you can easily pick up at a hardware store and throw together. As long as that's maintained, I wouldn't mind getting shot by one of these.
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#21 KaneTheMediocre

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Posted 16 August 2010 - 06:14 PM

Don't you think having a higher draw weight would cause it to preform better? Rather then having the elastic effect.



Don't you think having a higher draw weight would cause it to preform better? Rather then having the elastic effect.


Think of it this way: if it takes 80 lbs to pull back, but then is permanently bent in that fashion, will the bow fire?

Of course if it only takes 10 lbs to pull back, you'll only get 10 lbs back. Trying to theoretically find the best material commonly available (i.e. buying actual bow arms is not really an option here) is a lot more effort than building a bunch of bows and using them side-by-side.

But you don't need complex stress/strain analysis and elasticity calculations to know that EMT conduit is possibly the worst option available. It permanently deforms at such a low amount of deflection that you'd probably need 20' bow wingspan to get 8" of draw.


Then how about finding some wood rods, I feel like you've missed the point of my suggestion.



Then how about finding some wood rods, I feel like you've missed the point of my suggestion.


The point of your suggestion was "harder to pull back = better" right? If that is the case then it is wrong, because as I outline, it is not the only factor. There are a lot of cases where "harder to pull back = worse."




Oh my bad, I completely forgot that "harder to pull back = worse" is the reason real bows only have a draw of 10 lbs. Other then saying that EMT will bend and not flex back you gave no reason to suggest another material could not be substituted for the PVC arms with your only argument being "harder to pull back = worse".


1. Draw force is not the only important factor, elastic effects are very important. The energy released will be proportional to the draw force times the draw distance times the elasticity coefficient (which is always between 0 and 1). In the case of EMT, the elasticity coefficient is 0, so the energy released is 0. This would shoot slug darts 0 feet flat, and 0 feet angled, at a velocity of 0 feet per second.

2. Wooden bows are great, but a wooden dowel would make a poor bow arm. I'm not savvy to all the details of how wooden bows are treated and shaped, nor any particular types of wood that are best for it, but I do know that the wooden dowels I see at the hardware store would be absolutely terrible. But if you know what you're doing, a wooden nerf bow would be pretty cool.

3. Real bows have a wide variety of draw forces, from 20 lbs to 150 lbs. I can achieve ANY of those draw forces with CPVC, by varying bow length and string length, although for forces of 80 lbs+ the draw length would suffer unless I went up to 1" CPVC. I'd estimate that my draw force is about 40 lbs on the bow I built for the writeup. Also, just because my bow powers a nerf blaster, doesnt make it any less real. Nerf wars are not the matrix.

4. I can already tighten this bow to make it dangerously powerful with slug darts, and if I chose to make this shoot arrows, I could kill unarmored people with it. Since I'm not planning killing people with this, let alone shooting arrows through a guy in full plate mail, there is no benefit whatsoever to new, stronger bow materials. This makes your point completely moot.

5. Protip: sarcasm is good for making someone else look like more of an idiot than they already do. However, if you are an idiot to start with, using sarcasm just makes you look like a COLOSSAL idiot.

Edited by KaneTheMediocre, 16 August 2010 - 06:17 PM.

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#22 Edible Autopsy

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Posted 16 August 2010 - 09:20 PM

What have you found is an Ideal bow arm length?
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#23 jaybo1996

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Posted 20 August 2010 - 04:45 PM

Edible autopsy, how tall are you? Seriously, the ideal length is a few inches taller than you are, however, you really don't need all the power these things put out. I recomend just making it a comfortable length.

Edited by jaybo1996, 20 August 2010 - 04:46 PM.

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#24 Meaker VI

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Posted 20 August 2010 - 06:13 PM

Don't you think having a higher draw weight would cause it to preform better? Rather then having the elastic effect.



snip

snip

Then how about finding some wood rods, I feel like you've missed the point of my suggestion.

snip

snip

snip

2. Wooden bows are great, but a wooden dowel would make a poor bow arm. I'm not savvy to all the details of how wooden bows are treated and shaped, nor any particular types of wood that are best for it, but I do know that the wooden dowels I see at the hardware store would be absolutely terrible. But if you know what you're doing, a wooden nerf bow would be pretty cool.


The details involving why Dowels (and actually, any round shape) are terrible for use as bows can be found in basic bending theory. Since I'm rusty on it and no one here cares about it, the basis is this:
Posted Image
As you can see, this is an I-beam under load. What is happening is this: the fibers in the large flat portions of the I-beam (the flanges) are either in extreme tension or extreme compression, and are working to 100% of their potential, while the fibers between the flanges and the middle of the I-beam are not working at 100%, and those in the middle of the beam are actually neither in tension nor compression, and are thus doing no work (0%) and are dead weight.

This means that any round shape 'O' has infinitely small portions of the mass of the shape in either tension or compression, while the bulk of the shape is doing no work at all (think about the single line of the PVC pipe that is touching your work surface as being the only part of the material doing any work and you've got the idea). This is why bows are usually flat shapes or have a 'D' shape with the round pointing toward the user, and are not completely round.
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#25 KaneTheMediocre

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Posted 21 August 2010 - 01:38 PM

I think your bending theory is better than your geometry. An "O" shape has about half of it's volume within 0.3R of the extreme top and bottom of the bend, where the compression/extension ratio is largest. Not nearly as good as an I-beam, which has more like 3/4 of it's volume in this region (depending on the exact geometry of the I), but much more than a solid cylinder.

Anyways, all of this affects the amount of force required for the draw-- Material concerns still determine how high the compression/extension ration can get before inelastic (plastic) deformation occurs (In the case of wood, it doesn't deform, it just breaks). With a material like wood, this is fairly low, which motivates the flat or D shape of the bow arm--it actually MINIMIZES the compression extension ratio, in relation to the movement of the bow arm. So, although this also minimizes draw force, wood is strong enough that you can make reasonably sized bows with plenty of tension.

CPVC bends more easily than wood, so a flat piece would need to be larger (in terms of profile area / total volume, not length) to get the same tension. However, it can also deal with a larger compression/extension ratio, so the "O" shape works pretty well. An I-beam shape, for the reasons discussed, would also work great, but I think it would have other unrelated problems which I won't go into here.

The short story it, neither CPVC nor wood are perfect bow materials, but by picking an intelligent profile shape, we can make wood bend farther to compensate for it's small maximum compression/extension and make CPVC harder to bend, to compensate for it's small resistance to bending (I can't remember if thats the modulus of elasticity or not, but you probably get the idea). An "O" shape of wood would be terrible, as would a flat or D shape of CPVC.

Don't you think having a higher draw weight would cause it to preform better? Rather then having the elastic effect.



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Then how about finding some wood rods, I feel like you've missed the point of my suggestion.

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2. Wooden bows are great, but a wooden dowel would make a poor bow arm. I'm not savvy to all the details of how wooden bows are treated and shaped, nor any particular types of wood that are best for it, but I do know that the wooden dowels I see at the hardware store would be absolutely terrible. But if you know what you're doing, a wooden nerf bow would be pretty cool.


The details involving why Dowels (and actually, any round shape) are terrible for use as bows can be found in basic bending theory. Since I'm rusty on it and no one here cares about it, the basis is this:
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As you can see, this is an I-beam under load. What is happening is this: the fibers in the large flat portions of the I-beam (the flanges) are either in extreme tension or extreme compression, and are working to 100% of their potential, while the fibers between the flanges and the middle of the I-beam are not working at 100%, and those in the middle of the beam are actually neither in tension nor compression, and are thus doing no work (0%) and are dead weight.

This means that any round shape 'O' has infinitely small portions of the mass of the shape in either tension or compression, while the bulk of the shape is doing no work at all (think about the single line of the PVC pipe that is touching your work surface as being the only part of the material doing any work and you've got the idea). This is why bows are usually flat shapes or have a 'D' shape with the round pointing toward the user, and are not completely round.


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