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#1 ferball

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Posted 25 July 2012 - 09:00 PM

Is there any reason why no one flattens their bow arm on there cross bows. Flattening the arms will let you shorten the length a bit and still have a drawable bow, it will also make the point of the most flex and stress in the curve of the arm and not in the middle of the bow. It takes an extra 15 - 20 minutes to do, but well worth the trouble.

Backyard Bower This guy does a nice job of teaching PCV bows, some of his techniques translate well into nerf bows and cross bows.
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#2 Draconis

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Posted 25 July 2012 - 10:28 PM

Probably because flattening PVC (or reshaping with heat at all) can release toxic fumes. Especially if it happens to ignite. Using a different material altogether would probably be the best idea, but we don't want to go overboard either. Bow arms are very easy to make overpowered, which may present a safety hazard. It is just nerf, after all.
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#3 Curly

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Posted 25 July 2012 - 10:30 PM

Most crossbows are very long in overall length, so most don't really worry about the width. I also think that most people don't like combining melting plastic with unventilated spaces. I'm sure there are safe ways to do this, but the way shown looks unwise.

However, I think flattening in the way shown in the video may make two-piece bow arms a viable alternative to one-piece. 3/4" CPVC is the most common bow material used, and given it's 7/8" OD and an ID of a little over 5/8", it may not flatten as nicely as thicker, stronger PVC. Certainly this can be worked around, but I would personally look into springs or rubber tubing if a low-profile blaster is desired.

EDIT: After rewatching the video I found that there are children present when he's forming the bow. If you're going to risk lung cancer and fires that's fine, but make sure to get the kids out of the house first!

Edited by Curly, 25 July 2012 - 10:48 PM.

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#4 Carbon

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Posted 25 July 2012 - 10:40 PM

As Draconis said, heating PVC can release fumes that you don't want to be breathing. It bothered me that the video didn't mention just how important ventilation is when heating PVC. (That's also another answer about why it isn't done very often. Considering the age of the average nerfer, I can't imagine too many parents being crazy about PVC fumes in their kitchen. Hell, it's not something I'd want to do in *my* kitchen.)
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#5 Funky Mutha Facko

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Posted 25 July 2012 - 11:45 PM

I'm sure the reason it isn't done is because nobody thought to do it. It may be difficult to get the tee to work with a bow like that. I may apply this to the painter's bow if i find the time. Thanks for sharing this.
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#6 Daniel Beaver

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Posted 26 July 2012 - 08:48 AM

It is probably worth looking into alternatives if they can make bow powered guns lighter and smaller. Worth noting, however, is that current methods are very cheap and simple to implement, while also providing ample power. We also have the awkward problem that our barrels need to go through our bow arms.

Edited by Daniel Beaver, 26 July 2012 - 09:17 AM.

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#7 ferball

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Posted 26 July 2012 - 09:21 AM

PVC fumes are deadly and cause problems when the pipe is ignited, this happens around 700 degrees F, the molecules decompose and reform, causing most notable a variation of chlorine gas in many cases depending on the molecular composition of the surrounding air and a few other things. The melting point of PVC is 400 degrees F, bending can usually be done closer to 200f. So you have at the very least 300 degrees of wiggle room between bending pipes and gassing yourself. If the pipe is not "smoking" or discoloring you should be fine, I had more smoke and fumes coming off of my oven mits when I bend then I do off of the pipe itself. All that being said I could be wrong and I would welcome some one with an informed dissent to politely post it. If I die next week you can all laugh and say "I told you so".

MSDS PVC Pipe

I did two piece bow arms plugged into a tee and it works great. You don't want to flatten the 2-4 inches that slips into the T, A flattening jig work good for this. This minimize flex at the center of the bow so I imagine it would actually work better in T's than straight arms.

I realize that there is no pressing need for such innovations in the current batch of homemades, and it may not be worth the extra time for most nerfers, I personally like the look a lot better, and the lighter pull with shorter arms is nice. If some one got ambitious short re curve arms might make a small powerful crossbow doable. I can see a recurve shortening the needed draw so the overly long plunger tube would no longer be necessary.

Just some thoughts. My contribution to the madness.
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#8 Zorns Lemma

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Posted 26 July 2012 - 08:49 PM

Since you did the research, it means you have a lot of respect for what you're working with and understand the limitations.

I'm not as confident the majority of our readers share the same understanding.
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#9 KaneTheMediocre

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Posted 31 July 2012 - 05:53 PM

PVC fumes are deadly and cause problems when the pipe is ignited, this happens around 700 degrees F, the molecules decompose and reform, causing most notable a variation of chlorine gas in many cases depending on the molecular composition of the surrounding air and a few other things. The melting point of PVC is 400 degrees F, bending can usually be done closer to 200f. So you have at the very least 300 degrees of wiggle room between bending pipes and gassing yourself. If the pipe is not "smoking" or discoloring you should be fine, I had more smoke and fumes coming off of my oven mits when I bend then I do off of the pipe itself. All that being said I could be wrong and I would welcome some one with an informed dissent to politely post it. If I die next week you can all laugh and say "I told you so".

MSDS PVC Pipe

I did two piece bow arms plugged into a tee and it works great. You don't want to flatten the 2-4 inches that slips into the T, A flattening jig work good for this. This minimize flex at the center of the bow so I imagine it would actually work better in T's than straight arms.


Props for doing your homework, but do beware that depending on your means of heating, you don't have anywhere near a constant temperature through the PVC, so in order to soften the inside, the outside may reach a much higher temperature. If you really can bend at 200f, then boiling water is a good way to regulate the temperature and ensure that no part overheats--but I think you need more than 200f. On a related note, I've smelt some pretty bad something coming off of PVC that was just barely melting, so I'm a bit skeptical that no chemistry happens within 300f of the melting point.

I realize that there is no pressing need for such innovations in the current batch of homemades, and it may not be worth the extra time for most nerfers, I personally like the look a lot better, and the lighter pull with shorter arms is nice. If some one got ambitious short re curve arms might make a small powerful crossbow doable. I can see a recurve shortening the needed draw so the overly long plunger tube would no longer be necessary.

Just some thoughts. My contribution to the madness.


There is always a pressing need for innovations.
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