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+bow Mod

I crapped my pants when I shot it.

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#1 louiec3

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Posted 16 December 2009 - 09:21 PM

Well over the past 3 weeks I've been working on improving the +Bow, I wanted to get the best seal, make full spring compression, and use a square plunger rods because the round ones can turn easily.
When I began I realized this would make a potent nerf weapon so I decided to nerf it a bit and cut it down.
I modified the CAD plans and got to work on this awesome gun wondering if it would succeed or fail horribly.

I succeeded

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I call it Dr. Frankenstein

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Just to prove it is 100% compressed.

Well now I better tell you how to make one...
*If you have never machined with plastics, or sketched accurate pictures this is not a good place to start.

Print out some +bow templates. If you already have a +bow just print out what you need.

Start by sketching 9/16 squares around these pieces make sure the squares are not crooked or tilted.
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Do not sketch a 91/6 square on the circle!

On one circle sketch a 1/2 square and on both mark two holes for drilling in the same spot on both circles
The circle with the square needs 5/32 holes and the circle without the square needs 7/64 (which you will tap)
Both circles are 1/8in polycarbonate.

Next is easy just measure off two inches from the front and place those two holes in the same spot. I would leave the corner not rounded off because it might increase the durability of the piece.
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Drill the proper size holes, and cut out your pieces.
Now grab some 1/2 thick polycarbonate and cut it to 11.6 and 1/2 wide. oh wait you might need a mcmaster number 1749K14

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The vertical part of the notch is 3.1 away from the front of the plunger rod.
Take your two circles and put them together with 1/4in screws.
fit it onto your plunger rod and drill and tap the hole into the plunger rod.

Take your rubber skirt that you probably need a number for 9562K46(credits to split for finding this) and sandwich it between the front and back of your plunger head. Tighten a 1 1/4 screw down on it make sure it is very tight otherwise the skirt will move and you won't get a seal.
The finished product should look something like this...
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Assemble the rest of the pieces like a normal +bow, but don't put the spring on yet.

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just for comparrison old and new

Now cut your spring to a little more than9 and slide it on the plunger rod, but wait it won't fit bust out your dremel and sand down the edges of the plunger rod so the spring will fit.
with everything on the Dr. Frankenstein, that I forgot to mention because it is stupid if you forget it i.e. plunger handle, except for the plunger tube pull your plunger back until it catches if it doesn't trim a little off the spring repeat until it catches.
Once you finished everything put a healthy dose of silicone lubricant on the plunger and tube, and put everything together.

Now that you've read through all this you're probably waiting for ranges.
*Edit- I did range testing today with a 9in cpvc barrel (tight on my darts)
-with single bb 100-110ft
-cs stefans- 95-100ft
-1/4in slingshot 125-145ft

-Just for shits and giggles I shot a slingshot stefan at a 45 degree angle and picked it up 215ft away.

Edited by louiec3, 19 December 2009 - 12:46 PM.

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#2 Ice Nine

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Posted 16 December 2009 - 09:29 PM

For the record, cutting the catch notch on the +bow's plunger rod about an inch more towards the plunger head adds full compression if I recall correctly.

Also, on my current +bow the screw has held the plunger rod straight for three wars. On my old one, a dab of super glue performed the same purpose when the screw didn't hold it well enough.

Good job, I guess.
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Unholy Three: DUPLUM SCRTA, DUPLUM PROBLEMA (2009)

But Zeke guns tend to be like proofs by contradiction

Theoretically solid but actually non-constructive

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#3 Zorns Lemma

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Posted 16 December 2009 - 10:57 PM

Taking the spring to solid length weakens it over time. You might want to move the catch back .5" or so.

Also, power output is not the weak point of a +bow; efficiency is. Given how much energy a "stock" +bow has in the spring, compared to the ranges the average one gets, efficiency is less than 10%.

Finding a good barrel setup and sealing the front bushing is going to increase ranges much more than spring compression.

However, I do approve of the condescending tone in the writeup!
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#4 Ryan201821

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Posted 17 December 2009 - 01:23 AM

To solve the issue with rotating plunger rods, I usually use 3/4" screws instead of the 3/8" as suggested in the original writeup.

I like how you used the more efficient plunger head. I've yet to try Split's idea that you used. Having a good seal around the bushing and plunger tube is also very important. But really a +bow doesn't need to shoot any further.

Good job.
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#5 slowguitarman

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Posted 17 December 2009 - 10:22 AM

Just to kinda drive home the importance of sealing that bushing: I shot Angel's when he got it, and it sucked hard. It only shot 70', and that is no exaggeration. Once he got that sealed up, it shot a ton further.
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#6 Draconis

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Posted 17 December 2009 - 01:50 PM

Great job eeking out the most power out of the +Bow. You've done many of the same revisions that I've done to the LpL design. However, I do question the wisdom of using polycarbonate for the plunger rod. The switch to nylon for the Rev. 2 plunger was for a very good reason, that the polycarb rods would break at the catch point. Sure, yours is 1/2" thick, but that won't change the behavior of the material. Also, jumping up to 1/2" square does add a fair amount of mass to the plunger that is completely unneeded. The 1/2" round rod is overkill, and adding 27% more material is just silly, not to mention detrimental to the performance.
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#7 Ryan201821

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Posted 17 December 2009 - 04:34 PM

I was wondering about the same thing. You can substitute the polycarbonate with nylon, or polyethylene if you do end up having problems. Not to mention polycarbonate gets pretty expensive when it's that thick. I've never had problems with 1/2" nylon rod breaking in +bows though.

I'm also concerned how the gun will hold up with the spring being at full compression.
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#8 louiec3

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Posted 17 December 2009 - 06:21 PM

Ice Nine- I tried the super glue method before it worked, but I didn't want to trust a little bit of super glue; I wanted it impossible for the plunger rod to turn.

Ryan201821- I have always used 3/4 screws to hold on the handle.

Draconis- The reason I went back to polycarbonate is so the plunger rod won't turn; I had heard stories of the rev. 1 plunger rod breaking, so I went with the next size up 1/2in.


I wasn't trying to make this the best +bow out there if I was I would've gooped the bushing, went back to a lighter plunger, and not shorten it by 2 inches. I did this not to improve range, but rather fix problems I have identified. If you view it as overkill I don't care because I like it.
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#9 Ryan201821

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Posted 18 December 2009 - 02:19 AM

Oh hell no man, definitely not overkill. Besides, overkill is always good. Just constructive criticism. I like your work.
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#10 pinz321

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Posted 18 December 2009 - 08:26 AM

I like the idea. The problem is if will shorten the gun's life. That's my two cents. and just a final, wise quote from some wise (crazy) men:

What ever is worth doing, is worth over doing.


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#11 Zorns Lemma

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Posted 18 December 2009 - 08:40 AM

I wasn't trying to make this the best +bow out there if I was I would've gooped the bushing, went back to a lighter plunger, and not shorten it by 2 inches. I did this not to improve range, but rather fix problems I have identified. If you view it as overkill I don't care because I like it.


In that case you definitely should drop the extra draw on the plunger. Seriously, taking a spring to solid length or pre-compressing is not good for longevity of the spring or the blaster. The spring will most likely shorten and then start rotating and the unground ends will start catching on the plate in the back, preventing you from priming.

I haven't worked extensively with polycarbonate yet, but if what Drac says is true, the problems with the Rev1 plunger rods breaking is with the material itself. Perhaps try 1/2" square nylon to solve both the turning and the breaking issue? I wouldn't recommend polyethylene because its incredibly low melting point make it annoying to machine, however its phenomal tensile strength and impact resistance, along with low friction, might be appealing enough for you to try working with it.

Also, I hope you didn't take my first post too harshly. I thought you were trying to get into the 150 ballpark and was pointing out better ways you could get there.
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"In short, the same knowledge that underlies the ability to produce correct judgement is also the knowledge that underlies the ability to recognize correct judgement. To lack the former is to be deficient in the latter."
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#12 Draconis

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Posted 18 December 2009 - 03:01 PM

I was alluding largely to the idea that because 1/2" round nylon is overkill, 1/2" square is just unneeded mass. And that you can get better performance from SMALLER plunger rods in the 3/8" square dimensions.

Also, you may be interested in Split's take on this. http://nerfhaven.com/forums/index.php?show...l=\+Pistol
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#13 louiec3

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Posted 18 December 2009 - 05:46 PM

pinz321- best quote ever.

Zorn's Lemma- I may just be lucky but I've never had a spring catch on the back plate, however I might move the catch notch up now. I have a bunch of excess polycarbonate so if it does break I can just replace it.

Draconis- If I was trying to get the the best ranges I would move down, but right now the extra weight doesn't matter to me. I get the general idea of how splits plunger rod thing works, but I have no idea how he keeps it catching without turning.


Also for everyone who might be interested I found 1/2 square nylon it is part #8732K15
It is a lot cheaper than the polycarbonate, and if Zorn's Lemma is right it won't break.
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#14 CaptainSlug

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Posted 18 December 2009 - 11:31 PM

I haven't worked extensively with polycarbonate yet, but if what Drac says is true, the problems with the Rev1 plunger rods breaking is with the material itself.

No, they tend to break if the holes for the plunger head or handle are drilled or tapped too quickly which heats the plastic up and causes localized weakness. Or it is drilled too far off center.

Yes a square plunger rod is preferable. I went with round because it reduces the total machining time since you are simply drilling round holes to accommodate it, rather than having to cut out a bunch of square holes.

Edited by CaptainSlug, 18 December 2009 - 11:33 PM.

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#15 Draconis

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Posted 19 December 2009 - 03:15 AM

I haven't worked extensively with polycarbonate yet, but if what Drac says is true, the problems with the Rev1 plunger rods breaking is with the material itself.

No, they tend to break if the holes for the plunger head or handle are drilled or tapped too quickly which heats the plastic up and causes localized weakness. Or it is drilled too far off center.


Yes, that would also cause weakness, but the greater source of weakening is the material itself. Polycarbonate is a MARVEL of modern chemical and mechanical engineering. But sheets of the stuff are cast, which introduces a somewhat crystalline structure, and is partially why this stuff is so frickin' strong. This structure is then somewhat weakened by cutting in to it. A solid bar of polycarbonate could certainly withstand a great deal of stress in any application you choose, but once you cut in to it, a la catch point, you have introduced a flaw in the structure.

Nylon, by contrast, is generally extruded, which gives the plastic a grain, much like wood. With no crystalline structure, the nylon is then only weakened by the amount of material removed. It's just a REAL pain in the ass to machine.
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#16 CaptainSlug

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Posted 19 December 2009 - 11:43 AM

I've never had a polycarbonate plunger rod that I made break on me, or the people that bought them from me. Whether that's luck, or experience machining it is debatable.

Nylon isn't as difficult to machine as softer plastics can be. I've made from fairly detail parts from it.
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Plastics that have terrible machining properties: ABS, Polyester, and sometimes LDPE
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The little critters of nature, they don't know that they're ugly. That's very funny, a fly marrying a bumble bee. I told you I'd shoot, but you didn't believe me. Why didn't you believe me?


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