NerfHaven: Calibrating Oversized Dart Diameter to Barrel ID - NerfHaven

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Calibrating Oversized Dart Diameter to Barrel ID

#1 User is offline   Burr 

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Posted 01 April 2012 - 12:40 AM

Hello NERFHaven!

I'm very new to all this; I've been lurking a lot, and I learned so much. As a thank you, I want to share a method I recently developed as part of my project to build a NERF loser rifle from scratch for Humans vs. Zombies at my university. I needed very precisely calibrated darts, that are not only accurate and long-flying, but also very consistent in their performance.

Herein, I'll tell you how to make your darts fit any barrel bore-size perfectly. As long as the darts are no more than 0.050" larger than the bore-size, this method should work. Additionally, the darts will form a wonderfully smooth, hard surface - very good for shooting!

If your darts are smaller than your bore-size, this method will not work. Try putting your darts into the dryer for longer than usual. Maybe they'll expand enough to fit comfortably. But I cannot guarantee that, since I haven't tried it myself. Careful, they might melt. Anyway, disclaimer over, on to the show!

Materials you'll need:

  • 3" metal tubing that has an ID (inner diameter) which is the same as your intended diameter for your darts. We'll call this piece of metal tubing the dart template. I recommend that the ID of the dart template be no more than 0.010" smaller than the ID of the barrel, but definitely not bigger than the barrel ID. The tightness of the fit should depend on whether you are working on an air gun or a spring gun. Spring guns should be tighter, so that there is more friction to hold the dart in place while the plunger builds up air pressure. Air guns should be looser - but I think a 0.027" difference in ID between the dart template and the barrel is too loose. So there'll be some experimentation on your part. We're looking for perfection here, afterall! As for the 3" length, simply make sure that the tubing is 1-2" more than the dart length.
  • FBR darts - Stefans assumed. For a guide on making Stefans, click here. Now, my recommendation: expand the FBR using a clothes dryer (about 8-10 min). Don't use a hair dryer, and I can't guarantee that my method will work if you chose to stretch the darts. Do finish the darts completely before calibrating them. (I'm assuming glue tip, not felt tip.) Important: The darts might form a hollow at the foam end during the melting process. If this bothers you, construct your darts with 0.5" more foam than your intended length. Simply trim the darts to size after calibrating them.Perhaps increasing template length will alleviate this problem.
  • Pipe cutter. Implied, for cutting down the metal tubing to size.
  • Cooktop or similar heat source (e.g. camp stove). It's easier if it's a ceramic electric stove top, since you'll be able to simply set the templates onto the cooktop, but I'm sure you can figure out a way to work around that limitation given your situation. (E.g. put a pan on the cook top and set the template onto the pan.)
  • Heat-resistant gloves/gripper/towel.
  • Container full of cold water at least as deep as the dart template is long.
  • Thin, blunt tool - e.g. the eraser end of a pencil.


I'm using a 17/32" x .013" brass tube. The resulting dart diameter is almost exactly 0.500" - chambers perfectly in stock NERF barrels!

And I'm using the white foam backer rod from LogHomeStore.com because it's rumored to be one of the densest and the color is decently visible.

Procedure:
Once you have your materials picked out, cut down, and ready, you're half-way there.

  • Turn on one of the stovetop elements to High. Wait for it to warm up.
  • Put the dart into the dart template. Don't ram it in, but twist it in. Put it in tail-first. Make sure the glue tip of the dart is entirely inside the tube. You can use something blunt to help push the glue tip into the tube - that shouldn't deform the dart significantly enough to matter. Make sure there is 1" to 2" between the end of the foam end and the end of the tube.
  • Set the tube vertically onto the pre-heated cooktop element with the glue tip end pointing upwards. The opening of the pipe farthest away from the dart should be the part of the tube that is touching the heating element.
  • Wait 20-40 sec. The exact time will vary depending on the foam material you use. Experiement. For the FBR I used, 40 sec worked fine.
  • Using the heat-resistant gloves, lift the tube from the cooktop and submerge it in water entirely. Let stand until cool. (About 20 sec.)
  • Using a blunt tool, push the dart out of the tube. Push on the glue end. This is done b/c the foam might be sticking to the side of the tube. It'll be a clean break - no stuff left in the tube after the dart comes out.


...aaand you're done! Repeat as needed. Photos:

Posted Image

Posted Image

Yes, it's time consuming, but sometimes, you want to be a perfectionist. And sometimes, you are stuck with the tools and materials you have on hand and you gotta improvise to get a quality product.

Speaking of improvising, before I came up with this method, I have tried freezing darts, microwaving them, wrapping them in teflon tape, and melting them with a cigarette lighter to figure out their physical properties.

Well, I hope you guys enjoyed the tutorial! Sorry it's so verbose. All the lab write-ups getting to me. I'll be posting a topic about my homemade loser rifle in the next few months. Please, if you have any questions, I'll try to answer them to the best of my ability.

Cheers,
Illya "Burr" Moskvin

P.S. So I see you censor certain words key to my project. Ah well, so let it be. I know what I mean, you know what I mean, communication is not impeded, and it's kinda funny.

#2 User is offline   andtheherois 

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Posted 01 April 2012 - 01:18 AM

There's a reason why the term is "loser", and not what you wanted it to be. Mainly because there is no "losing" in nerf.

Anyway about your process; It's 5am here and I just skimmed it so I may be missing key points, but tl;dr it seems that You're using the metal tubing (in this case brass) to form your dart to the right shape, which in this case is changing the ID.

If I have that right then that's pretty cool. It definitely helps make darts more uniform than any other method I've seen. I may try this with a batch of blanks I have lying around that are just slightly thicker than I need. Have you tried just doing that with the blanks or is there a reason you make them first? Have you tried making a rig for this out of a row or two of brass?

Also, what university do you go to where stefans are allowed in HvZ?

This post has been edited by andtheherois: 01 April 2012 - 01:19 AM

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#3 User is offline   Burr 

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Posted 01 April 2012 - 01:35 AM

View Postandtheherois, on 01 April 2012 - 01:18 AM, said:

There's a reason why the term is "loser", and not what you wanted it to be. Mainly because there is no "losing" in nerf.

Yes, that's what I gathered while lurking. Did not notice there was a censor for it though. Anyway, there's definitely "losing" in HvZ, because there, distance matters - zombies have to get close to tag you. It's not all that different from a +Bow in principle.

Yes, you got the gist of it. I wanted the tutorial to be self-sufficient, so that if a noob like me read it, he wouldn't need much background knowledge to understand what was going on.

No, I haven't tried doing it with a row of blanks. It's crossed my mind. But I haven't started mass-producing my darts yet b/c I'll need to calibrate the weight, length, and balance of the darts first, and I'm still looking for a dart template with an ID slightly smaller than 0.527". But yes, later on, I'll make a rig.

Quote

Also, what university do you go to where stefans are allowed in HvZ?

Ah, it's not the university so much as the dorm I live at. My university is as strict about HvZ as any, but my dorm is the chillest place around. HvZ is student run and approved locally, and as long as the moderators approve each gun/dart combo, anything goes. And everything turns out pretty safe - no injuries so far afaik. It's Collins, at Indiana University. Everything around here is like that. I love this place.


Edit: Oh, and I make the darts first for a couple reasons: the way I make 'em, the glue tips tend to be over-sized, and this process makes them conform to the proper diameter. Also, I need the glue tip so that I can push on it with the blunt tool to remove the dart from the pipe. It gets a little stuck, and I don't want to damage it.

This post has been edited by Burr: 01 April 2012 - 02:15 AM


#4 User is offline   SlightlySane813 

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Posted 01 April 2012 - 03:16 AM

Very interesting concept. I will have to try this with the next batch of brass I get.
I was wondering though does this process make the darts any denser than the original unheated dart, and does the end result leave any kind of "skin" on the dart?
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#5 User is offline   nine 

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Posted 01 April 2012 - 08:02 AM

Nice job! I actually have been doing this for a while now, but with a hairdryer heating the foam. The stovetop method does seem like it would heat the darts much more consistently and efficiently.

View PostSlightlySane813, on 01 April 2012 - 03:16 AM, said:

Very interesting concept. I will have to try this with the next batch of brass I get.
I was wondering though does this process make the darts any denser than the original unheated dart, and does the end result leave any kind of "skin" on the dart?


In my experience, this method does tend to leave a skin on the foam.

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#6 User is offline   hamoidar 

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Posted 01 April 2012 - 10:46 AM

Nice, this seems like it produces extremely uniform darts. As for it being time consuming, you could make a dart stand out of multiple pieces of brass tubing. Using something like that would let you heat many darts at once.
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#7 User is offline   Zorns Lemma 

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Posted 02 April 2012 - 11:38 AM

Since you are doing this on a per-dart-length basis, given your instructions I would estimate an additional 1-2 minutes per dart. For a real war that consumes 500-1000 darts, this is an addition of 10 to 40 hours of prep time.

A method to stretch foam in bulk is much better. A simple one is just to take 10' sections of your barrel material (tolerance-rated ID tubing from McMaster is great), pull the foam through, and let it sit for 2-3 weeks.
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#8 User is offline   Daniel Beaver 

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Posted 02 April 2012 - 01:42 PM

View PostZorn, on 02 April 2012 - 11:38 AM, said:

For a real war that consumes 500-1000 darts, this is an addition of 10 to 40 hours of prep time.

That was my first thought. This might, however, be useful for my own power testing. I don't need a lot of darts to do that, and eliminating variability is crucial.

#9 User is offline   Zorns Lemma 

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Posted 03 April 2012 - 03:11 AM

You might be able to do 3' at a time using a warm oven and a longer piece of metal tube. The cost of brass seems prohibitive here though.
"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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#10 User is offline   Langley 

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Posted 03 April 2012 - 04:55 AM

I can't help but imagine This guy pulling a piping hot tray of darts out of the oven and setting them on the windowsill to cool. I would imagine that placing the barrel upright as with the OP is an important factor in preventing the dart from settling on one side, so I guess you would have to set up vertical tubes in an oven? Seems pretty ridiculous, but still not as bad as using hundreds of dollars worth of extruded t-slot to stretch your foam.
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#11 User is offline   LT DAN ICE CREAM 

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Posted 03 April 2012 - 08:47 AM

I would pay good money to see Chops in an apron cooking up some darts.

On topic, you mentioned that there is a hard, smooth surface formed during the heating process; how hard is the surface?

#12 User is offline   Colonel Zach 

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Posted 04 April 2012 - 06:06 AM

This seems like a complicated process, but it's actually pretty easy, once I read it over again! I seriously want to try this.
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#13 User is offline   Burr 

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Posted 04 April 2012 - 04:16 PM

View PostSlightlySane813, on 01 April 2012 - 03:16 AM, said:

I was wondering though does this process make the darts any denser than the original unheated dart, and does the end result leave any kind of "skin" on the dart?

The dart definitely becomes denser on the outside, but keeps its original density on the inside. There is a gradient of density. This photo should help answer your question:

Posted Image

However! There should be no skin on the dart if you do this process right. If the darts have a skin, then you have heated them for too long. Take a look at the photo below. The upper dart has been heated for 90 sec. The bottom dart has been heated for 40 sec. The surface of the 40sec dart is very smooth, while the surface of the 90sec dart is wrinkled. Additionally, I heated the 90sec dart with the glue tip pointing downwards, to illustrate what would happen. I neglected to add an unmodded blank for comparison.

Posted Image

View PostZorn, on 02 April 2012 - 11:38 AM, said:

Since you are doing this on a per-dart-length basis, given your instructions I would estimate an additional 1-2 minutes per dart. For a real war that consumes 500-1000 darts, this is an addition of 10 to 40 hours of prep time.

I don't think you would need this sort of precision in a NERF war. Again, I'm modding my darts for a specific role in HvZ games. (Which is actually a viable strategy there.) But using a rig with multiple brass tubes as hamoidar and andtheherois suggested should decrease prep time.

View PostZorn, on 03 April 2012 - 03:11 AM, said:

You might be able to do 3' at a time using a warm oven and a longer piece of metal tube. The cost of brass seems prohibitive here though.

That would not work. For one, Langley is probably right; doing so would unbalance the dart due to the way the foam would settle. But more so, it is not so much the heat from the cooktop element that molds the dart, but rather the fact that the metal of the tube heats up faster than the air pocket between the dart and the heat source. (Plus, foam is a poor conductor of heat.) This way, the dart doesn't turn into foam mush, but the heat from the metal starts working its way into the dart, melting the outside; thus the dart conforms to the diameter of the tube.

Thus, it is vital that the part of the tube that touches the heat source is as flat, broad, and uniform as can be (increasing surface area) so that the heat spreads to the metal without having to go through any tiny air pockets. Ideally, we'd put some sort of flat-topped plug onto the brass tube, and have that be the part that's touching the heatsource. However, then you'd have problems extracting the darts from the tubes, increasing manufacturing time, etc, etc. This works well enough.

Also, ideally, the tubes should be longer than 3" to increase the distance b/w the dart and the heat source, so that the foam at the end of the dart melts less. Because it does melt. As I've said, I have to trim about 0.5" off the darts - the part that gets partially melted. Unfortunately, that's foam wasted - another criticism against this method.

Take a look at this photo. From left to right: 40, 30, 20 seconds, unmodified blank. Unfortunately, I don't have my calipers here with me to confirm this, but it seems that the diameter of all four does not vary much - so 20 sec is enough to reform the darts. However, these were made to fit a 0.527" ID aluminum tube. 0.527" is not all that different from the foam's original diameter of ~0.538" ([edit]before the calibrating process[/edit] they wouldn't exit the tube, no matter how hard I blew into it). In order to test whether 20 sec is enough to reform the darts, I'd have to try a more drastic reform - from 0.538" to 0.500" for example. (Last time I tried that, I went with 40 sec, and though I had to trim more than I might have if I tried 20 sec, the darts worked very well in their new barrel.)

Posted Image

View PostLT. DAN ICE CREAM!!!, on 03 April 2012 - 08:47 AM, said:

On topic, you mentioned that there is a hard, smooth surface formed during the heating process; how hard is the surface?

I think it's not so much that the surface gets harder (the material is the same, after all, so that property shouldn't actually change) but because the foam is denser near the surface, the dart feels harder to the touch - there is more resistance when you squeeze it or bend it. Might increase durability!


Edit: Instead of setting up vertical tubes inside an oven, consider setting them up onto a cooktop heating element instead. I think that the standard diameter for the big ones is 11" - you could fit a lot of tubes on there.

Also - I have some hypothetical plans that I might try later, when I have more money. I think that when you calibrate the darts to the barrel, it is still a little too tight a fit - too much friction, not enough acceleration. So I'm thinking of working the brass tubes to expand the inner diameter - e.g. I have a 0.527" aluminum barrel and I want 0.515" darts. So I would take a 17/32" x .014" brass tube with an ~0.504" ID and force some precision-manufactured stainless steel balls through it (probably in 0.005" increments) until the diameter is ~0.515". For instance, here is a 0.515" stainless steel ball at Bal-tec.

This post has been edited by Burr: 04 April 2012 - 06:33 PM


#14 User is offline   iamthatcat 

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Posted 02 May 2012 - 06:40 PM

I tried heating some cpvc barrel material with a common coffee warmer instead of metal on a cooktop. I had some (19!) barrels cut to 2 1/2" for an absolver. There's a rubber band holding them together. The warmer is not a particularly powerful one. I tried mine on high and it deformed a few barrels so I would stick to low at first. In usage I found it best to load it with darts (to about 1/4" of the bottom) and then place it on the warmer for 15 - 20 minutes (longer for stock darts). It's hard to gauge but my darts melted a bit at the bottom when they were done. A little less gets a tighter dart but over 25 minutes started to deform the surface of the foam.

The fit I got with stefans and 25 minutes was a loose airgun fit. In petg it would need tightening rings. At 15 a springer fit seemed usual. It's not fully consistent with the darts in the center getting a bit hotter sometimes perhaps.

Posted Image

This is right after heating.

Posted Image

Here's some stock darts I ran through. They fit into cpvc much easier and seem to keep their size well.

Posted Image

#15 User is offline   b1g13en 

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Posted 02 May 2012 - 10:02 PM

View Postiamthatcat, on 02 May 2012 - 06:40 PM, said:

I tried heating some cpvc barrel material with a common coffee warmer instead of metal on a cooktop. I had some (19!) barrels cut to 2 1/2" for an absolver. There's a rubber band holding them together. The warmer is not a particularly powerful one. I tried mine on high and it deformed a few barrels so I would stick to low at first. In usage I found it best to load it with darts (to about 1/4" of the bottom) and then place it on the warmer for 15 - 20 minutes (longer for stock darts). It's hard to gauge but my darts melted a bit at the bottom when they were done. A little less gets a tighter dart but over 25 minutes started to deform the surface of the foam.



Have you tried putting the cpvc with blanks in them and heating it in the dryer?

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