The Snap-1 Mk2, Writeup Options

[Carbon]

This is a writeup and assembly guide for the SNAP-1 mk 2, a basic spring powered Nerf blaster. I have incorporated a few improvements into this version that have been gained from the succeeding two models

-Lighter plunger
-More efficient, easier to build gasket system
-More compact size
-Stronger trigger

Parts Needed:


Pressure Chamber:
1.25” Sched. 40 PVC
1.25” PVC Endcap
1.25” PVC coupling
1.25” x .5” PVC reducing bushing

Plunger:
.75” thinwall PVC (Sched 40 will work)
.75” PVC Endcaps (x2)
Cotter pins (I used 3/32”)
.5” aluminum rod (wooden dowel will work)
3/16” x 1.5” rubber fender washer
#6 Finishing Washer
5/32 x 7/8 washer
#6 x .75” Oval Head machine screw & nut
9.5” x .5” spring (you can find this at True Value Hardware. It fits around a .5" rod.)

Handle:
Split key ring

Trigger:
Clothespin (plastic is best)
Small nail (not finishing, needs a head)
Small angle iron
Small zip ties

Barrel:
Barrel material (crayola, brass, etc.)
.5” Sched 40 PVC

Tools (bare essentials):
Hacksaw
Power drill and bits
Sandpaper
Hot glue gun

Not essential, but will make things easier:
Pipe cutter
Small files
Dremel
X-acto knife

Plunger:

The size of the plunger determines with size of the whole gun, so we’ll start there. Take one of the endcaps, and drill a .5” hole in the end. Be sure to center the hole.

Start with a small diameter hole, and gradually increase the size to avoid gouging, and to keep the hole centered. You want your aluminum rod (or dowel) to fit snugly in this hole. Cut a small length of .75” PVC. The SNAP-1 has a fixed chargerod, so a short plunger is fine, and reduces mass. About 2” is good. When you put it together with the two endcaps, you want roughly .25" of PVC showing in between the endcaps.

Now for the plunger head. Take the other endcap and drill a hole large enough for your #6 oval head screw. On top of the endcap, place the washer, fender washer, and finishing washer. Drop through the screw, and tighten down a nut underneath.


As you tighten the nut, the fender washer will cup upwards. This is a good thing, as it will hug the sides of the pressure chamber and make a great seal.


Drill a 3/32” hole in the end of the aluminum rod and sand off the rough edges. Twist it through the hole, pop in a cotter pin, and wrap it around the post. Pull it snug against the cap.


Press on the bit of .75” thinwall you cut off before. Then add the plunger head. Wrap a small length of e-tape around the chargerod where it meets the plunger to ensure that it doesn’t slip inside the plunger.


You’ll want to round the end of the rear endcap, to allow the firing pin to slide up over it, then click into place. You don’t have to do this, but if you don’t you’ll have to hold down the trigger to prime, and run the risk of bending your catchpin. It’s possible with sandpaper, but you’ll have a much better time of it with a Dremel. (this is about 5 minutes of work with a Dremel and the drum sanding bit.).


Also, sand off any edges of the endcaps that keep them from moving freely in the PC. The endcaps don't need to be airtight, but they doo need to slide freely, so don't worry about sanding them too much

Set it aside for now, you’re done with the plunger.

The Pressure Chamber (hereafter called PC)

First, prepare the 1.25” endcap. You’ll need to drill a 9/16” hole in the exact middle of the cap. If you don’t have a bit that big, drill it as large as you can and sand/file out the rest. It needs to be centered, and large enough that the chargerod is loose in the hole. Also, drill several other holes in the endcap to help with venting pressure from behind the plunger (for both cocking and firing).


Now, you need to cut the pressure chamber to length. The best way to describe this is to see it:


You want the PC to be shorter than the length of your plunger, so when the plunger is at full extension, the spring is still compressed slightly. With this design, having the PC be this much shorter seems to work well.

Drill some pilot holes, and screw the bushing and coupler together:


Press this over the end of the PC, and set it aside.

End of part one (picture limit).

This post has been edited by Carbon: Apr 29 2007, 05:48 PM

[Carbon]

Trigger preparation:
Drill a hole slightly larger than your nail in the clothespin clip.


Then, cut off the end of the clip.


Take your nail, put it through the hole, and hold it against the end of the PC tubing.


You’re determining how much sticks into the PC, and how much you’ll need to trim off. You want the nail short enough so that it doesn’t drag against the plunger when the clip is closed, but long enough so it firmly engages the catchface. Trim the nail with a wire clipper/hacksaw/dremel/teeth, then sand it smooth.

Determining where to put the trigger.:

Grab your pressure chamber; you need to determine how long of a draw your plunger has. Using some manner of stick, press down on the plunger in the pc until it bottoms out.


Mark how deep your pushrod went in with your finger for the time being, or enlist someone’s help. Be careful! If you let got of your pushrod, it’ll probably embed itself in the ceiling/wall/somone’s face. Now, carefully remove the pushrod, and set it next to the PC. Line up the end of the PC with the mark on your stick.


Place the plunger endcap at the end of the stick. Take note of the rear endcap catchface is. Mark a dot on the PC about .5” short of that spot. (This alloys you to pull past the nail, then catch the endcap on it.).Drill a hole at the spot, the same size you drilled in your clothespin. (It's the middle dot...I was indecisive.)


Final Assembly:

Screw the coupler to the PC. NOTE: make sure your screws are short enough that you don’t penetrate the inner wall of the PC. If you can’t get small enough screws, you’ll need to cut them short with a hacksaw or Dremel.

Cut your chargerod so about 1” sticks out from the endcap. Drill a small hole in it, and attach a metal keyring for charging. You can do what you like here, but this will weigh less than most anything else. (My original used a .5” PVC tee for a handle.) I got sick of the ring rattling, and eventually used a few turns of e-tape to make it stand straight out. It's also easier to grab, now.


Place the clothespin/nail assembly in the hole. Hold it down, and try to cock the plunger. If the clothespin isn’t closed all the way already, take it off and trim the nail. You should feel the nail raise up and then slip back into place. Let the plunger forward, and see if it holds. If your nail is too short, it won’t hold, or it’ll fire if you bump it; it should catch firmly. If it doesn’t catch at all, make sure that you didn’t drill too far back. It sometimes takes a few nails to get it right, or a few holes. Don’t worry about having to drill a few times, you won’t lose pressure, as this spot is behind the plunger head.

Once you have it set, glue down the nail head. A dome of glue over the nail works well.


Then glue down the clothespin. Don't get any glue in the hole. Glue your trigger on top of that. Take small zipties and zip the pin together, going over the trigger to hold it in place. Run one ziptie through the clothespin spring to help hold it together.


All that’s left now is to make a handle, and your choice of barrel. Crayolad PVC works well for stock darts, and sticks right in the end. My preferred method for micro stefans is to glue the end of my 17/32” brass in 3” of PVC, then drill a hole straight through brass and PVC. I stick through a cotter pin, and then glue both ends for a seal. The pin holds it together, and also serves as a dart stop.

I cribbed my handle system from Boltsniper; cut cut two lengths of 1” pipe, as long as you want your handle. Cut one of those two pieces in half, longways. Then, glue those to the othe rpiece of pipe. You can cut off the top at an angle. Then, wrap some sandpaper around your PC tubing and use it as a sanding block. Sand the end of the handle so it follows the curve of your PC. Depending on your trigger location, you may need to make some additional cuts to make it fit.


This post has been edited by Carbon: Apr 29 2007, 05:49 PM

[Carbon]

The finished product:

Glue it down, and you’re done. Lubricate the barrel with some silicone spray and go shoot someone.


As far as ranges, this gun should easily be able to hit 70’. It’s also a very good size for use with the hopper clip.


I tried to hit all the steps in this writeup...let me know if anything is unclear, and I'll edit it in, or get more pics.

This post has been edited by Carbon: Apr 29 2007, 05:50 PM

[six-five-two]

Great work Carbon!!

I must try this.

This post has been edited by six-five-two: Mar 23 2006, 10:54 PM

[GeneralPrimevil]

Yeah, I think I'm gonna make one of these, only with 2" PVC instead of 1.25" since that's what I have laying around. I'll have to use 1.25" PVC and fittings in place of the 3/4", but big deal.

Very nice write-up, by the way. I didn't find anything missing...

[z80]

I might build something like this, but single shot and a large pistol. And great job, very easy to follow.

This post has been edited by z80: Mar 24 2006, 12:48 PM

[Carbon]

Thanks, glad it was easy to read.

Z80: The SNAP-1 is smaller than you may think.....



It really is large pistol sized, and currently single shot. Part of the advantage of a smaller plunger is a smaller gun.

General: Let me know what kind of results you get if you try that out...I'm curious about how this design would scale, and work with different fittings.

Well, I got some range testing done. Flat ranges:

Stock dart in PVC/Crayola: 65'.

Micro stefan in 17/32" brass: 95' and 99'

I'm not sure whether to be very pleased or a little annoyed that my best ranges to date have been obtained by my simplest gun....

This post has been edited by Carbon: Apr 29 2007, 05:50 PM

[ompa]

You should be getting those kind of ranges though, especially with a plunger tube with that kind of diameter. Maybe your other ones just need lighter plungers and/or better plunger seals.

~ompa

[z80]

I didn't realize it was that small, maybe I'll start this over spring break. Nice gun with good ranges, and simple. Good enough for me.

[GeneralPrimevil]

Well, the piston head (plunger head) willl weigh approx. 4 oz. without any holes. The piston itself will probably be made of whatever steel (aluminum if I'm lucky) tubing I can find. I have most of the differences between that and mine down, I just need to write a shopping list. After that, I will start work, probably finishing this over my spring break. Then I will have two homemades which work as, well, Nerf homemades should, shooting mega Stefans. I think I'm gonna do a SNAP-2 style thing with a modified Unkown breach.

So theroretically speaking, if I stick to the 4:1 cylinder to barrel ratio, I should be getting the same 100' ranges, right?

Measures of each piece that I have calculated so far:

• LoP~12"
• Overall Length~53"
• Piston Travel~10"
• Barrel Length~30"

I just need to buy a few things, then I will start work.

A few questions:
1.) Can I hold the whole thing together with sheet metal screws? Exception being the cylinder head and piston head. Those would be glued. The cylinder head is the reducer from 2" slip down to 1" female thread.
2.) Should I use "see bottom this post"?
3.) Should I make the piston travel longer? I have really stiff springs which are 16" long. I might even have a 20" somewhere...

LINK!
With that, I could pop out the four (in a cross pattern parallel to the base of the pipe) to remove the piston, spring, spring guide, and spring stop thingy.

Edit: that spring guide is threaded steel rod by the way. It is secured to the bushing plug via two lock nuts and two washers. There would be a coupling which would be were the pins are as well so there is twice as much material. That would also allow me to put this back together more easily.

This post has been edited by GeneralPrimevil: Mar 25 2006, 08:21 AM

[Carbon]

It's really hard to say about ranges. I was shocked that I got 100' with this gun, but I think it's a combination of plunger weight and friction points...I'm grinding down my plunger caps more now, so they don't touch the PC as much, and this gun's only othe rcontact point is the hole in the back. But yeah, I've been using 4:1 for the SNAPs, roughly, but I think it's more a function of the plunger, and how well it can accelerate.

As far as assembly, yeah, you can build the whole thing with sheet metal screws. The only things I usually glue on are the handle and the trigger.

I've thought about that design of plunger. The only thing to consider is trying to keep the head gasket up and away from the head of the plunger, and cupped upward. My old style gaskets tended to get a permenant downward bend to them, which adversely affected the range...

As far as travel....hmmm, I wonder how much would be too much? I think that after a point, you wouldn't be able to get the plunger to accelerate enough to make the extra distance worthwhile...dimishing returns, as it were. Also, what I've found is that SNAPs tend to get sort of long rather quickly (especially the SNAP-2, since the plunger has to be longer to accomodate the slot.)

Threaded steel rod? I think that'll cause you problems...the pring has to compress past the guide, and also accellerate over the surface. The threads will slow you down.

[m15399]

If I were you I would use an o-ring. The gasket just looks like it's asking for squeaky trouble.

To answer first question:
Why would you want to? It's simpler just to glue it all.

[Carbon]

Wasn't sure if you we're talking more to the General or to me, m15399, but I thought I'd answer to what you were saying...

I tried using an O-ring. This gasket is way easier than dremeling a channel into an endcap. And since the SNAP is all about The Easy... The only precision work for this gasket system is making sure you drill the one hole in the center of the endcap. Anyway, there's really no room for an O-ring with these size parts. I tried, and it really worked poorly. Also, a gasket system has more room for size variance than an O-ring.

As far as squeaky trouble...nope. True, you have to lube the PC with silicone before you start playing, but that's true for any PC. The "cup" gasket is similar to pressure systems in air pumps. The pressure keeps the gasket against the PC walls, minimizing blow-by. I haven't had any problems since I started using it. It has a fantastic seal; if I fire with my hand over the end of the barrel, the plunger stops. No air leaks. Let your hand off, and you'll get a huge whoosh of air.

As far as gluing...I really don't like it. Screws let me diassemble the gun and further modify/improve things, while keeping everything together snugly.

[m15399]

I was talking to general.

I'm not saying the seal is bad, I'm saying that because the cup goes forward, it might reduce the speed of the plunger.

[GeneralPrimevil]

Yeah...that wasn't the plunger. That was what held the spring at the back of the gun. I have later since noticed many massive problems and redid that image to what is now here. Yeah...self-explanatory. I rushed that image so there are some screwups, it also is not to scale. Pretty much, it is the same thing as the SNAP only 2" and with a different system of holding the spring at the back of the gun. Roll pins will be behind a 1.25" bushing cap. This will allow me to remove the whole piston, spring, etc. by just popping out two or four roll pins. The whole thing will be held together with screws, utilizing set screws to keep that rear bushing centered.