57 replies to this topic

[CaptainSlug]

I first started work on designing this homemade over a year ago. I now finally have a prototype that is working as I wanted it to.

Write-up V1.0
Mirrored at Instructables


Plunger draw: 4.5 inches
Plunger volume: 14.5 cu in
Plunger tube length: 8.5 inches
Spring load when primed: 30 lb

Main project goals
+ Half the machining time of a +bow
+ Half the material cost of a +bow ($40 or less)
+ Reduced plunger stroke length
+ Increased and variable plunger tube volume
+ Fewer parts
+ No "face rape"
+ Made from less than one square foot of a single thickness of polycarbonate
+ Easier to disassemble
+ One or fewer internal cuts required for completion
+ Easily upgraded with an optional pump-action foregrip
+ Stock is optional
+ Wider machining tolerances for most of the parts

Essentially I wanted to improve upon what has made the +bow so venerable, but up the stakes while starting on a clean sheet of paper.

The plunger tube has an inner diameter of 2 inches with 1/8" thick walls allowing it to be structurally independent.
The catch on this homemade is at the end of the plunger rod, rather than being notched into the plunger rod itself. This not only makes machining the whole thing easier, but it also means that there is no top or bottom side to the plunger rod.


The plunger rod, catch, and priming handle are in an enclosed area. The plunger tube and plunger head can be removed by unfastening 5 screws.

Because of the configuration of the parts, the plunger tube and plunger head can be replaced with a smaller or larger diameter set of parts. The plunger stroke can also be lengthened or shortened by equally increasing the length of the plunger tube, 1/2" frame rods, and plunger rod.

Rather than being capped off by a bushing, the end of the plunger tube is capped off by half of a 1-1/4 coupler wrapped in 3 or 4 layers of e-tape. This allows several different bushings to be used for single 1/2 barrels, 3/4 pipe breeches, or large shotgun attachments.

It may take me a week or two to make a duplicate working example in order to compile a complete write-up. I've had a very busy year and little time to devote to this.
I would also like to point out that I was unable to find any ring shaft seals that would fit this size of polycarbonate tubing. The two nearest sizes are either a 16th too big or too small.

Edited by CaptainSlug, 24 August 2010 - 02:26 PM.

[Galaxy613]

Man, I've been waiting for the official unveiling of this baby for awhile. I think you finally posted about this at the right time during a resurgence of homemade designs. I really like the idea behind this blaster.

[Lt Stefan]

That looks great Slug. It seems much easier to make than a +bow.


A couple questions:

1. What is the catch itself made from?
2. What makes the volume "variable?"
3. Is performance better than a Plusbow?
4. Does it use a full length spring?
5. Does machining require any different tools than the Plusbow?

I can't wait to build some.

Edited by Lt. Stefan, 05 August 2010 - 10:01 PM.

[ggk]

Fantastic design Slug. Since I first saw it I thought it was genius and I had to make one.
So here it is


Thanks for making this.


What kind of ranges are you getting out of yours?

BTW pump action FTW

Edited by ggk, 05 August 2010 - 10:32 PM.

[Zack the Mack]

Awesome design, great progression of the +Bow. Simple, elegant, looks like anyone with a brain stem and a bandsaw will be able to fabricate one. It's the AK-47 of Nerf.

I especially like that catch - I can see it becoming a critical part of RTP-like blasters. What's it made of?

[Darth Freyr]

Yeah, the pump action is fun. For the skirt head, 9562K48 fits with a 1.5" spacer inside. What spring are you using? I hope you don't mind if my write-up is up first. Also, did you have any issues getting a good barrel fit? If anyone cares, I'm probably also going to make another one that uses either a 12" PT or full spring, probably the latter.

[VACC]

In no way am I speaking for slug when I say that I would mind, to a great extent, if you posted a write up of HIS design. Besides, the design your work seems to be based on was preliminary. If he's updated the product, why wouldn't we want the newer model?

[Zorns Lemma]

What's the back peg on the plunger rod made from? When I saw your prototype at Deal, it inspired me into my current uni-directional catch face, but unfortunately my method requires using a lathe: not the most ideal for ease of reproduction.

[CaptainSlug]

I don't want to see any pre-emptive write-ups of something I've put so much effort into. Nevermind that I've made a ton of changes since those images were leaked and that the pre-emptive copies you guys made lack some of the key features that are the whole basis for this homemade design.

+bow typical plunger displacement volume: 9 cu in
2-11 plunger displacement volume: 14.5 cu in (or more)

A couple questions:

1. What is the catch itself made from?
2. What makes the volume "variable?"
3. Is performance better than a Plusbow?
4. Does it use a full length spring?
5. Does machining require any different tools than the Plusbow?

I can't wait to build some.

1. Two plastic spacers, a metal washer, and a conical plastic washer I made.
2. Because of the catch design, only a few parts need to be changed in order to increase the plunger diameter or length. The rest of the blaster is unaffected by those dimensional changes. You could basically substitute any of the parts ahead of the forward frame piece. Anything ranging in size from +bow parts to any size of SNAP.
3. Yes. Range in current configuration is 110+ feet, accurate and consistent to 90 feet.
4. Not at the current plunger tube length. The spring is shortened by 1-1/2 inches. I wanted a shorter plunger draw length to make priming a little easier.
5. Potentially a couple more sizes of flat blade wood-boring drill bits and a large countersink bit.

1. What spring are you using?
2. I hope you don't mind if my write-up is up first.
3. Also, did you have any issues getting a good barrel fit?

1. Shortened +bow spring
2. I do
3. No

Edited by CaptainSlug, 06 August 2010 - 08:16 AM.

[Lt Stefan]

How did you make the plastic washer? Since one of your goals was ease of machining/less time, I would assume you didn't use a lathe. But then again I could be wrong, of course.

[Doom]

Great work as usual. I encountered the earlier prototype as well and heard a bit about the project goals, and I was impressed then as I am now.

CS, you mention that you haven't found any "ring shaft seals" that fit this tubing. I was actually looking to use the same size tubing with piston cup seals (9411K13 on McMaster-Carr, specifically). As far as I can tell, piston cup seals should work well for a 2 inch piston. If you haven't already tried these seals, I would suggest them.

[CaptainSlug]

How did you make the plastic washer?

Sanded the edges of a 5/8" OD spacer. Alternatively I could have made one out of polycarbonate. But that is difficult to accomplish without a band saw, so I'm not likely to put that in the write-up as an option.

CS, you mention that you haven't found any "ring shaft seals" that fit this tubing. I was actually looking to use the same size tubing with piston cup seals (9411K13 on McMaster-Carr, specifically). As far as I can tell, piston cup seals should work well for a 2 inch piston. If you haven't already tried these seals, I would suggest them.

Yeah I ordered one of those last year to inspect it, they won't work.
Those are meant to seal at thousands of psi inside of hydraulic rams. They're made of a composite fiberglass and are extremely hard.

Edited by CaptainSlug, 06 August 2010 - 12:22 PM.

[Doom]

Yeah I ordered one of those last year to inspect it, they won't work.
Those are meant to seal at thousands of psi inside of hydraulic rams. They're made of a composite fiberglass and are extremely hard.

Any particular reason you don't think they'll work? I've used them for years in water guns. See this water gun for an example.

At first I thought they wouldn't fit in the pipe, but once I hammered it in and lubricated the seal, I was very happy. The friction might be a little higher than usual, but the seal was perfect. And they're very straightforward to install.

Edited by Doom, 06 August 2010 - 01:41 PM.

[CaptainSlug]

Any particular reason you don't think they'll work?

The 2" piston cup fits too tightly to work well as a spring plunger seal. The spring simply can't overcome the friction it creates well enough to get the plunger head up to an effective speed.
A shaft seal might work if stretched, rubber washers work okay, or o-rings could be used. At the moment I'm getting 110 to 120 feet when using rubber washers, which are also the cheapest option out of the three.
I will experiment with shaft seals next, and may not even bother trying o-rings because they're more temperamental to get fitting perfectly.

Edited by CaptainSlug, 06 August 2010 - 01:55 PM.

[td667]

Great job man!

[Draconis]

While it does not appear that McMaster stocks a 2" OD rubber grommet, Fastenal does. http://www.fastenal....=0709137&ucst=t They do have a pretty wide ID, but they are also orderable in single quantities, and are less than $1 each.

[burning-ice]

When can we expect a write-up on this creation of yours?

[CaptainSlug]

When can we expect a write-up on this creation of yours?

In a week or two. I have templates and the part list done, but I need to make two more working examples with so I can take pictures through-out the process.

[Salmon]

Excellent work Sluggy, I think one of these with a Chopper and some pump-action action would be very formidable in any war. And the catch design is nice and simple, I really like it.

[VACC]

I forgot to mention. Want.

[burning-ice]

When can we expect a write-up on this creation of yours?

In a week or two. I have templates and the part list done, but I need to make two more working examples with so I can take pictures through-out the process.

Yay! I'm excited for this. As far as the one you own...Ranges?

[lionhawk]

I'm gonna get this/make this sometime soon, this looks awesome.

[phillypretzel]

Maybe you already answered this, but does the catch at the end of the plunger rod require a lathe to fabricate? Thanks, and fabulous work (again): can't wait to get my hands on one.

[k9turrent]

Maybe you already answered this, but does the catch at the end of the plunger rod require a lathe to fabricate? Thanks, and fabulous work (again): can't wait to get my hands on one.

No I've made a simillar catch in the last couple days, I only needed a drill and dremel for the face plate and a set of hardware for the rod

[CaptainSlug]

I've finished machining and documenting the second 2-11. I will start compiling the write-up now, but it may take a free evening or two to get the whole thing written.
Until then, more teasers.

Optional pump-action

Total part cost: $35

Edited by CaptainSlug, 17 August 2010 - 06:59 AM.