34 replies to this topic

[Carbon]

For a compression spring I refuse to believe that a shorter spring is harder to compress until I see a verified source. F = -kx, so if you cut it down, x is then decreased because you can't compress it as much, resulting in a smaller force.

Changing the number of active coils will change the spring constant (k).

http://www.engineers...comp_calc_k.htm

[Diablo]

Thanks, Diablo. As far as a clip, I've decided that I dislike them. Sure, I can hold six or eight shots, but it increases the chances of a jam (at least in my designs), and makes it much slower to reload. I'll take four shots over six less reliable ones.

That being said, I hope to improve the range. 65 feet isn't awful for a multi-shot weapon, but I'd be a lot happier with 80 feet.

More tweaks to come...

I wasn't aware that you had four shots already on this gun. I read the topic a little more in detail and saw that you referenced to an inline clip. I took a look at your previous SNAP designs to get a look at what this clip is, but the images aren't showing up in the older topics (at least not for me.) Could you give a brief rundown on how the inline clip system works? I saw that jwasko already asked you a question about it, but I'm still a bit puzzled.

As far as your attempt to improve range, I also think a longer barrel will help you out. If not, possibly a barrel with a slightly bigger ID?

[Carbon]

Could you give a brief rundown on how the inline clip system works? I saw that jwasko already asked you a question about it, but I'm still a bit puzzled.

Sure.

An inline clip places a looser dart storage area in between the plunger and the actual barrel. The barrel is removable, and darts are loaded by dropping them in. The rear of the barrel is also flared a bit, to let the darts in without snagging. When fired, the air moves past all the darts, pressing the lead dart into the barrel and firing it. All you need to do is tip the gun down for a moment to seat the next dart.

I can't believe I didn't tag this gun for an inline right away, as the cocking lever is perfect for it. Looking a this picture:

The PVC to the left of the coupler is standard 1/2" schedule 40 PVC, and serves as dart storage (clip). The barrel (to the right) has brass nested in it with a flared end. The only part which I didn't properly show is the nylon washer that I have seated in the base of the clip. That keeps the darts from falling back into the plunger tube. I'm also using something Frost Vectron came up with, a small chunk of aluminum tubing in the clip to help move the darts forward.

Inline clip links:
The SNAP-4 with inline clip
My first inline clip posting
Frost Vectron's Sawtooth mod

Let me know which topics have missing pictures...I did some server work a few months ago and broke a lot of links. I fixed most of them, but there's a few I missed.

Edited by Carbon, 10 August 2010 - 07:59 PM.

[sam]

Switch to PETG! If i remember correctly your darts had a near perfect fit in it.
On a side note, I was messing around with this over break on my x-bow. Here is what usually happed, Fire once, and the dart wouldn't leave the barrel, then after that, it seemed to work just fine with each of the next few darts. I was using a 6" barrel with a 6" sch. 80 clip. Happen to know what was going wrong, or how to make it more consistent?

[Carbon]

Yeah, I know, I'm one of the last brass holdouts. Eventually I'll get some to experiment with.

As far as your inline, are you putting too many darts into the clip? I've found that the darts need a bit of rattling room...I have the same problem with this gun. I've discovered that if I put in four darts, I'll get a double fire, or a non-fire. If I use three darts, I'll get accurate firing every time. Four darts extends past the end of the clip, and shoves into the barrel when I put it on, so that may be the problem. Your clip may need to be a half inch longer...or try putting in one less dart.

[Prometheus]

For a compression spring I refuse to believe that a shorter spring is harder to compress until I see a verified source. F = -kx, so if you cut it down, x is then decreased because you can't compress it as much, resulting in a smaller force.

Changing the number of active coils will change the spring constant (k).

http://www.engineers...comp_calc_k.htm

Fuck. Thanks for correcting that. Glad you took the time to prove me wrong, not many people are worried about verifying their data. Props Carbon.

Edited by Prometheus, 25 January 2008 - 01:09 PM.

[Carbon]

Heh, it wasn't proving you wrong, so much as seeing what was actually right...I thought the same thing. Thanks to DeceitfulSteve for pointing it out.

[Carbon]

Lumpy bumpy mess be GONE!


I'm trying to eliminate the use of glue in all aspects of construction, so I came up with a new method of handle attachment. It's very similar to Ompa's preferred method, but simpler. This handle is made from 3/4" PVC, in the Boltsniper method. I took a 1/2" CPVC endcap, hammered it into the center tube, and then screwed it in from the sides. I drilled a guide hole from the bottom, and then an access hole on the top so I could screw it in. It's solid.

Likewise, I finally did what I should have done from the start: the clothespin is attached with a screw driven right into the PC. I cut the screw short with a dremel disc (the tip would bump the rear of the plunger, otherwise. Shorter screws would probably help).

I also made a new inline barrel. It's currently 9" of brass, going from 19/32" to 17/32" (joined in the same method as my pump action breech). The brass isn't glued into the outer PVC sheath, just held in place with o-rings. I haven't tested range yet, but darts are no longer fishtailing. Whether it's still a bit too long to get maximum range remains to be seen.

Edited by Carbon, 10 August 2010 - 07:59 PM.

[sam]

So, wait, what is the Handle screwed into? Does the trigger being screwed in help keep the nail from coming out of the PC?

[Carbon]

So, wait, what is the Handle screwed into? Does the trigger being screwed in help keep the nail from coming out of the PC?

The CPVC endcap that I jammed down the handle gives me something to screw into from inside of the pressure chamber (but behind the plunger). I drilled a hole in the top of the PC so I could screw the handle on, from the inside of the PC. The screw on the side of the handle keeps the CPVC from popping out.

The screw in the clothespin doesn't keep the nail from popping out...it's just better than hot glue. Although, using a longer screw as an adjustment on the clothespin to keep it from opening all the way is a good idea....