One thing I'd like to get out of the way immediately is that this is not a full write-up. Most of the focus is on the PVC pipe and fittings one can obtain in the States to make an SG-style ring catch blaster (I'm just choosing to use the acronym RCB). So essentially parts that are imperial rather than metric in their dimensions are being used. Besides the catch, this thing most resembles and functions like an RBP.
Inspirations for the blaster:
The overall mission of the project was to create something very comparable to a rainbow, but using as little parts that have to be ordered online as possible.
My goals were:
1. the catch is reliable as a rainbow's
2. the blaster is cheaper than it's rainbow cousin
3. no scrollsaw, or any other large shop tools required (a dremel is necessary, however, unless you like filing things for hours on end)
4. parts obtainable at local hardware store
All goals besides 4 were met. The blaster's powerhouse (a [k26]) and the pump slide were not purchased at my local Ace. The spring is from Mcmaster, and the pump slide was machined from a piece of an old water gun (one of those huge push-plunger ones).
While I won't detail the making of the entire blaster, I will go over some key parts of the design that I either haven't seen elsewhere or think that people could benefit from seeing. Most everything else is pretty easy to figure out.
Tee/Ring Catch Assembly
Below is a picture of the exploded assembly. Fittings are labeled. Note that the two pairs of reducers and garden hose fittings must be modified before everything fits together. Essentially the purpose of all this is a sturdy way of attaching the tee to the two 1-1/4" PVC segments, that requires minimal amounts of e-tape for spacing.
The first order of business is cutting the slot for the catch ring. You can really just eyeball it.
Next things to be sliced up are the garden hose fittings. Cut off right where the ridge protecting the threads is, as shown in the picture below. Do this to both garden fittings. Essentially what these do is act as perfect spacers between the 3/4" tee and 1/2" PVC that will be used to keep the catch in place.
Shove in some thinwall 1/2" PVC, be sure to use more than you think you'll need. You can see how at the end of each fitting is a segment with a slightly tighter ID, kind of like the ridge on a coupler that prevents pipe from going into the connecting pipe's area.
Now put one of the segments into the tee, pushing it in until the tee won't allow the garden fitting to go in any father. Make a mark, slightly off from the center of the tee, where you'll cut. So probably a tad more than an 1/8" or so. Don't worry about it too much, I eyeballed it. Just keep in mind that too small and your catch ring could snap or warp, too big and the slot in your plunger rod's notch will be too large.
Cut it at the mark and copy the cut onto your other pipe/fitting assembly. They should be nearly identical. Next prepare some regular walled 1/2" PVC for use as the catch. I first tried thinwall, but it proved too flimsy and would bend underneath the adjacent segments of pipe. Simply drill out a short segment of the normal PVC with a 5/8" bit. Then measure and cut out your ring. I went a little large, and then sanded it down to get a perfect fit. I recommend doing the same. You want it to slide vertically with minimal effort, but don't want much horizontal wiggle room.
Time to mutilate the reducers. Cut as marked in the image. The thinner segments are what we need, the large ones can be tossed.
Slide them over the exposed garden fittings. In the image below I've only put one on. You may need a little e-tape if the fit is too loose.
Drill, tap, and screw as shown. Socket screws are a must. Do the same to the other side of the tee. The screw placement leaves the reducer segments unconstrained, but that's not really an issue. They won't be under much tensile force, and will be screwed in later anyways.
Add e-tape around the tee as shown. You want the fit in 1-1/4" PVC to be very snug.
One last thing I need to address about the tee assembly is how you affix it to both 1-1/4" PVC segments. Screw placement is very crucial, what with all the different fittings and spacers used. I placed my screws on the top and bottom, to avoid the internal screws on the sides of the tee. On each side I have two screw, one on top and one bottom, that go through the e-tape and directly into the tee. They stop when the hit the inner walls of the thinwall PVC, as to not interfere with plunger travel. The next pair go through the center of the reducer segments, again one on top and the other bottom. They also go just as deep. I believe I used 1/2" screws, but they could have been 3/4". I forget which and will check later. So total, that's 8 screws, 4 on each side of the tee, 2 on top and 2 on bottom. Below is a diagram that helps show the assembly, but mainly shows screw placement more accurately than I can describe in words.
Plunger Rod Reinforcement
One aspect of Sg Nerf's design that I cringed at right off the bat was the catch notch cut into the PVC plunger rod. While I can't speak for his, I know that when I tried replicating his design, my plunger rod was horribly flimsy, and even though the plunger would be submitted to horizontal tensile forces, I still feared bending at the notch would be a significant issue. PVC is pretty soft after all. To remedy this I ran a slightly sanded 1/2" wooden dowel through that part of the plunger rod. It's kept in place (despite the friction fit that a hammer would barely budge the dowel from) by two socket screws.
Edited by TantumBull, 15 August 2011 - 06:06 PM.