Water Cannon

The Challenge
I was talking to Ralph Renzetti last night on Skype and he mentioned a problem with Shapeways in that he had found what he wanted at Shapeways (HO Water Cannons).. but .. he only needs two of the things .. not 20! He is building a rail grinding train and one of the things is a caboose with water cannons to put out any brush fires started by the grinding. I told him .. well .. I can probably do that .. and so this then .. is the result.
Elkhart Brass
pdfThis company produces Fire Fighting Equipment. Their Elkhart Brass Website has a download section including both 3D models and dimensional pdfs. While you may at first think the 3d file would be helpful .. in the end it would be serious pain to convert for a model. In the end the PDF is the easier way to go. We ended up with a PDF showing this company’s Water Cannon – the 7200 Cobra.
The Front – perhaps
frontI used the ‘Snipping Tool’ to grab a screen copy of what I call the ‘front’. I had to call it something and I figured that was as good a name as any .. I suspect it was better than say .. “Henry”. This gave me all the major structural parts .. being mostly round .. and very important .. a couple of dimensions. I saved this as a .png file as that keeps it’s detail .. a .jpg uses lossy compression and not as well suited for things like lines.
Tracing and Dimensions
front_dimI imported the file into Sketchup as an “image”. Now .. you can think of it much like a drawing under a sheet of tracing paper. I can now trace the drawing. I kept each of the major components with the intention of converting them to primitives. In the pic I colored them green, yellow and blue just to tell them apart. Each is grouped separately .. so they are individual objects. Notice I didn’t trace the twisty tube .. the “snail” .. not yet.

Next with that done I need to scale the drawing. Notice that there is a vertical and horizontal dimension on the drawing. I simply put a line at the top and bottom of the cannon and used the “Tape Measure Tool” to scale that dimension to the 19.416″ in the drawing. Instantly .. I have it scaled.

I put dimensions on just about everything I might need. I acually forgot a couple but that’s fine .. I kept this “dimensional Drawing” to one side in the Sketchup screen so it is easy to add dimensions I had missed. It is pretty easy to tell the dimensions are close .. that 3.076″ dia. on the output nozzle is only .076″ over 3″. The flange at .748″ is only .002″ over 3/4″. This was good to go then.

front_dim2Creating the flange, body, swivel, valve body and nozzle (my terms) was easy as they are all cylinders. Again .. each color is a separate object .. grouped .. which makes it easier to move things around and make changes as needed until you are happy and merge them.
The ‘Curvy Bit’
snail_1Using just the “Line Tool” and the “Arc Tool” I drew the tube that snakes it’s way between the base and the upper portion. The idea was to try and follow the lines of the drawing as best I could .. portions are hidden by pieces of the cannon .. but basically keep the lines flowing. Here .. I put it up against the extruded primitives just .. “for grins” .. as it were.
and the Fun Starts!
snail_2With all of the basic work done I can start on the curvy bit. I’m going to call it “the pipe” for the purposes of this article.

  1. The last picture is to the far left ..
  2. then just the pipe ..
  3. then .. I have broken the pipe into five parts. The three curved elbows will have magic applied to them. The two thin sections will just be extruded from the elbows.
  4. Finally I have drawn circles for the openings of each elbow along with an arch from center to center.
Curviloft Plugin
snail_3I used a great plugin – Curviloft. I used the tool “Create Loft Junctions following a given path”. Very simple to use .. you select the circle and arc for each elbow and run the plugin. It creates an object starting with the first circle to the second circle following the arc. You can do some crazy things with this tool such as lofting from a rectangle to a circle along a path .. but for this .. easy.

In the photo I also show where I extruded the two disks. This wasn’t needed as I realized I simply needed to extrude the right end (as shown) of the second elbow and the bottom of the last.

Step 1 – complete
snail_4I calling this “Step 1″ .. most of the parts arranged where they will go so I can get a look at it.

I need to add on the other ‘bits’ seen in the drawing .. squarish blocks, rectangular boxes etc. I’ve found that it works better if you build your mesh slowly .. cleaning it up as you go. If you add to much at once time you can run into problems with too many intersections – just take my word on that.

At this point the model is still full size. The next step will be to make a copy and re-size that to scale. I am doing one for Ralph in HO and one for myself in O scale.

I leave details to after scaling since this is a VERY SMALL model in HO and you will quickly start to run into the 3D printing constraints. This collection of primitives will easily scale down. The cylinders themselves are small .. In HO the one sticking up (3″ dia output nozzle) will be only 0.035″ dia. That is well within the minimums. The only issue the flange thickness in HO. At 3/4″ .. it scales to 0.22mm .. which is below the minimum of 0.3mm for wall thickness. That will be thickened to that .3mm .. which will scale back up to 1”.

So here is where we leave this for a while. You can gaze fondly at the body primitive while I go to Step 2.

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