Monday, March 23, 2015

Raygun XII

Basic shape is in CAD now:

I used a picture of the rough model as reference, adjusted a few details in the direction of a sketch I showed the client...then after building most of it, went back and tweaked again.

I'd made the body a little fatter than the mock-up (as well as leaning the "bulge" forward towards the barrel more) but after I'd placed everything else it was just too much. So I re-scaled. Rather; deleted one half, scaled the remainder, re-aligned it along the drawing planes, and mirrored it. If you are careful, there's a lot of elements in the "stack" of operations in Fusion 360 that remain parametric quite late into the modeling process.

I'd like to try making the rings a little bigger, also the "sight" a little smaller. On the latter, though, it is just barely large enough to contain a 5mm LED.

In any case, the current task is figuring out how it will all assemble. I'm half-tempted to smooth the fins and grip into the body with nice gussets, but that would mean one massive machining pass for each side, and a larger billet. So it seems most sensible to break it into body, fin, handle, trigger guard, reflector dish, nozzle rings, front nozzle escutcheon.

In fact, I am thinking the escutcheon may be lathed out manually. And also possibly do the same for the "sight"; that would make a cleaner shape, and more importantly, save a lot of time in CNC machining. Plus, then, the fin might be made in a single piece instead of fitting two pieces together.

So this takes me deep into what they call "Design for Manufacture" (which includes as a subset "Design for Assembly.") Fortunately, again, I have a couple decades of theatrical scenery and props behind me in figuring out what order things have to happen in order to be able to reach the bolts for one part that will be later hidden by another part.

It doesn't make it easy, though. Especially in a basically new material and process. I have to keep in mind as I go the likely tolerances of the various processes -- high on the list, how well I'll be able to align the billet for top and bottom machining steps.

Plan that looks best is that most of the parts bolt into the main body; the fin, handle, and trigger guard can all have tabs that slot into the main body then are bolted into holes tapped in the main body. If I was more sure of my fit-up I would just use tabs and close fit, but I'm not and I don't want parts to wobble. The main body then slips together with a locking tab at the back (which will have to be manually milled) then a couple of bolts in front; these get hidden by the donut assembly, and that in turn gets held on by tightening the nozzle escutcheon down on a set of threads.

Already I have two problems with this scheme; getting a tight enough join at the rear, and the fact that the escutcheon doesn't have wrench is hard to access due to being inset in the reflector dish.

The scheme I'm toying with for the "sight" is to lathe that separately, and have a tab from the fin go into a milled slot, where it will be retained by a threaded pin driven from one end of the sight. But this gets a lot more complicated with the LED and the turned acrylic "nose" (the part that gets illuminated) having to somehow be attached. At least for those, glue should be sufficient (and well allow access later if necessary -- an important part of any assembly plan).

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