Wednesday, July 1, 2015

Raygun XIII

I've finally hit the part of the CAD I thought might take a little time. Just as I'd reached the point in project scheduling where I was hoping to blow through and not take a lot of time, of course.

To wit; not just getting all the parts connected, but fitting all the internal mechanisms in there:

There is surprisingly little space. I thought, since I was creating the shell from scratch instead of depending on the vagaries of slush-casting, I'd have a lot more wiggle room. But there's not even room for the battery capacity I want. 

At least I'd foreseen having issues with the trigger. I was smart enough to make a scaled mock-up, complete with spring and stop pins:

If I'd been at the shop I would have laser-cut these pieces from the actual file. As it is, they were achieved through the high-tech method of tracing directly off the computer screen. And then I wasted more time figuring out how joints work in Fusion 360 so I could test the completed action in software.

Notice how many iterations I had to go through before I found a working compromise between room for the finger, a decent take-up, and a comfortable action.

Of course getting all the other parts into CAD took a little time with calipers (I actually ran down to the hardware store to make sure I was measuring the exact hardware that would be available at assembly time):

The electronics are from both Adafruit and DigiKey, with a last-minute replacement of the limit switch with one with a stiffer action from, of all places, "Sprint-Shack." Oh, and yes; that's a quick CAD mock-up of my own DuckNode LED controller. Which only barely fits -- this thing really is tight inside.

Of course all these complicated shapes do no-one any good if they can't be manufactured. So as another sanity check, I set up several simulated CNC runs in Fusion itself (I'll probably be working up the actual G-code in the simpler Cut3d). There were various issues with fouling the tools, but with end mills at the longer end of the range I was able to get all the cuts completed -- and get a sense of how much the final aluminium is going to vary from the CAD version (and important question when there are so many pieces fitting so tightly together!)

And maybe CNC isn't the answer. Besides the way that all the corners will be rounded over (unless I spend even more effort with pencil mills and hand files and so forth), there's the matter of time and the cost of tooling. So...will Fusion 360 export in a file format Shapeways will accept, and what is the cost of printing these parts there?

It will, and, oddly affordable. Using the aluminium-powder infused SLA as rendered by Shapeways, above, that piece alone is $40, meaning the entire gun could probably be run off for around $160. And the only real change to the files is to put the bolt holes in, but set them for the self-tapping qualities of sheet metal screws.

So it will work. If I can't CNC it, I can print it. And although it is a tight fit, there's nothing critical about the electronics. Well, except maybe for the speaker. I'm also having a lot of questions about whether that surface transducer is actually going to work. I flirted for a number of hours today (I guess this was a long day!) with having a separate "sounding board" that was fit into the gun and secured with JB Weld, but the theory is really that the whole gun becomes a vibrating surface, and there really wasn't room anyhow. 

Lastly -- this has been a rather busy week, really -- I made it out to TechShop for a class on the ShopBot. So now I'm checked out on a machine that can rough a 3d shape out of MDF very quickly, working off a good 3d model. Which was all along a possible approach for this thing; do an MDF master, then use it as a buck to pull ABS on the vacuum-former, or mold it up and slush-cast in plastic.

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