Monday, July 6, 2015

Raygun XIII.II

So still haven't started cutting metal.

Been working hard to get there...pretty much exhausted myself; ended up crashing early on the evening of the 5th and sleeping over ten hours.

Where I am now, is where design for function, design for assembly, and design for manufacturing all butt heads. The shape of the gun is fairly fixed now; it's been through too many stages of prototyping and approval for me to make significant changes in dimension or shape. So I have to design the actual milled parts to support that shape.

Which also, of course, have to fit together. And it has to be possible to assemble them (not the same thing; this takes into account assembly order, tool access, and so forth). And they have to be manufacturable. Which is to say; I need to be able to create those shapes on the mill.

So one of the things I've been pushed into over this past week is to generate all my GCode in Fusion 360. There's one obvious utility; this means I can tweak the GCode right on my laptop during the actual milling session.

The stronger necessity, however, is to have better selection over which operations are performed on which part using which tool.

The CAM software I learned (and cut with) previously looks like this:

It is a friendly-looking interface, with helpful pictures. Fairly powerful, and even more advantageous, it has already made a lot of the more complicated decisions for you, presenting a simplified pallet of choices that is easy to navigate.

The CAM interface for Fusion 360 (which apparently is based around a fairly mature existing CAM package they licensed) looks like this:

There are a lot more options.

The advantages here are several; first, you have more algorithms (such as the spiral finishing path above) that can optimize speed and final finish. Even more importantly, there is a lot more choice in what you cut. In the above, the finishing pass is restricted to just the object itself; it isn't attempting to make passes through the entire bounding box.

But beyond that -- for several of the parts I have, I need to make sharp corners in order for them to fit together. But these same parts also have compound curves that need to be gone over in contour passes with a tiny ball-end end mill. Fusion gives me the opportunity to create specific operations that will place the flat end mill right into those right-angle corners, whilst leaving clearance for the finishing passes on the rounded bits.

More or less. It takes even more work to set all this up in the files. In a number of places I am better off re-thinking the mating surfaces so I don't have to do these passes this way.

And the big downside is I don't know what a lot of the options actually do. Which means I have a lot more work in setting up feeds and speed and clearances to make sure I'm not going to crash the head or do something else nasty and expensive.

Oh, yes. And I spent a while worrying about whether I could even get the end mill down into some of the deeper features (especially on the main body, which is over 1.5" wide). I looked up various end mills at Grainger and other companies, pulling down lots of numbers on available flute length (the real key to cut depth), as well as other numbers for stick-out and collet clearance.

And I'd forgotten that when I ran off my first test part, I'd already purchased my own starter set of mills. And the primary one has a nice generous flute length that is at least 1/8" larger than any of the ones I'd been looking at. Long enough, in fact, to have no trouble at all reaching down into the deepest pockets on my workpiece.

That still doesn't solve everything, though. There are still spots where the cut is going to end up rounded over, and I have to compensate for that in the mating surfaces. And there are still a few spots where I didn't think out the geometry properly and some of the cuts are actually impossible (as in, overhanging material). So I still have a few days of tinkering before the files are really ready.

And then when I hit the machines, I expect to find out a great deal more.

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