Monday, September 8, 2014

The Arduino Problem

There's probably another name for it. I think of it in terms of the Arduino shield, however.

When the first Arduino board was made, due to either mistake or some rationale which has long been forgotten, one of the headers was offset by about half a standard pin space.

This meant that protoboard doesn't fit on top of an Arduino with standard headers. And that meant that ever shield (aka the stackable daughterboards which fit on top of an Arduino and add functionality) had to echo this error in pin placement.

So what happens when the next edition of an Arduino board comes out, or a third-party wants to make a compatible? If they want to remain back-compatible with the existing shields, they have to reproduce that same pin spacing. The Arduino board is basically stuck with it, and the longer it goes uncorrected, the more difficult it would be to correct.

I'm in a similar spot with my grenades. I was noticing today as I was cutting tape for the tops that my hand-ground 3/32 grooving tool has shrunk to close to 1/16th. And there are a couple places where I may have been mislead by my earlier research, or that I find aesthetically compromised; the button should probably be shorter, the "crimp" further from the base, the grooves deeper. And I really should have worked out how to give the blue and green caps a different visual look.

Plus, there's multiple places I've learned better ways to machine, or necessary choices. Like adding a "tape slot" to the solid-body grenades, or like the changing angle on the "crimp" so it can be cut without scratching the metal of the base.

But I'm already shipping second orders to previous customers. So I have to keep as much of the look of the very first production run, in order that they continue to look like they are identical. And as much as possible, matching the look of the other major fan-made runs, so one cosplayer can get away with wearing a dozen cold-cast grenades from another builder on his webbing, and using one of mine as a "hero" prop.

I'm still tinkering with the process. The last two full-function ones took 2.5 hours each from start to finish. I'm leaving the compound rest at 15 degrees through the process and only moving the turret twice. As another trick, I clamp the bits into the tool holders at an angle (I can get away with stuff like this on aluminium!) That way, I can leave the tool holder aligned for grooving, and make several of the tool changes without losing zero on the DRO.

I'm still finding little tweaks. I just realized today I need to break the internal edge of the through-hole; what happens, is when I press the plug in the front of the grenade is very slightly deformed. And in some, the rough, sharp edge of the front of the hole now pinches the button and scratches it when it is pressed.

I've also realized that pushing a "dead" tool (that is, with the lathe stationary) into the metal to find zero is a bad idea; I'm leaving tiny pock-marks on the piece.

And so it goes. I'm eager to stop lathing these, and move on to something different.

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