Home Straight

Home Straight

Sunday 25 March

As well as being a pun on CNC'ing in general, the title refers to the current state of the cage build. We're not home and dry - I still need to do the base-plate, but since that will have to support the PCB, it will need holes drilled in it for screws that match the holes on said PCB, so I'll wait until the slots PCB is finalised before doing the baseplate. There's also some tweaks I could do to better-centre the mounting holes on the baseplate - we're not quite perfectly centred on one of the holes; I'll roll that into the final iteration. However, we're definitely on the home straight, if not home and dry…

This is what the most-recent piece looked like before being removed from the Carvey:

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Worth noting is the positioning of the clamps. Milling Aluminium this thin can be awkward because the bend in the sheet can be significant, but also because the sheet can vibrate significantly while it's being machined. The design above makes this a lot worse because there's a lot of cut-outs in the centre, further reducing the structural integrity of the piece, and making it more prone to vibration.

The solution I came up with was to make the source-sheet I was machining as small as possible so I could place the clamps as close as possible to the work-area, and to space out the clamps regularly along the piece. To simply hold the piece in place, only one of the four additional clamps would be required, but to keep vibration within acceptable limits, not only were all the clamps required, but their positioning was important too. I originally pointed the top-left clamp such that it held down the top-left corner, and the huge gap between clamp-points along the long top was too much - the Aluminium sheet was vibrating like a piano string. Shifting the clamp to be more central damped out those vibrations enormously, and the rest of the cut was uneventful.

After taking it off the workspace, popping out the internal bars, bending the appropriate pieces in the appropriate ways, and putting the rivet-nuts into the top-bar it can be assembled thus:

Stacks Image 1099
Stacks Image 1102
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As far as design goes (if not colour) it actually blends in quite nicely with the rear of the existing case. Now if only I had black-anodized Aluminium...

I *do* need to take off the tab-remnants with a file, and smooth down the edges of the metal to get rid of any burrs, but this is basically it, apart from the base-plate, which isn't hard - that's just a series of drills (slots and holes) followed by an outline cut. The only tricky thing with the base-plate is the positioning.