2020 corner plate

Update 4 years later and being more experienced; do not use this. PLA is not stiff enough for a printer frame. Use aluminium or steel brackets. Blind corner joints + 2028 brackets create a very stiff corner at just 50 cents worth of hardware. Use 2028 brackets instead of 2020, it makes a big difference.

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I created this part to be quick to print (30 minutes) and to more easily construct square frames than with the standard a