LACK external MK3 LCD holder

Maintains door openability with more LACK enclosures stacked on themselves. 
Enables you to control the printer without having to open the enclosure. 

LCD cables must be guided onto the top of the printer's frame and then towards the front of the enclosure. Cables are long enough.

LCD cover from the Bůža MK3B upgrade fits.  Use the lack_LCD_HOLDR instead of the stock LCD holders mounted to the front plate of the printer's frame.