Retro-fit a CNC engraver or router to make a 3D printer?

I am new to this idea, I have a Xenetech 3D printer that I have used in my shop for more than 15 years, bought it used in 2000 but the control MPU finally cratered (showy failure, lots of smoke & bad smell). At any rate Xenetech wants about $5K to repair and replace the MPU, says this one is totally obsolete. I had been using the engraver to engrave steel sideplates for machineguns, It served well for several years and would entertain the notion of setting it up to be convertible to a 3D...

Retro-fit a CNC engraver or router to make a 3D printer?