Mendel 90 Resurrection

Mendel 90 after cleaning

     Last august my local Craigslist turned up a piece of 3D printing history, a Mendel 90 scratch-build. It was in a sorry state when I got it, what follows are my modifications to convert it into a functional and semi-modern machine. Not shown is that it was coated in cobwebs from a couple years of disuse, so I started with a good cleaning and then it was time to strip parts down for upgrade and repair.

TR8 lead screws installed

     As I received it, this Mendel had M8 or 5/16" threaded rods for the z-axis movement that looked to have been twisted with a vise or badly mishandled, result was a 20mm bend out of true over the entire length so the printer was functionally limited to half of the original 200mm build height. I had a couple TR8 lead screws leftover from an older project, so the first fix was to rebuild the x-axis with updated ends to integrate them. Then it was time to do something about the extruder and electronics which were both non-functional.

Mendel 90 with corrected extruder being tested

     Turning over the electronics turned up some burnt traces on the Ramps board, mostly those related to the heated bed control area, so not critical to basic motion testing, but I swapped it out with a working spare regardless. The extruder that was installed originally was a Greg's Wade reloaded for 3mm filament, not ideal considering the hot-end is an E3D v5 clone for 1.75mm filament. Fixing this was mostly just tracking down a compatible 1.75mm version of the extruder body online, then printing and installing it. With those quick fixes done it was time for a full scale test-print.

3DBenchy attempt with original extruder and gantry

      After several weeks of fiddling with it this was the best result I could get out of it. The main issue was the gantry jamming on one end and flexing at strange angles, often half-way through a multi-hour test print. Eventually I decided to rebuild the x/z gantry setup with a more modern design to fix this issue, ultimately settling on the 'Bear Exxa project' upgrade since I'd used some of the parts from it in refits to the Sculptor over the last 3-4 years and they've proven to be some of the most sturdy parts on it.

Mendel with Bear Exxa half installed

     Installing the axis upgrade was simple, the project has excellent documentation and assembly instructions, so it was mostly making minor tweaks to accommodate the Mendel's design, mostly mirroring things from left to right since the Mendel design is flipped in that direction relative to current i3 designs. The largest change needed was cutting a strip off the right-hand side of the electronics bay to compensate for the x-axis motor position change. With that sorted out it was time to fire things up and test the print quality.

3DBenchy on Mendel Bear

     Much better print quality strait off, guess that's what almost 10 years of design refinements will do to things. I've yet to install the part-fan assembly and a couple other components but this is much better than the melted mess from the inital testing. Overall it's been fun reactivating this old relic and turning it into a reliable printer for future projects.

Mendel Bear ready to print