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

Ender 3 Upgrade: Dual Extrusion with SKR 1.3

Endurance ready to print

      Time for the reveal of a long-term project that's been around in various forms for a couple years, Duel-extrusion. Back in Febuary I'd started to experiment with converting my Ender 3 to dual-colour extrusion using a spare Lite6 hot-end and V6 clone that I found on Amazon.

Thing:3516409 mount

     Mounting the hot-ends for initial testing of the idea was fairly simple, there's lots of good mounts for V6 series hot-ends on Thingiverse, I specifically went with thing:3516409 to start with since it allows for reconfiguring from single to dual extrusion with only a couple printed parts as mounts. The next issue to tackle was electronics.

Ramps stack on Ender 3

     Now, the Ender 3 default electronics are fairly good for a basic single extrusion printer, but don't allow for duel nozzles, so I swapped the silent 1.1.4 board from my last upgrade out for a spare Ramps/Mega2560 stack that I normally use on my MPCNC. The Mega2560 isn't rated for 24V power but there is a fairly old work-around that solves this problem on the RepRap wiki, I then wired a spare LM2596 buck converter to provide the needed 12V power for the processor board's onboard regulator and the hardware side was ready for inital testing.

BigTreeTech SKR 1.3 with stepper drivers partially installed

    Unfortunately, this was right at the start of April 2020, so testing things out got put on hold until June since all of my printers were fabricating PPE gear as part of BCC3D.ca's efforts. This showed that Ramps at 24V is ok for short-term use, but I had one of my extruder stepper drivers blow out, so a better solution was needed for long-term usage. Some research on newer 32-bit boards showed that the BigTreeTech SKR 1.3 board fit the needs of this upgrade perfectly.

Custom dual hot-end mounts

    The other short-coming that was revealed was the dificulty in aligning the duel hot-ends correctly since this type of dual-extrusion setup needs the nozzles in the exact same horizontal plane or close enough to make no difference with the intended layer-height. The Thingiverse mount had both hot-ends locked at the same height at the top but not at the bottom, so I pulled a copy of the Ender 3 source-file into Fusion 360 and started drawing up a custom mount pair to fix the issue. 

Design in progress

     My solution to the problem has the right-hand hot-end at a fixed height bolted to the stock hot-end mount posts since that's the zero reference point for the entire printer coordinate system. The left hot-end is tucked into a dead-space on the side of the tool-plate that's normally used for mounting optional auto-levelling probes but is the exact right size to fit a V6 heat-sink while allowing both nozzles to reach the full width of the bed. With all that sorted out it was finally time to calibrate and try this out.

First Duel-extrusion print straight off the bed

     Now, obviously there's a fair bit of slicer tinkering needed to get a custom duel-extrusion system setup, so I loaded a couple lengths of scrap filament into the extruders and printed several test objects (thing:2388496, dual block object) to get the horizontal offsets correct in the firmware, then created a custom version of the Ender 3 profile in Prusa Slicer v22 with some custom startup gcode to get things heated correctly. Other than that I just turned the 'ooze shield' settings on, drew up a simple vase as a test part and turned it loose.

First dual-colour print after inital cleanup

     Clearly things aren't perfect, still some tuning with the retraction settings given the blobs all over the surface, but I'm quite pleased with how it turned out for a first print after all the work that's gone into this upgrade. The SKR board has proven quite robust and reliable, been running it non-stop for about 4-months now without issue so they're now my first choice for new printer controllers going forward.

Design Study: Castor wheels from scratch

PLA Wheel

      While working on another workspace upgrade project, I decided to try making my own castor wheels from scratch using some leftover bearings that were floating around in the parts bin. I started off from the known dimensions the castors that are on the bottom of my main workbench, about 1.5 inch tall, and the specs of the 625 bearings that I was planning to use.

Castor wheel parts version 1

     A bit of drafting in Fusion 360 ended up with the version 1 parts, they worked fairly well once assembled since I've done rotating parts with 625 bearings before, but they weren't rotating around the vertical pivot like I was expecting them to when turning, so what was going on? 

Castor wheel mounts version 3

     I pulled up some example of high-end castor wheels online and quickly found the two issues with my design that were causing the rotation to jam under load. First up is that commercial castors actually have the centre of mass/vertical rotation shaft centred over the outermost 25% of the wheel rim area. This means that the wheel is constantly trying and failing to escape from under the load, manifesting as the sideways force that makes the wheels rotate to the point of least resistance relative to where you're trying to move them. 

Castor wheel version 3 with bearing collar installed

     The second detail is a simple mechanical part choice to make sure the wheels don't bind or stick under the load they're rated for, a simple ring of ball bearings around the vertical shaft between the wheel bracket and mounting plate. It's sort of a knock-off 'thrust bearing' more than anything else, so I drew some modifications into the parts to create a 3D printable version for testing and light load applications. Current plans are to use these for a small storage cart for around my workshop, so more to come later this summer.

Finished castor wheel version 3

Upgrading the Ender 3: Bond-tech gears, Bed Leveling Knobs and Part Fans

Ender 3 as currently configured

     After 6 months of using the Ender 3 in stock configuration I ran into a few areas that were showing signs of failing. So I thought I'd do a couple upgrades in the process of fixing them. Three key areas that were showing issues were the bed-springs, extruder idler arm, bed surface, and part-fan duct, so I picked out some upgrades for them.

1.75 mm Genuine BondTech drive gear kit.

    As the extruder is one of the highest wear parts on a 3D printer, any breakdown there is going to show up instantly in the printed parts. So I opted to upgrade to some BondTech drive gears with the original motor-end result is that I'm now able to print flexible filament without issue and haven't had a jam due to chewed up filament since. The housing is a PLA version of the official STL files from BondTech's website. They're surprisingly easy to print with an FDM machine-some slight supports in a couple minor areas and on the idler/compression arm and that was it.

Extruder Motor with BondTech mounting bracket

Fully assembled extruder block in use

   The next area that needed upgrading was my bed-levelling knobs. I came into the shop one morning to find one had spun clean off the bottom of the bed assembly from the vibrational force of normal operation. So I decided to install the same nyloc nuts solution that I've been using on my i3MK2 clone with some custom 3D printed replacement knobs.

Custom and Stock leveling knobs

New Leveling knobs fully installed, note M4 nyloc nut locking mounting screw

Flex-sure branded spring-steel build plate

    And speaking of the bed, I've been through a couple different printing substrates before settling on the current setup. I started with the official mag-bed upgrade after encountering bending issues with the strange flexible plate that came with the printer. The Creality mag-bed upgrade is much better than the starter plate, but the upper surface is far too rigid for practical use. Mine quickly developed cracks and started flaking apart with little bits stuck to prints. I was pleasantly surprised when a batch of spring steel plates that fit the Ender 3 build plate showed up on Amazon. It works perfectly with the magnet sheet from the official bed. I stuck some BuildTak on top and I've been using it ever since.

Radial part cooling fan (thing:3102082)

Electronics bay fan cover (thing: 3312856)

    And lastly are a couple upgrades from Thingiverse. First one is a 5015 radial part-cooling fan mount to replace the stock 4010 radial fan, (I've found that it gives about the same airflow with much lower noise levels, always a plus when working in the same space with the printer). The other upgrade is an elegant electronics bay intake cover, probably the simplest and most effective one I've found to date since it literally just snaps into place straight off the bed after printing. Combined, these two mods reduce the printer's noise level from a howl down to a minor background noise that is comfortable to work around.

Mega Kossel Upgrade: Direct Drive Effector with Titan Aero

Titan Aero Heat Sink

     Happy New Year! Over December 2018 I was experimenting with flexible filament, 90A TPE specifically, and ran into issues with running it on the Mega Kossel, so I decided to upgrade the extruder to full direct drive to correct the issue. I've had an old Titan clone in my parts bin since 2016, so the logical route to go was upgrading to the E3D Titan Aero with a pancake stepper motor.

Motor and Titan body mounted to modified Ultibots effector

     While I was waiting for the parts to arrive I started looking for an effector design to mount it on. The Ultibots D300 series design files turned out to have what I needed, but it was meant for some specialized type of rod-arm joint. Pulling the source files into Fusion 360 made it easy to customize both the effector and part-cooling duct. The remixed files are on Thingiverse (thing:3321195).

Titan Aero Volcano 90% installed

    Once the effector was sorted out, it was simply a matter of following the Titan assembly instructions to get it mounted and mostly assembled. Getting the drive gear in is probably the hardest part, it kind of has to be slid in sideways before the motor is installed, I ended up using the screw that connects the motor and extruder body to hold the body in place during that step. The idler arm is the other tricky bit, you need to slide it into its slot before installing the motor, otherwise it's a pain to mount, I ended up sliding it in at an angle and snapping it over the end of the motor shaft, not the best way to mount that bit.

Cooling fans installed, Noctua 4010 on the left, 40x40 radial on the right

    With the mechanical side of stuff assembled, it was time to mount the fans and sort out the electrical side of things. For the main heat-sink fan, I decided to get one of the much vaunted Noctua fans to see what all the fuss was about. The difference going from a 3010 axial fan for the heat-sink to the Noctua is instantly noticeable on initial power up, the 30mm fan was loud enough that I could always tell if the printer was on when in the workshop, the Noctua is completely silent by comparison, I can't even hear it unless I'm right next to the effector to clean the nozzle, so I'm probably going to replace all my constant on fans with them over time. Installing the part fan is slightly odd, there is one short screw to connect the fan duct to the effector that goes in first, then the fan gets slotted in and bolted down, the top hole needs a longer screw since it doubles as the second connector to the effector.

Wiring nest under the print-bed

    The last bit of installation was figuring out why the pancake NEMA17 wasn't working. Plugging in the working wire from the old extruder just resulted in the motor sitting there and making noise, so I thought one of the coils might be connected backwards or something. Digging into the documentation, it turns out that 25mm NEMA 17 motors have the coil pinouts reversed relative to longer models, so I had to use some jumper lines to build a cross-over cable to fix the issue, it's the black/grey/yellow/orange set of wires in the picture above.

Mega Kossel ready to print

Flying extruders and Deltas, Round 2

Mini Kossel and Mega Kossel with Flying Extruders

     Back in February, I tried installing a flying extruder on my Mini Kossel, didn't work out very well because one of the carriages would randomly slip during the first few layers of a print and suddenly it was air-printing and making a complete mess. So I switched back to the normal extruder configuration and kept it that way until I built the Mega Kossel

Mega Kossel Flying extruder V2

    For this version I decided to use elastic bands to hold everything in place, worked a bit better but still hit the same issue of random carriage slips. After watching it do this a couple of times I realised that the root cause was the extruder assembly's inertia damping the carriage movement and overwhelming the motor on the tower, causing the drive belt to slip on the pulley and produce the effect I'd been seeing. At that point I was just trying to get the new printer working, so I striped the flying extruder components off and set things up for a conventional long Bowden system. Further research into Kossel design was obviously needed to sort out what the solution to the issue was.

34mm (left) & 48mm (right) NEMA 17 stepper motors

    It was while building the Sculptor that I finally figured out the issue, it was the NEMA17/34mm steppers that were originally part of my Mini Kossel kit that were the root cause of the problem. Like most ~$300 kits, it had fairly light stepper motors for powering the motion mechanics, and while they were sufficient for normal use, I'd found some old forum posts that recommended longer NEMA17/48mm steppers for use on delta printers, and indeed I'd followed that advice when building the Micro Kossel in the first place, so I did a motor transplant and installed the 48mm motors on the Mega Kossel. The difference was quite noticeable once I powered it up and homed the effector. With the original motors it was possible to shake the effector about 3mm sideways even with the motors powered up, with the new ones the effector felt like it was glued in place, zero wobble or shake that I could detect. 

Mega Kossel Flying Extruder V2

    I used the Mega in that state until early November, then decided to try the flying configuration again. Surprisingly, it worked perfectly even without the counterweight that I'd used in the previous versions so I decided to stay with this version for the foreseeable future. 

Mega Kossel with flying extruder

Supersizing a Kossel Mini

Mini Kossel

     This time I'm upgrading the printer I started out with, a basic Mini Kossel kit, to a larger and taller frame. After replacing the original wheels with steel wheels last year, the aluminum towers finally wore down to the point that one of the carriages basically fell off the tower.

2020 Aluminum extrusion after running steel wheels for 14 months

     The obvious choice for replacing the damaged towers was OpenBuilds V-slot, same outer dimensions as the original extrusions allowing reuse of the printed frame parts. I also ended up swapping the steel wheels with the Delrin versions, don't want a repeat of what happened to the old towers.

Enlarged upper triangle

Enlarged lower triangle

     Since I was upping the size of the frame anyway, I cut the old towers down into new sides for the bottom triangle, the idea was to allow for mounting the power supply under the bed with the rest of the electronics, as well as allowing for upgrading the build plate in the future. Dimension wise, the side rails are now 30 cm long, allowing for anything up to a 25cm build plate. Reassembly was mostly the same as the original build process, just scaled up by a large margin.

Upgraded frame

     I did learn some new tricks to make assembly more precise, probably the most useful was using a spare section of extrusion to set the end-stop height to exactly below the upper triangle. All that's needed for this trick is a 3-inch C clamp, a spare or unused piece of the extrusion and the end-stop assembly.

The simple way to set endstop height

     Once the frame was rebuilt, the other parts that needed replacement were the rod-arms, the originals were both too short for the new size and one was cracked after a rather spectacular malfunction last fall. For the new rod-arms, the parts list is quite simple, 12 Traxxas 5347 joints (Amazon.ca), 6 12" lengths of 8-32 threaded rod, an 8-32 tap and AndrewBCN's assembly tool (Thingiverse, thing:701248). The 8-32 tap is optional, it just makes assembly easier by pre-cutting the first couple turns of the thread in the Traxxas joints.

Parts for new rod-arms with completed arm

     With the new rod-arms done, the next step was reinstalling the electronics and print bed. Since I'm not replacing the current print bed, some new mounts were needed, along with a new mounting bracket for the Re-ARM/Ramps boards. After creating a Fusion 360 mock-up of the bottom triangle, it was fairly easy to design new mounting brackets for the print bed, the Re-ARM was even simpler since the manufacture provides a cad file of the boards physical layout. The resulting STLs are here for download.

Re-ARM and electronics installed

Power supply mounting bracket

Mounting bracket installed on power supply

     As you can see, the power supply ended up under the bottom triangle, just wasn't space for the control boards otherwise. The brackets I've designed for mounting the power supply are in with the other STLs above, you'll need to mirror file with your slicer program to get both the left and right versions. Only other parts needed for mounting are some M4x20mm screws and the power supply, I'm using this one, but the brackets should work for any similar module.

Print bed installed with dust covers

     One of the recent improvements for deltas that's been trending on the net lately is adding protective covers to the corners over the lower pulleys and electronics bay. I've been meaning to add them for a while and came up with a simple way to make them out of some spare foam core.

Kossel on foam core for tracing

Kossel and Print bed outlines on foam core

     Yep, that's it, just stick the printer on the foam core and trace around the base with a marker. I also used an earlier version of the print bed supports to center it under the printer frame and then traced it out as well. After that it was just putting the printed parts in their approximate spots, trace the outlines and then cut out the section that's left. I did use a drill to put 3 holes in each for ventilation over the motors but that was basically it. last step was wrap the edges with electrical tape for safety and colour the top black for aesthetics.

Corner covers finished and installed

      Now, obviously the power supply is currently serving as the structural base for the entire frame, not the best idea for long term stability or noise. I found these tennis ball feet (thing:2158108) on Thingiverse, they're printable adaptors that let 3 standard tennis balls serve as vibration damping feet, so I used the Micro Kossel to print a set and installed them.

Tennis ball feet 2/3 installed

   And that was pretty much it, only things left to do were recalibration running a few test prints which turned out nicely.

Completed Mega Kossel