Thursday, 30 November 2017

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

Saturday, 28 October 2017

Building a Prusa i3 MK2 from Scratch

Prusa i3MK2 'Sculptor"
    So, time to reveal what the mystery replacement for the Micro Kossel is, I've repurposed the electrical harness into a Prusa i3MK2 clone build. Sourcing the parts was a bit of a nuisance, but most of it had close matches at my local hardware store or was stuff I had on hand.
Imperial equivalents of the M8 (5/16") and M10(3/8")
 with 1/4" threaded rod for the z-axis screws
Idler arm for the extruder with a 625 bearing from OpenBuilds
     Now, some of the parts for this machine do require CNC cutting normally, but following some of the tricks used by Tom's 3D build from march, I printed the frame template on paper, glued it onto and cut it out from some 3/4" plywood for the frame and 1/4" plywood for the y-carriage.
3/4" plywood frame with template attached
Frame and y-carriage ready for painting
     After cutting out the wooden parts, the next step was to paint and seal them, otherwise they'd change size with the ambient humidity. I used some black acrylic for the first coat, then followed up with a coat of Varathane to seal them.

Main frame waiting for paint to dry
Y-axis parts and tools
     While waiting for the paint to dry I moved on to assembling the y-axis/base frame. Assembly is fairly straightforward, only major thing that you need to watch is that the frame is completely square and flat. Squaring the frame is fairly simple with an old woodworking trick, just take a tape measure and check that both diagonals are the same length, if they match the frame is square in that plane. As for making sure it was flat, I used the one surface in the workshop guaranteed to be perfectly flat, the top of the table saw.

Checking the diagonals for squareness
Checking the other diagonal
     Once that was assembled, the next step was adding the vertical frame, then installing the x/z-axis assembly followed by the extruder carriage to complete the primary frame assembly.

Main frame assembled
Extruder ready for installation
    With the Extruder installed, it was time to sort out where to mount the main control boards. The normal place for them is on the back left of the main frame, but the cables on the LCD module I'm using are only 10cm long, so I've mounted the Ramps package on the front left side with the power block on the back.

Installing the Ramps casing (Thing:761806)
Power brick with custom brackets
Raspberry Pi Zero W for Octoprint host
    I designed a couple custom L-brackets for mounting the power supply and Pi camera, with those installed, it was time to sort out the firmware and calibrate the z-height. For the print-bed, I'm just using a sheet of Buildtak stuck to some 3/8" plywood, basic but workable.

Completed i3MK2

Thursday, 28 September 2017

Decommissioning the Micro Kossel

Micro Kossel
    After almost 18 months of heavy use the Micro Kossel was long overdue for maintenance and wear checking, so I decided to partly disassemble it last week, this unfortunately lead to the discovery of several fatal flaws that would have required basically replacing the frame to correct, so I decided that it was time to retire it.

Micro Kossel parts after disassembly
    Most of the flaws were wear and tear issues that some of the PLA parts hadn't stood up to well at all, specifically the AMZ3D transparent red carriages and green rails and corner/motor brackets. I don't have photos but the motor corners were warped badly enough that the motors were stuck pointing about 20 degrees up from the normal horizontal position, making any attempt to tighten the drive belts pointless, they'd just slip off the mounts or the plastic would just melt further and worsen the problem over time. 

Micro Kossel frame rail with cracked section

Micro Kossel frame rails with cracked sections
     As you can see, the Seacans green PLA fractured across the layers on these sections, a highly atypical failure for a printed part, normally you'd see fracturing along the layer lines with PLA, not this glass-like fracturing. It's worth noting that the Tinkerine Lavender PLA shows only minor damage where stuck nuts and bolts were removed, and that's mostly cosmetic, so I'll probably be reusing those parts in a future project. 

Carriage plate showing stress fractures
    The AMZ3D PLA carriages are by far the most alarming of the parts, two of them cracked at the hinge point (lower left of the image above), and all three where showing some alarming stress fractures that you can just see in the picture above, I've warped the contrast to make it a bit clearer, my camera has a hard time seeing them but they're very clear to the naked eye. Taken together, these issues mean that it was just a matter of when, not if, that the hot-end would come off axis during a print and make a complete mess at minimum, start a fire at worst, so I've dismantled the frame and salvaged the electronics for a new project, here's a preview, but more on that next time.

Mystery parts for next project

Monday, 18 September 2017

Stress Testing the Mega Kossel: Building C. Laimer's Tourbillon Watch

Tourbillon Clock
     After the painting project from last time, I decided to try building a more mechanically complex project, Christoph Laimer's Tourbillon Watch (thing:1249221). It's a very complicated model with very tight printing tolerances, all the parts need to be as close to perfect as possible or the clock won't work properly. 

Printing the mainspring pinion gear on the Mega Kossel
     Obviously the first step in this project was lots of printing, about 100-120 hours in total, perfect for shaking out any glitches in the printer. Aside from a couple of spaghetti incidents caused by the print bed shifting on it's mounts, actually printing the parts was the easiest part of the project, tracking down compatible screws was the hardest part, I ended up reaming most of the screw holes to accept M2 screws since those were the closest that I could find.

Clock parts organized for assembly with mainspring being assembled
Mainspring clamped for assembly with printed machine vise
    Actually building the clock took a few days, the virtual walkthrough and assembly videos were invaluable for this stage, always making it clear what part was installed next at every step of the process.

Mainspring fully installed with outer casing in place
Clock parts set out for assembly
   I ended up using some 14-gauge wire cut to length for the gearing axles, long needle nose pliers are crucial for installing them in the upper center plate. Other tools I used were a 3/64-inch drill bit for reaming the gears mounting holes and a Philips screwdriver for the M2 screws. After a couple of days work I had it assembled and mostly working, one of the gears is a bit sticky on its axis, but it's mostly complete.

Test fitting Clock face components
Completed Tourbillon Clock

Tuesday, 22 August 2017

Prop Replica Making: Building the Sidewinder pistol from Mass Effect: Andromeda

Mass Effect: Andromeda Sidewinder
     After upgrading my Mini Kossel to a Mega Kossel, I was browsing Thingiverse for something interesting to test it with, I was searching the names of some of my favorite games, and Rawrbomb's Mass Effect: Andromeda Sidewinder design looked like one of the best modeled props from the game available.

Sidewinder V1 parts waiting for painting
     Printing was fairly straightforward, most of the digital prep work was mostly just orienting the parts for printing with my Mega Kossel, the default orientations are optimized for a prusa i3 style machine, so I ended up sticking most of the parts on end with a large stack of support material. Final step before printing was choosing which parts to do in black or white, so most of the gun's frame is in white PLA with some of the details in black PLA. Total print time was 52 hours 41 minutes and used 369 grams of filament including the support material.

Sidewinder right side initial paintwork
     For the painting, I started with the raw parts after removing the support material and gave some sections like the barrel and grip cages a coat of acrylic paint on all surfaces. Others sections got partially masked and painted in stages for the full effect, while others were left mostly untouched since the print was already the correct colour. For some of the detailing, I used coloured sharpies to prime the area, then 'weathered' the area, then recoloured with the sharpie again. 

Sidewinder left side initial paintwork
     This worked reasonably well, but after rewatching this YouTube video, I thought I could do better, especially as some of the weathering was only highlighting the layer lines in a few spots. So, after a quick trip to the local paint store to get some more colours and brushes, I repainted it to more closely follow the in-game texturing, with a little bit of rusting around the edges and seams. I've still got a bit of weathering to do at some point, but I'm very pleased with how it turned out.

Sidewinder left side final paintwork

Tuesday, 8 August 2017

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 (, 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