Sunday, 12 February 2017

Experiments with Flying Extruders and Deltas

Mini Kossel with flying extruder
     Not long after finishing the Re-ARM upgrade, my geared extruder suffered a failed bowden coupler, so rather than reprint the entire thing, I decided to switch to an alternate configuration that I'd read about called a 'flying extruder', basically suspending the extruder motor over the effector/hot-end, allowing for better print quality with a wider range of materials.

MK8 extruder with suspension bracket attached
     I started by replacing the failed extruder with a MK8 variant that was in my spare parts pile, then tracked down one of the designs for the suspension mounts from Thingiverse (thing:1295606). It's a fairly good starting point, but it is missing a couple of parts for mounting on a standard Kossel frame, so I had to design some custom parts for the pulley mounts, the files are here.

Moving extruder power cable to the effector wire harness
Heat-damaged PLA fan duct skirt
     One unexpected issue cropped up during the process of changing the Bowden tube, which on an E3D Lite6 requires a full stripdown and rebuild, so I had to remove the lower half of the effector I've been using (thing:1569106) and found that part of the hot-end had rotated and melted part of the lower half of the effector. My solution was to rework part of the design and add a small loop on one side to allow use of a zip-tie to secure the heater wires, thus locking the rotation and preventing a recurrence. The file for the reworked part is on Thingiverse (thing:2103488).

Remixed and improved ducting skirt, note the zip-tie on the right
    With that issue corrected, I designed some custom brackets to use a couple of spare 608zz bearings and the MK8's old idler bearing as pulleys. Other parts use were some old washers and pipe fittings from the workshop junk bin for a counter weight, a roughly 30cm piece of 1/4-inch steel rod for the main shaft across the top, a 1.5m length of thin rope/string, and about 30 zip-ties. I also added some temporary loops to the carriages allow using some zip-ties to hold the extruder in place while I installed the upper pulleys.

Pulley bearings, 1/4-inch shaft and part of the counterweight
Using the cable to loosely suspend the extruder during install
Temporary anchor for zip-ties
      Initially, I had thought to try running with just zip-ties holding the extruder block to each of the carriages, but that proved unworkable due to the zip-ties restricting the range of motion. The basic idea of suspending from the carriages would probably work if you used some form of elastic for the cables, but that still leaves a 400-gram weight sitting in the middle of the frame, so it would definitely lower the maximum attainable speed.

Initial configuration idea, doesn't work with rigid cables
Initial Z-tower pulley mount 
Upper pulleys 2/3 installed
    As you can see, I'd initially thought to use just the zip-ties to hold things in place, but that resulted in some strange glitches during homing, so I switched to the full counterweight option. After I'd installed the first couple of pulleys, I realized that the counterweight would hit the back of the z-tower carriage, so I designed a short arm with a 608zz on the end to act as a spacer. Other hardware used in the spacer arm was 3 M5x35mm bolts, 4 M5 nuts, and 1 M5x10mm bolt.

Spacer arm fully assembled
Spacer arm fully installed just below the top triangle
     As for the counterweight, I just used a small scale to measure the approximate weight of the extruder assembly, roughly 395 grams, then found a combination of old washers and stuff that was reasonably close to that weight to use for the counterweight, ended up at 405 grams, then tied the lot to the end of the string/rope. As for the print quality, I still need to retune the retraction settings, but it's a drastic improvement over the original configuration, with a much finer surface finish. Here's a couple of #3DBenchy prints for comparison, the Green one is from the filament comparison post with the original configuration, the gold one is done with the new configuration.

#3DBenchy 32-bit on the left, 8-bit on the right

Tuesday, 24 January 2017

Re-ARM of a Mini Kossel

Panucatt Devices Re-ARM board Bottom View
     Last month, I covered some of the key upgrades on my mini Kossel, and most of them were things that improve the extrusion path. This time, I'm switching the controller board from an 8-bit Arduino Mega 2560 to a new 32-bit Smoothieware-based board called the Re-ARM for Ramps

New and Old: Re-ARM/Ramps (top right), Arduino Mega2560 (bottom left)
     Physically installing the Re-ARM was fairly simple, I just needed to remove the print bed and lift the Ramps assembly out from underneath. After that, a few minutes work with some pliers to gently separate the Mega and Ramps boards, then mount on the Re-ARM's headers with some gentle pressure until things are snug. Don't forget to set the Re-ARM's power mode before installing the Ramps, it's impossible to change the jumper with it in-place.
Re-ARM/Ramps with mounting bracket (on the left)
     After assembling the boards, I found that my Mega2560 mount was incompatible with the Re-ARM's footprint - mostly just a tolerances issue, the mounting bracket I was using is a bit sloppy, so I loaded the Re-ARM's digital reference into Fusion 360 and drew up the bracket above. It's designed to raise the Re-ARM to just the right height to allow the optional Ethernet adaptor to pass between the 2020 t-slot extrusions on the Kossel's base, and bolts down with a couple of #6 or M4 wood screws. The STL for it is here

Re-ARM/Ramps mostly installed
    Once the main boards where installed, it was time to add the graphics display. With the Arduino Mega, I'd used a Smart Controller display panel, but it wasn't compatible with the Re-ARM so I swapped it out for a Full Graphics Controller instead. The only real gotcha with using this display on the Re-ARM is that you need to splice part of the EXT2 cable to tap into one of the 5V rail pins since the main logic rails are operating at 3.3V.

Spliced line on EXT2 cable, it's the edge opposite the red reference line
5V pin for EXT2 splice

     And with that plugged in, I used the Micro Kossel to print some mounting brackets from Thingiverse for the display and then used some M3x20mm screws to install them.

Full Graphic Controller with Mounting brackets waiting for installation
Using zip-ties for cable management, helps keep things nice and tidy
Bracket fully installed using M4x0.8mm cap screw and M4 hex nut

     With that installed, all that's left is to remount the print-bed and deal with the software side of things. I'd originally used 3 M3x20 screws to hold the print-bed down, but these made it very vulnerable to warping and difficult to level after a reinstall, essentially requiring recalibration every time I needed to access the electronics. After running across thing: 1982435, I decided to make my own version with an extra slot for my heat shielding. Files are here.

Print-bed mounting blocks waiting for install
Test fitting heat shield
Finalizing exact positioning, note the M3x20mm screw and bolt for holding glass
     After sorting the heat shield, I still had a minor issue with the bed trying to float on top of the mounts, so I drafted up some extra wide M4 washers to hold things in place with some spare M4x20mm bolts I had left over from another project. You can see the floating issue in the next picture's lower left corner.

M4x20 bolts and custom washers waiting for final installation
Glass holder clip with M3 thumb wheel for holding the 195mm glass down
     As for holding the Buildtak/glass plate combo I use for an actual print surface onto the print-bed, my glass is an odd 195mm diameter, not the more standard 200mm or 220mm that you normally see, so the glass clips are customized for it. With that installed, it was largely just a matter of learning how to configure Smoothieware with the Mini Kossel's parameters, the official documentation, combined with the Re-ARM's setup guide were fantastic on this, then the usual calibration and it's done.

Retrofit complete, ready to print

Saturday, 7 January 2017

Project: Proteus Delta, part 7

Proteus build plate
Happy New Year! Today it's all installing the heat-bed and it's supports. I'm using one of Ultibots 300mm print-bed kits, the same setup used in their D-300 design, so I needed a support that could grip the edges of the bed with minimal overlap. I'd measured the spacing on the bed mounting brackets early on, so it was mainly a matter of drawing up something that would work for 3D printing in Fusion 360. The STLs for my final design are here.

Proteus print-bed support parts ready for assembly
     The parts are all designed to fit on my Mini Kossel's 180mm bed, each wedge takes about 2 hours with 0.2mm layers at 50% infill, so about 18 hours total for a full set of 9. For fasteners, you'll need 40 M3x16mm screws, 50 M3 nuts, and 6 M3x40mm screws for anchoring the bed layers together and to the lower frame. Assembly is fairly straightforward, I just used a screwdriver and wrench for the fasteners, along with some spring clamps to hold things in place during assembly.

Assembly tools for the print-bed support
Support half-assembled, note the use of clamps to secure parts
Fully assembled bed support
    I've printed the parts in PLA, so I'm using a couple of these Pyron flame protectors for bed insulation, I've been using the same thing on my Mini Kossel for almost a year and haven't had any problems.

Cutting pattern for flame protector
Print-bed stack cross section
     Once the insulation is installed, it's simply a matter of tightening the bed clamps into place with some M3 nuts or thumbwheels, I'm using these printable ones from Thingiverse.

M3 nuts, screws, and printed thumbwheels

Bed clamp ready for tightening
Print-bed ready for final install
Once the bed clamps are tightened, the only step left is to connect the thermistor and power leads to the Duet 0.8.5 and level things so the bed surface is square to the towers.

Heat-bed connectors on Duet 0.8.5
Print-bed installed and squared
     And that's it for now, next time it'll be assembling the effector and Prometheus system.

Friday, 23 December 2016

Project: Proteus Delta, Part 6

Proteus Delta current state
      After doing some research online, and getting my multimeter out to poke around at things, it turns out that this kind of power supply's outputs are very simple, two sets of three for positive and negative output linked in parallel, with the other three points being the mains input. I've also used the multimeter to fine tune the V-ref or reference voltage to exactly 24 volts, the next image summarises what's what.

Power supply outputs labeled and organized.
     Once that was sorted, I powered up for a brief connection test, just to verify that everything worked properly. After getting a positive result, I started on the last of the fixed parts, the electronics cooling fans. I'm using a pair of 80mm*20mm box fans to keep the Duet 0.8.5 from overheating, they're a bit loud but produce lots of airflow. I'm using this fan grille to help keep some of the wiring out of the fan blades.

8020 fan positions around the Duet 0.8.5
     That's all for this update, next time it's installing the heat-bed, so Happy holidays and see you next time.

Heat-bed partially assembled for testing

Wednesday, 7 December 2016

Upgrade suggestions for inexpensive Kossel Mini kits

Mini Kossel current state
     I just finished a partial refit on my Mini Kossel, and realized that I hadn't mentioned it on here yet, so here's a brief tour of the upgrades and modifications from this past year. Most of the important ones I've made are related to the plastic handling components, so I'll cover them by following the filament path.

Filament Spool Holder
Spool Holder Base (Customized variant)
     Starting from the top of the filament path, the first modification I added was this spool holder by Creative Tools, specifically the OpenScad remix done by GeoDave on Thingiverse. This is by far the nicest spool holder I've used to date, most of the other ones for deltas ether occupy the upper triangle completely or are just a printable stick that bolts onto the side, so this is a massive improvement over those options.

Greg's Wade's Extruder, bowden variant
     After the Mini Kossel's previous MK8 extruder suffered a dulled drive gear recently, I decided to replace it with a Greg's Wade's extruder, an old and proven design from the RepRap project. I've had it running for about two weeks at this point, and it's been very solid and reliable.

E3D Lite6 nozzle
     Next on our tour is one of the first upgrades I made, the E3D Lite6 hot-end. The Mini Kossel kit came with a 'metal J-head' hot-end that malfunctioned the first time I turned it on, and started oozing plastic out of every joint in the heater block, regardless of what I tried. After researching hot-ends online, the Lite6 quickly came up as a reliable and easy to use option for a beginner, and I've not looked back since.

MK3 aluminum heat-bed with Buildtak on glass topper
     Finally, we come to the heated build-plate or print-bed, the foundation that everything is printed on. I started out with a MK2a PCB heater and glass combination that was included in the kit, but the heater was warped when I got it, so I sourced a MK3 aluminum heater as a replacement and I haven't had any issues with it since. The Buildtak print surface is something I started using on the Micro a few months ago, and I decided to add a sheet to one side of my glass bed after I ran out of the glue stick that previously served to improve bed adhesion. And that's my workhorse printer's key upgrades finished, for now.