My 3D Printer Worklog (Mix G1)

Hello all,

I just wanted to share my experiences building a 3D printer, partly because the model I got is not the most common one around and I'm keeping records anyway, so why not put them up This is NOT a build tutorial for the Mix G1 (I'll leave that to Mixshop as they're the ones making money off this), but I talk about my experiences as I go along.

This is the first 3D printer I have owned, but not the first one I used. I picked this printer up because of the fun I was having with a Makerbot Replicator 2X in the lab. Knowing how a 3D printer actually works from having to go through the failed prints stage with the Makerbot definitely helped in building this printer, since I knew going in what parts I would need to enable what actions. Additionally, I settled on the Mix G1 because of the price (cheaper than a Prusa Mendel where I'm from) and because it looked like a platform that I could build upon. My guess is this thing won't look anything like a stock Mix G1 in 6 months time. The plan for now is to use this one to print the plastic parts for a 2014 era Reprap when I upgrade

Unboxing
When my order arrived, I was pretty surprised how much stuff the Mixshop guys (at least from their forum/blog I think they're all guys) managed to place in the box. I ordered the Mix G1 kit, some filament, an extra connectors kit, additional Kapton tape, and some ABS filament. Everything came in small boxes, zip-loc bags, or a combination of the two. Here's some pictures of the stuff:


To clarify what came in the "DIY kit", here's a description of the stuff:

All "vitamins" for the assembly of the printer
Printer-specific parts are laser cut, printed, or injection molded
Power supply is a generic 12V@20A PSU with a 110V-220V switch on the side, with 3 sets of +12V/COM, all shorted together from what I can tell; it also has a green light when turned on
PCB Heatbed MK2a with 2x thru-hole LED and 1k resistor
RAMPS 1.4 board on generic Arduino (does not have the marking of an arduino.cc board)
Wire ranging from 24 to 20 AWG; the thinner stuff comes on a ribbon cable
1 roll of Kapton tape (6mm wide)
1 sheet of Kapton tape, enough to cover a build plate as one piece
The green wire is 24AWG solid wire (why you'd bother packing solid wire on something with moving parts all over the place is beyond me)
The extruder resistors when hooked up in parallel give 3.6 Ohms (measured with Agilent U1242A multimeter)

Notes for assembly that may be confusing:

- It now comes with their newer extruder designed described here [forum.mixshop.com]
- Extruder is pre-assembled but thermistor and resistors are not installed (they come in a plastic bag with the extruder)
- It also uses the base described here, rather than the laser cut side plates on the assembly video: [forum.mixshop.com]
- Motors have the same colour wire as the RAMPS 1.4 wiring diagram, but the wires are ORDERED DIFFERENTLY from the RAMPS wiring diagram. My motors had: Blue A+ (2 Green B- (1A) Red A- (2A) Black B+ (1

There are some extra connectors, but for the pins there were certainly not enough, given that I only get those pins right 2/3 of the time due to the lack of the expensive crimp tool you actually need. When I was done the electronics, I used 4 of the pins from my other set.

The plastic parts as I mentioned come either molded or printed. The parts that are molded are the following (names from [reprap.org]):

X Holder
Base Part 1
Base Part 2
X Motor Holder
X Motor Holder 2

In addition, some parts with STLs were laser cut out of what looks like fibre board:

Belt Clamp
Y Motor Holder

The rest of the pieces were printed. I'd put the quality of the printed parts at the lower end of the scale: the Makerbot could do about the same job on its 0.3mm setting with the speeds turned up to 110mm/s. Here's some shots of the parts:

The pictures intentionally have less white balance to show the texture of the plastic of the molded vs printed part.

Although I am still far away from using it, here's some pictures of the filament:


In the second picture, that's a bag of dessicant hiding inside the spool (it shipped that way). Subjectively I think the filament spool is very tightly wound and the texture is inconsistent. How that will affect prints I'll have to see later. I can post measurements of the filament if someone can tell me how to do that properly. The ABS is soft enough that my caliper can squeeze it and give an inaccurate reading.

Next up: Mechanical assembly

I've got the exact same printer and it was nice to play with it. I'm looking forward to see what modifications you are going to do!

It was my first printer and the first extruder wouln't extrude 1.75mm PLA. After a few weeks, I managed to make a groove mount adapter and use a different hot end. It is now printing like a charm.

My 3D Printer Worklog (Mix G1) - Part 2

Mechanical Assembly

(As a note I'm about a week ahead in progress from this post.)

The assembly went decently well, after the first few steps, as part of the assembly video from the creators here:
[www.youtube.com]

What confused me quite a bit was that the base pieces were completely different from the video. You essentially ignore 0:16 to 0:56 in the video because the power plug and switch have plastic housings, and the side plates that used to go in the YZ plane do not exist with the new printer design. Just put the "Base Part 1" and "Base Part 2" together, and do not attach this stuff to the base until the Y motor is attached.

It's hard to see in the web page, but the way all of the stuff is supposed to go is like this:


I changed around the wiring layout - described in the next part. My main issue is this:
Do they ACTUALLY expect you to run a 110V-240V line from one corner of the printer, underneath all the nice moving parts of the Y-axis to the plug? As I'll be saying this a lot about the electronics for this printer. How about... no!

Also something I figured out was to just hand-tighten all of the nuts and threaded rod until the final calibration, because I was loosening and re-tightening stuff all over when it came time to attach the X axis.

Aside from that, the assembly went pretty much as it went in the video. I did however have to toy with the Y-axis to get it right later on.

Electronics Assembly

I have to credit the Mix G1 people for the mechanical design of the printer. Despite the way it relies on the nice alignment of the two base plates for the Z-axis being right, mechanically it is pretty sound. I moved the printer around quite a bit to bring it from where I work on it to where I can print without having to suck fumes (BTW I'll tell you this early - that fluorescent yellow ABS Mixshop sold me is borderline hazardous with the amount of fumes it generates). All the moving around - upstairs, downstairs, to the garage, etc. and the I haven't broken anything major / the most realignment I had to do was the 4 screws to level the build plate.

The electronics however looked a lot like an afterthought, because they didn't provide good spots for wire ties / zipties / spiral wrap, and in my opinion, a lot of the wire was too small. The thickest wire I found in the kit was 20AWG.

Depending on the length of wire, the heatbed would lose some of its efficiency.

Math:
(Wire guage chart [www.daycounter.com])
Assuming you use about 1m of wire from the power supply, to the ramps, to the heatbed, and back...
Not counting the connections, that 1m of wire has 0.03 Ohms of resistance.
Using the measurement of my heatbed at 1.4 Ohms and the wire measurement, that means the 1m of 20AWG wire has about 2% the resistance of the heatbed. (Power = Resistance * Voltage squared) I'd rather have that 2% of power for heating my bed and not my wire, thank you very much!

I used 14AWG wire for the wires between the PSU and the RAMPS and the RAMPS and the heatbed, and 18AWG wire for the extruder. Also to keep connections from getting loose, I tinned the wire (coated with solder) that went into the screw terminal on the RAMPS board and used ring terminals to connect to the power supply. Unlike the video in which the author had some obsession of using Kapton tape for everything, I used heat shrink tubing.

I changed the layout of the base plate to put the power supply, switch, and plug all in the same corner:

That means all the 110V fun is contained to less than 15cm lengths of wire and all at the same corner. I ran the 12V wire over top of the 110V stuff as well, so if the bed were to crash against the wire it would get the 12V and not the 110V.

To prevent the extruder from hitting its own wires for any Z, I glued a post to the top z holder and from there I ran an elastic band which I tied to the wires. The extruder wires then tie to the "unused" bit of smooth bar on the +X side of the printer. (Plan is to try some spiral wrap there as well.)


In case you need to twist a long length of wire in a hurry, throw it in a hand drill! (don't use the part that was in the drill though)


For the heat bed, I wired it "upside down" from the video. (The holes are just big enough for 14AWG wire BTW)
I put the thermistor on the back side of the bed and I plan to use the side with the traces for the heating. I bought some cheap glass (actually asked local glass shop for the cheapest 3mm stuff) and that was mounted on the side with the traces. With this config, I know my temperatures will read lower than some, but I get the heat where I want it - on the side that prints. The other advantage is the thermistor gives a better idea of what the temperature is, rather than always being exposed to a higher temperature than the print surface.

Note after taking the picture I put some Prolimatech thermal compound over the thermistor and Kapton tape over all of that. I also used that thermal compound for the thermistor and the wire wound resistors on the extruder. I'm using some old stuff that came with a Megahalems heat sink that I got for my computer, so I wouldn't know if it's the same stuff as the PK-1 that they sell now. In any case, the heating / cooling works well enough for me to print ABS and PLA with.

Next up: First prints

...darned smileys I just noticed them in the OP. Replace the sunglasses smiley with "B )"

First Prints

Anyway, my first print was with the Mixshop ABS to make... replacement parts of course!
I had covered a piece of glass with Kapton tape (using the soapy water method), so that was still drying when I wanted to try the printer. I used an uncoated pane of glass instead, and it worked anyway. If it ain't broke...

The included filament holder worked relatively well, but I did not want the X axis motion to cause issues. I therefore tied the filament to the top -X post. I tried different combinations of this, but a ziptie off a piece glued to the post worked well enough.


During these prints, my Y axis was very wobbly, and that wobble caused deformations in the first print that actually completed. Still - not bad for the very first print! I'm happy for my experiences with the Makerbot for making the initial issues easy to fix.


One thing that was really bad was the Mixshop ABS filament! I have since stopped using it, and plan to throw it out as it could end up causing more frustrations than the $20.00 that remains of it. Even with two windows open and a fan blowing against the printer (don't ask why that didn't cause my prints to lift like crazy), the fumes are still so bad that I get a sore throat and runny nose for an hour after about a minute of exposure. That seems crazy, given that I can be around Makerbot ABS filament (red, black, natural) printing all day with no effects near to what I have with the Mixshop filament. To add to that (which is why I feel like tossing it), is that the filament is coiled so awkwardly that it jams against itself at points, requiring me to always be nearby to unjam it. It just isn't worth risking all my prints with X-axis or extruder motor jams, and having to wear a respirator to be around the stuff. The awkward coiling of the filament also has stress points where the plastic is discoloured, so that can't be good for prints either.
As a note, this is my only (and likely last until they switch suppliers) Mixshop filament. I only bought one, but to know they have a dud that both gives off horrible fumes AND is spooled in a way that likes jamming is too much.
After the mucus membrane torture, I promptly went on Amazon and ordered some Jet natural PLA filament (which I am trying now).

Fixing the Y-Axis
Well after the choking, gagging, and frustration over the filament, I decided to power down the printer and fix the Y-axis. The issue was that it wobbled from side to side (in the X direction) while it was moving. I traced that problem down to two issues:

1. The bearing holders, which were a bit loose, allowing the bearings to move within the mounts
2. Alignment in general

I tightened everything along the X axis to ~249.0-249.5mm instead of the prescribed 250mm, and I properly centred the Y axis belt by centering it in the X direction. That lessened the wobble, but it wasn't quite enough. After that, I added some cyanoacrylate glue on one side only between the linear bearing and the Y axis mount, as shown below:


...then right after fixing the Y axis, I broke the X end stop while putting all of the wires back


I actually didn't find the replacement STL (the ones on the Mixshop web site were for a different kind of switch), so I designed a new one. The replacement was also one of the last useful prints I got out of the yellow Mixshop filament.

EDIT: I uploaded the switch holder to Thiniverse under [www.thingiverse.com]
(Pardon the badly made CAD - I'm still learning to switch from Solidworks.)

Edited 1 time(s). Last edit at 08/28/2013 09:56AM by frontier204.

I upgraded my Mix G1's firmware from Sprinter to Repetier, mainly for the PID autotune which works quite nicely for PLA.
I used this configuration for most of my PLA prints, which include some of the larger replacement parts for the Mix G1 (e.g. base part 1 and part 2).

Attached here is my configuration.h file, which I made to be a drop-in replacement for the Sprinter one posted on the Mix G1 forums. I also copied and converted the thermistor table from the Sprinter "included" with the Mix G1.
That includes the direction of the motors and the endstops, since I rewired my RAMPS rather than flip the directions of stuff in firmware. The baud rate is 56k because that was the first one that worked for me, but that doesn't prevent you from trying anything else.

In case the attachment doesn't work, here's a Dropbox link as well:
[dl.dropboxusercontent.com]

Citing my sources:
Original Sprinter: [forum.mixshop.com]
Repetier: [github.com]
Note the configuration.h should be valid as of the commit that happened before this post.

I've used up at least 30% of my Jet PLA spool so far, with surprisingly fewer failures than I expected. I was working quite a bit on trying to get the filament to feed without jamming, and I finally came up with this strange looking contraption:



I ran an elastic band across the top of my Z-axis bars, and wrapped that elastic band with some tubing. As the filament feeds, it brings down the elastic band, and when there is enough tension, the elastic pulls on the filament spool to roll out some more filament. This system reduces the stress a bit on the extrude motor, so it doesn't have to pull the filament all the time. This rig also allows the filament to feed from about the same spot all the time, so I do not skip on the X axis as that motor attempts to pull the filament as it travels.

In addition to the elastic bands, I also added some end caps to the filament spool to make them roll more easily on the threaded rod. The end caps are listed here: [www.thingiverse.com]

Here's some of my longer prints [www.thingiverse.com] (~2 hours) and [www.thingiverse.com] (~5 hours):


There's definitely still some room for improvement. Here's a closeup of the corner of that box showing a whole lot of Z-axis artifacts:

The banding is even across both sides of the box (i.e. a peak on one side is a valley on the other side of that same layer), so my guess is it's the artifact from the Z axis threads being constrained at both the top and the bottom.
I'll replace that with a cap that only connects the smooth bars and not the threaded ones, similar to the original Mendel:
[reprap.org]

I think this is where my printer will start to NOT look like a stock Mix G1...

Wow I'm thankful I printed all of the replacement parts right after I got dialed in. As I saw when first unboxing this thing, the printed parts' quality left some to be desired. After 2 weeks heavy printing (~5hr per day), I've removed or replaced the following parts:

2 X/Y Pulleys (Damaged)
1 Extruder tensioning plate (Damaged)
3 Endstop holders (Damaged - replaced with my own design [www.thingiverse.com])
2 Z Top (They were the cause of Z-wobble - replaced with a cross bar similar to [www.thingiverse.com] but with 2x 1/4" threads.)

Additionally the screws holding the bearings onto the Y axis mount got loose and damaged my Y-axis belt, so that has to go as well. The screws were probably my fault though, since I picked too short a length.

I'll post my design for the Z-brace when I figure out how to integrate it with the filament feeder and a "tent" to contain drafts/fumes during ABS prints.