Project: FFF 3D Printer “Eta” Part 7

Hello Sunday!

I’ve been a bit busy repelling the fusillade that is life, with varying success. Those of whom live in close proximity to me may have experienced paranormal sounds and or mumbled exclamations emanating from my lab-cave, but worry not, its just me trying to get my printer online.

A Series of Iterative Incidents of Murphy’s Law

Where I left off, It was 4 weeks ago (Five weeks now, time really does fly), and I had just finished the physical construction of my printer. Most of it, that is. I started by installing the endstops onto the smooth rods. I used microswitches for the Xmin, Ymin,Ymax, and Zmax endstops, and an opto endstop for the Zmin, to ensure accuracy. As my system is a Hbot, I decided to use both min and max endstops to help prevent any accidental crashes.


I attached them using zip ties and strips of latex cut from surgical gloves,  to prevent them from slipping on the smooth rods.

All the wire I used was twisted for convenience, neatness, and signal clarity. Next, I began configuring the software tool chain for controlling my printer. I used Marlin, an open source firmware for the RAMPS 1.4 control board, Pronterface for direct printer control from my computer, and Cura for slicing.

Attempting to configure a printer is akin to teaching a baby how to move, and then trying to catch it as it bolts off the dinner table headfirst. Eta did ram her print head into the boundaries several times until I got it to understand which axes were which and which endstops applied to what, but it turned out all right with no damage.

MOSFETS and overthinking solutions

I spent a better part of my time planning figuring out how to power the obnoxiously large heated bed that I decided to use, due to its high rated amp consumption. 30A is no joke, and my lack of electrical engineering skills could very well jeopardize my printer, and possibly my continued presence in my house.

After much research, a good deal of headbanging and SP road trips, I finally settled on using three IRLB8743 Mosfets to switch the current to my bed. The RPF ‘fet on my ramps board was simply unsuitable for the task, so I didn’t even try it out in fear of combustion. I soldered the fets to a PCB, wired them up in parallel using thick housing wiring, added a 10k resistor to keep gate at ground, and slapped the largest heatsinks the shop had to offer on fets.

It’s pretty self explanatory what’s going on here. To all of those facepalming about why I’ve mounted a PCB in a metal box, its so that it is less likely to catch fire. The PCB is mounted on a biscuit of wood, and everything is fixed down. With zipties and hot glue. Clearly brilliant engineering.


A rough diagram I drew when I was visualizing how the mosfet circuit would be made.

Finally, I bolted down all the connectors, checked every joint and connection thrice, and finally turned on the 12v 50A PSU and activated the heated bed!

But nothing happened. Or more accurately, nothing bad happened. I ran the heated bed for several tests, it heated up properly, no melting, no fumes, nothing. The mosfets were room temperature even after running the bed for 30 min. I somewhat suspect that the heated bed is drawing approx. 14-18a, judging by ohm’s law and the PSU’s fan’s duty cycle. On the flip side, the system I engineered could possibly take up to atleast 60a at 12v.

Better more than less, I suppose.

More software tweaking was done, I installed the LCD control screen into a large box, and hooked it up as well. The fourth box as enough space for more additions as well, like an E-Stop button or arduino.

This slideshow requires JavaScript.

Here we encounter another incident of Murphy’s law, where my computer decides to crash. Permanently. After a quick series of diagnostic tests, I decided to abandon the 14 year old PC, and instead use an old laptop I had laying around, so that was quickly solved. I like to use Linux mint for my lab computers, due to its lightweight, features and speed.

Worse congestion than a cold in Monday traffic

I’m using a e3D v6 clone, featuring an all metal body. I hooked up the hotend, bowden tube, and the extruder body, and started running configuration tests. The hot end heated up, fan ran, and everything was peachy until I tried to extruding plastic. The filament went smoothly in, and then the extruder gear began grinding like a lion with anxiety. I unwound the filament, and then tried pushing it through manually, and it kept hitting something inside the hot end.

If that wasn’t bad enough, thermal creep started, and the plastic melted in the colder part of the hotend, which is bad because that can’t be cleared easily. With my plastic firmly frozen in the upper heatsink, I was forced to disassemble the hotend to clean the jam, and use a blowtorch to burn out the filament in the heater block and nozzle.

This proceeded to occur with mildly different scenarios three more times. Finally, after the pneumatic press-fit joint proceeded to join the rest of the hot end in failing miserably, I decided that I need to take a short haitus from building Eta, while I wait for the replacement parts to arrive.

I estimate that I’m about 90% done with Eta, as I just need to install the new hotend, calibrate, and slap on the final safety features. Until then, I’ll be working on other projects, Comic con is approaching!

Signing off,



Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s