Let's Make Robots!

Doboz: Repstrap 3d printer made of Aluminium and plexiglass

3d printing, a bit of 3d scanning


Hello everyone ! Since this machine has just finished producing its first "offspring", i thought i would submit it here to commemorate.

This is my first generation "Repstrap" machine , on which i worked for many months.

  •  A repstrap is a derivative of a Reprap (open source 3d printer) , that is not created using 3d printed parts (sort of like "bootstraping" such a machine) 
  • as with most machines of this kind, it prints 3d object using thermoplastic filament that gets melted and extruded via the print head, depositing layer after layer  
  •  The structure is made of L-Shaped aluminum : outer volume is 39*35*45 cm Early build of the structure
  •  Total build volume ( maximum size of objects that can be printed inside of it) is 21*18*23 cms - I used a threaded rod approach for all axis of the cartesian bot (in hindsight, not the best idea, as low quality threaded rods make movement way too slow) 
  • Custom, low cost home made electronics to control all stepper motors , the print head heating , and the heated build platform (used to avoid warping in cooling objects) Doboz-electronics
  • it also has a very limited 3d scanning ability, using a simple IR-Led/Photodiode combo , to generate 3d "height maps" of the objects in the machine .
  • overall, a rather slow but rather reliable machine ( many 24/7 prints) It has already allowed me to experiment with different mechanical components, and has just finished printing its first offspring; a mini reprap!


A 3d printed mini turbine

Baby is born!

The build process was spread out over about 8 months, with many prototypes, and experimentation, i had never worked on something this complex before, and even with the occasional tantrum etc, great experience :)

You can view more info and aspects of the build process on my site :http://www.kaosat.net/?tag=repstrap





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Sorry for the late reply guys!



  • i took a look at your CNC machines, and they look fantastic !  mightly impressive work ! i might have missed it, but , big big question: did you manage to make some pcb milling ?.
  • Yeah, the extruder is the hardest to manufacture using diy methods and tools, but it is still feasable, using lots of experimentation, based on what elements you can find locally (or not, in the end i managed to find some relatively cheap print heads online, but i had working , full diy versions before that, but given my lack of precision metal working tools, the quality was not top notch)
  • Extruding 3mm Nylon must be feasable as well , although i would be a bit wary of fumes, and you would need to find the adapted melt and cooling temperatures, most likely.
  • the general movement speed is not  limited by the extrusion feedrate at all : in fact , i had to go to almost the lowest possible speeds for the stepper that is driving the filament , as the machine is so damned slow , but after a few adjustements it works just fine
  • your are right about noise and dust :) , i originally built my repstrap to be used both for plastic extrusion and milling /cnc , but given that i live in a tiny flat, i put the idea of CNC aside for a while ( i actually leave the printer running at night sometimes and i can sleep , would not be possible with a Cnc :))


  •  tinhead got that right, i use the reprap software , or rather to be more precise, i use a modified version of the reprap 5d firmware (one of the many, many firmwares for repraps, that can be uploaded to the atmega/arduino/sanguinos controlling the machines, and the commands are indeed text based GCODES sent via usbSerial . The host (pc side software, is homebrew, a bit unusual : as it is a server /client solution for remote monitoring and control  ( still in early development): http://www.kaosat.net/?p=1731
  • the main problems:  speed (the new "child" machine will be somethings like 40 times faster, huzzah!) , slightly flawed electronics design (my fault, went really "guetto diy") , the endless fine tuning 


... early tests were promising but I had a problem with the table not being flat causing differences int the cutting depth.

I did not get to do any testing recently, but the last I did came out pretty usable. For truhole stuff I'm positive I can mill them as it is now, but my target is SMD and I don't think I'm there yet, especially since I do not own the right endmill for the job currently.

Regarding the movement speed, it looks like you are using nema17 steppers, you did not provide any info on their specs, but I'm using similar motors on the Phoenix and I get up to 10 mm/second stable movement on all axis, 12 mm/s risking lost steps.

So depending on the drivers you use, you should be able to at least double your current speed which looks to me close to 100 mm/minute.

Two tricks come into play to gain speed:

1. Voltage - stepper motors loose torque on higher  RPM's due to inductance. Driving them on higher voltages but keeping the rated current get's you more speed. I'm currently driving the thing on 24V, while the motors are presumed to be  rated for 3V to 6 V (ain't got a datatasheet on them).

2. Microstepping - stepping in full steps creates resonance due to vibrations, each motor has a frequency at which resonance becomes so bad it simply does not step anymore. Using microstepping reduces vibrations and resonance while lowering the torque somewhat (there is a lot of theory on that), and you get extra resolution as a bonus.


While I currently have my own CNC machine (yeah also work of love :) ) working quite well, the original impulse was to build a RepStrap. However I was trown aside from my original intent by the fact that I wasn't able to manufacture a decent extruder at that point and that even if I was to succeed in making it there was still the problem of the plastic filament I could not find locally (ordering it was out of the question). So I diverged in doing a cutting machine instead.

I'm toying with the idea of having an extruder attachment added to the Phoenix extruding Nylon ( 3mm grass trimmer "blade"), I did not attempt anything yet though not sure how well it would work considering it's a different kind of plastics.

Regarding your build I have one question: Is the general movement speed limited by the extrusion feedrate?  

I have one too _raising_hand_

What software are you using?  Would it be software related to reprap control or EMC2 which I believe TinHead uses?

Question to all 3D Model experts (TinHead or ckaos)
RepRap has its own software, then there is EMC2... can EMC2 run a filament extruder?
What parts are compatible between the packages and what parts aren't? 

Since Doboz is basically a RepRap machine the answers are:

1. ckaos must be using some software/script that sends the G-CODE trough the USB serial connection to the Arduino where it get's interpreted and executed - as I did when using the Arduino based solution. EMC2 cannot use USB or serial ports because everithing is calculated on the PC and the resulting control pulses  are applied to the stepper drivers trough some direct interface, usually the ye olde parallel port

2. Considering the above AFAIK EMC2 can run a filament extruder it is just another axis ... I think I saw some discussion about this

3. Mechanically the RepRap is simpler then a CNC due to the fact that the forces required are lesser. Electronically wise ... well both have some type of stepper drivers, the main difference is in control so it's one way or the other. 

Very enlightening... I forgot about EMC2 running through the parallel port...  I also vaguely remember real-time kernel extensions, to avoid the possible problems with all the interrupts on the PC, is this correct?  That is why they also distribute it as a LiveCD image - to cut down on the complexities of installation?

"as I did when using the Arduino based solution" - Why the change?

and finally another question for all 3DWizards :
What is the biggest "problem/issue" with your current setup? 


EMC needs the realtime patches for the Linux kernel to work, this means you need a custom kernel compiled to include them ... no issue for me but for most users a problem it seems, hence the live cd.

At some point I had a bug in the setup causing random lockups. Since all my hardware/software is custom built I had no idea if it was in the Arduino or the drivers themselves. So since I had to trust at least one side, and the Arduino code was already filling up the ATMega168 flash, I dropped it in favor of the trusty EMC. It works great and has realtime controls, I never wanted to switch back to the old setup.

My biggest problem is the noise the thing does, add to it the dust, the constant maintenace needed, the limitations caused by the bit diameter ... you get the picture :)

I can tell it was a labor of love, difficult as that can be sometimes.  At this point how many successful parts has your Repstrap made?  Is it busy now?

Thanks a lot Grog! Yes, you are quite right, however long the process , it was still definetly worth it : It is fascinating to just create/download a 3d design, and then have it appear before your eyes as a real object!

Also now that it has matured, i will be able to print elements for mobile robots (amongst others): i have been drooling over the amazing machines on display here for quite a while now:) 

As for the total number of parts printed so far :

  • at a quick glance, around 100-150 parts that are completely ok (acceptable quality, mechanically functional)
  • perhaps around 40 incomplete/botched prints (things that went wrong , diverse failures, unaceptable quality)
  • the quality and reliability got steadily improved, so there were only 2-3 failures out of the last 50+ batch of printed parts :)

Unfortunalty i had a major electrical problem last week, and its motherboard "died" ( i have no idea what is wrong, all electrical checks are ok, all indivudal components still work, but no reaction), so waiting for replacement parts to repair it, otherwise, it would be printing, as almost always :)