Introduction: 6x6x6 3D Print: Delta CNC

About: I am a Dutch design engineer, living in Wales (UK) and working in steel industry until recently, as my request for voluntary redundancy did get accepted. I am married, and I am a father to a little boy. I like…
As a runner up winner in the recent 'Real Challenge', I have been awarded with a custom 6x6x6 inch 3D print for my 'CNC machine for machining large pieces of polystyrene foam'. I realised what an opportunity this presented and thought of many things to do with it. Make a 3D print for something at work and impress the boss? Design a custom iPhone case, cram 30 cases into the print and flog them on Ebay? Print someone else's design?

I don't think so..

I desired a bit more of a challenge. How about using the 6x6x6 print to create all the custom bits for a simple, elegant and fully functional CNC machine? I am not talking about a conventional 3-axis gantry-type CNC mill, but something a bit more exciting. I set myself the challenge to design and build a machine based on the Delta Robot, capable of milling/drilling in soft materials, and have all the main custom components for the motion platform fit in the 6x6x6 inch envelope of the awarded 3D print.

This inctructable has initially been published after the completion of the design phase. The first few steps will discuss the objectives, background, software & electronics, mechanical design and conclusions. In addition there are several steps to be completed afterwards, showing the actual build of the machine. A change log is attached to this first step. Current version: V0.11

Enjoy,
Richard Tegelbeckers

Step 1: Objectives

Objectives:
  • An important objective is to create a design for a Delta-robot based CNC mill, where the majority of custom components for the motion base will fit in a 6x6x6 inch envelope.
  • The components in the 6x6x6 envelope must be printable on one of the Objet 3D printers at Instructables.
  • Elegance is high on the agenda. Not only for the way the machine looks, but also in the way the motion base moves.
  • As I already have a large CNC machine, I will initially try to 'borrow' as many parts as I can in order to keep the cost down.
  • The motors must be powerful enough for the machine not to lose any steps, without having to resort to gearing.
  • Speed is not the biggest priority.
  • The accuracy of the mill should be sufficient for drilling small circuit boards (think free version of Eagle PCB) and milling small items.
  • Last, but not least, it should be fun to design, build, and use the contraption!

Step 2: Background: Delta Platform

The Delta robot has been developed in order to enable high-speed picking and packaging. For CNC milling the speed is not really an issue, but there are other advantages that make the delta platform useful:
  • There are no costly linear slides, only pivot points.
  • All the important motion mechanisms can easily be located above the work piece, away from debris.
  • Simple mechanical concept, with low variety in components.
  • The way a delta works is just more interesting than the majority of linear platforms...

The picture in this section is from the original patent, which expired a few years ago. Further reading: http://en.wikipedia.org/wiki/Delta_robot

Step 3: Software & Electronics

In terms of electronics I am initially going to use the setup from my large CNC mill. I did have some trouble with Chinese stepper drivers before, but this has been sorted by replacing them with second hand YOOCNC drivers from Ebay. Although the YOOCNC drivers are Chinese as well and are also based on the same Toshiba TB6560 chips, they are of much better quality. I have looked at many designs around TB6560 chips and noticed a lot of issues. Many are related to the use of very basic opto couplers for feeding step signals into the TB chips.

In order to be fully flexible for development purposes, I have two different options for connecting the stepper drivers to the PC. First of all there is the Arduino, which currently is loaded up with GRBL. The second option is the connection over parallel port using a 5-axis interface board. The last option should enable me to run LinuxCNC.

At the moment I do not know how to go about sorting out the software. I will worry about that after I have an actual mechanical assembly I can play with. Some links I found suggest that I do not need to start from scratch:

http://kvarc.extra.hu/step/motor/emc/emckinematics.html

http://forums.trossenrobotics.com/tutorials/introduction-129/delta-robot-kinematics-3276/

Step 4: Mechanical Design

See the pictures for my design. I managed to fit the 3D printed motion base components into the 6x6x6" envelope and was left with enough space to add hinges and handles! The main reason why I was able to make good use of the space, was the separation of the tool holder and the motor base into three separate components. By doing this, the tool holder is able to grip the drill and the motor base is able to grip the overhanging steel tube from the main frame. The tube can be used to pass wiring from the motion base to the top of the machine, where eventually the permanent electronics can be mounted. I made sure the motor arm will be sturdy by connecting it to both shaft ends.

You will notice there is nothing in the model holding the rod ends onto the shafts. I am planning to sort this by using elastic bands or tension springs between a pair of links. The doors can be lifted out. Hinges are universal, ie. not handed. Take out the pins from one end, place them in the opposite positions, turn the door around and the door opens the other way around with the only thing wrong being the text on the handle now reading: 9x9x9... Hinge locations not being used as hinges can be used to lock a door by inserting thin pins.

Attached to this step is a small movie file. Open it up to see a short animation of the motion base. There are some random oscilations on the motors in order to generate movement.

Step 5: Conclusions

I achieved the objective of containing all 3D printed components in the 6x6x6" volume. Hooray! As I was aware the parts would eventually be printed on an Objet, I was able to design around the knowledge that there is support material to take care of overhang. This can be an issue with reprap and makerbot type of printers with only a single print head for the build material. Also, the Objet is superior in resolution. I made use of this feature by applying tight tolerances in certain areas. If necessary I will need to rework as required, but I hope I will have gotten it right for the majority of parts!

If I would have designed the parts for being produced on a more basic printer and without the 6x6x6 inch restriction, I would have designed everything in a slightly different way. For example, I would not have had to split the motor base and tool holder into three separate parts. Still, having designed functional 3D printed components for the first time, I now want to do more! I am certain I could increase the accuracy of the Delta by adding some gearing... The tool holder could be replaced with a purpose designed unit with integrated light weight 3D print extruder... I am sure now: Stage 1 is to get permanent access to a 3D printer, Stage 3 is world domination. No idea what Stage 2 is though!

Step 6: The Build, 3D Printed Parts

Some time ago I sent an email to the good peoples at Instructables in regards to the custom 3D print I won. I was informed that 'None of the prizes from Make it Real have been sent out.  Our 3D Printing individual will be contacting all of the runners up shorty'.

More will be added to this step, as soon as there is progress on this front. For now, see the pictures for my suggested print. I left a gap of at least 0.5mm between components in order to prevent them from sticking to each other. I still have to generate a final STL file, but will do so at the moment that it is needed. I am planning to publish the as-built design files after actually assembling a machine myself.

Step 7: The Build, Electronics

More info to follow in this step after actual build...

Step 8: The Build, Fabrication

More info to follow in this step after actual build - This might be very soon, as the fabrication is very simple.

Step 9: The Build, CNC Machined Parts

There are only two parts to be CNC'd: the wooden top and wooden base plates. I still have to add mounting holes, but will work this out when I will get to it. Should be easy enough on my big CNC. More info to follow...

Step 10: The Build, Mechanical Assembly

More info to follow in this step after actual build. So far I assembled a pair of link arms and added a photo to this step, showing how I am planning to use rubber bands for keeping the arms connected.

PS. Can you spot the most important tool in the picture? It is the one with the wooden handle...

Step 11: The Build, Software

More info to follow in this step after actual build. I just hope I don't need to start from scatch... Advice welcome!!!

Step 12: The Build, 6x6x6 Delta CNC in Action

More info to follow in this step after actual build...
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