Picture of CNC machine for shaping large pieces of polystyrene foam

This instructable shows how to shape polystyrene foam, using a CNC machine. Starting with a brief introduction, design software necessary for creating an STL file is discussed. This is followed by a method for creating G-code, using an STL file as input. After this comes the introduction to GRBL, an arduino based system for using G-code to control stepper motors of a CNC mill. Stepper drivers are mentioned, after which the creation of large CNC hardware is described. The instructable finishes with next steps.

Richard Tegelbeckers

PS. I plan to expand/update this instructable as I gain experience and make improvements to my machine. Come back to check if you are interested! Also, if you would like more clarity on any of the steps, leave a comment and I will try to help out. I could potentially add more pictures as I took photos/videos of pretty much everything I did.

Step 1: Introduction

Picture of Introduction
I became interested in CNC machines, shortly after being let down by a 3D printing firm in the UK. Intrigued with the reprap efforts, I decided that having a drill-like tool wizzing around in three directions would be an easy target to achieve. I did my research and ended up slapping together a small machine, using an old flatbed scanner, an ancient printer carriage and a defunct CD player. I learned from the experience and used it to come with the following objective: to create a large 3 axis CNC machine, capable of machining polystyrene foam. The machined foam can then be covered in a protective layer (eg. water based latex), before pulling a composite fibre mould(ing) from it.
cyiangou21 year ago
hello, I really like your project and I would like to do it. Can you help me please how to connect all electronics parts or how to program the arduino?
Thank you
donkeyknee2 years ago
Finster1012 years ago
Cool machine! Do you have any pics of the part you molded from the mold you showed cut in this instructable? I'd love to see the finished product.
RTegelbeckers (author)  Finster1012 years ago
Thanks for your comment! The red gel coat resin I used was over ten years old, having been at the bottom of a badly sealed bucket. As such it did not want to harden out properly. I applied the laminating resin with extra hardener in the vain hope to compensate. This only resulted in the generation of too much heat, which caused the melting of the polystyrene mold in certain places. I left the part in a corner of my workshop as after several days the gel coat was still tacky. By now it must be ok to still do something with the part. As you reminded me by posting your question, I will dig it out next time I am in my workshop and finally finish it off! In the first week of July I have some panels to machine on the big CNC, so I will have a go at it whilst 'babysitting' the machine. Pictures will be posted soon after that...
cjc03062 years ago
Hi RT! Congratulations on a fine build. I am in the process of building a similar machine inorder to print some prototypes of my inventions. Since I have left over aluminum 1 5/8" tent poles laying around, I decided to build the foam cnc with them instead of square tubing. The current design Im prototyping measures 32" x 60", so I need a large machine. I have already built a 3D printer so Im pretty familiar with cnc technology. Any suggestions would be greatly appreciated, thanks.
RTegelbeckers (author)  cjc03062 years ago
Hi. How do want to connect the aluminium tubes to each other? Welding aluminium is not easy and usually requires a TIG welder.

In the near future I will make some alterations to my own machine. On the horizontal axes I want to further reduce the backlash and add gearing, by replacing each coupling with a chain and two sprockets. A ten tooth sprocket on the motor and a twentyfive tooth sprocket on the drive shaft will give a 1:2.5 reduction. Check my instructable in a few weeks as I will document the upgrades.

My z-axis is not very stiff in sideways direction, especially when the tool is all the way down. Not much of a problem for shaping large pieces of low density foam, but could be an issue in other applications.

Good luck wih your own machine!
Vika843 years ago
Good Luck babe! xx
RTegelbeckers (author)  Vika843 years ago
Thanks gorgeous! Sorry for having spent the last two months in my workshop... xxx
FoolishSage3 years ago
This is a really cool build! Can you estimate how long it took and how much it ended up costing?
RTegelbeckers (author)  FoolishSage3 years ago
Thanks! The total cost for the small machine was £70 (mainly for electronics)and it took the occasional hour over a few months. The second, larger machine took several days over the last two months. The total cost for parts and consumables was £665. I also spend £28 on job specific tools, just as reamers (8mm & 10mm) and drill bits.
RTegelbeckers (author)  RTegelbeckers3 years ago
I noticed I missed out on a few items on my initial costing. I now worked out the total cost for parts and consumables as being £728. This does not take into account the materials I already did have. See step 6 for a Bill Of Materials.
mgingerich3 years ago
Have you considered building custom motor drivers? I'm making a CNC with from scratch electronics right now, and it's worked pretty well so far. Way cheaper too. Just something to think about. Great instructable!
So I am not the only cheapo person on the web. That's nice to know, so how are you planning to build the electronics from scratch? I am sort of a person with shallow knowledge in this field, and would appreciate you sharing the knowledge that you have with me.
I'd be happy to. My way of doing things was a little unconventional, since I'm controlling my CNC with a microcontroller. The schematic on page 3 of this instructable is the main part of my motor driver. four of these are needed to control one unipolar stepper motor. I'll let you know when I write a more detailed instructable on it.
Here's the link: http://www.instructables.com/id/How-To-Make-an-Optocoupler/
Very interesting, looks much easier than using some relays. Thanks! I shall be making my CNC's main chassis today. I just finished gutting a printer, and scanner, so now I have some steppers, worms, etc. The only thing is that I cant decide on what material to make the body. Wood, plastic, steel, I dont know what it should be made of, probably wood or steel though. Thanks for the insight, I have a picaxe 18x lying around that will work great with the opticoupler.
Glad I could help :) What tools did you use to machine your steel? I'm restricted to wood so far because I don't have access to a shop. Let me know when you get your machine built!
RTegelbeckers (author)  mgingerich3 years ago
I have used a 'custom driver' on an x/y table I played around with, years ago. I used four PN2222 transistors, four MJE3055T transistors and four MJE2955T transistors to drive a single stepper. I used a DPDT relay to switch between the two stepper axes, losing holding torque in the process. The maximum current would have been in the order of 1A at 12Volt. I will now make a driver based on a Toshiba TS6560, which I can get for £2.24 each, incl. delivery: http://www.instructables.com/id/How-to-make-a-driver-for-a-stepper-motor/
The driver is not only good value, it also is economical on the ports needed on the microcontroler: per axis it only needs one line for steps and one line for direction. This means a bottom of the range arduino uno can easily handle three axes and will be left with a few lines spare. On top of this, it will allow for microstepping. This is essential on my rig as each step would otherwise be 0.4mm in size. It saves me from having to add a costly gear reduction to the motors..
ketirock3 years ago
Very Impressive.
Vika843 years ago
I managed to get movement by using the 12 volt pololu based electronics from my first, smaller CNC machine. In one direction the main carriage did move sort of ok, but in the other direction it needed a bit of help as it was jurky. The Toshiba based drivers running on 24 volt should in theory be good enough for the job. As I only give it a quick try, I hope I can still get them to work by tickering a bit more. Otherwise I will be very interested in your custom drivers!

PS. The price for the TB6560 drivers was pretty good: £36.65 for all three incl. delivery - source: Ebay
RTegelbeckers (author)  Vika843 years ago
OOPS! I was logged in under my wife's credentials for the last comments... Check out her instructables and especially the one for the Swan if you want to impress at a diner party!