Last updated: 4 March 2015
After building a RepRap 3D printer years ago, I have not used it once. The parts it creates are not accurate or robust enough for my purposes.
I do however have a need for a machine that can cut small aluminium parts like brackets, and also medium-sized wood parts such as drawers or boxes. Mrs Naut would also find it useful to have a machine to cut out complex shapes such as stencils for artwork.
With the experience of building a CNC 3D printer under my belt, I decided to strip the 3D printer of its motors and electronics, and re-use them in a desktop CNC router.
Design requirements for this CNC router:
- low cost, under £150 (the contents of my spare change jar):
- must re-use the NEMA17 motors and electronics from my 3D printer
- must use my Dremel as the spindle
- work area of at least A2 size (420mm x 594mm) – to be useful to Mrs Naut and also for making larger items such as boxes
- must be capable of cutting 6mm aluminium plate – it’s OK if it takes its sweet time about it
- repeatability of +/-0.1mm, resolution of something less than that – from reading forums this kind of accuracy from a lightweight desktop machine is achievable
- must be relatively quick and easy to build – I do not want to spend weeks machining parts
Base design considerations:
While there are many build-it-yourself kits and designs out there, these are mostly for larger routers or are Chinese-sourced items or questionable quality. They are all also quite expensive – the larger the system, the higher the cost (at an exponential rate). If I were to plump for a larger unit I think I would go with the beautifully designed Platform CNC kit – this is a stand-out design and even comes in orange.
As is usual in design work, everything is a series of compromises. A larger or more rigid machine will be heavier, and therefore will require larger steppers. Excluding the cost of the motors themselves, the additional cost of the drivers and controllers alone is significant when stepping up (no pun intended) from NEMA17 motors running at less than 2 amps, to NEMA23 motor running at up to 5 amps. Needing to keep it cheap with my NEMA17’s, I needed to compromise on size/rigidity.
I spent some time a couple of years ago designing an A3 work area, desktop CNC router made out of MDF. While I had fun doing the design, in the end I abandoned the project as it would be very time-consuming to cut all the parts without a CNC router, and I did not want to invest all this time on a design that was not proven… this project may yet live again. Just for fun, here’s a screenshot of the last design:
Learning the lesson from this abandoned MDF router project, I focused on designs that had already been built using available components.
In the mid-priced desktop range the options really come down to the choice of linear guide system. Excluding more expensive options like round rails or linear bearings, the choice narrows to aluminium extrusion with either:
Within these two options, there are three main reference designs. I wanted something quick and easy to build, and with proven capabilities (e.g. videos). Therefore I decided to base my design on one of these:
- Shapeoko 2
- OpenBuilds OX
- OpenBuilds Routy
The Shapeoko 2 initially caught my eye as it used NEMA17 motors. However, there are lots of reports of flex and chatter in the forums, and the design does not look very rigid (20×40 aluminum extrusion). Tellingly, the the Shapeoko 3 has been announced with “200% thicker” rails – something of an admission about the rigidity of the Shapeoko 2 I think… The final nail in the Shapeoko’s coffin was the lack of availability of MakerSlide in the UK.
I found the OX after looking for suppliers of linear guide aluminium extrusion in the UK. This led me to V-slot, and from there to the most popular desktop CNC design on OpenBuilds, the OX. There is a large community around this design, and most user opinions are favorable. However, the OX uses NEMA23 motors, and I could not find anyone who had built one with NEMA17s. Also the OX uses 28 (count ’em) v-slot wheel kits – at nearly £5 a go this would blow my budget without even considering the rail…
After discounting the OX, I finally found the Routy. This was a previous design by the OX builder, used to make parts for the prototype OX and videos are available online showing it cutting aluminium. While it appears that not many people built one and opinions are not generally favorable, this may largely be down to an incomplete/incorrect BOM that was published on the OpenBuilds Routy page, and the rise of the OX in popularity. Planning to CAD my own in SolidWorks, this wasn’t a problem for me.
Creating CAD drawings:
With the base design selected, I downloaded a bunch of CAD files from the excellent OpenBuilds site and set to work in SolidWorks.
As of early March 2015, I settled on a basic structure:
- 20×60 v-slot all round – stronger than 20×40 but not as heavy as 20×80, a good compromise
- double-width X-axis gantry rail – although this may change to single 20×60 linear rail plus 2″ x 1″ 10awg (3.2mm) aluminium box section, as the box section will be easier to join to the v-slot
- approx. 800mm long x 600mm wide footprint – will need to adjust to achieve the required work area
…more to come…