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My CNC Router Adventures

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My CNC Router Adventures

Postby mangozac » Tue Jul 19, 2011 8:24 pm

So it's finally happened - after more than a year of stuffing around contemplating CNC machines I finally have one!

For those who haven't been following the CNC Machining for Miniatures thread I recently bit the bullet and ordered a "Walter 2520" machine from CNCDIY. They're a cheap Hong Kong/China based manufacturer and all up I paid about AU$800 to land it here (around $300 of which was shipping). Shipping was via UPS and only took about a week. I was pleasantly surprised to find that it had arrived not only without any noticeable damage but also without requiring any assembly!

Here's pics from the moments following unpacking:
Photo0380.jpg

Photo0379.jpg

Photo0381.jpg


The control electronics for the system are designed for use with an old x86 PC with a parallel port, however I'm planning to use my laptop to run it (admittedly against the recommendation of some, but it's a challenge I'm willing to accept). In order to do so I will be building a Planet CNC USB CNC controller. In order to protect my laptop I will be ensuring that all signals between the USB controller and the machine are optically isolated. Because of this I had to wait until the machine arrived so I could see exactly what kind of isolation (if any) the control electronics offered. So I popped op the control box and had a look:

Photo0383.jpg


The board on the right is the spindle variable speed power supply. The red board on the left is the parallel interface and stepper drivers (heatsink mounted underneath). Underneath the whole lot is a large switchmode power supply. Good news is that the interface card looks like it has optical isolation on every signal - when I get a chance I'll test it out with a multimeter to confirm! I will be designing a PCB for the USB controller myself, so with the driver board already having optical isolation I'll only need to include isolation for the limit switches. The machine as purchased doesn't come with limit switches, but adding a few microswitches will be a piece of cake. Plus they'll wire up so nicely with the movable cable ducting on the X and Y axes.

In terms of software my plans for starting out with routing/engraving are:
- Inkscape for drawing the design -> saved natively as .SVG
-> SVG import into PyCAM to generate G-code
-> Planet CNC USB CNC control software to control the machine from the G-code file

The only cost in the above toolchain is the USB CNC controller, at $100. Inkscape is a fantastic piece of open source (free) software I use for both hobby and professional work projects. PyCAM is also open source and my evaluation of it so far has proven it to be quite good. Only actually running the output on the machine will tell!

So as noted above, my next step is to build my USB interface card. In the long term I'd like to mount all of the control electronics under the base of the machine, but for now I just want to get moving so I'll simply retrofit the existing control box.

Watch this space!
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Re: My CNC Router Adventures

Postby blind pig » Wed Jul 20, 2011 12:21 am

*Jealous*

I know dicking about with electronics is your thing (and something I would love to do but fail miserably at as a nerd :oops: ), but can you not buy an off the shelf thing that does what you want to make?
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Re: My CNC Router Adventures

Postby mangozac » Wed Jul 20, 2011 6:56 am

Fair question. Yeah Planet CNC do have an off the shelf 4-axis controller board you can buy, however it's a bit overpriced and doesn't feature any isolation. Isolation can always be tacked on but combined with the first reason it's really no big deal to build my own. I'll try to get the board design drawn up over the next couple of nights and then go into the office on Saturday to etch and assemble it.
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Re: My CNC Router Adventures

Postby mangozac » Wed Jul 20, 2011 7:42 pm

Well upon further study of the driver board I have discovered that it features a header (socket) for connecting limit switches, all of which are optically isolated from the parallel port connector! This means that all I have to do it design a simple USB board containing barely much more than a microcontroller and USB jack!

Sometimes things come together ;)
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Re: My CNC Router Adventures

Postby Lane » Wed Jul 20, 2011 8:33 pm

Not sure a Simple USB interface will be enough.

One of the issues when the were designing the SmoothStepper was pulse timing.
Most stepper drivers use a step - direction input, meaning one input says what direction to rotate and the other is a pulse telling it when to turn. The frequency of the step pulses determines the speed. On a single axis this would just be a problem of the feed rate being off, or stuttering if they arrived unevenly. Run two axis at the same time with uncertain timing between step pulses and you could end up with CRAP. A diagonal move is two axis moving at separate constant feed rates. A circle is two axis moving at variable feed rates that must be perfectly coordinated.

IIRC their solution involved a buffer and timed output pulses.
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Re: My CNC Router Adventures

Postby mangozac » Wed Jul 20, 2011 9:26 pm

I'm sorry I should have used the correct terminology - USB motion controller. The Planet-CNC USB to stepper driver design, which uses its own PC software to send commands through USB to the microcontroller which generate the pule trains. Indeed I've read enough to know that USB-parallel port adapters are useless!
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Re: My CNC Router Adventures

Postby Lane » Thu Jul 21, 2011 5:04 am

OK, know you mentioned using their USB controller before but then you mentioned designing your own so I was unsure.
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Re: My CNC Router Adventures

Postby mangozac » Thu Jul 21, 2011 7:49 am

I'm just making my own PCB of the Planet CNC design to suit my setup.
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Re: My CNC Router Adventures

Postby mangozac » Thu Jul 21, 2011 8:27 pm

OK the controller PCB layout is complete. Not the prettiest board I've ever done (in fact close to the opposite) but since I'll be etching it by hand it doesn't really matter (only the red lines will show up as copper tracks). I might yet add a ground plane copper pour more for the hell of it than the extremely slight RF protection it will give.

controller.jpg


I'll etch it up and assemble on Saturday morning - and maybe even test it out! I've designed it so that it will drop straight on top of the driver board that came with my machine.
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Re: My CNC Router Adventures

Postby mangozac » Mon Jul 25, 2011 10:06 am

Update time:

I had a shocker of a weekend where absolutely nothing worked as planned in any of my projects. I built up the Planet CNC controller on Saturday and spent ages mucking around without getting it more than half working, and then not working at all! Note that the USB connector in the picture in my last post is actually wired incorrectly - fortunately I did notice this before I made the board and corrected it. Here's the final board installed in place of the parallel port connector on the CNC DIY stepper driver board:

motion_controller.jpg


I last night realised what I had done wrong and upon fixing my mistake and plugging everything in this morning it worked like a charm first go! It was exciting to see the machine executing the first 25 lines of G-code (all that the Planet CNC evaluation software will allow) or programs, however it did run up against limits a few times. I'd better sort out these limit switches ASAP.

I've actually found a few things I'd like to do change on the motion controller board already - for instance it would be cool to add a spindle on/off control relay (which the Planet CNC software does support, I just need to add the electrical connection).

So I'll purchase a license for the software and get ready to rout out some parts!
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Re: My CNC Router Adventures

Postby Seb » Thu Jul 28, 2011 12:39 pm

Brilliant stuff Zac, good to see the project underway after talking about it when you were down in Melbourne :D

Was very interesting reading through all the tech in your efforts to get the set up running. Look forward to your updates.

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Re: My CNC Router Adventures

Postby mangozac » Fri Jul 29, 2011 8:06 am

Thanks Seb! Yeah I've been talking about it for ages so it's great to finally have things happening! Now it's just a matter of finding the time to finish it off and start playing!
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Re: My CNC Router Adventures

Postby Bar » Thu Aug 04, 2011 3:55 am

Incredible.
Thanks for the link to this thread Zac.
Am i to understand you will eventually be able to route parts from digital files???
What kind of filetypes do you need?
Are you able to alter existing files for your purposes?
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Re: My CNC Router Adventures

Postby mangozac » Thu Aug 04, 2011 8:16 am

Hey Bar great to see you here on RA!

Yes, the idea is that you draw up designs on the computer and then machine them out. The first step I'm planning to achieve is "flat pack" designs, whereby the design is simply routed out of styrene sheet, which you then assemble into a 3D shape. Kind of like cardstock templates of models.

The next step from there is to have the machine rout out parts in full 3D. There are many limitations (like no undercuts at all, and the size of the cutting tool limits the amount of detail), but if the parts are broken up the right way there's no reason why some nice parts can be produced that again only need a final pass of detailing. I heard on the grape vine that this is how the Quantum Gothic parts were designed.

Something like the main hull shape of your Arrowhead model would be a prime candidate for this process. That is if you had the patience/skill to design all of those curves in 3D CAD first!

The software which drives the machine takes an industry standard file format called NC or G-Code. The NC file is effectively a list of commands telling the machine how to move each axis. The NC program is generated by a CAM program, into which you feed a CAD file to generate from. I'm attempting to stick with open source CAM software at the moment, and can accept two formats: .SVG (Scaleable Vector Graphics, produced using Inkscape) for flat pack (which can quite easily import from PDF by the way) and .STL, which is a very common standard format for 3D models.

To be honest I'm still getting used to the file conversion process. I did try something last night but the SVG import screwed up and I couldn't get an appropriate toolpath to be generated. Hopefully I'll find some time on the weekend to play some more and maybe even get to the point of cutting something out!
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Re: My CNC Router Adventures

Postby mangozac » Thu Aug 04, 2011 7:25 pm

So here's a couple of questions, aimed probably at Lane since he's the man in the know with this kind of stuff ;)

So I need to buy some milling cutters for the machine. It's got a 1/8 ER11 collet (although I did buy a set of collets with other sizes too) so I suppose I should stick to 1/8 shank tools. I figure I need the following:

- Ball end cutters:
- 3mm
- 2mm
- 1mm

- Square end cutters:
- 3mm
- 2mm
- 1mm
- 0.5mm (for routing out shapes in styrene sheet)

Obviously the smaller cutters are more likely to get broken than the larger ones, so I'll grab a couple of the 1mm ones. Also, the 2mm cutter might be unnecessary. It also might be a good idea to get something big like a 5mm square end cutter for roughing out shapes...

Any other suggestions?
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