Sunday, 30 June 2013

Adventures in CNC - Part 1

The saga begins....


The time has finally come. After years of wishing and wanting, I am finally going to invest in a CNC Router system.

In this series of articles, I am going to chronicle my experience acquiring a CNC router. Please keep in mind that this is my first experience with CNC so this will be a trial by fire learning experience for me in the extreme.
I hope that by sharing my experiences, I can help other CNC newbies avoid some pitfalls, or at the very least provide some schadenfreude filled comedy as you watch a guy flush a few grand down the pipes. If all goes well, I will end up with a fully functional CNC Router and not a $5000 abstract aluminum sculpture. Stay tuned!

Some basics


CNC (Computer Numerical Control) is a catch-all term that describes the automation of tools via computer control. Many tools can be converted to CNC such as lathes, mills, welders, and routers. 3D Printers also fall into this category.

XYZ Axis
CNC machines of any kind will have a number of axes of motion. The standard is 3 axes labeled X, Y, and Z. The X and Y Axis are the motion of the tool across the length and width of the table. The Z axis controls the height of the tool above the workpiece. By manipulating these axes, the tool can be positioned in 3D space.

3D or 2.5D
A CNC router like the one I am building can be used to carve intricate 3D shapes in your workpiece. But is it really 3D? Not quite. My system is actually considered a 2.5D machine. Where did the extra Half-D go? The length (x-axis) and width (y-axis) are fully covered. But the depth (z-axis) can only perform 'Top-down' cuts. For example, if I was trying to carve out a model of the globe, I could carve out the top hemisphere, but nothing below the equator.

You better shop around


Getting into CNC is a big investment so it pays to do your homework. Like with any major dollar purchase, spend time looking at all the options. Join CNC related forums, read reviews, and Google till your fingers ache. Here are some things you should be considering:

What do you want to do with it? 

It seems obvious but you really need to think about your needs now and into the future. If you are planning to make custom guitar bodies, it is no use getting a machine whose cutting surface is too small to fit a standard Strat. Don't forget about the Z axis (depth of cut) when calculating this.
What material do you plan to work on? Will it be only wood or do you want to do some metal work? You will need a stronger machine to cut harder materials. If you are looking to do a lot of metal work you may be better off looking at a CNC Mill.
You also want to consider how heavily you plan to use the machine. A system that is expected to run 12 hours a day in a manufacturing environment will need to be much more robust than one used occasionally for hobby use.

Shipping and Handling

Don't underestimate this! Even shipping a medium sized machine locally can easily add $1000 or more to the purchase price. And if you need it shipped internationally, make sure you are sitting down when you get the estimate! Don't forget about the taxes and duty that will be added as well.

What tools can it use?

Better CNC routers will be able to use an Industrial Spindle as a cutting tool while cheaper models may only have brackets for standard hand routers. A Spindle will add around $1500 to the price but will run longer and quieter with more power to boot. Then again you could buy a lot of $120 hand routers for that money.

Build Quality

This is a big one! A CNC router is in theory a simple device. If you break it down, it basically consists of three components that move along guide rails using linear bearings. Threaded ball-screws are turned by motors to push or pull the components along the rails. The rest of the machine consists of a frame that holds the guide rails in alignment.
What makes a CNC machine complex is the precision required during these movements. Any sort of flex or distortion in the frame will result in errors in the desired cut. A cheaper machine will most often cut costs by using cheaper ball-screw assemblies or lighter materials in the frame construction. This results in less accuracy.

Assembly required

Some machines come in a crate fully assembled and ready to run while others will arrive as a box of parts requiring you to do all the assembly. Make an honest assessment of your comfort level in assembling a complex machine. You can save some money with the kit but only if you have the tools and know-how to DIY.

Motors & Electronics

This is what makes your CNC machine move. When you break it down, the electronics in a basic CNC system consist of three motors connected to a computer. The computer precisely rotates the motors which in turn moves the three axis of the machine.
The components required to connect the motors to your computer consist of:
  • An interface board that connects to your computer via parallel port or USB
  • A motor driver board (one for each motor) that receives signals from the interface board and routes power to the motor
  • A power supply capable of providing power to all the motors
Fully assembled machines have all this built and connected for you. If you go with a DIY model, you will most likely have to buy these components yourself and wire up the machine. Expect to spend around $500 if you need to buy these yourself.

Software

Beware, this is a budget buster! Like any computer system, a CNC machine requires software to run. Some of these programs can be ridiculously expensive for a hobby user so be sure to include this in your budget.
First you need something to design the part you want to make. This is done with CAD (Computer Aided Design) software. CAD programs allow you to draw models of 3D objects to precise dimensions and can range in price from free (SketchUp) to incredibly expensive (AutoCAD).

After your part is designed, you then will pass the file to your CAM (Computer Aided Manufacturing) software. CAM programs take the model of your part and calculate how the CNC router will move its cutting tool to produce the object. The result will be a list of instructions your CNC machine can understand in a format called G-code. More advanced CAM programs can actually contain CAD functionality so you can design and manufacture the part in one program. These programs tend to be expensive so expect to pay $500 to $1000 for something decent.

Finally, you will need CNC control software to drive the actual machine. The control software takes the bare machine instructions (G-code) and tells the motor drivers of your CNC what to do. Mach3 tends to be the popular software for this and retails for just under $200.

As you can see, your software bill can be quite high when all is said and done. Some CNC packages will come bundled with software so be sure to take this into account when comparing prices.


Check out Part 2 where we look at some actual machines and try to sort out the men from the boys.


5 comments:

  1. I've always enjoyed reading your blog and this particular post was especially good. Thanks for sharing it.

    ReplyDelete
  2. Congratulations for getting a CNC router, finally! However, i have a few questions. What do you need the machine for? Have you always been fascinated with this kind of machine. I know one can benefit a lot by using this machine. Anyway, keep us posted.

    Thermwood.com

    ReplyDelete
  3. The outcome will be a rundown of directions your CNC machine can comprehend in a configuration called G-code. More cnc machining propelled CAM projects can really hold CAD practicality so you can plan and produce the part in one project.

    ReplyDelete
  4. Great thoughts you got there, believe I may possibly try just some of it through out my daily life.
    CNC Routers

    ReplyDelete