G Code, CNC and Steppers

Twenty years ago an A3 plotter would cost you the same as an entry level 3D printer nowadays.  A milling machine for a hobbyist can be purchased second hand for about U$2 000 and for a further U$2 000 can be modified to CNC. Hobbyists are doing this even more cheaply. From your automated milling machine hobbyists are now building components for their home built robots.  This even includes the servo or stepper motors but with cheap Chinese supply this becomes unnecessary. An entire software package to generate code is available from Mach 3 at about U$100.00.  Planet-CNC can supply you an entire USB-CNC controller.

I have gathered some very useful links to show you all (and myself) where we are going with this. The one thing that will stand out is that next time you go browsing there will be many more websites dedicated to CNC – we really are moving into the fast lane where the computer can work for us.

First of all most CNC tools used by hobbyists use G code. But what is CNC?

CNC is Computer Numerical Controller. This is the code which is generated by CAD packages to aid the cutter to stick to your design cut out. The G Code, possibly you may use,  is an open source language used by most hobbyists and of course is available for Linux as well. A great link to learn more about CNC is found here, the Technology Student.

A Wiki description on G Code is found here.

A very informative website with a tutorial on learning the G-Code is Bob Warfield’s CNCCookBook. I won’t even attempt to add another link on this subject because I found this to be the best, also with nearly 30 years experience in machining the facts are all there.

Wanting to build a robot? Go to the Robot Shop, claimed to be the biggest and best online store for your robot needs. If you like browsing around you will also note that their pricing is also very affordable. Of course you can possibly go to eBay but if you are in a rush why worry, the Robot Shop has supplies for everything you need.

Now milling machines and lathes are a different beast – I am not a machinist but can vouch that you get what you pay for. In South Africa a good place to start is Adendorff Machine Mart. Their lathes and milling machines are affordable (remember these are not toys so they still do come at a price). I have checked their equipment and yes, they can be converted to CNC but I accept no liability for this statement. They have stores all over the country – have a look and speak to the staff.

Want to build your own from scratch:  The Instructables website is always a good read especially their 3 axis milling machine for model makers.

Build Your Own CNC Router is a wonderful website, packed full of tutorials, parts, and it has it’s won forum. Kit for a pick and place machine as well.

Where to source stepper motors or servo motors?  Most of the CNC machines I have seen use stepper motors. A great source for stepper motors are dot matrix printers – the old variety. The modern stuff has nowhere near the same build quality – so be warned. The stepper motor must have 1.8 deg per step – 200 steps for 360 degrees. 1.8 degrees seems to be the standard, don’t go higher. The Chinese online webstores are a good place to look as well as eBay. Most websites will advise you stay away from servo motors and they do have a point – they are not as reliable neither are they as cheap.  In my mind though, the servo closed loop is more accurate but servo motors come at a price. (I lean towards servo motors because older radar sets used them to align display sweep to antenna – they would run for years without failure but they rotate at a constant speed and not put under the same stress as CNC router movement. Geared steppers would then possibly be a better bet for close tolerance work).

Stepper and servo motors are used extensively in marine and aviation equipment.  Most of the older Sperry gyro equipment used steppers to drive the compass repeaters. These were extremely good quality and I doubt even after twenty years of running they would show sign of wear but do check the winding resistances – all stepper motors run hot and I found this was normally the first cause of failure when conducting repair – hi resistance.