Maker Space – CNC and 3D Printing

Why 3D printing and CNC machines top the maker charts

Building your own guitar? Cutting a face-plate for your new amp?  Designing and manufacturing decals?

For those of you just starting out, welcome to the club!  The Maker fraternity in South Africa is believed to be very much alive and well in Cape Town and Johannesburg where believe it or not Cape Town is supposedly the capital.

Not even 5 years ago CNC machines were slowly becoming the rage, 3D printing only just starting to make an entry into the maker space. Although using similar parts standardisation was a key issue. Stratosys is just one such manufacturer which dominates the market, with their smaller brother Makerbot being possibly the defacto for small scale prototyping.  CNC milling and lathing has always been a favourite topic amongst DIY modelers and professional craftsman.  They have become more accurate and cheaper.

Differences

A 3D printer is known as an additive device, milling subtractive.  One removes, one adds.

  • There are four main components to both – having a minimum of three axis, Z or up and down, Y- and Z-  lateral and lengthwise movements.  More axis can added, usually a fourth for head tilt.
  • Moving gantry or moving bed
  • Router, spindle with cutting bits or extruder which heats a plastic.
  • Computer controlled, either onboard or external notebook or PC.

The motors used in CNC and 3D printing are either stepper or servo.  Stepper motors are favoured for their pricing, servo for speed and preciseness. (Steppers can be very precise, usually the rotor can move CW or CCW in 1.8 degree steps. 200 steps to a revolution).  Servos use a feedback loop. Steppers can use calibrated optical sensing.

The Nema standard is used for the physical sizing of stepper motors.  Be careful of the Nm torque ratings – the Nema standard may incorporate more than one holding torque capacity on any available size.  This is especially seen in the more popular Name 23 range.  The more holding torque, the more expensive.

The above models will include stepper motor drivers, usually PWM drivers in H-Bridge format, controllers – the interfacing to PC and a power supply.  As stepper motors are not DC driven (rather PWM) the builder would step with a much higher voltage but at a constant and therefore controlled current.

Arduino shields are more often than not inadequate as motor drivers (current limitation).  Home brewed drives are popular. See below.

There is no constraint on bed size.  Bed flexibility is an issue, likewise the gantry.  The better the quality, the higher the tolerance.

A common question coming up on the forums is how to calculate motor size. The common answer to this is bigger is not necessarily better. Accuracy is.  The sizing of spindle motors is very important.  There must be no stalling or overheating through the cutting process. Likewise, in 3D printers the extruder can be the most expensive part to the printer. Head clogging is common amongst the cheaper ranges. The bed and work area also needs to be kept at an optimum temperature.

Parts and accessories.

We now have a slew of outlets advertising 3D modeling kits and parts for CNC machines.   Ball and lead screws are very expensive so shop around. In my own checks the retails stores all seem to be very competitive.  It would be great if local manufacturers could also start playing in this space to force prices down.

Stepper motors:  Be careful of the holding torque for a specific size. Where you may be getting a bargain could be due to a torque difference.

Power supplies and drivers:  Don’t underestimate and under-power.  Suppliers will match drivers and motors. Ghecko drives are thought to be the best.  There are others, Wantai is also known to be reliable.

The beds and gantry are either made from aluminium extrusion, MDF or plyboard.

eBay is usually a good place to go to get pricing but a word of caution:  Shipping charges are exorbitant.  Some of our SA suppliers are not making big margins. Support them if you can.

Lastly, not coming from an expert but rather a Googler and reader, there are great plans out there. (see under further reading). But make sure that whatever you built can be dismantled easily and cheaply.  The parts must be re-usable. Build with an intent to make better. Build with an intent to cut wood and aluminium.  Build  to a size which will cater for any work-piece.  Visualise.

Software:   This can prove to be an expensive exercise.  Most kits come with their own software, CAM, which translates your model from CAD 3D to G-Code which brings your machine to life.  CAM software can be expensive. There is a CAM project linked to FreeCAD (see below under further reading).  G-Code users tend to stick to Linux and with this in mind it is of importance to note that you may best be using a laptop or PC with Linux and WINE preloaded. Do check below for MeshCAM, which runs under WINE. G-Code, and getting to grasps with G-Code is just as important as getting your build 100%.  See below. More about this subject next week.

Kits in South Africa

Much to our surprise South Africa does have a kit source for CNC machining,  the Cron-Craft CNC Machine from The 3D Printing Store, Highveld Techno Park, Centurion.  The kit explanation and picture files are top class. I’d love to get a reader’s review on this product.

Although I will almost certainly be building either from kit or home brewed, the amount of information, advice and guidance in home brewed CNC machinery is very good. Exceptional actually.

Parts Suppliers in South Africa

Further reading:

Torque Conversion calculator Nm to Oz to Kg etc:  Convert Units

How to select a CNC spindle motor?   Kinla

CNC Zone – forum and great place to hang out

Ghecko Drive – Stepper motor basics

CNC Router Source – plans for CNC machines

Cerebral Meltdown – CNC plans

Build your own CNC Machine – with motor drives – Lirtex.com

Instructables – Motor drive

FreeCAD – yes, it is free and a very good program for the price. Check out the CAM project!

MeshCAM – runs under WINE on Linux. GRZ Software.

Get to know your CNC:  How to read G-Code  – Makezine

PWM and Chopper Drivers

Add comment

You entered an incorrect username or password

Sorry, you must be logged in to post a comment.