Please note that we are not running at the moment.
Please contact us for further information

To CAD or not to CAD, that is the question?

Whether 'tis nobler in the mind to suffer the slings and arrows of outrageous fortune, or to take arms against a sea of troubles and, by opposing, end them, etc., etc.

By John Oxlade, April 2010. e: john.oxlade@gmail.com
with additional material by William Shakespeare (who's not on email)

 

A prototype bogie design

We've all heard of people who build models or miniatures where every last component is made on their bench. Then there are those who buy locomotives without ever cutting a piece of metal. Somewhere between these two extremes sit the rest of us.

With the advent of inexpensive, sometimes free, Computer Aided Drafting (CAD) software, it is now within the realms of most people with a PC to be able to draw components for their engineering projects more accurately than ever before.

Computer Numerically Controlled (CNC) machinery is way too expensive for most amateurs, but many companies are only too keen to do jobs for people to try and claw back some of the huge capital costs of their equipment.

Put these together and it is now easy for someone to draw up components on their PC and have them laser, water or plasma-cut from sheet, turned or milled; all without getting their hands dirty.

Using CNC machinery also has another couple of benefits not normally available to the amateur ... they are fast, very accurate, and can repeat the same thing over and over 'ad nauseam'.

An Eaton hydrostatic drive I drew up to work out how it would fit in a petrol hydraulic loco I am designing

For most model engineering jobs, repetition is not usually a problem, but a CNC laser-cutter can make short work of frames and the cost is not that high. When you consider how much time you can save hacking the frames out of a sheet of 12mm steel, having them laser-cut has got to be a good choice. The cut edge from a CNC laser-cutter is good enough that for frames you don't even have to clean them up afterward.

I am not going to try and teach you how to use CAD software in one article, that is not practical, but I will give you some tips to help you on your way. You really need to go on a course to learn CAD or at least download online training aids from the Internet - but a class is best.

Unfortunately with changes to the adult education system in New Zealand a lot of the night classes previously offered by high schools have ceased. I got in before the change to the system and joined up for a "taster" course at a local school. I then went on to sign-up to 'proper' AutoCAD classes at the local polytechnic. Even after over 60 hours of formal CAD tuition I am by no means an expert and unless you used CAD every day I doubt you would be. I did however learn enough to draw up components to be cut or machined by commercial equipment, thus drastically reducing the time it would take to make parts myself. Some may see this as cheating, but I feel that the engineering skill has simply been moved from the workbench to the PC. Both are skilled, just in different ways, and isn't it better to actually build something rather than give up as you are not seeing progress in a 'reasonable' timeframe?

The aspects of CAD that are most likely to be of use to the model engineer (I'm thinking railways here) are:

CNC turned wheels

  • Draw up a profile of a standard coach wheel and have them CNC-turned. A tedious, repetitive process can be handled by the machine.

Laser-cut frames

  • Draw the frames of your next project and have them cut out of sheet.
  • The finish on the edge cut by the laser is probably good enough to be left as-is.
  • All the marking out lines can be done with the laser.

CNC laser-cutting has a couple of general "rules" that can be broken on occasion

  • Although you pay by the time the job is on the machine (so the bigger the job the bigger the cost because the laser has further to travel thus using up more gas), you also pay for the more times you stop and start the laser, so long continuous cuts are best, Swiss-cheese is not.
  • You can laser-cut holes, but they cannot normally be smaller in diameter than the thickness of the plate you are cutting. 10mm hole in 4mm plate is good, 4mm holes in 10mm plate is not. Sometimes the machine operator might be able to do it (I have seen very small holes in 10mm plate) but this requires manual intervention and the price goes up accordingly.

CAD software

The first thing you need to know is that if you can't draw, CAD software won't help. Most of the 'problems' in using CAD are drafting problems, not software issues. If you can draw, CAD will help you draw better (more accurately).

AutoCAD

Probably the best known, longest established software for CAD is also frightfully expensive for the amateur; though AutoCAD Lite is cheaper and does most of what you need.

AutoCAD is not the best out there for drawing in 3D.

SolidWorks

SolidWorks is the de facto standard for working and generating models in 3D; though I haven't used it.

Services

I am happy to run short courses in CAD for model engineers in the Waikato or Bay of Plenty. Failing that, if you have paper drawings you want converted into CAD drawings to be laser-cut, I can do that for you. In either case, email john.oxlade@gmail.com for more details.

References

Websites with software (or info on software):

Or just do a search for "free cad software" on Google!

Information

  • CADtutor - and online resource for people wanting to learn AutoCAD (www.cadtutor.net)

 

  

All information on this website is © Copyright Cambridge-Rotorua Live Steamers Inc.  |  This site last updated: 25th January 2012

Website developed and maintained by John Oxlade of john2consulting who is a member of the Cambridge-Rotorua Live Steamers Inc.