North West Leicestershire Society of Model Engineers

Modern methods in model engineering

Model engineering has evolved quite a lot in the last few years

For a very long time model engineering has used very traditional techniqes and skills that some times can take years to master.

I in no way suggest that the old methods are obsolete (quite the opposite) or that the new methods are easy just that the model engineer now has a much much bigger "tool box" 

in this article I will discuss the various new type of methods and how they can help us.

 CAD (Computer Aided Design)

In the last few years cad programs have become a lot easier to use and the price of them has dropped quite a bit, in fact some CAD programs are free to download and use!

So what is it and how does it help us, CAD is quite simply drawing on a computer doing drawing on a computer adds flexibility that you can't get be conventonal methods. For instance if you were drawing a Conrod and decided you wanted it longer and thinner you and stretch the drawing, the same thing on paper would have to be completely redrawn. Added to this flexibility are other features like 3d modelling, this will allow you to draw a virtual model and check it all fits before you make it. A lot less frustrating than finding you have spent hours making a part for the scrap bin! Powerful manipulation tools are also available so that you can rotate Locomotive motion to check clearances etc. Here is an example of an early stages 3d model it's a 2.5" Bulied rebuilt Battle of Britain class loco I am making.

Battle of Britain locomotive

This 3D modelling can be used in the next two methods I will cover. So in a way it is very important component of modern machining methods and in industry, it has become in the most part an essential element of manufacturing.


CNC (Computer Numerical Control) Machining 

 CNC machines are just conventional machine tools that have computer control. The most common of these is a milling machine. CNC machines have been around for quite some time however as with most new technology it has been prohibitively expensive. Now however machines and parts to convert machines has dropped significantly, this added to the endless help and tutorials available on the Internet it is within the reach of most competent engineers. So what's the benefit of having a CNC machine? The immediate benefits are the ability to machine arcs and forms that would be very difficult to impossible by conventional machining. Here is an example of a home built CNC machine.

CNC Machine

it cost me about £800 to build including the cost of the machine (an XL1) the machine before conversion was a little limited as to what it could machine. Taking endless light cuts would end up time prohibitive now however, it can run for hours without needing to stand over it. At this point I can link back to the CAD, as a diagram drawn in cad can be converted to a program that will produce a part. For this you need a program called a CAM (Computer Aided Machining) package. This program converts a drawing into a CNC program that will go and machine the part from a block of stock. This is not automatic as you still need to decide what size the stock is and what tools you use and in which order you are going to do the operation. However it does make it very easy to do.

Here is an example of tool paths made by a CAM package that the CNC will follow to cut the part.

CAM tool paths


 3D Printing and casting

The third and final method in this article comes last and quite nicely works very well with the other two above. 3D printing is a very new technology and for our purposes has two types that we are interested in. Firstly the two types of printing and what benefits and drawbacks they have.

SLS printing

Selective laser sintering is where a laser melts grains of metal together the part is made from layers of metal dust selectively melted to form a part each pass is then covered again with another layer of dust, that is then melted to the previous one. Once done the part is withdrawn from the dust and will leave a formed part that is semi porous this can then be brazed together by brass to form a solid part.

This method is quite slow and the machines to do this are very expensive and currently out of the range of the general public. There are companies that will make these parts for you from a 3D model that you send them.

this is an example of what you would get back with this process.

Boiler feed pipe

As you can see the detail achievable is quite superb 

Standard 3D printing

This is becoming widely available and the cost is quite low there are various ways of printing either using hot melt plastic build up or resin infused powder similar to the method above only using resin to bond the powder rather than a laser. Once a part is made in either plastic or wax it can be used a a template to check clearances or be used as a mold for investment casting. The parts can be printed at home and then sent for casting or the whole process can be done by one of the many companies now using this technology.

here is an example of 3d printed cylinders

Plastic cylinders

Obviously as you can see from the detail this is really a game changer for our hobby the level of detail that's now possible at a fairly reasonable cost is fantastic.


To summarise there are lots of new technologies available to us as model engineers to me it's nothing to be scared about and there is no distinction between old and new methods all are valid none should be dismissed. I have a lathe from 1939 and a CNC machine from 2014 and I use both equally. As long as you enjoy your hobby there are no wrong methods.

Doug Sleigh

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