CAD Files - the good, bad and ugly

Graeme Smith, BE(mech), 3D Product Designer

A 3D CAD file, (3-dimensional Computer Aided Design File) is a requirement for RAM3D to print your part. 3D CAD is common in the engineering industry, however, for individuals and smaller businesses, these systems can be expensive. There are alternatives available and these can be problematic when it comes to using the file you have created. 

The types of files we use are...

  1. A Solidworks file, The CAD software we use here at RAM3D,
  2. A generic solid model such as parasolid, iges or step files. These are 3D CAD formats that can be shared between many different CAD programs,
  3. An STL file. This type of file contains a description of thousands of small triangles that define the shape of your part. These are used extensively for 3D printing and are the type of file our programming software uses further on in the programming process.

Good quality CAD systems create robust CAD files. Good quality CAD systems will also output files in all the above types.

Some cheaper and online CAD programs only offer the file to be saved as an STL, (option 3). While these may be OK for hobbyists with home FDM printers, often these CAD programs create an error ridden file that is difficult or impossible to use to program your part on our high-end production machines. 

If you provide a 3D CAD file of the types in 1 or 2 above, then we will make the STL file here. We will make a good quality STL with no errors. Additionally, the benefits of sending RAM3D your solid models instead of a STL file are…

  • We can repair a CAD model prior to creating an STL file. 
  • Addition of threads, cavities or other features at customer request. At RAM3D we help get the best result for you. Sometimes we suggest small changes to help the build. With a 3D CAD model, we can do those changes for you, (an STL we generally can’t)
  • Creation of the STL file with the optimal resolution… Too few triangles and the part will appear flat sided, (tessellated) and too many triangles and the file may become unmanageably large. There is a sweet spot beyond where you get no benefit in part quality for any increased STL resolution.
  • Creation of a good STL file with few triangle errors. We examine every STL file we receive. We check that all the triangles in the STL meet the bordering ones with no holes or overlaps. This ensures robust data for the machine to use to make your part.
  • We can add supporting structures if necessary. Although the bulk of the part support is added later in the process, we have on occasion needed to add removable struts or structure to help a part build and retain shape. This is best done on a CAD model.

You can send us an STL file but be aware that there are limitations to their use. Another alternative is to let RAM3D CAD model the part for you. Once you have a CAD model it can be used in many other facets of your business, from patents through to promotional material.

Part optimisation for 3D metal printing, SLM

Graeme Smith, BE(mech), 3D Product Designer

When designing a part, a designer often has a manufacturing 'method' in mind. When designing a shaft, the designer looks to design around an axis of concentricity and the method for manufacture is turning. When designing a bracket, the designer may look for ways of holding the part for milling and how to minimise milling operations.

When designing for Selective Laser Melting (SLM), a designer still needs to have a method for manufacture in mind, however, there are very different part considerations.

When designing for SLM, the designer is open to create the part as they wish. They need to consider for tool allowances; part holding and geometry are gone. Instead of a large chunk of material to resist the loads, there can be a much more detailed structure that transfers the loads more effectively but also lightens the part and makes it look a lot better. Parts that had to be separate for conventional manufacture could now be made from 1 piece. We call this design freedom.

There are a few considerations to keep in the back of your mind when designing for manufacture using SLM, the four rules:

  • Reduce Part volume…The part should have as little material as possible. Material volume equals cost. Get rid of material that serves no purpose. Consider hollowing the part out.

  • Consider Build direction…The part may need to be orientated in a specific direction to best achieve the part detail or to best resist potential deflections. Parts with some symmetry and parts that blend in changes of cross section work well. We love curves, organic blended shapes work the best. Get rid of those sharp corners!

  • Allow surfaces for support…There will be some support needed to hold your part to the build plate, however this can be small. Supported surfaces will have a slightly different surface finish due to the removal of the support. Most downward facing surfaces (below 30˚ to the plate) will require additional support, try to eliminate them where possible.

  • Allow for post processing…Consider the critical surfaces that may require further processing. Bearing and sealing surfaces for example. Sometimes it is worth adding a little machining allowance or datums to help post processes.


RAM3D Design Rules for Metal SLM

When to use Metal 3D Printing?

Graeme Smith, BE(mech), 3D Product Designer

Many people are confused by where and when to use Additive Manufacture (AM) and Selective Laser Melting (SLM). Firstly, we need to define the difference between subtractive manufacture and additive manufacture?
It simply comes down to where you spend your time and money. If you spend your time and money removing material to create the part you want, that is subtractive manufacture. If you spend your time and money adding material to create the part from nothing, that is additive manufacture.

Turning/Milling/grinding etc.
are subtractive manufacture. Starting with a billet of material, you spend money making swarf. To save cost you often leave as much material on the part as possible resulting in a non-optimised part.

Casting/Molding etc. are additive manufacturing techniques as the material is placed onto the part, however, these techniques require a large tooling component, hence cost, and a lack of flexibility to change. Also, the parts must be relatively simple to make the tooling feasible.

Selective Laser Melting, (3D printing of metals) is purely additive manufacture and requires no tooling. Each change in design is easily handled in the programming. Highly complex and hollow parts are easily achievable allowing optimised design.

At RAM3D, the parts we see on a daily basis generally fit into one of the following 3 categories…

1. Prototype
Usually a part more suited to a casting/moulding type process but is still being developed. RAM3D can make your parts in metal to a fully functional state prior to any investment in tooling for production. The part will cost more than a cast part but there are no tooling costs and the part can be altered easily between revisions.
If you are open to redesign, then SLM is a viable production method and is cost competitive for parts that have been optimised for the process.
On many occasions, we have had clients come to us with a one-off prototype that is often a solid piece destined for casting or similar. The RAM3D designers can offer a design service or advise the customer how to alter the part’s design to make the part stronger, lighter, and therefore cost competitive using dedicated design for production, using additive manufacture.

2. Part direct replacement
This is often a tricky area where a customer just wants to try/test the technology by making a part that is currently made by another process. We can do this but the result will often be more expensive, since the part is not designed for the process.
The best way forward in these situations is to give the RAM3D designers the existing part design, tell us what the part is used for and include geometric constraints, loading and material. We will suggest improvements to remove mass from the part without compromising strength. This will improve the part by reducing weight and will greatly decrease the cost; making it competitive with the current method of manufacture.

3. Part design optimised for SLM and part functionality
Often used where you have a part that is limited in its use by the manufacturing method. Usually the part cannot be created conventionally without a large compromise in design, (for example where you may have to make it in multiple parts due to manufacturing limitations, however, it would be better if it were made in one piece).
Design for additive manufacture requires a very different outlook compared with design for subtractive manufacture. When using subtractive manufacture, often excess material is left on the part as it may be costly to remove resulting in an overdesigned part. Also, the method of material removal will often determine the part’s shape. (i.e., pocketing a machined part). That method of material removal can also compromise the part’s usability, strength, and function.
Using an approach focussing on design for additive manufacture means that the part will only have material where it needs it and all applied loads are transferred in the most efficient way possible. The result will be a highly optimised part in both functionality and cost.

Example of the lug showing internal lattice structure which has been added by RAM3D’s designer

Example of a connection lug of one of Bastion Cycles custom made parts for Carbon-Fibre bicycle.

RAM3D currently print in the following materials: Inconel 718, Stainless Steel 15-5ph, Titanium 64. 

Call us to discuss you projects on 07 557 0344 or email us at

The process of printing 3D parts

Written by Phil Owen & Rew Noland

It is a often misconstrued that a 3D printed part magically appears straight out of the printer and is “good to go”.  Firstly 3D printed parts come out of the machine attached to a build plate via support which has been carefully placed to optimise the build. Material is also placed in openings and overhangs to help support the build process.  If the part has been designed specifically for 3D printing, it often requires less support, is easier to clean up and process.

We then cut the part off the build plate and carefully remove the support from the part. When the base part is fully exposed, we can move on to finishing the part. Where support has been placed there will be raised dimples or grids, so we file, die grind and/or linish these areas to achieve a smooth finish.

When the part is smoothed back and we are happy with it, we move on to media blasting. We have a few different media we use to try maintain a consistent finish over the whole part. The material of the part can also determine which media we use. Our standard final finish is done with glass beads and is often sufficient for a majority of parts.

Some customers require a higher level of finish so we can also rumble parts.  This is an additional service and incurs an extra cost.  This process is good for reducing minute irregularities, de-burring and produces a clean, smooth surface.

Hand polishing is another option to take it the next level of finish and this is suitable for the likes of implants and decorative items.

We are looking at options for better finishes with new tooling and machines, so watch this space for more updates!




Graeme Smith, BE(mech), SLM Product Designer

Over the coming issues I am going to look at part design for the SLM additive manufacturing process and how designers can optimise parts to provide the best part at the best price.

Part 1. Understanding the cost of additive manufacture

As a design engineer I like nothing better than designing a part that functions perfectly and looks good for a reasonable cost. But designers are being pressured to create cheaper and cheaper parts. This is often achieved by compromising on function and forgetting about looks. We have all done it…a piece of RHS welded to a plate with a couple of holes drilled in it. Result…cheap, does the job but heavy and really ugly. Imagine if sleek, light and perfect for purpose was also cheap? Additive manufacturing could be your answer.

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