3D printing can seem daunting to many people as the technology is demonstrated on the news to create all sorts of weird and wonderful products, even human tissue. For the average person though, there are 6 main aspects that you should be aware of when 3D printing. These are terms we will discuss with you as variables to alter quotes and will help you understand exactly what you need from the printer.
1) Plastic types
*Note* We now are capable of supplying industrial-grade, maximum quality SLA and Polyjet 3D prints using UV cured resin. This particular service is completely unique and separate from plastic extrusion printing, thus the following guide does not apply. A specific guide for SLA and Polyjet printing is available on that link.
There are two main plastic types used in small-scale 3D printing, Polylactic Acid (PLA) and Acrylonitrile Butadiene Styrene (ABS). There are five other plastics we print from in unique cases; Polyethylene terephthalate (PETT) ‘T-Glase’ and Nylon by Taulman 3D, ‘Polymax’ and ‘Polyflex’ by Polymaker and ‘Woodfill by Colorfabb. These are all thermoplastics, able to be heated, molded and cooled rather easily and safely, hence their popularity in 3D printing. Each plastic has its advantages and disadvantages, for any job we will advise on which option suits your needs best. We are always looking into new experimental filaments so this list will continue to grow.
- Our plastic of choice that we print most of our jobs in is PLA, a hard and brittle plastic. This plastic is easy to use, fast to print from, affordable and has a glossy surface finish. We also have a large amount of colours of PLA available at any time. PLA has a big advantage of handling large prints well due to its ability to hold its shape while cooling. PLA’s disadvantage is that it is susceptible to UV damage and deform under heat (above 60*C). Prints in PLA should not be left out in the sun on a hot day or used in any application where ambient temperatures exceed 60 degrees celsius.
- The second most common 3D printed plastic we use is ABS. ABS plastic is well-known for strong, flexible and durable and it can survive harsh outdoor conditions better than any other 3D printing plastic. ABS is great for end-use components and functional parts like those used in 3D printers. ABS’ disadvantage is that it is slightly more difficult to print from which can result in longer lead times. ABS does not handle large objects as effectively as PLA does (parts greater than 180mm wide).
- The third commonly used plastic is Polymaker’s Polymax. Polymax filament is a special type of PLA which exhibits extremely strong mechanical properties for 3D printed parts while being rather easy to print from like normal PLA. It is easy to post-process and overall a superior PLA. Polymax only comes in white and black at this stage and is slightly more expensive than PLA or ABS prints.
The other four plastics we offer are specialty materials which are as unique as they are difficult to print from. These four we keep in limited supply and will always advise whether it is worth attempting prints in them. If your application calls to test the limits of 3D printing and you want to see something brand new, by all means inquire about these plastics and we will explain how we can get them working for you. Each of these four plastics has a higher cost to print from due to more expensive materials and slower print speed required.
- T-Glase filament (PETT) and nylon are a specialised industrial-strength plastics which are most similar to polycarbonate of all 3D printing plastics. They both offer high strength and high temperature stability while T-Glase does come in a translucent colour to simulate polycarbonate. These two plastics are often able to be used interchangeably where the maximum strength is needed and they share the same disadvantages in suffering warpage on large prints and are more expensive with longer lead times.
- ‘Wood’ filament is wooden fibres held with polymer binders to produce parts that look, smell and can be sanded just like wood. We would only recommend this filament for use in architectural models to demonstrate doors, pergolas etc.
- Flexible filament an experimental, rubber-like plastic. This is completely different from normal PLA in that it is extremely resistant to breaking and allows creations of some remarkable objects, snap-fit phone cases are no issue. This plastic is experimental at best and its suitability definitely depends on the application.
I will always recommend PLA due to its ease of use, cost and surface finish however when strength and corrosion protection is needed, I will get parts made from ABS plastic. Polymax is recommended for parts which do not require heat resistance but require high strength.
2) Layer height
3D printers make their parts by putting down thin layers of plastic to build the part by sheets. Each of these sheets can vary in size dramatically depending on which type of machine made the part. Layer height is the simplest way to control the cost of a part and its surface finish. A thinner layer will give a smoother result, but takes longer. Most commercial plastic 3D printers vary in capability between 0.1mm and 0.3mm thick layers of which we are capable although a print with a layer height of only 0.05mm has been achieved. By standard we print at 0.25mm height. This is because it gives a great finish, is fast and also many peoples prototypes feature dimensions using 0.5mm, such as a part being 20.5mm tall. Prints in 0.3mm will be more affordable while prints down to 0.05mm will be more costly due to the time they take to print.
3) Infill % and wall thickness
3D printers draw shapes by first drawing the outline as a ‘wall’ and then filling in the ‘floor’ with a solid sheet of plastic. After this, they then fill in the inside of the part with a honeycomb or square mesh. This allows the process to be very fast and holds the shape well. The higher the infill, the stronger the part. By default, we print at 10% infill for props, 15% infill for prototypes and architecture and 20% for end-use parts. Walls are typically required to be a minimum of 1.6mm thick which involves 2 walls drawn on the inside and outside of the shape at 0.4mm thick each. By standard we do 2 walls for props (1.6mm thick) and 3 for prototypes (2.4mm thick).
We can increase the infill % and wall thickness as required for prints to make them stronger however this does increase the printing time and material costs. I will always advise on what settings are best for your application to give the strength you need at the lowest price point.
Since plastic 3D printers operate by putting down layers of plastic on top of each other, when it comes to overhanging structures (such as the eaves on a miniature house), the printer is required to build ‘support’ structures underneath. These are basically like scaffolding as thin, low density lines purely to hold up the overhang. After a print, these supports are removable with pliers and then the point of contact is filed and sanded down for as smooth as possible a finish. Our printers can handle overhangs as low as 10* without needing any support structure which means we can handle some very complicated pieces without supports for a perfect finish however near perpendicular features that jut out from the main structure, will need some cleaning up afterwards. I personally do this for free.
- Dissolvable Supports. As of July 2014, we now have a printer capable of using dissolvable supports to leave no marks, just a clean print which needs support. This is experimental at this stage but is possible. Can only be used in conjunction with ABS prints at this point in time.
5) Tolerances and minimum feature size
Our 3D printers have a standard nozzle diameter of 0.4mm which common among all 3D printers. This means that each and every line of plastic drawn out to create an outline is 0.4mm thick. For ultra-fine detail of surfaces, this represents our absolute minimum feature size. While we can print at layers of 0.05mm, if we were to print for example embossed lettering, the thickness of each line that forms the individual letters must be 0.4mm for the best finish. This is usually never an issue however for ultra-fine detail, that is the limit.
With tolerances, the printer typically has an accuracy of +/- 0.2mm. This tolerance is a factor of the plastic cooling and expanding slightly along the walls of parts, resulting in solid sections tending towards the +0.2mm tolerance while holes tend towards the -0.2mm tolerance. Tolerances do not build up over the length of a piece. It is critical to understand that these tolerances result in overall a +0.4mm for any interferance or tolerance fits. For a 10mm rod to fit into a 10mm hole, they must be altered to 9.8mm for the rod and 10.2mm for the hole in order to print with a tolerance fit.
When printing with ABS, this introduces the additional factor of shrinkage. ABS prints will typically hold their dimensions very accurately until around 80mm after which parts will begin to suffer shrinkage as they cool down. This is typically in the range of 0-1.5% such that an ABS print 200mm long, could end up printing 197mm long. There are many factors that determine how much shrinkage an ABS print will suffer and certain geometries will hardly shrink at all. This can and will affect the tolerances. To account for this, large ABS prints I will often print a very quick, low density test run to determine the shrinkage factor before re-doing the print with an appropriate correction factor applied to it.
6) Build size
3D printers vary in size greatly, however most printers on the market including industrial sized printers can print objects around the size of a human head or a loaf of bread, printers have different dimensions in different directions. I own 4 printers personally and my colleagues own similar sized ones. The largest PLA printer we use primarily has a build volume of 285mm (L) x 150mm (D) x 150mm (H) while the largest ABS-capable printer we have access to has a build volume of 200mm (LxDxH).
Models required to be printed that exceed this size can be built by parts which is a practice we routinely use to create oversized props and models.
All information and images contained in this guide are original content of 3D Prototypes and Models and must not be re-created without direct reference to this web page.