Wednesday, 7 October 2015

Another 3D Printing glossary

In writing this glossary I looked through quite a few 3D printing glossaries. Below is a list of words that are or could be commonly used in the world of 3D printing without being specific to any particular print process. I hope that this does not over or under complicate things. 

3D Printing - see Rapid Prototyping 

Additive Manufacturing - see 3D Printing (in fact this usually refers to more industrial applications of 3D printing)

Auto-fix - this is short hand for "I'm naive and I don't mind surprising results!". Always be wary of anything offering to auto-fix your file and if you do see Diffing Tool.

Build Time - Depending on many factors this is how long it take to build a part in the printer. This is not the same as the total time needed to prepare the file and the printer, print the part, post-process the part, package and deliver. 

Diffing Tool - usually a software tool for comparing two pieces of text much loved by programmers for finding bugs. If you carry out a fixing procedure on the whole model it pays to step backwards and forwards to spot unexpected differences between before and after model states.

Error - this is what frequently happens if you do not look after your 3D printer properly or if your printers have just done too much hard work and something eventually breaks.

Faceting - When the triangulation of the print file is visible in the surface of the printed part.

Feature Size - the smallest features that can be physically printed. This can easily become an obsession. Often better to ask at what size a feature becomes clearly visible. There is always a big difference between the minimum size of structural elements and surface relief details.

File Size - There is an optimum level where mesh size is just right for the resolution of the printer. As triangles get increasingly small, files getting increasingly large and time is increasingly wasted. Files for 3D printing rarely need to be more than 20MB.

Hole - gaps in meshes used to define 3D prints. In the same way that holes in skin are bad for you, holes in meshes are bad for 3D prints too.

Layer - almost all 3D prints are created one layer at a time. Layering is often visible on the side walls of a print. Finer layer thickness is often desirable as layering is less evident visually.

Manifold - "in mathematics, a manifold is a topological space that resembles Euclidean space near each point. More precisely, each point of an n-dimensional manifold has a neighbourhood that is homeomorphic to the Euclidean space of dimension n". In 3D printing it means a mesh without holes - sometimes known as watertight.

Meshing - the process of converting a vector or NURBS model (the design file) to a triangulated mesh or shell used for 3D printing.

Normal - surface or triangle direction defining inside from outside of the model.

Post-processing -  This is the part that the manufacturers and resellers keep quite about. Up until this point it all looks pretty straightforward - then the work begins... 3D printing is not vending and alas is nothing like Star Trek's replicators.

Rapid Prototyping - until recently, rapid prototyping was the term used to describe what has come to be known as 3D printing - or additive manufacturing.

Shrinkwrap - often a last resort when fixing a hideously bad file quickly, the shrinkwrap tool in Materialise's famous Magics software really is magic. And like all good magic the shrinkwrap is most powerful when you can't tell its been used.

Support - parts with overhangs need to be supported as they are printed. Powder based systems are self-supporting whereas other printers need to print a support. Removing supports is usually no fun at all.

STL - the stereolithography file format was created so that people could print to the very first commercial 3D printers. It contains triangle coordinates and normal directions but does not contain unit, colour or indeed any other information.

Texture - in colour 3D printing this refers to an image file mapped on to the surface of the mesh containing colour information to be printed. Not to be confused with physical surface texture. Remember you need a colour 3D printer to print image textures.

Watertight - a manifold shell - i.e a part with no holes.

XYZ - cartesian coordinate system used to locate points in (Euclidian) space. Z usually denotes height in 3D printing but this is not always the case with software modellers.

For more information about 3D printing at Lee 3D please visit

Wednesday, 1 April 2015

The rise and fall of the ZPrinter?

One outcome of ZCorporation's acquisition by 3D Systems is that we are no longer quite sure what to call the technology we use.

In the beginning, ZCorp's printers were 3 digit numbers prefixed with Z. So Z402, Z406, Z810 began the series and then in 2003 the ZPrinter 310 was released and the ZPrinter was born.

Strangely the next machine to be announced was the Spectrum 510 in 2005. Despite the Spectrum non sequitur, the next machine was the ZPrinter 450 in 2007 followed by the ZPrinter 650 in 2008, precipitating a minor avalanche of ZPrinters in the next couple of years as the increasingly small ZPrinter 350, 250 & 150 arrived.

Then in January 2012 ZCorporation was no more. 3D Systems bought the company and began to absorb it into the 3D Systems brand.  

Despite this and just months after the take over, the last and biggest ZPrinter arrived, the mammoth ZPrinter 850. Almost immediately news came through that the entire range of ZPrinters was to be rebranded as the ProJet x60 range.

What is a ZPrinter?

Briefly ZCorp made 3D printers that printed binding fluid using HP printheads on to a bed of powder.

ZPrinter 310

In the early days ZCorp experimented with different powders for different applications. The early printers like the ZPrinter 310 shown above were flexible, hands on machines. 

Powders for flexible parts and for casting etc. lost out in time to what the company referred to as high performance composite. Essentially plaster of Paris with some modifiers to improve flow, part strength and finish. 

With the 450 the ZPrinter became a more complex machine but one that requires less user intervention.  They made it easier to use, with automated powder handling and a built in post processing unit. The result was that it was a machine optimised for general purpose plaster printing which was what the majority of the users actually wanted.

ZPrinter 450

The automated powder handling of the later ZPrinter range was a great success from a users point of view. While it slowed down various aspects of the 3D printing process, not having plaster powder blowing up in your face when reloading the machines meant this was a small price to pay.

Some of the later ZPrinters have an automatic de-powdering feature. This proved to be something of a gimmick and must have added a significant cost to the price of the machines that featured it for no significant gain except for the marketing brochure. 

So what is the point of all this?

The question remains what do we call this technology? Bringing the ZPrinter into ProJet range and calling it ProJet x60 is really not very helpful for the average user. If I say that I am running ZPrinters most customers know what I am talking about. If I say we are running Projet x60s mostly customers are just baffled. 

Officially the technology used by the Projet x60 printers (ZPrinters) is Color Jet Printing or CJP. This brings the product in line with 3D Systems preoccupation with ProJets "Jetting" stuff. Again no one can remember what CJP stands for and the acronym blends into a background of stand-back jargon.

The thing is the full ProJet range has some great machines and some proper clankers. With a fistful of completely different print engines that are suitable for completely different applications.

Since the explosion in interest in 3D printing and the following blizzard of silly stories what we want most in this industry is clarity.

ZPrinter had brand power

Yup, that is the bottom line. The ZPrinter brand was distinctive and effective.

The ProJet brand is just confusing. It makes sense for the 3500 range where the material is all jetted to build the part. At both the top of the Projet range the 7000 is an SLA machine and again at the bottom of the range the 1200 is a kind of miniature SLA - the funny thing is that the SLA process cannot be described as jetting - there ain't nothing jetted there!

The ZPrinter really is a 3D printer. It uses HP inkjet printheads and prints in layers to build depth - that is in the Z axis. It was a good name, a good brand, now it is history, so this is an attempt to record its passing.

RIP ZPrinter.

ZCorp/3D Systems machine release timeline

1997 - Z402
2000 - Z402c (colour)
2001 - Z606
2002 - Z810
2003 - ZPrinter 310
2005 - Spectrum 510
2007 - ZPrinter 450
2008 - ZPrinter 650 
2009 - ZPrinter 350
2010 - ZPrinter 150, 250
2012 - ZPrinter 850

For more information about ZPrinting please visit

Tuesday, 10 February 2015

Notes on the cost of 3D printing

This post sets out to address the cost of plaster 3D prints - also variously known as ZCorp, Sandstone and Colorstone. 

All 3D print technologies have different pricing parameters so the points below do not necessarily translate to other processes. Plaster printing does not need supports to be printed as the part is fully supported in the bed of plaster powder as the print progresses. Unlike the SLS process which is also powder based, all of the unused powder can be reused in the next print.  

In addition to the powder used to make the part, a greater expense in binder fluid, cleaning fluid and printheads needs to be factored into the material cost of the print. Despite this it is usual (but not universal) to charge per cubic cm (£/cc) of material used.

For many parts including most architectural massing models consideration needs to be given to whether or not a part can be hollowed out to reduce the amount of material used and ultimately to save cost.

Parts need to be cost effective for the long term success of a bureau and hollowing parts is key to this.

For many heavier 3D printed parts there are 3 possible outcomes to treating a 3D print:

  • Print solid
  • Print hollow and leave unused powder trapped inside the part
  • Print hollow and leave an opening to remove unused powder
Buildings usually sit on the earth and are consequently not viewed from the underside. This makes it possible to hollow most building massing models leaving the underside open to remove unused powder.

Hollowed 3D print

Solid models may be needed for vac forming etc and in some parts just have the wrong geometry for hollowing and need to be made solid.

Other parts can be hollowed but a hole or other opening is unwanted and then unused powder may be left trapped inside the part. Consideration needs to be given in such circumstances as to whether it would be desirable for powder to leak out if a model were broken. 

So let us take an example of a cube measuring 100 x 100 x 100mm.

  • Solid this occupies 1000cc
  • Hollowed with a 4mm wall thickness it occupies 221cc
  • Hollowed with a 3mm wall thickness it occupies 169cc
This sheds some light on those stories of horrendously expensive prices sometimes quoted (and sometimes paid) for 3D printed parts. Be careful of this when getting quotes for parts online, software is not likely to pick up on the fact you are asking to print a lump of material that could do with being hollowed. A human is usually better able to spot this kind of thing.

In the case of our 100 x 100 x 100mm cube it is worth noting that the difference in volume between the 4mm wall thickness and a 3mm wall thickness is 52cc. Which priced on a cubic cm basis could be a 23% difference in price. 

Choosing an appropriate wall thickness depends on various things. The size and strength of the part, its purpose, whether it needs to travel and even on very tight deadlines the time available to remove it from the machine and get it to the customer.

Generally we hollow parts for customers as part of our file optimisation service at Lee 3D. To do this we use Magics RP, the industry standard software for preparing models for 3D print. This allows us to hollow complex parts with a uniform thickness.

For more information about 3D printing at Lee 3D please visit

Friday, 6 February 2015

Optimising CAD models for 3D printing in plaster or sandstone

This post is geared towards customers planning to use the Lee 3D online quoting and ordering service. However, it should be useful to anyone modelling for 3D printing using these materials. Please note - optimising is not the same as fixing. If you are considering using an online service it is assumed that your data is print-ready. Optimising is about getting best results.

The Material

Plaster printing using ZPrinter (renamed as Projet x60 series) is sometimes called sandstone, colorstone or similar. Whatever you choose to call it, the material is predominantly plaster of Paris bound with a water based binder in the printer and most commonly hardened afterwards with cyanoacrylate (superglue).

When freshly printed, the models do not have their full strength. We sometimes use the analogy of concrete vs steel to describe the material properties of unfinished and finished parts. Concrete is great under compression but poor under tension, whereas steel is strong under both compression and tension. 

So, parts fresh from the printer have limited strength in tension and therefore thin parts are liable to fail and more especially, thin cantilevering parts are liable to break off. 

Finished parts, hardened with superglue have good all round strength.

Part Orientation

Part orientation affects surface finish and strength of parts.

Strength of parts due to orientation only needs to be considered for thin parts. A thin column printed horizontally is stronger than if printed vertically. Thus, part orientation will affect minimum part size (fig. 4).


Architectural models rarely get printed at 1:1. If you are modelling in software at 1:1 and you want to print at scale, you need to think in advance about the size of the final model.

If you are printing to scale and want to use an online quoting service you must think about the size of parts as they will be printed. 

Remember that you are making a model. Columns may look weirdly thick in software but when they are printed at 1.2mm diameter they will be thin!


Hollowing parts reduces cost. However, if you hollow parts and leave the powder trapped in the model we will have to charge for the unused powder as we cannot remove it. This may lead to your order being rejected. 

So, consider how unused powder will be removed from voids and remember that powder does not flow out like water - it needs to been blown out with an air brush. Small holes are not adequate for removing large quantities of powder.

It is not easy to model complex structures with consistent wall thicknesses. If you are not careful, weak points can appear as illustrated below (fig.1).  From the outside, these can be difficult to see without viewing the part in section. Thin parts, if they do not break, can become translucent once glued giving the part a patchy finish.

It is usually better to model parts as solid in design software and then use Materialise Magics (or similar) to hollow the part effectively. This will produce a uniform wall thickness which will produce uniform strength and finish. 

fig. 1

Minimum Part Thickness

Everyone asks what the minimum size we can print is, to which I usually answer that it is geometry dependent. It is also usually worth considering the end use of the part. If the part is likely to be handled a lot, then make it strong. If the part needs to fly to the antipodes, make it strong. 

If its useful life is for a single meeting in which you need to make a crucial decision, then perhaps take some risks to make it look great for that meeting. If the model will spend the rest of its days inside of a Perspex display case, make it detailed (it may take us a little longer though).

Below are some rules of thumb to determine minimum thickness for various features:

1.  Freestanding wall features

The fig.2 below shows a fine wall detail well supported by the core of the model which is hollowed to about 3mm. The table shown in fig.3 contains suggested minimum wall thickness for differing wall heights.

fig. 2

fig. 3

2.  Column features supported at both ends

As shown in fig. 4, these features are strongly dependant on print orientation. Some files cannot be oriented so that all fine details are horizontal and in this case all parts need to be thickened for printing horizontally. Table fig.5 shows suggested column heights for parts printed in either orientation.

Please note that free standing columns are much less sturdy than columns supported at both ends and need to be made significantly thicker.

fig. 4

fig. 5

3.  Shadow gap and surface relief size

Fig. 6 shows shadow gaps on the surface of the model. The smallest readable shadow gap is of the order of 0.3mm. Bold shadow gaps should be 0.5mm or greater.

Some thought needs to be given to depth of shadow gaps. It is difficult to remove powder from gaps narrower than 1mm, so there is little to be gained from making these deeper than a couple of mm.

fig. 6

Relief details are readable from 0.2mm at the minimum. To clearly see surface relief, a minimum size of 0.5mm or more is recommended.

4.  Hollowing

Hollowing thickness depends on the size and strength of part required, usually 3mm or more.

Walls need to be of adequate thickness after hollowing to give the part sufficient strength for us to remove it from the printer.  

You cannot make a part the size of the build volume with a thickness of 1.5 or 2mm - it will collapse. We will check every part and will need to modify or reject parts that are too thin. 

fig. 7

For further information about the Lee 3D online quoting and ordering service see 
Optimising sandstone or plaster models

For more information about Lee 3D go to