True to CAD, High-Fidelity, Surface Texture,Entrapped Cavities, and Printed Assemblies


True-to-CAD, High-Fidelity, Surface Texture, Entrapped Cavities, and Printed Assemblies

Best Practice

p/n 33-D216 Rev A


There are numerous 3D printing technologies - each with unique attributes and limitations. There are likewise numerous end-use applications each with unique requirements. Nearly all applications can benefit from a technology that is able to accurately reproduce part geometry, achieve smooth surfaces, create entrapped cavities, and enable high feature fidelity, sharp corners, and extremely small separation distances between articulating part surfaces. These capabilities can only expand the functionality of the printer as it enables more application breadth to serve a broader customer need. This breadth includes things like prototyping plastic injection molded parts, creating jigs and fixtures, making optically clear parts and flow visualization, painting/dyeing, indirect manufacturing and numerous functional requirements like snap fits and complex printed assemblies. Unlike any other technology currently available, the 3D Systems MultiJet Printing (MJP) process in particular provides these properties through its use of high-resolution inkjet technology combined with a melt-away support material system. 

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Left:  M2R-GRY diagnostic part showing high fidelity, true-to-CAD sharp features and near microscopic holes with machine-drilled cylindricity and controllable and repeatable interference fits with dowel pins, 2) M2G-CL printed assembly with internal functional bearings, fine mesh structures and printed hole and screw fine-pitch functional threads

The MJP printing process generates a part with over 1.1 billion drops per cubic inch of part volume allowing the creation of even the smallest details. The support wax technology instantly solidifies in place during part formation and greatly contributes to sharp features and smooth surfaces. The wax also allows for simple and hands free post processing removal of support from even the most complex geometry and entrapped cavity without scarring of the part surfaces.

True-to-CAD and Reproduction of Fine Features

There is nothing that typically needs to be done to accurately match your part design dimensions with an MJP printer. For most geometries, the part should come out true-to-CAD the very first time printed and every time printed. The printer was designed with a scale factors for each material that is built into the 3D Sprint software. These scale factors automatically correct for the material you wish to print. You can also adjust the scale factors if desired for your specific needs. Part accuracy is independent of orientation for even the smallest and sharpest of features so you do not have to worry about numerous special part design rules, part orientation and placement issues or special printer setups.


M2R-GRY diagnostic part showing isotropic geometry capability where holes and small, sharp features are created correctly at any placement angle. 

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Left:  Setting the dowel pin hole size to exactly equal the pin diameter creates a tight slip fit, Right: Screw holes, inserts, and tapped holes can all be printed exactly as the would be drilled and work on any part surface placed at any angle. 


Top Left: MJP 2500 M2R-GRY, Top Right:  Competitor technology – material extrusion

Middle Left: MJP 2500 M2R-CL, Middle Right:  Competitor technology – material jetting

Bottom Left:  MJP 2500 M2R-WT, Bottom right:  Competitor technology – material jetting


Surface Texture

Surface roughness and 3D surface texture is important for many applications including painted and dyed surfaces, reproducing injection-molded textures, making molds for casting and forming or for any need that requires a professional looking part. MJP technology creates a smooth surface in all orientations. It is also possible to utilize the technology to simulate surface textures for engineering, aesthetic or scientific (flow chamber or flow visualization) needs.


M2R-GRY diagnostic part showing numerous detailed surface textures.


M2R-GRY printed sculpture and hand-painted final model


Left: Competitive material extrusion technology, Right: Projet 2500 MJP M2R-TN Figurine


Left:  Competitive material jetting technology, Right:  Projet 2500 MJP M2R-GRY Figurine

Smallest Feature Resolution

For some application requirements, it is often desirable to know parametrically the reproduction capability of the printer. One simple and common method of quantifying part fidelity is to print geometric features of variable dimension and characterize those that the printer is able to reproduce. Such measurements are often made for holes and slots, as well as for protruding features such as shafts and beams.


Diagnostic pattern to quantify feature resolution.

This type of pattern can be positive (protrusions) or negative (holes). The following figure shows such a pattern for a traditional process using a competitive process compare to 3D Systems MultiJet Printing process.


Competitive material jetting process 3D Systems MJP

Competitive process and MultiJet Printing cut holes and positive protrusion fine feature capability.

2.5mm thick diagnostic part with square and round holes at 0.9mm, 0.8mm, 0.7mm, 0.6mm, 0.5mm, 0.4mm, 0.3mm, 0.2mm 0.1mm.

Patterns such as this can also be printed with variable heights as the support material can often completely plug such holes in a manner that is impractical if not impossible to remove. For example, this can affect articulating joints and bearing surfaces between moving parts which can be different depths depending on the specific design.


Hole test diagnostic with variable heights

IMG15.pngCompetitive process and MultiJet Printing cut holes fine feature capability.

Therefore, the 3D Systems’ MJP technology is able to resolve positive protrusions and holes as small as about 100-200mm (0.004”-0.008”) in size and the melt away supports allow for very deep features or flow structures.

Slip Fits

Rapid prototyping opens up the traditionally strict manufacturing rules for legacy manufacturing processes, like casting and injection molding. One particularly useful capability is the ability to print slip fits for functional assemblies. A slip fit is composed of a circular overhang requiring support material for its construction. The support material must be removed for proper function. Slip fits such as this can be quantified with a simple diagnostic part with varying gaps and is often printed in multiple directions.


Simple slip fit diagnostic with a single size shaft and five different rings, each with a variable slip fit gap.

The gap for a functional turning slip fit using this diagnostic is shown below for both a competitive material jetting process and 3D Systems MJP technology.


Rotational slip fit for single size shaft with five different rings

The 3D Systems MJP technology is able to create a slip fit turning shaft with as little as about 100mm (0.004”). Slip fits with this size gap typically turn easily and smoothly after post processing. Tight fitting gaps such as this reduce the amount of slip-fit slop and allow for better functionality.

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Left:  MJP Projet 2500 HD Mode, Right:  Competative material jetting technology Highest Resolution Mode

Very tight slip fits may take some amount of rotational torque to free the rotation after post processing. Carefully turning the part multiple times often will  free up the rotation of two mating parts. Also, larger contact areas and/or smaller gaps between the sliding surfaces will both tend to increase the torque required to free the part. Therefore, a larger gap may be needed if the bearing surface is wide or the shaft size is small such that the torque required to free rotational motion will not break the part. Typically, 200mm will work in all cases; smaller gaps may work, but only for specific geometry.

Entrapped Cavities

Another unique requirement for many customer applications is the ability to print entrapped cavities. Each additive manufacturing technology utilizes a specific method to support overhangs. For example, Selective Laser Sintering (SLS®) and Color Jet Printing (CJP®) utilize the powdered build materials themselves, which naturally surround the part. SLA parts are built in a liquid bath and this technology must create very small structures to support overhangs, which are typically easily removed but leave behind scars on the part. Heat is used to remove MJP supports allowing for hands free processing for even the most complex parts. This capability is useful for very small structures like capillary flow visualization, but also useful for larger structures like making a simple pump with an entrapped cavity. With MJP technology, any entrapped cavity can be created as long as the cavity has a single small hole for the melted support wax to be removed. The fluid simply drains out.


Simple printed pump after the wax support is removed (left) compared to a competitive process (center) where the support is trapped and/or the part can be broken during support removal (right)

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Left: Support trapped within the part in competitive technology, Center: ProJet MJP 2500 part where the support is melted and drained out of holes.  Right:  Often post processing of water soluble supports will destroy the part due to expansion of the support material. 


ProJet M2R-CL rigid clear material part with complex internal passageways that were easily removed with melt-away supports (clear coated for best optical clarity)

Entrapped Support Marking

It is possible to entrap the support within a part with MJP technology. Basically any cut or hollow cavity within the part without a drain hole will be filled with support material by the printer. Features such as this are very easy to create in CAD. This is useful for engineering or fixture needs for adding numeric marking to knobs or assembly features or for pure aesthetic purposes.


M2R-CL medallion with entrapped text and graphics

The high-resolution capability of the MJP process is particularly useful for this of capability because it allows for very small marking and/or features. This capability can also be used to add white colorization to parts.


M2R-CL Rigid clear with nearly microscopic entrapped support colorization and graphical pattern (clear coated for best optical clarity)

While this capability can be produced in CAD, 3D Sprint also has a built-in feature. The engrave tool can make both text and drawing based markings on a file either protruding out from the surface, cut into the surface (inward or outward engrave) or entrapped with a given height (into the part) and depth from the surface.

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Left:  3D Sprint Engrave menu capable of inward, outward or engraved text or drawings

Few technologies have this type of capability and none in the same price range. One unique aspect of the ProJet 2500 is that three different clear materials are available for the printer that span a wide range of material properties from rigid (polycarbonate-like), to stiff and tough (ABS-like), and also flexible and extremely tough (polypropylene-like). Entrapped support marking can be used for all of these clear materials.

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Left:  M2G-CL (Armor) snap buckle with entrapped support marking

Right:  M2G-DUR (ProFlex) box with functional hinge and snap fit with entrapped support marking


Printed Assemblies and Mechanical Design Elements

There are a number of key 3D printer attributes that are important in the design and production of printed assemblies including surface roughness, accuracy, concentricity of shafts and holes, smallest feature resolution, slip fit capability, and entrapped cavity creation. The capabilities of MJP technology are ideal for this need and can be used to make all the foundational mechanical design elements like beam members, shafts and frames, rotating elements, gear designs, spring designs, ball bearings, and wheels designs, etc. 


A set of functional bearings printed at different scales.

There are numerous applications for such printed assemblies. For example, this can be useful in a medical model to simulate a printed bone structure like a spine or joint. An actual rotational hinge can replace a living hinge in applications such as connectors. Complex kinematic requirements for a fixture can be printed as an assembly for part fit checks, or go/no-go gauges for part assembly lines in manufacturing, etc. One interesting component of a printed assembly is that of a printed gear assembly.

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Gearing system composed of a simple two-stage reduction

Each member of a gear train assembly must be carefully positioned during design such that there is no overlap between the meshing teeth. If the gear teeth overlap, the system will become locked together during printing. Also, in this type of component, it is often impossible to keep the part separation distance above the 100-200um requirement to avoid the parts sticking together during printing because of the extremely tight gear mesh that can be required to achieve appropriate part size, gear ratio, and teeth engagement. In this case, it is possible to print the gear teeth mesh with a gap smaller than that possible to create two completely separate parts. There will be a gap in the actual CAD design, but it will be so small that there will be some slight joining of the two parts at the tangent points of the gear mesh where the separation distance is the smallest. The trick for such tight tolerances is to break the weld after printing by turning the gears slowly. Start by rocking the gears back and forth lightly and proceed to turning the gear or the shaft multiple manual rotations in order to smooth out the break points and allow for a functional rotational part. 

Shells and Infill Capability

The high fidelity and melt away support system allows a part to be hollowed and filled with a complex lattice pattern if needed. The function works by creating a shell of any desired thickness and then adding an infill within the shell with a given density. 3D Sprint software comes with tools to add the shell, a drain hole to the shell, and to filled the internal cavity with either support or numerous different lattice structures. This capability is common in extrusion based rapid prototyping technologies to reduce cost and/or weight of printed parts, typically with no impact on the visual or dimensional accuracy of the part.


The combination of the thin wall and sparse lattice structure results in a lightweight but rigid part.


Cut away view showing a thin shell filled with a 3-dimensional lattice structure. The combination of the thin wall and sparse lattice structure results in a lightweight but rigid part.

The support material costs less than the build material and so using the shells and infill capability in 3D Sprint allows for a substantial cost reduction. The exact amount saved is dependent on the shell thickness and the percent acrylate in the infill pattern you chose and is typically in the range of 40-70% weight reduction and  20-35% cost reduction.


Complex printed assemblies, Top: Wind-up spring storage mechanism, Lower Left: Wind-up spring storage mechanism, Lower Right: Flywheel mechanism


Cut away view of a complex printed assembly of a clock gear train


Feature Fidelity, Entrapped Cavities, and Printed Assembly Examples

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M2G-CL (Armor) carbineer with sharp features, optical clarity, entrapped support material text marking, and printed gaps between the parts allowing articulation.


Prototype U-shaped snap fit with a printed rotational shaft and hole bearing surface


M2G-CL (Armor) carbineer with a printed shackle allowing two degrees of rotation of the shackle


M2R-GRY printed assembly with two cantilever snap fits, printed machine threads able to mate perfectly with standard machine screws, and precision printed holes with sheet metal screws


Drill/Tap, Press, & Screw Diagnostic (Projet 2500 M2R-CL) From left to right the following features are shown: 1) Drilled and taped hole with hardware, 2) Press fit precision dowel pins, 3) Screws added to 3D printed injection molded bosses, 4) Press-fit brass inserts, and 5) machined precision holes.

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Rapid prototype of a complex functional injection molded water nozzle with plastic fins around the circumference for over molding, smooth surfaces, small holes, and sharp features


Dental Surgical guides made with approved Class VI M2R-CL material


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Dental models made with M2R-TN, high-accuracy, high visual contrast material with smooth surfaces and batch post process capability


M2G-CL buckle with ABS-like material capabilities


M2R-TN Connector with fine features and high contrast visualization


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M2-EBK 30A elastomeric vibration damper with smooth surfaces and sharp corners

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M2G-DUR (ProFlex) printed assembly box with entrapped support text and robust snap fit hinge


Color iris printed assembly created by printing as an assembly, disassembling, dyeing the individual parts and reassembling


M2R-CL and M2R-GRY parts professionally painted with a two-part polyurethane 7-1-2 paint/catalyst/thinner – 3 coats in rapid succession



M2R-GRY spray painted and as printed 

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M2R-CL Scanning Electronic Microscope (SEM) images of 500mm square holes and rods with super hydrophobic surface capabilities 


M2R-CL dyed and clear coated automotive lenses with smooth surfaces and optical clarity


M2R-CL Shells and Infill diagnostic allowing cost reduction and/or high strength to weight parts to be created


M2G-CL (Armor) light prototype of a complex fluid reservoir



A strong and stiff quadcopter canopy using the shells and infill capability to make a light and strong structure


Common “3D Printing Hobbyist” part quality diagnostic “Benchy” Top:  Normal size vs. reduced scale, Bottom:  Same reduced scale part held with fingers for size reference