Wax Pattern Splitting in 3D Sprint

p/n # 33-D208 Rev A

ProJet MJP 2500IC Pattern Splitting with 3D Sprint

Many pattern geometries can be printed on the 2500IC. This includes geometries that are larger than the boundaries of the build envelope. 3D Sprint, or your favorite CAD program, is capable of splitting large patterns into smaller segments which can fit onto the 2500 IC in one or multiple builds. These segments can further be joined using common industry methods to yield large wax patterns ready for casting.

Wax Pattern Joining Overview:

3D Sprint has the capability of automatically generating guide pins and holes, which allow you to align and strengthen segmented models into a complete model. Alternatively, CAD programs, such as SolidWorks, can be used to split models and manually place alignment pins and holes. This method allows for more customization when splitting the model and placing pins but requires significant CAD program expertise and is much more laborious compared to using 3D Sprint.

Splitting Large Geometries:

The 3D Sprint " Split Tool " is a functional way to segment large geometries for printing. Patterns can be split on a simple plane with pins or may be split using the line tool for irregular cuts.  3D Sprint will automatically generate connectors when using the plane split tool. There are many options for connector dimensions that will be application specific. We recommend simple straight cuts and avoidance of teeth or dovetails on edges to be joined. For any information regarding the split tool please reference your 3D Sprint help documentation or contact [support]. 

Geometries can be split in a variety of ways. Every place a pattern is split there will be a seam. It is important to understand how, and where, to split your patterns to achieve the best possible casting. The following are a few considerations when splitting a pattern:

  1. Turbines/Impellers/Airfoils:

Avoid slicing patterns across impeller blades or airfoils of any kind if possible. Smoothing and joining the seams becomes much more difficult in the case of thin patterns.

  1. Small text or features:

Splitting across text or embossed features will diminish the quality of the text/feature and be difficult to join seamlessly.

  1. Hard to reach areas: 

Areas with limited access or places that are difficult to reach can make joining and smoothing the seam very difficult.

Split Tool Connector Settings:

Connector settings are highly configurable. The specific settings chosen will depend on your pattern geometry. Here are a few recommendations which should help you create connectors which can both strengthen and align your printed segments.

Connector Clearance: Additional length added to pins to separate the two split pieces. If you have a need for a larger seam set this value to a nonzero number. (Recommended: 0 inch (0 mm))

Type: Cylinder or square type connector. (Recommended: Cylinder)

Connector Width: Width of connector pin. (Recommended: At least 0.12 inch (3 mm) where applicable.

Connector Length: Length of connector pin. (Recommended:  No more than 1/2 of connector width)

Clearance Width: Clearance for pin and hole width. This will enlarge the hole AND shrink the pin. (Recommended: 0.007 inch (0.178 mm))

Clearance Length: Clearance for pin and hole length. This will deepen the hole AND shorten the pin. (Recommended: 0.007 inch (0.178 mm))

# Of Connectors: Number of pins and holes. (Recommended: At least 2 but do not overcrowd)

Inset: Distance from the nearest edge. (Recommended: 0.1 inch (2.5 mm) from closest edge)

Spacing: Distance between each pin (Recommended:  At least 0.12 inch (3 mm))

Summary Table:

Connector Clearance

Type Connector Width Connector Length Clearance Width Clearance Length # of connectors Insert Spacing
0 Cylinder At least 0.12 inch (3 mm) At most 1/2 of Connector Width 0.007 inch (0.178 mm) 0.007 inch (0.178 mm) >2, do not crowd 0.1 inch (2.5 mm) 0.12 in (3 mm)

Connector Considerations:

  • Deep holes will increase your post processing times. Short pins and shallow holes are ideal for alignment purposes. If you wish to add longer pins to your model you may increase this length, but you will see increased processing times. Additionally, long pins are prone to damage and breaking during handling.
  • Wax is malleable and will distort if your clearances are set too tight. If this occurs you will have “one shot” at pressing your model together.
  • Pins located too near a boundary can cause outer edges to split when joining pieces together. Place connectors at a suitable distance from the boundary (inset) and other connectors (spacing).
  • The Connector Width and Connector Length are independent parameters, so if you change one, be sure to change the other to maintain the 2 to 1 ratio of width to length.

Example – 20 inch long (508 mm) Control Arm:

One example of a pattern that is too large to print in one piece would be this control arm. The pattern measures approximately 20 inches (508 mm) long, 12.5 inches (318 mm) wide, and 3 inches (76 mm) tall. This pattern must be split into three segments to fit on the on the 2500 IC build platform.

i.e. 1-20inch Control Arm.png i.e. 2a- 20inch Control Arm.png

The first split utilizes the plane tool to segment one of the ‘arms’ off of the main body of the pattern. Care is taken to avoid any text (3D systems logo) and any defining features (such as the hole).

Intersecting text or features such as these are to be avoided whenever possible. Ensure that the Clearance for Parts is set to 0.

i.e. 2b- 20inch Control Arm.pngThese connectors were created using the recommended settings discussed previously. The Connector width is set at 1/4 inch (6.35 mm) with a Connector length equal to half of the width, 1/8 inch (3.175 mm). This maintains the 2 to 1 aspect ratio of diameter to length.

An optimal CONNECTOR clearance for the Clearance width is 0.007 inch (0.178 mm)—this ensures a snug but still workable fit. The Clearance length is also set to 0.007 inch (0.178 mm). This will give some additional length to ensure a good coupling of the two pieces while not drastically increasing post-processing times. The 3D Sprint default values are much smaller than this and must be changed for best results.

3 connectors are used at an Inset of 0.1 inches (2.5 mm) and a Spacing of 0.12 inches (3 mm) in the “BOUNDARY” layout. This will auto place the pins based on the boundary of the split. Less than two connectors is not advised.

This same process is repeated for the second arm.

i.e. 3a- 20inch Control Arm.png i.e. 3b- 20inch Control Arm.png

The settings are the same as the first split with the exception of the # of connectors.

Measurement of connector dimensions:

i.e. 4a- dimensions.png i.e. 4b- dimensions.png

The delta between the two radii (hole radius and pin radius) is equal to the clearance entered for the connector width. The same is true with the length dimensions for the pin and hole.

Connector width clearance = 0.1285” – 0.1215” = 0.007 inch = 0.178 mm

Connector length clearance = 0.1285” – 0.1215” = 0.007 inch = 0.178 mm

Note that the actual diameter of the pin is now 0.243” and the diameter of the hole is 0.257”. This gives a clearance of 0.007 inch (0.178 mm) all the way around the circle. Both the pin and the hole diameters are adjusted to meet the clearance specification. The pin diameter is NOT 0.25 “ (6.35 mm) any longer.

The length of the pin is now 0.1215 “ and the length of the hole is 0.1285”. The pin length is NOT 0.125 “ (3.175 mm) any longer.

i.e. 5a- 20inch Control Arm.png i.e. 5b- 20inch Control Arm.png

This pattern can now be printed in one job and joined after post processing.

Limitations and Caveats:

The 3D Sprint software will not always default to good parameters for the connectors when the dimension are small, because the width and inset size minimums add up to be larger than the thickness, and so they both can not be simultaneously satisfied. A 3 mm wide connector inset 2.5 mm from both edges requires at least 2.5 + 3 + 2.5 = 8 mm thickness. If you are placing a connector on a 5 mm thick section and want to keep a 3 mm connector width, then there is only 1 mm of inset from the edges. If you are placing a connector on a 5 mm thick section and want to keep a 2.5 mm inset from the edges, the connector width is zero! The 3D Sprint Split software attempts to resolve these dilemmas by scaling everything down.  For wax patterns it is best to avoid small pins and insets or use with extreme care.

Some simple geometry examples (English units):

  Default Width Default inset
1.57 inch cube 0.118 inch 0.098 inch
1.0 inch cube 0.118 inch 0.098 inch
0.79 inch cube 0.118 inch 0.098 inch
0.50 inch cube 0.100 inch 0.098 inch
0.39 inch cube 0.079 inch 0.079 inch
0.20 inch cube 0.039 inch 0.039 inch

Some simple geometry examples (metric units):

  Default width Default inset
40 mm cube 3 mm 2.5 mm
25.5 mm cube 3 mm 2.5 mm
20 mm cube 3 mm 2.5 mm
12.75 mm cube 2.55 mm 2.5 mm
10 mm cube 2 mm 2.0 mm
5 mm cube 1 mm 1 mm

Pattern Joining:

After post-processing, the edges of the alignment pins and holes should be gently deburred and slightly rounded using a gentle touch with a very fine abrasive pad or #0000 steel wool.  Please consult the [Pattern Repair] document for information on how to join wax patterns.