This is a reference on how to use the tools in Millbox to apply features to units to:
- enable milling the design,
- prevent sintering distortion, and
- manage the units post-milling.
Sprue placement guidelines
Each design has its own requirements for sprue placement, and different material types make it difficult to define where exactly to place a sprue.
As you apply sprues, think of yourself as a structural engineer designing a bridge. Sprues can be thought of as bridge support structures that are dependent on the design and material used. Poor sprue designs for the material properties can result in structural failure for the milling application.
Since each design is unique, we give some guidelines on sprue placement.
Guidelines can be recommended but with experience with final milling results, you can balance post-milling work, maintain CAD design aesthetics, milling/nesting throughput, and prevent units from falling out.
Things to be aware of
- More sprues = more post-milling finishing time and reduced machining detail.
- Leave enough space between two adjacent sprues for the largest tool to move freely.
- Too close of sprue placement or not enough space can result in a tool to bind causing tool slips and losing calibration and breaking tools because material was not roughed out.
- Avoid placing interproximal and contacts.
- Doing this requires more time to achieve the details designed post-milling and hand finishing is less accurate for contact dimensional accuracy to your design preferences.
- Avoid applying sprues where machine finish details needs to be maintained.
- Keep sprues far enough away from critical fit surfaces.
- Surface areas like margins and mating surfaces for hybrid objects. For CAP strategies, it's best to make sure at least 3mm or more away from these areas to allow edges to be defined by the 1mm tool.
- Some brittle materials--such as zirconia--sometimes have micro-fractures and stress present in material.
- These micro-fractures may cause units to fall out as the stress is released when milling.
- They may also result in a fracture regardless of how you sprue.
- Worn tools will cause a unit to fall out of a unit.
- Worn tools put more pressure on a unit due to their dull edges; the sprue is unable to handle the force from the tool applied to the unit and fails.
Unit and sprue adjustment menus
These are the various views to show the menus that appear when you click on a unit and when you click on a sprue. When you select to modify a sprue, the unit may show the equator that is highlighted in the image to point out. The unit equator curve is to help optimize where to place sprues to minimize undercuts.
- Individual unit adjustment menu - Activated when left clicking an STL unit
- Sprue adjustment menu - Activated when left clicking a sprue object.
- Adding features to units - Using the tools menu to add additional features to modify the units.
Switches you to the sprue adjustment menu to allow you to add individual sprues.
Removes all of the sprues on the selected unit.
Alternatively, you can select an individual sprue to switch to the sprue adjustment menu to fine-tune sprue deletion.
Type select object dropdown
Changes a type select object if it was imported incorrectly.
Details of the type object select can be learned about in this article. Left click the type select option box to activate the dropdown list to make the change.
Note: This does not reprocess the STL to generate or not generate the necessary curves. If you are unsure of how to identify curves are needed to mill units properly, the recommended procedure is to delete the unit and re-import the STL with the correct type object select.
Changing unit offset
Changes an offset value of the unit.
Enter the new value and click the checkbox to confirm. Millbox will adjust the offset curve to the new value.
Note: Make sure that the offset is greater than the roughing tool by 0.5mm. Setting it smaller than that will cause a seam or incomplete roughing due to background strategy settings. Even if the offset value is set to a tool diameter that can fit, milling is a roughing operation that requires the diameter plus additional offset values.
Deletes the unit.
Adjust cavity surface offset
Adjusts the surface offset, which changes the fit of the unit.
This is an advanced method and should be used with caution as fit results will be impacted by making changes.
If you find that a fit is being changed to the same offset every time for cavity based designs, you can
- Update the CAD material settings should for that material, or
- Set the material group and object type in Millbox settings.
If you find you are chasing fit using this tool and the offset values are not constant, there might be a different issue that is not being addressed. Final fit has many other variables that contribute to the final fit.
Here is are some issues to look into:
- Material quality (shrinkage variability)
- Machine calibration/maintenance
- CAD design parameters
- CAD library design
- Scanner calibration or quality
- Other users adjusting design values in design from set values
Machining has many variables that CAP has helped define to achieve the best, consistent, milling results. CAP is not able to test all materials, tools, machines, and variables that impact milling output.
Please keep this in mind as it is not possible to offer the same level of support for milling non-CAP products such as specially-created packages for individual customers requirements.
Select multiple sprues by CTRL+Left clicking each sprue to add them to the selection. This allows you to group edit the sprue type, sprue thickness, or delete them all.
Pin cutting options are strategy-dependent. Pin Type can be turned on to set the type to not-cuttable in the Configuration menu.
At Material and At Object will adjust the diameter of the sprue at those locations to that thickness.
Adding a Stabilizer
There are multiple stabilizer options available. To access the menu, click Tools button, then Stabilizer button.
Select the stabilizer design type, then Left-click the unit to apply the stabilizer.
CAP recommends the default stabilizer for most situations as it's the most proven stabilizer bar at this time. The default type is the first selection in the stabilizer selection menu.
Users can optimize sorting units from the sintering trays and other post-milling activities by adding an engraving to the unit design.
To apply an engraving, click the button and select insert. You have to remember the unit name to label it, as it's not possible to check while engraving.
To modify an engraving, select modify after clicking the engraving button, and select the engraving to modify.
The default setup does not allow duplicate engraving codes in a job. If you want to use shade engraving instead, the option will have to be changed in the configuration.
Adding vertical supports
These are typically used for large bridges to prevent the bridge from distorting from the material weight as the unit sinters. Typically paired with a stabilizer too.
Curves and surfaces
This option brings up tools to fix any issues that Millbox did not properly handle. Typically used for fixing issues such as redrawing margin curves, detected cylinders for drill holes, and adding blockout surfaces.