Model preparation


Using 3rd party programs for model preparation

There are many programs out there (both free and paid) that can help you prepare your model for printing on the Lotus EZ.

Often these programs can slice the model for you as well which means you can upload a zip file instead of having the Lotus EZ slice it. This saves some time and also sometimes can allow for a greater amount of control over the slicing parameters. If you do this, it is important to remember a number of key points:

  • The program may ask for the physical parameters of both the build platform and LCD specifications. The following can assist you with setting these programs up correctly:
    • X resolution: 47.25microns (or 0.04725mm)
    • Y resolution: 47.25microns (or 0.04725mm)
    • Pixel width: 1440
    • Pixel length: 2560
    • Physical width: 68.04mm
    • Physical length: 120.96mm
    • Physical height max: 175mm
    • Often programs will automatically mirror images for you when slicing the files. If your program does this, it is important that you turn off this option. The Lotus EZ’s display is flipped deliberately for the correct slicing of models loaded directly to the dashboard, so that your model prints in the correct way. However, 3rd party programs which are often written for other manufacturer’s printers, may have this built into their system instead - rather than flipping their display - as they intend users to use their software, where this is achieved.

    • Ensure that the resin profile’s layer height you use on the Lotus EZ matches that which the 3rd party program slices at. If you decide to slice a model into a zip file on your computer, it will slice it at a height you determine. If this does not match the resin profile you use on the Lotus EZ, you will have elongated or shortened models!

    • If you decide to slice your model on a 3rd party program, this will mean that if you decide to print with a layer height later, you cannot 'regenerate' or 'reslice' this model on the Lotus EZ dashboard. This is because the STL file has not been stored on the Lotus EZ. You must therefore either choose to upload the STL directly to the Lotus EZ to allow it to slice it, or reslice it in your chosen program at the desired layer height. Again, it is important that when changing layer heights, that the resin profile used, matches this height.

    • Any settings in the resin profile used on the Lotus EZ other than layer height and exposure times will be ignored when using a pre-sliced zip file. For example, if the resin profile has Anti-aliasing or Pixel dimming enabled, this will not be used on the model that is pre-sliced by another program as these settings are used when the Lotus EZ generates the slices.

    • NOTE: As of version 1.3.0 of ChiTu Box, a popular model preparation software package, we've noticed that exporting models from this software can generate major errors in the model. For example, uploading a model prepared in ChiTu Box (e.g. supports, holes added and orientation etc) that is then sliced in the Lotus EZ dashboard, large triangles can appear, sections of the model can be missed and other similar errors. These errors do not appear when the same models are prepared in identical fashion in other programs.

      As such, we recommend you check all your layers if you use this program prior to printing. You can see the model layers and their details by browsing to the models page on the dashboard and selecting the "View layers" icon. You can then scroll through each layer and double-check there are no errors. We have found these errors occur most commonly with the base of supports and when adding holes.
    Orientation of models

    There are a number of reasons you will often find advice for specially orientating your models for printing with resin. One of the first reasons is to reduce the amount of supports required.

    Angling your model 30 to 45 degrees instead of upright at 90 degrees from the build platform, can reduce the number of overhangs. When angled, these areas are able to build off themselves, without the aid of a support.

    Another significant reason, specific to DLP and LCD SLA printing, is by angling a model that is tall, you are reducing the overall height of the model. In resin printing that cures a whole layer at a time, height equals time. This is a simple way to reduce the time, but reducing the number of layers required to complete a model.

    Another very important reason to angle your model, is to avoid large surface areas. By strategically tilting the model on the X, Y or Z axis (or in combination) you can reduce surface area for each layer, depending on your model. Reducing surface area helps reduce the force required to pull each cured layer from the FEP film, thereby reducing the risk of layer lines.

    There is no one-size-fits all approach to model orientation however, as all models are different and will require slightly different approaches to orientation and supports.

    However, if your model has a large solid base, and generally builds upwards from itself without significantly large surface areas (such as figurines and sculptures), orientating your model may not even be necessary and you may achieve greater quality printing the model's base flat on the build platform.

    Hollowing models

    In SLA printing in general, hollowing a solid model is a great way to reduce the amount of resin that is used. This will help you save money in the long run. This also means it reduces the amount of resin you have to pour into the vat for printing.

    However, printing hollow models at certain orientations can sometimes lead to suction cups, where suction forces can cause issues with print quality or at worst, print failure. Please see our section on Suction cups for more information.

    There are many software suites that can help you hollow your models, such as Meshmixer by Autodesk, or ChiTu slicer by Shenzhen CBD Technology Co (both free to download and use) but there are many more out there that can hollow models and even more!

    Avoiding suction cups in your model

    Suction cups occur during printing when there are openings to hollow spaces in your model. When a model gets to the point while printing where a section opens up into a larger hollow space, the suction force it experiences while peeling it from the FEP film at the end of each layer is much greater. This is because the 'cup' like effect traps air and resin within the space.

    This suction force can cause warping, separation between the very thin layer lines in your finished print, or print failure altogether.

    Trying to avoid suction cups can be tricky however when hollowing models for cost saving measures and to reduce suction forces generated by large surface areas.

    Some programs have an advanced feature that allows you to insert suction holes to break up such 'cup' like areas. These holes allow air to escape within suction cup areas. You can also help avoid suction cups by orientating your model more strategically to prevent or minimise their size.

    In your model preparation software of choice, try orientating your model at different angles to see if you can decrease them. Most software packages can view the model at a layer height which will help you identify at what point this occurs in the model.

    You can also simply orientate the model so openings to hollow sections face the build platform instead.


     

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