Convert STL, OBJ or PLY to a solid model

Dicussion
1

Hi everyone,

Does anyone know how to convert the resulting file from scanning with Revopoint POP 2: STL, OBJ or PLY to a solid model to work in a CAD software: Catia, Rhino…?

Kind regards. Thank you in advance,

Juanjo

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Let’s get our terminology straight:

Surface Models: STL, PLY, OBJ are in this category. They are technically hollow, but if they have a continuous surface, they are considered “water tight” (meaning suitable for 3D printing). STL is typically a collection of triangles with their vertices coincident with those of their adjacent triangles; they have various sizes and orientations to approximate the actual object.

Solid Models: STEP/STP, SAT and other formats derived from them (AutoCAD’s DWG, TurboCAD’s TCW, SolidWorks, etc.) have higher-level definitions that support curved surfaces and mathematical operations.

A Surface model can be used in a 3D printer to produce solid (note the lower case ‘s’) that can be indistinguishable from one printed from a Solid model, but Surface models tend to be very large if describing curved surfaces (again, note the lower case ‘s’). Solid models can describe the same object more accurately with a smaller file size because of the difference in how they work.

Rhino (short for Rhinoceros) is a CAD package favored by jewelry designers; it is a Surface modeller (their ‘solids’ are called “polysurface solids”).

Catia is an advanced design package. I haven’t seen a declaration, but it is probably a Solid modeller.

Pretty much every CAD package can load STL & OBJ files. A lot can load PLY files. I have used STL files as a reference for building a Solid model (they’re easier to modify).

So… all the file types exported by Revo Scan or Revo Studio can be used in most CAD packages.

2 Likes
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Hi Jeff,

Thank you for your reply, I really appreciate it.

But I want to work with the surface model (STL, OBJ or PLY) in a CAD software to do reverse engineering. What I need?

For example, I want to generate a mold from a scanned part. Do you have any tips or advice?

Thank you

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As I said, pretty much every CAD package can load STL & OBJ (most can also load PLY).

When you have them loaded, any vertex you can see is going to be as close as possible to the corresponding point on the original object.

Unless your STL file is very large, you can use those vertices as reference points for drawing a higher-resolution model in a Surface modeling program; you can also create a more accurate model in a Solid modeling program. Even if your STL file is on the small side, you can still use it as a reference for drawing a more accurate model in a Solid modeling program.

Molds can be tricky, depending on the technology you will use.

If you want to do it at home, then you can investigate using liquid silicone in a YouTube video.

If you want to make small quantities, you can investigate Sand Casting. This is suitable for manufacturing metal parts and is commonly used in the auto parts industry.

If you want to go into production to print thousands, then it depends on the fabrication house you will hire. Some of them (probably not the cheapest) will take your model and create a mold of it for you, adding the drafts to allow removal after the object has cooled. Making your own drafts will be difficult if your CAD software doesn’t have it as a native function, so I’d recommend against it unless you have the time and money to experiment.

1 Like
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Thank you again for the information. I will investigate it.

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I use catia for my day job and have done for… decades, and I’ve dealt with scan data for half that time.

Unless you have CAD software specifically marketed at picking up features in STL files and semi automatically building surfaces for you, the process is this - and its better than the semi auto one. So long as you know how to use your CAD system, this way will produce a properly constructed CAD model.

  1. Import the STL to CAD
  2. Find a few choice reference features on the STL (Plane, cylinder) and move the STL to align those exactly with the CAD system’s reference axis that you want to build your model from.
  3. Start tracing. Cut sections, estimate and interpolate, to build new CAD entities that follow the surfaces of the scan. Each CAD system has different ways to build NURBS surfaces over point clouds, so read the help page or find a relevant YouTube tutorial.
  4. It all depends on the complexity of the shape and the purpose of the model, but let’s say the scan is of something that assembles to the part you’re working on. You only need to model the mating face, not the whole part. If you’re making a car door mirror case from a scan of the broken bits, you will need to model it all.

EXCEPTION TO THE RULE:

There is a new kid on the block, as a plug in for Blender, which is a point cloud based modelling tool. It now has a sketch based CAD like modelling tool, that seamlessly interacts with scan data. I have not tried it, but it could be exactly what’s needed fror accurately adding to and tweaking scan data. If that sounds more like what you want, check it out.

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Thank you Adrian. I’ll keep it in mind.