FreeCAD will do this for you.

Open the STL, convert mesh to solid, export as STEP file.

Check what version of STEP his system accepts, as you might have to export in an older version of the format in order to be compatible.

I guess you know that a STEP object is just a ‘dumb’ (lump of clay) 3D solid, so for instance, you could not pick a hole within it and change its diameter from 6mm to 8mm.

Given your clarification, Paul …

The logical answer must be for ‘someone’ who can open the STL to do so, and then save it as an older file-type, for you.

… Happens a lot with word-processing, etc. etc.

MichaelG.

On 12 January 2025 at 09:52 DC31k Said:

I guess you know that a STEP object is just a ‘dumb’ (lump of clay) 3D solid, so for instance, you could not pick a hole within it and change its diameter from 6mm to 8mm.

But you can simply cut the 8mm hole to replace the 6mm one.  All that “dumb” means is that that a STEP file doesn’t preserve any list of features from the originating CAD system.  It is just the final shape of the model.

And if based on a scan of a real object, conversion is not likely to be straightforward, proper reverse engineering software could well be needed.

I have converted them in F360 and exported a STL file from there that can be opened in Alibre. beware if it is a complex part made up of a lot of triangles it will slow both F360 and Alibre down considerably

On 12 January 2025 at 11:50 DC31k Said:

On 12 January 2025 at 10:15 Paul L Said:

What  is really needed is the ability to edit the STL model.

As above, the STL file is a (generally triangular) mesh format.

The two most well-known mesh-editing programs are Meshmixer and Blender.

If you put ‘meshmixer alternative’ into a search, it will suggest other options.

A lot of what will work best for you depends on the shape of the object. If it is an ‘engineering’-type object, converting to STEP and working on the 3D solid might be a good move. If it is a more ‘organic’ or ‘sculptural’ object, keeping it as STL is probably the way forward.

Exactly so.   STL is an output format, containing the minimum information needed to print an object in 3D.  Makes STL a poor choice for many purposes, though worth a try for others.

Though STP can be edited the result may not be useful. Many STL editors only repair and simplify.  Others allow the shape to be manipulated or merged with other shapes.  Paul: what sort of object was scanned, and what sort of edit is needed?

• Sculpted objects, such as figurines, aren’t too hard, once the editor is understood. A common ‘maker’ requirement – 3D printing dragons and such.
• Converting STL to an engineering 3D-CAD model is harder.  Most of the information needed is missing from STL.   Possible to create an STP file from STL that 3D-CAD will read, but it will only deliver a near empty starting point; shape and proportions, no measurements or anything else.  The operator has to provide what’s needed to complete the model with whatever level of detail is needed. Potentially a lot of hard work.

Scan and convert might be a good way of capturing the curves of a propeller, car body, or model aircraft but unsuitable for turning a Thomas the Tank Engine die-cast into a full 3D-model with view to building and running a 5″ loco.

Is this is a one-off?  STL tools aren’t easy to learn, especially the advanced ones.  How to edit a sculpted object might take a few days concentrated effort, much longer to do a complicated engineering object like Thomas.   Conventional methods might be quicker and require less learning.

Version incompatibilities could be a problem too.  A 10 year old Solidworks might gag on a new STL!

Sadly there doesn’t seem to a straightforward way of scanning an object as a well-populated 3d-CAD.  Or am I wrong?

Dave

This isn’t the YT I had in mind but it does seem to pretty much cover the same ground (I’ve only wizzed through it)

As you will see, this not the simplest process to understand (at least it wasn’t for me) but the more basic ‘cut & replace’ approach was much easier for me in practice, provided the model is amenable to this of course.

Modifying a scanned model using Solid Edge

Regards,

IanT