Converting .STL 3D file to Autocad format

[FurtiveFreddy]

I've got an .STL file created by someone else (don't know what software they used) and I need to convert it to a format my CNC machine shop can bring into Autocad, so presumably that needs to be .DXF or .DWG?

I've tried a couple of free conversion programs without success. They either fail or the file they produce can't be opened in a DXF viewer.
Any utilities recommended?

[tivver500]

According to 'interweb' AutoCAD can directly import .STL files (but I haven't tried it.....)

[Sporky]

I think you can do this in Rhino3D - free full-feature 90-day trial too.

https://www.rhino3d.com/download

If I remember I'll have a look this evening - assuming I can find an STL file to try it out with.

[Mr Pointy]

FurtiveFreddy said:

I've got an .STL file created by someone else (don't know what software they used) and I need to convert it to a format my CNC machine shop can bring into Autocad, so presumably that needs to be .DXF or .DWG?

I've tried a couple of free conversion programs without success. They either fail or the file they produce can't be opened in a DXF viewer.
Any utilities recommended?

Can you put the file up on Dropbox (or similar)? Someone migt be able to convert it for you.

[FurtiveFreddy]

I've downloaded Blender and exported it from that as a DXF then opened it with a free DXF viewer, so the file seems to be recognised but whether it will work properly in Autocad I'm not sure.

Also the engineering company wants a PDF as well, presumably line drawings of each elevation with dimensions? Is this something which is usually created automatically from the 3D view from Autocad or will I need something else to generate that?

I'm waiting for more clarification from the CNC boys and if I'm still struggling by tomorrow I'll post the file up somewhere.

[Russ35]

Is there not going to a drop in quality if your starting with an .STL, depending on the settings used to create the .STL?

i.e. a hole not actually being quite round etc.

[FurtiveFreddy]

Russ35 said:

Is there not going to a drop in quality if your starting with an .STL, depending on the settings used to create the .STL?

i.e. a hole not actually being quite round etc.

Do you mean the conversion process will reduce quality?

[Russ35]

.STl format is basically tens of thousands or more (depending on your design) of triangles that make the shell of your design. So it would depend on the resolution that the .STL file was saved at, the higher (or finer) the resolution the better.

Have a watch of this video and he shows editing an STL in Fusion 360

https://www.youtube.com/watch?v=yxC-kwuksug

[FurtiveFreddy]

Russ35 said:

.STl format is basically tens of thousands or more (depending on your design) of triangles that make the shell of your design. So it would depend on the resolution that the .STL file was saved at, the higher (or finer) the resolution the better.

Have a watch of this video and he shows editing an STL in Fusion 360

https://www.youtube.com/watch?v=yxC-kwuksug

Yes, I can see that in Blender, but wondered if a file conversion or import into Autocad would interpolate it.

Maybe the best thing is to start again from scratch?

I have a small part made of metal I need to digitize into AutoCad + PDF for a CNC firm to manufacture.
What's the most cost-effective way to do that?

[Sporky]

Depends on how complex it is, and how accurate you need to be. Set of digital calipers and a protractor will do some jobs to an acceptable accuracy, fer example.

[FurtiveFreddy]

Sporky said:

Depends on how complex it is, and how accurate you need to be. Set of digital calipers and a protractor will do some jobs to an acceptable accuracy, fer example.

I think this needs more than that. It's quite small and an odd shape and some of the dimensions and angles are likely to be quite critical.

Is laser scanning the best way?

[drewk1]

A STL will not have any useful geometry in it. As already stated it’s a shape comprising of triangles.
You can reverse engineer a cad file from STL but you need proper software such as Polyworks or Geomagic.
Best bet is just to measure the part and produce a drawing of what you need.

[Sporky]

I did a test; I can indeed open STL files in Rhino3D, and save them out as DWG.

However, it is correct (as someone said) that the STL file is basically a mesh, so you get the triangles that form the surfaces, and so the output is a 3D DWG.

You can then start reducing the meshes down to sub-elements, but it's going to be a lot of work to end up with base geometry.

I'm also unclear on what the CNC house actually wants from you - I could use MADCAM to generate G-code to machine an identical object - in theory - but they may want the three elevations. Or it may be an object which isn't easily described in three elevations.

Sorry. Probably not a terribly useful answer.