SKP to IGES or STEP (for metal fabrication)

The screenshots I posted a few entries back show the “S” step file I uploaded to Xometry.

Just now, I created a brick in SketchUp:

Exported it as a “millimeter” STL file and imported it into FreeCAD:

Converted the mesh to a shape, exported it as a STEP file, and uploaded it to Xometry:

Here’s their 3D view:

Still not sure what you might be doing wrong …

[added]

BTW, here’s the brick.step using Autodesk’s A360 viewer:

I think you’re missing the steps to convert the imported STL mesh to a FreeCAD shape. Only shapes can be exported. You need to open the Part view first:

Then click on the filename in the left panel to select it (or use Control-A to Select All). Then click on Create shape from mesh…:

Then select the shape in the left panel (or use Control-A) and use the File >> Export option:

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in general, doing a file format conversion does not change the file content of course, i.e. facetted meshes won’t convert to NURBS surfaces typically used with 3D CAD exchange formats as STEP, Acis SAT or IGES.

I’m not sure about the STEP file format, but the IGES format exported by FreeCAD outputs planes (144 - Trimmed Parametric Surface) bounded by (142 - Curve on a Parametric Surface) lines (110 - Line) for the case of the brick. There are twelve of these sequences … one for each triangle in the model. I suspect that any SketchUp STL export of lines and faces will translate into the same IGES entity types with no problems. I’m not familiar with STEP files, but I’ll look into its format when I get a chance.

Side note: From about 1982-1990 I wrote a number of IGES importers in FORTRAN for GE Calma systems. Most of the issues revolved around inconsistencies between various exporters, notably defining the normal vector to an arc … most exporters used the right-hand rule and some, for whatever reason, used the left-hand rule. When I’d see a radiused part that looked like this:

I had to reverse the sense of the vectors during the import. It’s somewhat depressing to see that folks are still using Hollerith ASCII format ;(

sure, if the used application is doing an appropriate conversion but still representing a curved surface made of lots of facettes even if using curves as boundaries and not as one surface regularly expected by users of NURBS modelers importing STEP/SAT/IGES data.

The old IGES format should be avoided anyhow because of the flavours concering trimmed NURBS surfaces or support of the manifold solid b-rep object entity (#186) may lead to problems in the destination application.

Jim,

I don’t know what I did wrong with my brick, but will give it another try now that you have shown me your success.Many thanks for your sticking with me!!!

Jerry

BTW, the “curves” I see in the IGES file for the brick are composed of three straight lines. There are no surfaces other than planes with three lines for the boundary. In other words, the edges and faces appear unaltered. The downside, of course is that a nice-looking dome in SketchUp will end up being a bunch of facets (just like the STL file). At least within the FreeCAD software, no attempt is made to generate NURBS or other surface types beyond a flat plane in the IGES format.

There is one other entity, the 402 (Form 1) which says that my brick is made of 12 entities, with pointers to each of the straight-line bounded planes. Dissecting the IGES file related to a 24-segmented dome (created using Follow Me), shows 286 line-bounded planes (most of which have three edges, but some have four).

I’m not sure how one would create and export anything like that from SketchUp in the first place … but I agree with dumping the antiquated IGES format. The info I came up with (above) is based on the proposed 6.0 version, circa 2001. I only looked into the IGES file in detail since I’m already familiar with the format.

Always glad to try and help :slight_smile:

Hi Jim,

Followed your excellent instructions carefully and managed to get my brick to work!!!
However xometry still complains about my object although it now does load. I passed my object thru both netfabb and mesh lab, so I am not sure what is wrong. I am including my file if you wouldn’t mind looking it over. It is a pretty simple object.normandnewtab.skp (93.7 KB)

I recall your questions about bending tabs in another thread. Your part has a couple of problems.

The first, and most critical I believe, from a sheet metal fabrication point of view, is that you need to make the bends with a 0.0625" (1/16") inside radius. See this for Xometry’s specifications for this: Sheet Metal Bending: The Basics

Second, your geometry doesn’t form a proper solid, in both the SketchUp sense as well as Xometry sense. The way you’ve laid your part out would normally make this easy to do, but the bends aren’t there … just sharp corners.

Do you have a nominal set of dimensions and angles describing the final part? I can guesstimate from your current geometry, but it’d be a lot more accurate to start with the references (and tolerances).

I’m not sure how Xometry feels about faceted curves instead of true arcs, but this sample 1/16" thick 1"x1"x1" part with 48 segments in the bend converted and uploaded as a STEP file just fine:

Xometry seems to think it’s okay and quoted a price and delivery:

With some refinements to your model, it should be something that Xometry can make for you.

q.e.d.

never said nor meant this but simply to stay away from the IGES format if you can use STEP or SAT.

yep.

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Jim,

The final product should be made from 20 gauge sheet metal. I just used 1/16’ thickness for convenience. How did you make the bend in your example, i.e., which workshop did you use?

Jerry

I created an outline of the “el” and then used the Push/Pull tool to extrude it. This is simple enough to do, but the bends where the cut metal is angled results in a helical surface along the edge as it wraps around the bend. This is a little more difficult, but it seems like something that shouldn’t have to be spelled out.

If you haven’t already, you should download their sheet metal guide. Like any manufacturing process, there are limitations and trade-offs. I played around with the sheet metal workbench in FreeCad, but it only does bends that are at right angles to everything else. Kind of a Follow Me / Extrude operation.

I sent this drawing off to Xometry to ask them what’s the best way to present your request:

It’s been 25 years since I did any sheet metal design and times have changed (a lot). However, it’s still basically a flat part that’s cut and bent. Maybe a 2D flat (unfolded) layout will suffice. I’ll let you know what they say about it.

Jim,

I started with FreeCad and noticed the same problem with their sheet metal software. That is why I switched to Sketchup,
although I really like the parametric approach of FreeCad.

Jerry

From Xometry:

Thanks for reaching out. In general, we can work directly off of the CAD model when manufacturing sheet metal parts - we don’t need a fully dimensioned print. This is not always the case, but for this part I believe we would be able to work directly off the model.

As for your second point - you’ll have to specify what kind of tolerances you will require for the features in question. Our standard sheet metal tolerances are +/- 0.020. You can add specific tolerance requirements on the “Features” tab after you have uploaded your CAD model.

I didn’t quite get a clarification as to whether or not they need the radiused bends, but it doesn’t sound like they do. I took your model and reworked it for 0.0375" (20 gauge) and converted it to a FreeCAD shape. Then I exported it as a STEP file (not an IGES file, @sketch3d_de :slight_smile: ). Here’s how it looks in A360:

I uploaded it to Xometry and this is the result (kind of pricey, if you ask me):

I took the “underside” faces of your model and extruded them “upwards” 0.0375" and then connected the corners and deleted the inside stuff. I shortened one tab and made the other a mirror image.

jh_newtab.skp (29.6 KB)

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Hi Jim,

When you say connected the corners do you mean the bends? If so I had to do that also.
And deleted the inside stuff means you had to make the object hollow (as I did)? Why did you make the tabs smaller?

I agree the price is a bit steep. I will want to do multiple pieces but each is a bit different.
One offs are always more? It seems we have done the hard work designing the piece and cutting the flat projection should then be easy as it will programmed for the machine? I don’t know if the bends are done manually?

Jerry

Jerry

It doesn’t sound like Xometry needs the bends to be specified … they will bend it so that the flat pieces end up where you want them. I tried several different approaches in using groups and converting to STEP files. Ultimately, I decided that it needs to be a “solid” before it’s acceptable to Xometry.

I thought it might give more clearance for bending … it was just for examples sake and trying to find you a workflow that will work. I would start with the flat model and extrude the thickness outwards. Joining the peaks and erasing the inside easily makes it a solid that is acceptable to Xometry. You can also attach notes and drawings to clarify critical dimensions.

Jim,

Because sheet metal is so expensive, I am going to try plastic. I am changing some of the bend angles and will make the plastic slightly thicker. Why am I getting all the extra lines on the planes?

normandnewtab.skp (80.4 KB)

Jim,

I erased the tabs and redrew and re-rotated them and now the superfluous lines are gone. Earlier I sent your sheet metal design to shapeways to see if the plastic would be thick enough and to check the color. It will be here Monday. Thank you for all of your help!!
Jerry

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