Hi Michael,

I use MOi to create the parts files for the tube bender 95% of the files go through without problems sometimes I find they dont import I make sure that when I create the path curve the direction or the start of the curve is all the same way. If i import the dxf path into solidworks and export the same file from SLD the step imports no problem. What is the STP format that MOI uses? Both files exported and overlayed look exactly the same so it must be an export issue.

Any advice welcome.

Hi Alex, STEP is a complex format and there are all kinds of different ways that things can be configured.

For example a planar face could be exported as a specific "PLANE" entity type, but it could also be exported as a generic NURBS surface. It could represent a reversed normal direction by setting a reverse flag or it's possible to flip the geometry itself and not set the flag. Various things like that.

It sounds like your receiving application doesn't like to handle certain configurations. It may be difficult to figure out exactly what it's sensitive to.

First of all, what type of objects are you sending through step format, is it curves only? If not then you must be doing some other stuff in SolidWorks since the DXF transfer will just send curves over.

If you're sending solids, one thing I notice in your Solidworks settings you have "Split periodic faces" set to be on. Periodic means a smooth closed surface, that would correspond to the moi.ini setting
[STEP]
ExportSplitClosedSurfaces=y

So the first thing I'd recommend trying is to set that option in moi so it will be treating closed surfaces similar to SolidWorks.

If that doesn't make any difference then the next level of investigation would be if you had the simplest possible example that works from SolidWorks but doesn't from MOI and send the .3dm file and both the STEP files out from MOI as well as the one made by SolidWorks so I can try to examine them and try to see what is different between them.

It will make it easier if there is not a lot of stuff in the file, the simpler and fewer pieces the better for this kind of analysis.

Thanks, - Michael

Thanks for speedy response with the pipebend software I export a solid - the dxf is just for creating the path way.

Same dxf in both programs to create the solid - and the MOI exports work 90% of the time. Its really quick designing tube parts in MOI much quicker than designing the same part in Solidworks. From the error in the pipebend software its like it cant read the ends on this particular file and its usually the same error. Maybe something how the ends of the shape are completed into the solid.

I have had a look at both solids in Rhino and there is differences on how the the solid shape is created.

In Moi I usually create the path and then run the PIPE script. I have also tried drawing in the circle at the start of the curve to get Sweep but doesnt seem to make much difference.

See what you think.

Hi Alex, ok so I'm understanding a couple of things better - in that file you posted
you've got the MOI generated pipe in red and the SolidWorks pipe in green.

I wasn't quite understanding that part before.


> I have had a look at both solids in Rhino and there is differences on how the the solid shape is created.

Yes it looks like the main difference is that SolidWorks generates parts of the sweep using a trimmed torus
or cylinder analytic surface when it's possible to do so, while MOI's sweep always makes a fitted surface
using the general purpose sweep refinement process.

For example the first section starting from the outside has surface control points like this from MOI's sweep:


While the SolidWorks first section has control points like this - it's a trimmed piece of a torus:


- Michael

So basically they're structured pretty differently from when the sweep is generated, and then the STEP file generated from that will inherit those differences like the SolidWorks STEP file probably has torus surface entities in it.

Although they are structured differently, they are very closely describing the same shape. I made a very highly refined mesh to get a better visual without display artifacts and they are very closely overlapping each other:



- Michael

As to why it sometimes works with MOI's output and sometimes not, it's hard for me to speculate on that since the error is happening inside the pipe bender software.

Have you sent in a file that doesn't work to their tech support to see if it's something they can tune up?

If they require their STEP input to only contain analytic torus and cylinder entities, you'll probably need to use SolidWorks to output that since MOI isn't able to generate that particular type of restricted output right now.

One thing I don't get is why is it using STEP at all instead of taking in the DXF ?

- Michael

Thanks Michael for the investigation - perhaps its just the larger radiuses Ill keep on mental tab on when Moi Fails see if I can pick up the pattern. When it does fail I usually import the same DXF pathway and import that into solidworks - so that all makes sense that there is an underlaying difference on how different surfaces are created. I have tried to contact the Pipebend software developers but they are in China and no reply. With tube bending most parts are 3d so thats why you need to import a 3d STEP file. On this spiral file its 2d but in the pipebend software I overide the rotation on each bend and end up with a 3d spriral. Ill send a picture of that once its bent.

Here is the same machine we use in action to give you a better idea of the process. Some thing like this part in the video I can design that part in MOI in a couple of minutes it really is a killer app for this type of work.

https://www.youtube.com/watch?v=178HPP3v3x4

Hi AlexPolo,

It sounds like the pipe bender CAM is expecting analytic surfaces like toroids and cylinders rather than freeform spline surfaces. I ran into the same problem a few months back when trying to import a STEP generated by sweeping in MoI into a sheetmetal CAM program. You can solve this by using extrude and revolve instead of sweep. Those commands generate clean analytic surfaces. Of course, it's a lot more work.

- Peer

Thanks Peer I tried to simplify the shape as the outer shape can either sqr or round ultimately the machine doesnt know which tool set you put in but still same problem - here is another part created in MOI with essentially the same components a few 90 degree bends - a few straight sections and 1 large arc this file imports into the tube bend software without problems - strange that it work most of the time but with the occasional file its a no go - Ill keep experimenting see if I can pinpoint the issue.