Dealing with Mediocre CAD Files and Splines

[Stoney83]

How do you guys deal with mediocre cad files… got some files that would actually be really good except they are full of splines and have some illegal boundaries.

They machine Ok and make a pretty good part but leave blemishes that can’t be eliminated without redoing the cad model. Things that should be easy like adjusting a radius are impossible and certain cutter paths don’t work or have lots of “spikes” on the CAM. Things that should be done with basic 3 axis cutter paths are 5 axis style cutter paths.

Is there an effective way to tell customers and engineers to STOP drawing with splines.

I tried explain this to the customer and even sent a dxf that will eliminate most of the problems but they will have to the 3D work.

 

[LockNut]

This could be a setting in whatever conversion system was used to output the file. Could be settings in whatever you used to import it into your system. Yes, I would speak with your customer and ask them.

 

[SeymourDumore]

What kind of CAD files are you talking about?
If Solid models, then there should be no reason to get splines unless actually intended so.
If OTOH it's 2D drawing files, then I am willing to bet your customer used Inventor to create them.

 

[Stoney83]

Fusion 360 solid models…. and they where constructed with some splines and some hard geometry.

Does fusion 360 have the ability to convert splines into arc’s easily?

The same shape can be created without using splines. They also have some geometry thats not tangent when it should be. I would think fusion 360 would give them an alarm when they fold a surface into another surface in such a way it leaves a “dent”. There not very big dents… .015-.020 but you can see it in the part and I don’t know to smooth it out on the mill. The cutter comes almost to a dead stop at a couple locations that are fairly straight. Maybe I should disable gouge protect and see what happens?

I think they are using something like Adobe Illustrator or photo shop to create an organic shape then dumping it into fusion 360 without properly cleaning up the file.

 

[AD Design]

While taking formal CAD classes we were all told to avoid using splines when modeling as they can be easily misinterpreted in drawings. I suspect there are many designers/engineers that never heard that recommendation or were self taught. Many of the drawings/models I was sent seemed to confirm this. Surface modeling files were even worse. Can't offer any help other than to echo what others have already posted, tell the client it's causing problems. Good luck.

 

[memphisjed]

Converting splines to arcs or polylines is thre or four mouse clicks in a number of cad programs. I love splines, easy to edit and no tangent issues. Convert to arcs is last step just before machine file.
I hate poly lines- stupid neither arc simplistic or spline edit easy.

If you have sharp divers it was modeled or translated into a stl file at one time. You can go thru fusion surface repair / normals check to find the bad triangles. You will not get a straight or flat, or nice curve back out without some fancy remodeling or sub-d effort.

 

[Mtndew]

How do you guys deal with mediocre cad files…

I either ask the customer to send a stp file, or I try my best to fix the one they gave me if they can't send me a model.
Sometimes I have to re-draw some of the part if it's garbage to begin with.

 

[SeymourDumore]

Converting splines to arcs or polylines is thre or four mouse clicks in a number of cad programs.

You ain't got that option in AutoCAD ( prolly one of very very few missing options ).
You can convert a two bit whore into a polyline with your eyes closed, but you ain't never gonna get arcs' let alone circles from a spline.
I vehemently abhor splines unless it's absolutely needed.

 

[SeymourDumore]

While taking formal CAD classes we were all told to avoid using splines when modeling as they can be easily misinterpreted in drawings. I suspect there are many designers/engineers that never heard that recommendation or were self taught.

Well, unfortunately Autodesk and it's Inventor development team did not get that memo!
For example, if you model a 2" cylinder with a 1" hole perpendicular through it, the resulting drawing view will show a spline instead of a circle!

....Aaaaand the sad part: vast majority of the CAD jockeys on the Inventor forum believe that to be the correct behavior of the drawing environment!

 

[winger]

Ran into this a few years ago. It was a feed cam. As best as I can describe a snail curve with a hook. A bunch of arcs with different centers. Looked fine in the paper drawing but when I plugged it in my cad, most of the curve end points didn't intersect. Reverse engineered and was done in either Autocad or Inventor and probably only 2d.
I'm sure the cad jockey didn't know what was important for mfg, but it looked fine on paper.

Dave

 

[memphisjed]

most of the curve end points didn't intersect. Reverse engineered and was done in either Autocad or Inventor and probably only 2d.


Dave

This is why splines are better. One curve is continuous by definition*. Left as defining feature easy to edit, find and follow tangents. Converting a copy to arcs or lines for making as last step. Polyline or bunch of small lines is the worst. Is the arc approximation inscribed, circumscribed, or kinda in the middle?
*simple curves, not math curves- they can get all imaginative if left unsupervised.

 

[SeymourDumore]

Reverse engineered and was done in either Autocad or Inventor and probably only 2d.

Rest assured, it was likely NOT done in AutoCAD!!!
I will swear by AutoCAD's capability simply because of it's inheritance and my (up-to-date) experience.
At the same time, whatever garbage is coming out of Autodesk as of late ( aside of ACAD ), I would not be surprised of anything, read and research Post #9 as an example!

 

[AD Design]

For example, if you model a 2" cylinder with a 1" hole perpendicular through it, the resulting drawing view will show a spline instead of a circle!

-Could you show an example of this? I abandoned AutoCad after being introduced to Pro-e and don't recall what it can/can't do. Use the attached image if you wish.

 

[winger]

The drawing was done by the engineering dept of the company I worked for and they used Autocad and Inventor.
I learned on Autocad and unlike Alibre that I use now, you can close a sketch with open lines.

Dave

 

[winger]

I should have added that they were using a lot of interns back then. But it was still signed off by the dept head, but probably looked ok and printed ok, until it was zoomed in.
I had to change the pocket size a little and tried to make a solid model to confirm everything when I couldn't close the sketch because the ends didn't coincide.
Thank for the hint of using spines . I'm not a cad jockey but know enough to struggle by. Maintenance machinist by trade but I have a hobby cnc mill at home.
Odd thing, is I could have made this on a rotary table without a major problem.

Dave

 

[Doug]

This was about the mid-1980's.....

I went to my customer's office to discuss a prosthetic device design he'd sent to me. A dxf file that I have no idea how he made it. Double lines, intersections didn't actually intersect among other problems. When printed none of these problems showed up. All sorts of problems showed up in CAM and the mill toolpaths.

One of my topics of our meeting was to let him know of these problems and that I had to spend time correcting them.

Waiting for him to get off the phone I was sitting in the company's reception area and what to you know? There's a trade magazine with the guy's pictured on the cover with a story about how his company was at the forefront of revolutionizing the manufacture of custom prosthetic devices.

I decided because of the magazine story this was not the time to bring up the subject of poor drawings. I let him bask in the glory of the magazine cover for a few weeks.

 

[Stoney83]

Thanks for the input.

I got the parts looking good with different programming than I would otherwise use.

There’s still a couple things not 100% percent right. One funny movement on the mill and a .030 radius that would be better at .060 or .100. Pretty sure the customer will be happy with the parts and sent them the prototypes Friday afternoon.

 

[SeymourDumore]

-Could you show an example of this? I abandoned AutoCad after being introduced to Pro-e and don't recall what it can/can't do. Use the attached image if you wish.

Here you go.





The image clearly shows that the side view is not a circle, rather a spline with 50 control points as created by Autodesk Inventor.
No, it is not an AutoCAD problem, rather an Inventor problem created by morons who apparently should have no business writing code for a CAD application!

 

[Panza]

Maybe this won't solve your problem since you're always into this but the way I deal with this:
When I give people a quote I look at their drawings/model and if anything is strange or not up to a certain standard I will inform them that they need to make drawings to ISO standard if I get the job. If they don't they will have to pay for me redoing the drawings.
Regarding splines in Autocad: I have never needed to use splines in the 25 years I've been using autocad, and they are usually trouble when someone else has used them in a drawing I get.

 

[memphisjed]

The example given is a spline. A circle projected onto a cylinder does not result in a circle definition. The projection parent is the circle.
Iso standards allow multiple stacked polylines for the same hole, inner and outer wall. Complete cluster trying to figure which is which if the hole was not defined as perpendicular to begin with.
If someone gave a perfect hand drafted paper to you would you have to model it? Does that incur charge? Can I say only my chosen software is acceptable- no dxf, pdf, dwg, stp allowed?
The dimensioned paperspace drawing is not to trustworthy scale to begin with- models should be story stick uno.