Dealing with Mediocre CAD Files and Splines

[SeymourDumore]

if I was to machine the bore itself, using the top (or bottom) edge as the driving contour, it results in circular moves (turn on Smoothing to "Fit Arcs")

Yeah, but that's just it!
There should not be any smoothing or arc-fit!
It is a circle, plain and simple, there can be no arguments or questions about it!

Here is a screenshot from FeatureCAM, true circle is projected, no smoothing or arc fitting:

 

[AD Design]

Out of curiosity, if you begin the cut from mid-plane (center of 2" cylinder) cutting in both directions will it still be defined as a spline? Doesn't help the CAM side of things doing this but I find this to be a glaring error on the CAD end. Further, how about a cut as a sketched circle that uses a trajectory that's also sketched? The plot thickens...

 

[SeymourDumore]

Out of curiosity, if you begin the cut from mid-plane (center of 2" cylinder) cutting in both directions will it still be defined as a spline? Doesn't help the CAM side of things doing this but I find this to be a glaring error on the CAD end. Further, how about a cut as a sketched circle that uses a trajectory that's also sketched? The plot thickens...

Yes, if the plane is cutting through the whole circle, it will be represented as such.
But for the stupidity, take a look at this:


This is the same file, but it also includes a "blind" hole.
The representation from the back of the blind hole projects a circle, but the through hole is a spline.
And this is somehow acceptable to the developers AND the users of Autodesk Inventor!

 

[AD Design]

Seeing this (it's not a bug it's a..)"feature" suggests that any through hole cut into a non-planer surface (corner for example) will be represented as a spline when viewed from the axis origin.....unless it's a blind hole? I don't know what I'm more amazed about, the screw up of the software developers at AD or the user community that tolerated this all these years. I'm accustomed to limitations/quirks of different CAD programs but I regard this as a basic feature (put-hole-in-object) for any CAD program and a basic failure for Autodesk Inventor. Apologies to the OP for hijacking the topic but I've never seen this mentioned on the net or by users that are fans of Inventor that I've worked with. Thank you Seymour for posting this with examples. I would have been fired from the job for something this stupid that no other CAD developer has had trouble with.

 

[Areo Defense]

Somebody has to say this...All these fine examples typify exactly why life is much easier with a cam system that is model centric, with usage of geometry boundaries relegated to very rarely used circumstances. In such systems the entire model is part and in your operation you select the faces to machine with the path type of your preference. Weird face edges? Who cares, they are irrelevant to "Honey Badger CAM".

@Stoney83 , long story short, if you have issues with geometry such as this, you really need to up your cam game. You have what you have to work with so you'll need to figure out situations like this to get the job done. I looked back through the thread to see what cam you're using or perhaps you are free-handing a program?

 

[CarbideBob]

The representation from the back of the blind hole projects a circle, but the through hole is a spline.
And this is somehow acceptable to the developers AND the users of Autodesk Inventor!

Which it what it should be.
You say back of the blind hole, I think the top must be spline.
Back end of through hole is a spline since it is 3D. This world is not flat.

 

[SeymourDumore]

Which it what it should be.
You say back of the blind hole, I think the top must be spline.
Back end of through hole is a spline since it is 3D. This world is not flat.

Come On Bob!
Are you serious about any of that?
The world isn't flat, but it's 2D representation is!
By your reasoning, a line cutting through the same cylinder shouldn't be a line either?
Are you saying that 100% of the CAM programs out there are wrong for recognizing it as a circle and not a spline?
Are you saying that Solidworks, NX, Solid Edge or Key Creator is also wrong for creating a circle in it's 2D representation?

 

[triumph406]

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.

From what I've seen very few (if any) cad drafters know ISO standards, I've been doing drawings since the days of the drawing boards, and if somebody asked me to make a drawing to ISO standards I wouldn't know were to start.

If somebody told me that they were going to redo my drawings, at my expense, they wouldn't get the job.

--------------------------------------------

So what do you require to see on a drawing that would make it ISO compliant to your satisfaction?

 

[triumph406]

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

Better stay away from a lot of aerospace parts, depending on what part of the fuselage/wing etc the part goes it could likely be almost entirely defined by splines and surfaces.

 

[SeymourDumore]

with usage of geometry boundaries relegated to very rarely used circumstances. In such systems the entire model is part and in your operation you select the faces to machine with the path type of your preference. Weird face edges? Who cares, they are irrelevant to "Honey Badger CAM".

Hmm ... rarely used circumstances ... like laser, turret punch, waterjet ?

 

[Areo Defense]

Hmm ... rarely used circumstances ... like laser, turret punch, waterjet ?

Firstly, a sign of an advanced system is when you have to use boundaries, you can simply use model edges and there is no need to replicate model edges by extracting curves.

Secondly, and perhaps most importantly, another sign of an advanced system is regardless of whether your path is simultaneous 3-5 axis or simple 2d paths, the model's faces are the drivers for the path and you don't need chain boundaries, let alone duplicate geometry edges that are already there by having to extract edges.

I have programmed plenty of 2d milling paths in NX, that would be identical to routing, laser, etc-, and don't use face edges and certainly do not use any sort of extracted geometry.

 

[SeymourDumore]

Firstly, a sign of an advanced system is

... and then there is the real world.

 

[[email protected]]

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.

I would ask him to send you the files in a different format. i have found that .iges files work the best however have him send you a .step , .iges, .x_t (parasolid) and make sure you set your importing and or conversion setting accordingly... there are also solid model healing setting in most cad systems.
play around with the different files and imports and see what works best.....
best regards

 

[Strostkovy]

I wish support for ellipses in cad programs and machinery was more prominent. Ellipses and sinusoidal g codes are the futuuuuuuure.....

 

[Areo Defense]

... and then there is the real world

I don't know what you are speaking of. What I do know is comes down to how much cad/cam we need and how much it costs; everything else is irrelevant.

 

[SeymourDumore]

I don't know what you are speaking of. What I do know is comes down to how much cad/cam we need and how much it costs; everything else is irrelevant.

Just because your opinion is that the manufacturing world must be based on solid modeling and all else be damned, it still does not remove the need for 2D drawings, or, heaven forbid, 2D geometry to be used.
For example, what would be your choice of nesting software to create the most efficient pattern for material usage or most efficient cycle time?

 

[Areo Defense]

Just because your opinion is that the manufacturing world must be based on solid modeling and all else be damned, it still does not remove the need for 2D drawings, or, heaven forbid, 2D geometry to be used.
For example, what would be your choice of nesting software to create the most efficient pattern for material usage or most efficient cycle time?

I never said must but, inarguably, model based everything is the pinnacle. Even though the previous statement is true, I agree there is still a need for 2d. There are many shops making parts that were hand drawn and never needed to be modeled; I come across them once in a while in aerospace/defense too, but people shouldn't confuse functionality of different tiered cad/cam. I don't have any choice in nesting software, I don't have a need for it, not my lane. NX has associative nesting modules and I believe 3D nesting as well, although that's nothing special these days; a number of systems can efficiently 3D nest.

 

[precisionmetal]

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.

Interesting thread!

Stoney, my "guess" is that the blemishes in the part simply come down to how your CAM program is creating code for your machine.

I learned this the hard way, and spent a lot of time beating my head against the wall when I got into the wire edm business. Most of my work came in as either making a complete part from a solid model, or handed part(s) that had been machined, and still required wire edm work (once again: defined by a solid model). As such, I found myself almost always "extracting" geometry from solid model, and mostly SolidWorks. Even projecting what appeared to be a perfectly radiused edge often created "some" garbage in the projection (often because the intern who produced the model would go "fillet crazy"), and those intersection of fillets is something that SW did not handle well (at least back 15 years ago).

A wire machine is brutally honest when it comes to profiles -- if an arc/spline gets broken into a few hundred straight-line moves in the machine code, the wire machine is more than happy to precisely duplicated those moves and it will all be apparent on close inspection. Typically, cutting a profile in a CNC mill using a half-inch or larger end mill will hide all these imperfections -- so they may exist, but simply are not visible because of the diameter of the cutting tool.

Have you looked at the block of code defining the tool path where are you having blemishes? I "suspect" you may find an indication there.

Very long (too long) story short: It's quite often faster to simply remodel the part, or drive the tool path from precise sketches you have created *from* their geometry.

Keep us posted!

PM

 

[SeymourDumore]

almost always "extracting" geometry from solid model, and mostly SolidWorks. Even projecting what appeared to be a perfectly radiused edge often created "some" garbage in the projection (often because the intern who produced the model would go "fillet crazy"), and those intersection of fillets is something that SW did not handle well (at least back 15 years ago).

^^^This^^^

Specially when said just-out-of-internship fella provides a 2D dimensioned drawing with "show fillet edges" turned ON!
Talk about incomprehensible garbage!

For the record, I do a fair amount of wire EDM work where profile extraction is absolutely necessary, no matter the sophistication of the CAM software!

 

[triumph406]

Typically, cutting a profile in a CNC mill using a half-inch or larger end mill will hide all these imperfections -- so they may exist, but simply are not visible because of the diameter of the cutting tool.



PM

Cutting a spline smoothly is dependant on the spline tolerance, not tool diameter