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Drawing vs 3D CAD Model

Drawing vs 3D CAD Model

Drawing vs 3D CAD Model

(OP)
I have a model that will have to be cast, but it has some very complex shapes. Using Unigraphics, I am unable to get a radius into a region I KNOW they are going to need it, the program just will not put the radius into it.

So here's my question. The Model will be sent to the customer along with a drawing. If I call out a larger radius on the drawing than they find on the 3D part, will that supersede the model? Or should a notation be included on the drawing to indicate that the larger radius is prefered regardless of what the model shows.

Unfortunately due to the complex geometry of the part the Model has to be provided as well as the drawing.

Thank you for your time,

RE: Drawing vs 3D CAD Model

Put a note on the drawing stating: "Model provided is to be used for producing the casting due to the complex shape". Or something similar.
If you can't get NX to give you the radius value in a dimension, then you may have a generated a shape from blends that is not a true radius, but a curved surface. Have you tried doing a cross-section at the point you want to dimension the curve at?

"Wildfires are dangerous, hard to control, and economically catastrophic."

Ben Loosli

RE: Drawing vs 3D CAD Model

In today's CAD world, the 3D model is the configuration control master, and, if there is a drawing, the drawing consists of views from the 3D model.
They should match, period.
Actually, I think you have a bigger problem than the old Model vs Drawing battle.
If you can't get the model to the configuration you want, how could anybody make the configuration you want?

Harold G. Morgan
CATIA, QA, CNC & CMM Programmer

RE: Drawing vs 3D CAD Model

Who are "they" in "they are going to need it"?
If it's manufacturer, make a note like "RADIUS X.XX IN THIS AREA PERMITTED"
If it's customer and radius is functionally required, make your best effort to model it like looslib suggested.
Either way make sure the note will be noted. Many shops tend to ignore the drawing, go purely by the model, and refer to the drawing only after something goes wrong.

RE: Drawing vs 3D CAD Model

I agree, make them match.
If the drawing is going to have changes, and not the 3D model, might as well use ACAD.

Chris, CSWA
SolidWorks 14
SolidWorks Legion

RE: Drawing vs 3D CAD Model

(OP)
To clarify, I think it is a problem in how UG determines a radius.

The geometry is a constantly changing shape. I am able to get most of the draft angles and radii in, but in the location indicated by the picture the coding of UG is not permitting me to put a large enough radius, and it is failing inside the circle. I believe in practice this problem is non existent and the manufacturers would prefer the radius and it would make their job easier, but I am spending hours trying to get UG to do something it is failing to do.

What I am getting from the conversation is that the model HAS to be right and that the drawing is only present in case of problems or to provide the person receiving the part elements they can check.

Which puts me in a quandary as to how to solve this problem. *sigh*

Unless someone knows a good say to use documentation to allow the manufacturer to put in the necessary radius. I'll take this to the Siemens forum and ask for solutions on the UG side.

Thanks again

RE: Drawing vs 3D CAD Model

Quote (ctopher)

...might as well use ACAD

rofl

How much experience do you have using NX? Have you exhausted all of the different approaches you can take to create this radius, or just the blending commands? While it may take some time and effort, if you can draw it you should be able to model it.
I have never worked with a solid modeling system where the drawing was the master definition; it is always the model.

“Know the rules well, so you can break them effectively.”
-Dalai Lama XIV

RE: Drawing vs 3D CAD Model

I was typing when you posted...
Is it a constant or variable radius that you need? Have you verified the integrity of the surrounding surfaces in that area? NX should be able to do this with a little investigation. It would be a good idea to pick the brains of those in the NX forum.

“Know the rules well, so you can break them effectively.”
-Dalai Lama XIV

RE: Drawing vs 3D CAD Model

There are lots of ways to attack this in 3D. There are many ways to define fillets:
  • Edge fillet (used 99% of the time)
  • Face fillet
  • Fillet to edge or line
  • Variable radius

RE: Drawing vs 3D CAD Model

(OP)
I have been using Unigraphics since 2008, I have over 20,000 hours in the seat. Though with NX 9, which we have only just gotten I only have about 400 hours in the seat.

I have used ever option, including trying to use my own sweep sketch, but they won't join, and due to the complex geometry it isn't tangent to the two surfaces. The edge is moving in all three dimensions, and the angle on the seam is constantly changing as well. It is simply beyond the capabilities of the program as far as I can tell. And because part of the Siemens company and my company work in the same field I'm not allowed to send our models to them for help.

So yeah, that's where it is at.

RE: Drawing vs 3D CAD Model

That's a good amount of time using the software. >50,000 hrs myself, but I have yet to experience NX9.
Sometimes in situations such as this you have to go back and recreate the surface elements that are giving you problems. By doing so, you may find slightly different approaches that allow you to proceed with the radius in question.
Again, ask on the NX forum... I have been ever thankful for advice received over the years from its members when I have come across similar problems.

“Know the rules well, so you can break them effectively.”
-Dalai Lama XIV

RE: Drawing vs 3D CAD Model

I'd start by looking for discontinuities between the faces circled in your pic.
The 'examine geometry' command may also be useful.
Have you tried the different 'overflow resolution' options within the blend command?

RE: Drawing vs 3D CAD Model

1. As ewh says have you tried surfacing or similar? In NX little brother I sometimes had to go back several steps and change order to get this kind of thing to work when surfacing so I have some appreciation for your frustration.

2. Are you being forced to play the purchasing 'telephone game' or could you actually talk to the foundry about your issue?

3. On the drawing if you have a call out for that radii generally just make sure it is clear that it's "ALL AROUND" - perhaps even adding that to the drawing.

The casting house is probably going to do some work on the model anyway to allow for shrink etc. so it may not be a killer.

Posting guidelines FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm? (probably not aimed specifically at you)
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?

RE: Drawing vs 3D CAD Model

(OP)
Hey cowski,

Yes I've tried the different overflow options. And Examine Geometry either Passes everything or there are no results. (I have never found Examine Geometry very helpful)

I can get a radius so long as the value is smaller than .3 mm, and no casting, scratch that, no cost effective casting will be able to maintain that.

RE: Drawing vs 3D CAD Model

(OP)
We are designing this for a customer who will source it. I have no contact with the supplier as a result. So I have to make the drawings / model as clear as possible.

Thanks for everyone's help by the way.

RE: Drawing vs 3D CAD Model

OK, so put in a .3 mm radius and apply an appropriate tolerance in the drawing that covers what the foundry will want (while meeting functional requirements...).

While having the model ready for the foundry to take with minimal effort/matching the drawing... are good general practices at some point the effort (i.e. $) to achieve that may not be warranted.

Posting guidelines FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm? (probably not aimed specifically at you)
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?

RE: Drawing vs 3D CAD Model

I agree with Kenat. Let the drawing define the acceptable range, and move on to the next design. In the real world, where I work, I get paid to put parts on the shop floor, not to create mathematically perfect CAD models. CAD does not define the part, the purchase order does, by specifying whether drawing or CAD file takes precedence. At least, that's what the lawyers say.

RE: Drawing vs 3D CAD Model

Hard to tell from just a picture, but there are some indications that the principle surfaces have some funkiness to them. Fix that, and your fillet should happen.

Time was, UG would allow users to adjust Parasolid tolerances. Tightening tolerances on the preceding features and loosening them on the fillet might get you there.

RE: Drawing vs 3D CAD Model

Hi, Twullf:

I took a quick look at the picture you posted. Something like this can be done with surface modelling.

If you post a section of this model, we can give you some suggestion.

You need to take a different approach as your current one leads to invalid geometries.

Best regards,

Alex

RE: Drawing vs 3D CAD Model

I am intrigued as to why a designer with 20,000 hours experience on a high end CAD system feels that a machinist or whoever picks up the part to be made is going to be able to fix a model that they cannot?

RE: Drawing vs 3D CAD Model

Quote:

CAD does not define the part, the purchase order does, by specifying whether drawing or CAD file takes precedence. At least, that's what the lawyers say.

I agree that the model "should" be identical to the drawing, but here we always put a disclaimer on purchase orders stating that the drawing is the criteria for acceptance. The model may be provided, but is reference only.

RE: Drawing vs 3D CAD Model

Quote (TWJR)

...we always put a disclaimer on purchase orders stating that the drawing is the criteria for acceptance.

Always wise, but that won't stop the manufacturer from carving away blindly from the CAD. If you can't reconcile CAD and drawing, best to be material-safe on the CAD model.

I've wrestled with stubborn fillets on-and-off for half my life (as many of us have). There is most certainly a brute force solution to getting a fillet in there, even if it means carving the solid up into surfaces and stitching back together. (UG/NX is particularly good for this.)

Also, it is not always the best course to use the design CAD model as the model to be used by the manufacturer. You may want to make a second model specifically for manufacturing. I usually do this and hand them a lobotomized, featureless model so they don't need to wrestle with feature regeneration time, etc.

RE: Drawing vs 3D CAD Model

Again, take a long hard look at the surfaces being filleted and the features generating them. There's probably something to fix. If there are imported surfaces or lofts or sweeps or spline-driven surfaces, look for faces or splines with an excessive number of defining points or poles. UG/NX has some great tools for examining this.

RE: Drawing vs 3D CAD Model

I don't know why but I REALLY bristle when told that the model geometry is "invalid" by either the machine or some @%%^#$@%#$ programmer. The geometry shown in the OP's picture looks fine to me, nothing invalid about it. What is meant, and if you hold the programmer's head underwater long enough you will get him to admit, is that the 3D modeling software is not capable of solving the geometry.

RE: Drawing vs 3D CAD Model

Depends on the industry... my current employer requires parts to be modeled at nominal, with very few exceptions.

“Know the rules well, so you can break them effectively.”
-Dalai Lama XIV

RE: Drawing vs 3D CAD Model

As for sending the part to GTAC, that should be allowed even if your compnay competes with Siemen's in similar areas of industry. GTAC has very strict rules on who can see a part that they receieve froma customer. I know John Baker has said that even he cannot see a part that has been sent to GTAC for help. Non-disclosure agreements are in place between the companies by nature of the license agreement to use NX.

As others have said, try te NX forum, maybe with a portion of your total part and see if someone else with NX can get the blend you need.

"Wildfires are dangerous, hard to control, and economically catastrophic."

Ben Loosli

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