Sharing well constructed CAD models II 8

[SiW979]

thread561-234523

Sometime ago I created a thread trying to encourse people to share their we constructed CAD models so that others may play around with them an possibly learn a trick or two.

Anyway the thread has been closed, but a reference to it is at the top of this one. I've got another CAD model here of a piece of round tube with a sqashed flat end,which one of my users aksed me to show him how to do, so have a look and see what you think, I'd be interested to see other peoples interpretations and also critiques of mine.

For anyone who never saw the original thread, I would recommend you have a browse through some of the excellent CAD models that people posted on there.

Enjoy I

Best regards

Simon (NX4.0.4.2 MP10 - TCEng 9.1.3.6.c)

http://www.jcb.com

Life shouldn't be measured by the number of breaths you take, but by the number of times when it's taken away...

 

[cadmantools]

Closed end spring

 

[crazydiamond]

To cadmantools;

what is the purpose of the last two features (sketch & extrude)?

Thanks in advance for any reply.

Ron
Design Analyst

 

[hudson888]

Simon,

I think you'll find this a slight improvement and examine geometry will tell that story for you as well. You just use a little control over the shape when you have a straight line meet and arc as one of the section curves of the freeform sheet that you're building using curve mesh.

You wouldn't normally check this but I urge you to look at the curvature comb of the edge of the sheet as it meets the flat section in your model. The funny little inflection is what may cause you some grief.

If you want to shell to 2mm thickness, while it always surprises us what NX will occasionally do, the minimum radius in your transitional surface really ought to be larger the 2mm. That is why I thought it would be better to just show how it might be controlled to achieve that outcome.

Best Regards

Hudson

www.jamb.com.au

Nil Desperandum illegitimi non carborundum

 

[hudson888]

cadmantools,

That spring looks good, as mentioned it appears that you can ditch the last couple of features without fear of foul, but some people might like to have them included as part of a wider reference set to use for mating conditions or assembly constraints.

I have seen something similar posted here in response to questions about building springs that did similarly well with law curves. However I do think something like this really belongs in a post such as this one.

In this case I'd just like to see one enhancement to the model which would be to make it sufficiently parametric that I could use it in a part family. Presently one of the first things that I noticed was that increasing to number of coils or reducing it significantly tends to produce errors.

Best Regards

Hudson

www.jamb.com.au

Nil Desperandum illegitimi non carborundum

 

[Bishbosh]

Gents,

Any chance of theses models in NX4 for us in the sloooooow lane.

Andy

 

[MickyV007]

Andy,

during lunch break I took the "Hudson-approach" to model the flattened tube in NX 4.0.4.2. The only difference between my model and Hudson's model is the continuity, which is G0 instead of G1 for the 'Trough Curve Mesh".

Could anybody be so nice to explain the differences between these different options (G0-G1-G2), because i couldn't manage to use G1 continuity?

Michaël

 

[SiW979]

G0 is just a connected curve and will give you a sharp edge at the transition between the two faces.

G1 is tangency, whis will mean that you get a nice smooth transition between the faces which is much more desireable but the radii of each curve at the point of joining is different

G2 is curvature symetric and really aimed at people who create very high quality aesthetic surfaces which need to reflect light nicely etc. Bascally G2 cuvature is ensuring that the radius of each curve at the point if joining is identical.

There is G3 as well in later versions of NX which is even higher quality still.

Have a look at the attached image for clarification.



Best regards

Simon (NX4.0.4.2 MP10 - TCEng 9.1.3.6.c)

http://www.jcb.com

Life shouldn't be measured by the number of breaths you take, but by the number of times when it's taken away...

 

[SiW979]

Also it is important to note as I have learned in recent months, that the quality of the surface you create is linked directly to the quality of the curve that was used to create it. You cannot assign G2 continuity to a surface that has been created to G1 standard etc. To assign G2 continuity to your through curves mesh, you will need to esnure that your splines have G2 continuity.

Best regards

Simon (NX4.0.4.2 MP10 - TCEng 9.1.3.6.c)

http://www.jcb.com

Life shouldn't be measured by the number of breaths you take, but by the number of times when it's taken away...

 

[hudson888]

Continuity someone already did...

http://en.wikipedia.org/wiki/Geometric_continuity

The very short version below.

G0 Touching
G1 Tangency
G2 Curvature
G3 Flow

And the model in NX-3 with at least G1 continuity. I have refined the technique slightly, but on the other hand changed it simply because there are a couple of things that later versions allow me to do which the earlier ones didn't.

Best Regards

Hudson

www.jamb.com.au

Nil Desperandum illegitimi non carborundum

 

[MickyV007]

Thank you Simon,

it explained at lot. Still one question though, why do i have the possibility to create continuity aswell with the primary curves/lines, as with the cross strings?

I was able to put a G1 continuity at the primary strings but not at to the cross strings.

And i don't see the possibility to create G1 continuity with the bridge curves (aren't those standerd G1 or G2?).

Michael

NX4.04.2 / TCE 9.1.3.8_build_0711 / NX6.0.2.8

 

[hudson888]

For MickyV,

I've attached your model with G1 continuity applied. I don't know for sure what gave you grief, but as a suggestion you did have the modelling tolerances set awfully darned tightly. Also perhaps in selecting curves and adjacent faces you need to turn the tangent face chaining behaviour off in the selection preferences.

You'll notice that I changed the modelling tolerances and have now managed to shell the part out to 2mm.

Otherwise great job, and since you mentioned that you had to do this during lunch break, and we can therefore assume your boss is reading this, I think you ought to be paid for taking the initiative to learn better skills!


Best Regards

Hudson

www.jamb.com.au

Nil Desperandum illegitimi non carborundum

 

[SiW979]

Michael

Basically the bridge curves are set as default as G1 if you double click on one and to open up the bridge curve dialogue, you will see two buttons, one called tangent, and one called curvature, just experiment by clicking on each one of these whilst the bridge curve is active and you will see the bridge change shape slightly.

The reason that you cannot set your cross strings to be G1 to anything is that there is no other surface to select/refernce when you create the very first surface.

However the primary strings do have a surface for you to select for G1 (the tube surface and the flat surface) however when you mirror the suface and you you now have 4 surfaces to reference when you fill in the last through curve mesh.

1. The tube face
2. The flat section face
3. The first through curves mesh
4. The mirror of the through curves mesh.

Look at hudsons model again, double click on through curves mesh (11) and notice that G1 is set in all 4 boxes, when you click on each of the buttons next the G1 box, you will see each surface highlight that has been selected.

Basically what I'm trying to say is if you want to assign G1, when doing the TCMesh, you need to reference a surface, not a string.

hope this helps. ;-)

Best regards

Simon (NX4.0.4.2 MP10 - TCEng 9.1.3.6.c)

http://www.jcb.com

Life shouldn't be measured by the number of breaths you take, but by the number of times when it's taken away...

 

[hudson888]

P.S. Since Simon and I are posting over the top of one another part of what you are looking for in continuity has to do with the alignment of the control polygons of curves or surfaces involved. Not the knot points but the poles!

You can see this for yourself by playing around with the studio splines. I think I've described all this before. Elsewhere on the forum, but the G number can be equated with the number of poles that need to be aligned with the adjacent object. GO touching at the ends means that no poles are aligned, G1 tangency means that the first pole is aligned and so as the continuity increases to G2 then two poles are involved, up to three for G3.

Working with single segment curves, as somebody noted the other day in another thread, you also need to increase the degree of the object in order to actually increase the number of poles until there are enough to be able to create that alignment. Which I think helps explain part of what Simon alludes to in taking about needing to have curves that meet the standard you expect of the surfaces you intend to create.

In general then to recap from that earlier post...
G1 > Degree 3
G2 > Degree 5
G3 > Degree 7,
at a minimum in common surfacing practice.

Best Regards

Hudson

www.jamb.com.au

Nil Desperandum illegitimi non carborundum

 

[hudson888]

BTW MickyV,

I never toughed your bridge curves because I just didn't think to. As luck would have it we were only ever chasing G1 continuity on this model and the surface righted itself with very little encouragement from me!

Best Regards

Hudson

www.jamb.com.au

Nil Desperandum illegitimi non carborundum

 

[MickyV007]

Muchos gracias Simon and Hudson,

you were a great help, i learned a lot today and will keep practicing with the different posibilities. I'm sure this will improve my modeling abilities.

But to stick to the original thread, i've att. a model which use law defined splines to create a in/out spiral/wire/... . Hope you like it.

Best regards,

Michael,

NX 4.0.4.2

 

[ewh]

Hudson,
I've asked it before and I'll ask it again, when are you going to go on Seimen's payroll?

"Good to know you got shoes to wear when you find the floor." - [small]Robert Hunter[/small]

 

[SiW979]

Here's another model which is very sketch and expression based. Open the expressions editor and change the total width value between 825 and 1500. Notice the number of rectangular cut outs increases once you get past 1116. There was a hell of a lot of though that went into this, but the time savings that are made by creating a part family of the part are massive!!!

The secret to creating really good sketches is using plenty of reference geometry and a clever mix of geometric constraints and expressions.

Enjoy



Best regards

Simon (NX4.0.4.2 MP10 - TCEng 9.1.3.6.c)

http://www.jcb.com

Life shouldn't be measured by the number of breaths you take, but by the number of times when it's taken away...

 

[cadmantools]

The last two features in the spring model is a used as a simplified model of the spring. It makes up the SIMPLE_MODEL reference set.

 

[hudson888]

ewh,

I expect that Seimens are just as happy to have me help you guys for free, but whenever they do want to call I'm sure I'd be open to offers

Maybe I ought to set up an arrangement with my local Pizza parlour as did the developers of Samba at one time. The licensing being open source, there was a stage where rather than accepting donations additional support could be sought with the understanding that the gift of a voucher for a Pizza would be accepted. I suspect that some people's needs are as modest as they are honourable

Best Regards

Hudson

www.jamb.com.au

Nil Desperandum illegitimi non carborundum