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Eccentric Reducer Difficulties...


Lee Mac

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Hi Guys,

 

This is actually the first time I have posted a thread in this forum... just started to do 3D modelling about two days ago - and finding it pretty tough tbh.

 

This question is in relation to my other thread:

 

http://www.cadtutor.net/forum/showthread.php?t=32658

 

Regarding a Piping Program I am making.

 

After completing the program in 2D, I decided to see what I could do in the world of 3 dimensions... - but things got difficult pretty quickly..

 

Let me start by saying that I have minimal drafting experience and only really have experience in LISP - so there may be some stupid questions coming your way...

 

I have succeeded in modelling fittings such as pipes, elbows, caps, and concentric reducers - as most of these just use either a standard revolve or extrude function.

 

But I am now attempting to model an Eccentric Reducer.

 

I have search this forum and found various threads pertaining to eccentric reducer modelling, but haven't really found them that useful.

 

I have attached a diagram of what I am hoping to model.. and, before the wave of criticism hits me - remember, I have minimal experience as a draftsman.

 

I was hoping to use the extrude function, but along a path that would alter the diameter of the original circle that was being extruded and I am not sure if that is possible. So I am at a bit of a loss as to how to proceed.

 

I appreciate any help anyone is willing to give and if you guys need anything done by LISP, just let me know and I'll be more than happy to lend a hand.

 

Thanks

 

Lee

Eccentric.jpg

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are you doing this in 04 Lee? In 07 or newer its a simple loft.

 

 

edit, i didnt use any guides or make the thing hollow but that is also simple. I could use a guide curve for the top and bottom. Again this is 07 or newer as this options wasnt available in pre 07 autocad. You can make a similar object but only with a surface as far as i know in 04.

eccentric.jpg

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here you go lee. modeled in acad05 so you should be able to open it. Its a surface mesh. I drew two circles where they needed to be. a straight line connecting the bottoms and i drew 3 lines connecting the tops, fillet between them, and used PEDIT to create a single polyline out of the now 5 sections. used the BREAK command to split my circles since i only want 180degree arc(you need 4 lines to create an edge surface). Used the SURFTAB1 and SURFTAB2 to control the mesh(set to 50 in this file). then after create half of it i used mirror for the other half.

EccentricReducer.dwg

eccentric2.jpg

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For 2004 compatible 3dSolid, a process, though a bit heavy handed for practical use, was discussed in this thread:

 

http://www.cadtutor.net/forum/showthread.php?t=7713

 

Essentially, a pre-calculated elliptical cone(Solid) is sliced top and bottom to create an offset reducer with circular ends (Ronso is concept originator).

 

As previously implied, I wouldn’t necessarily recommend going to that much trouble when a mesh would likely serve just as well. The method is interesting, however.

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For people using AutoCAD 2006 or earlier.

First draw two circles in the right positions –note that the left quadrants are right one above the other. The lower circle is centered in the origin.

Connect their centers.

r1.gif

r2.gif

 

Connect their quadrants as I did (see my yellow lines) and extend those lines until they met each other. Let’s mark this point with V.

 

r3.gif

r4.gif

 

Connect this point with the origin. The center’s line must be superposed with this last line!

From the origin, draw two lines (mines are green); one goes to an "unused" quadrant of the bottom circle (mark A), the other one is perpendicular to the yellow line (let me mark this with B).

 

r5.gif

 

Start the CONE command, and at the first prompt, specify that you wish to draw an elliptical one (option E). To define the ellipse, type first C (meaning "center") and click the origin. Now it will prompt you for the distance of the first axis –click the point we marked with A. AutoCAD will prompt you to define the distance to the second axis end. Enter (GETDIST) and click the origin, than click the point B. To determine the height of the cone, enter again (GETDIST) and make two clicks; one in the origin, the other one in the point V. Your cone is ready, just it is along the OZ axis.

 

r6.jpg

 

Use the ALIGN command: the first source point is the top of the cone and the first destination point is V. The second source and destination points are the same, so click twice the origin. Press enter and choose to don’t have the object scaled.

 

r7.gif

Use the slice command twice. First the cutting plane is a ZX plane going thru the origin, while second time use the same ZX option but for point to define the plane click the upper’s circle center.

r8.gif

In the last image I marked an unwanted face we got on our solid. Use the SOLIDEDIT command to delete it. Before you leave the command, you can EXTRUDE the two planar circular faces and you can apply a SHELL to make the solid a tube.

 

Probable there are a lot of things to experiment, but I am not going to complete your homework.

Happy modeling!

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those are close. i guess from there you could extrude both faces out to get your straight section and fillet the edge. Not sure how it would attack the fillet since the bottom edge is linear. ill have to give that a shot though, very interesting

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Many thanks Guys - a very interesting method indeed :)

 

I say a video from one of the guys on here, showing a demonstration of how to make it like that - (but as Matt said, of course, there are no fillets).

 

Thanks to Fuccaro for another brilliant Tutorial :)

 

I shall look into the surface mesh, as provided by Matt for my first option (as it provides the best representation), and if that fails, I shall investigate the "cone" method... all, of course, to be written into a LISP :)

 

Thanks once again guys - (this is not the last you will be hearing from me in this forum though... :P )

 

Cheers

 

Lee

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Just out of curiosity - why program this. Wouldn't it be cheaper to simply purchase a program that does this already?

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Just out of curiosity - why program this. Wouldn't it be cheaper to simply purchase a program that does this already?

 

JD Mather - this may seem odd, but I have no need for a piping program whatsoever.. - I have merely made the program "for fun". But I wish for it to be "complete".

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Matt, am I going the right way about making it "thick"?

 

I have created another mesh using the same method, but with ID dimensions and then have "meshed" the two together at the ends...

Eccentric3.jpg

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that works fine lee. it really depends on what you want to do with the model. the Mesh 2 Solid lisp should convert that(each half) to a solid then you can use the SOLIDEDIT>Body>Shell to create t he same thing but as a solid. using the mesh2solid may fail at the top/bottom depending on how you align your Z axis. It may end up having to be two different lisp routines for each half but thats nice since you can incorporate all this into your lisp routine.

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here is a screen shot after running the mesh2solid lisp(partially). This is where the SURFTAB setting of 50 will kill you becuase it converts each square of the mesh in two and extrudes from there. If you had your surftab settings low the lisp wouldnt take long. after this was done i would use the slice command and then mirror and union. for each square on your surface you need to hit the enter key:( or at least i do.

Eccentric.JPG

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dont you like a challenge lee:) incorporate the mesh2solid lisp into your lisp. What are the rest of the pipes in this routine you are writing? or does it matter?

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Well, its really annoying because I have modelled:

 

  • Pipes, 2D, 3D (Solid)
  • Elbows, 2D, 3D (Solid)
  • Caps, 2D, 3D (Solid)
  • Concentric Reducers, 2D, 3D (Solid)
  • Flanges, 2D, 3D (Solid)
  • Eccentric Reducers, 2D, ... struggling with 3D..
  • Ducting, 2D, (3D seems impossible...).
  • Tees, 2D, ... struggling with 3D.

I have attempted to model the tees, but get stuck at this point (my 3D knowledge failing me). :(

Tee.jpg

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well lee there are a few way you could attack that T. You could draw the core and subtract it. You could draw the T as a solid and use the SOLIDEDIT>BODY>SHELL command and remove those 3 faces and there are other ways im sure but those are the first two that come to mind.

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here i drew this real fast. the one on the right you could use to subtract from your T. the one on the left was a copy that i used the Shell command on(note, if you type Shell in the command line you get the operating system command line)

shell.jpg

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