Quadripartite Vault

[Andrew_Amp]

Hello, i'm new here - this is my first post.

 

I am trying to draw a 3D model of a quadripartite vault in AutoCAD 2007. The vault is rectangular, not square, so the arches to all four sides and the cross ribs are elipses, not arcs. The longitudinal and lateral corss sections though are arcs.

 

My 3D CAD i a bit rusty and i am thinking this project is beyond my skill set at the moment - previous 3D experience is limited to basic shapes (mainly for shopfittings) - this is far more advanced and i've hit a bit of a wall.

 

I've managed to set it out in 3D, and i've also managed to extrude the ribs (all of them, including the cross ribs), but i am struggling to infill the spaces between the ribs.

 

I can see that it should be possible with the information i have to hand - i have the edges defined with the ribs (3D solids) and i have the curvature defined with the lateral arc at the highest point - but for the life of me i've no idea how to fill in the gaps.

 

Also, the infill pieces need to have a thickness - the upper surface is the finished line of the vault, but ultimately i need to design formwork to be able to construct it, and the formwork thickness is 35mm down from the finished surface.

 

I've tried using the loft command but this hasn't worked - the elipses that define the boundaries (even drawn with pellipse) don't seem to be join-able each other due to them being in different planes i think (although the ends do meet at a common point so i am puzzled as to why this should be).

 

Anyway, i hope i've not confused the situation, i've attached a JPG screen capture which hopefully will help.

 

[SEANT]

While Loft is capable of creating the necessary geometry, it may not be essential. The attached was done with Revolve, Slice, and Solid Boolean operations.

PreArch.dwg

Arch3D.dwg

[Andrew_Amp]

Thanks a lot for this, i think i can see now how to create the longitudinal arches, the extrude along a path drawing was very helpful - think of it as a large donut and then use Boolean tools to crop out the section i want.

 

However, there is a twist in the other arches where they meet the columns and i'm not sure if the examples take this into consideration.

 

Made a little progress this morning using loft, here's where i'm at...

 

 

 

Having trouble setting out the bottom guide line to ensure a constant thickness at the moment...

[SEANT]

With regard to constant thickness; perhaps loft just one of the outer surface, then use the Thicken command to create the 3dSolid.

[Andrew_Amp]

Hmmm, don't seem to be able to loft the single pellipses, it tells me they are not valid objects...

 

QUOTE: The guide is not G1 between first and last sections. The selected entities are not valid.

 

Not sure what this means.

[Andrew_Amp]

Ahh! The problem was with the guides, not the pellipses - i used one of them instead of both and it seems to have worked. Trying to thicken the surface...

[Andrew_Amp]

OK, next hitch...

 

QUOTE: Object intersects itself. Surface cannot be thickened with specified value.

[Andrew_Amp]

Looked into this further, the surface starts convex but then becomes concave at the column - it needs to be convex all the way down. I think this is because i have an issue with the guides, for some reason it won't let me select both of them - i can select one or the other and produce a convex end on the guide i select, but the other end is concave.

 

I think if i can solve this the thickness issue will also solve itself (hope).

[SEANT]

AutoCAD can be somewhat of a beast when it comes to 3D modeling. It sounds like you are making steady progress, though. Keep us posted.

[Andrew_Amp]

OK, have created the surface (solved the guides issue) - just checking it against the model to ensure it is dimensionally correct. Have tried to thicken it but it comes up with:

 

QUOTE: Object intersects itself. Surface cannot be thickened with specified value.

 

So, my presumption was wrong sadly - is still have an issue to resolve here.

[Andrew_Amp]

Update...

 

The lofted shape sadly was dimensionally inaccurate so i am back to where i started.

 

On the plus side i have now looked at the wireframe again (one of my elipses was actually a spline on the model - the lofted shape was all pellipses when i put the two together the edges didn't marry up) and have redefined my perimiter shape with pellipses - but it won't loft using either of the guides now (although it will if i choose either one as a path oddly).

 

Update...

 

Solved the lofting issue - have the surface and it is dimensionally correct now

 

Any ideas how i achieve the 35mm thickness from here?

[Andrew_Amp]

Update...

 

Thanks to the help so far, it currently looks like this:

 

 

Have the first surface in place, mirrored to infill both sides of the vault. However it is still just a surface and needs to be offset into the interior space to provide a 35mm thick solid. At the moment i have hit a wall here, all of my attempts have failed and i am out of ideas.

 

I am feeling very out of my depth here...

[fahim108]

You are trying for a solid model or a surface model here?

[SEANT]

 

Any ideas how i achieve the 35mm thickness from here?

 

 

Have the first surface in place, mirrored to infill both sides of the vault. However it is still just a surface and needs to be offset into the interior space to provide a 35mm thick solid. At the moment i have hit a wall here, all of my attempts have failed and i am out of ideas.

 

I am feeling very out of my depth here...

 

The only Surface => Solid option available to vanilla AutoCAD is the THICKEN command; it doesn’t have the ability to stitch together individual surfaces. If you’re still getting the “Object intersects itself. Surface cannot be thickened with specified value” warning perhaps you could try a smaller value, then SolidEdit-Face-Offset.

[Andrew_Amp]

You are trying for a solid model or a surface model here?

 

I would like a solid model, and have tried lofting a shape with thickness, but the thickness varies over the curve - ultimately i need to produce some formwork so the goal of the project is to define the shape (including thickness) then design supporting ribs in timber to produce the mould. So it is critical that a constant 35mm thickness is achieved.

 

The surface as drawn currently is my best effort so far, but i am on a steep learning curve here - although i have been using AutoCAD since Release 10, it has been in general 2D stuff with my 3D experience being limited to far simpler shapes.

 

The only Surface => Solid option available to vanilla AutoCAD is the THICKEN command; it doesn’t have the ability to stitch together individual surfaces. If you’re still getting the “Object intersects itself. Surface cannot be thickened with specified value” warning perhaps you could try a smaller value, then SolidEdit-Face-Offset.

 

Will give it a go and report back...

[Andrew_Amp]

QUOTE: Select faces or [undo/Remove]:

A 3D solid must be selected.

 

No solids detected.

 

Very odd...

[SEANT]

Have you tried the THICKEN command with a smaller value, 1 mm perhaps. If there are no proprietary concerns, post the outline geometry. A better demo will stimulate better suggestions.

[Andrew_Amp]

Tried thicken with smaller values (went down to -.01) with no success.

 

I have attached an earlier draft which should give you the geometry - hopefully this will be useful.

[Andrew_Amp]

OK, the game has moved on a bit - i tried slicing the surface and it won't let me - this means, i think that the surface is not going to do what i want it to either. I am back now looking at a solid and the loft command again - at least, even with a sold that has a varying thickness, i can slice it - if i can slice it i can then draw over the top arc and then i can offset the line to get my 35mm thickness - this will set out the top of the formwork ribs so it should get me to the finishing post (if i can get the loft command to work again - seem to have the same issue as before, won't loft using both guides).

 

What this means is that i will end up with a 3D model that is known to be wrong, but knowing where it is wrong will allow me to compensate to produce the formwork. At least that's the theory.

 

Ideally the 3D model would be right, but either CAD isn't capable or (more likely) i don't have the skills set to do this - i'm therefore trying to think outside the box, trying to achieve the goal without producing a dimensionally accurate model. It's a risky strategy, but i'm all out of ideas here.

[Andrew_Amp]

Minor update - solved lofting to produce a solid. The thickness issue has reappeared, but i have been able to slice the model and i therefore think i can overcome this by tracing over the top arc and then offsetting this new line 35mm to give me the under surface at this point.

 

Now working on the other surface... Model currently looks like this: