Author Topic: loco chimneys in 3d  (Read 9696 times)

paul craig

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loco chimneys in 3d
« on: September 09, 2013, 06:50:08 AM »
I am really having trouble getting my head round the best way to create a loco chimney for 3 work. First the ones I want to create are tapered, and some have integral skirts, others separate skirts(that's the bottom part), so I know how to create the outside, but where they fit on a boiler, the shapes are different, and I seem unable to get it right. I have never used mesh, so can anyone point me to a useful tutorial which might address my problems please?

because I cannot see any other way of creating the shape around where it fits the top and side of the smokebox.

the drawing attached is the half sections, so anyone help please?

paul

minstrel

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Re: loco chimneys in 3d
« Reply #1 on: September 09, 2013, 07:41:57 AM »
Well, a simple approach would be to create two profiles - one for the inner, one for the outer.  Sweep them both then 'solid define' each.  At that point all that remains to be done is to perform a 'solid subtract' ... Finished.

Notes - in the attached .dcd file you'll see a very crude and quick mock up of your drawing [it just for illustration purposes].
Notice I work off a construction line [any temp line will do]. 

Also notice, knowing that I need to subtract the 'inner' from 'outer'...so planning ahead I over extended the inner profile to make this a breeze for the solid subtract!  Then when you position it onto the boiler just perform a 'solid add' on the newly created stack and the boiler.  Dcad should do the rest 8)

Hope it helps show you one way to go about it...

edit - added image files as well.
« Last Edit: September 09, 2013, 08:22:03 AM by minstrel »

paul craig

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Re: loco chimneys in 3d
« Reply #2 on: September 09, 2013, 08:08:16 AM »
Hi minstrel, whilst I applaud your work, you do I think seem to have missed the nub of the problem.

As the chimney intersects with the smokebox it sweeps down by the sides, and does not have the same radius at the bottom front and rear, as the sides. which is why I thought about mesh.

The left hand drawing in my sketch shows that sweep, and clearly the different radii. If you look in the area I have outlined, you will see what happens with the chimney base.

But the rest I like and understand.
Paul

minstrel

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Re: loco chimneys in 3d
« Reply #3 on: September 09, 2013, 08:27:13 AM »
Paul,

I just added another image to my previous post...I think that is what you are after, isn't it? 

The tip here is to over compensate the profiles to have enough 'beef' to adhere to the boiler geometry.  Then when you
'solid add' it should mesh nicely.

Granted, there are much harder and more accurate ways of doing this...so I'm also looking forward to more ideas!

paul craig

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Re: loco chimneys in 3d
« Reply #4 on: September 09, 2013, 10:13:35 AM »
Almost minstel, except the front and rear edges should be curved, not straight, which again is why I think it needs to be drawn and using the mesh facility.

I think there are times when I can over think it, but at this time, it seems to me I actually need to do the tapered piece to a point in the air where it then eventually gets joined with a swept piece at the bottom. Then I add the bottom or skirt. However I think the only way to do the whole bottom piece is create an outline, and then use the mesh facility in dcad, before trying to see whether it will work as a 3d solid.

Paul

Dr PR

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Re: loco chimneys in 3d
« Reply #5 on: September 09, 2013, 12:27:08 PM »
Paul,

If the radius of the curve in the skirt is different front/rear than the sides you will need to use a grid. "Surface Connect" is the way to do this. It is a bit tricky, so be prepared to make several attempts before it is "right."

If you also need a radius or edge around the bottom of the chimney you will need to "Extrude Along a Curve" and that is another adventure.

For both procedures just make half of the grid - the part on one side - and then mirror it on the other side to complete the skirt around the chimney. In fact, you probably can get by creating only one forth of the skirt, then mirror it lengthwise and then side to side. Making smaller sections like this is much faster and usually easier than trying to create the full piece in a single operation.

Phil
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paul craig

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Re: loco chimneys in 3d
« Reply #6 on: September 09, 2013, 02:47:51 PM »
As usual you have kept to the nub of things, now I have to figure out the easy way!!
I was hoping it might be simpler, but I was sure I needed to surface connect.

Having never done it before are there an hints and tips? I understood that you need to join the
points in order, but how do you set that up?

Paul

Dr PR

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Re: loco chimneys in 3d
« Reply #7 on: September 09, 2013, 03:44:16 PM »
For Surface Connect you need to draw a bunch of "template" lines - these can be lines (V) or curves (C).

Then you start the Surface Connect function and select the lines in sequence. The program stretches a grid surface over the lines.

There is a LOT more to it, and there are quite a few helpful posts on the forum. I won't repeat them all so here are a few:

http://forum.designcadcommunity.com/index.php?topic=4237.msg24485#msg24485

http://forum.designcadcommunity.com/index.php?topic=4075.msg23388#msg23388

http://forum.designcadcommunity.com/index.php?topic=752.msg3524#msg3524

http://forum.designcadcommunity.com/index.php?topic=726.msg3398#msg3398

http://forum.designcadcommunity.com/index.php?topic=4667.0
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paul craig

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Re: loco chimneys in 3d
« Reply #8 on: September 18, 2013, 05:08:06 PM »
Ok Phil, have read and even understood what was written, but so far cannot be sure if what I am doing it correct.

The attached file shows what I have drawn, and so far cannot get either surface connect or patch to give me any thing like what I want. The black lines are the side and rear profiles for the quarter as you suggested, but my guess is I will need more profile shapes. In which case any idea how I can do that since they follow the sweep line on the smokebox.
The other problem I cannot really resolve is how I can cut away the sweep section since I constructed it with an horizontal extended circle plane, and then a vertical cylinder driven through it and solid subtracted.

I want the connect between the vertical profiles, and then the top circle, and the lower sort of elipse, in a shape that is round.

Any bright ideas please, because any thing I do with setting points etc seems not to get me anywhere.

Paul

Dr PR

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Re: loco chimneys in 3d
« Reply #9 on: September 18, 2013, 07:59:53 PM »
Paul,

You need intermediate lines to form the shape of the Surface Connect. You will have to do this in several steps.

First you should create two separate curves, one the small radius at the bottom of the casting, and the other the larger radius curve above it. Curves, not planes or lines.

You might be able to extrude the small curve along a curve (Draw/Extrude along A Curve). Use gravity snap to draw a curve along the bottom edge of the casting (the edge of the large hole under the chimney). Then extrude the small radius curve along the new curve. Be sure you set a handle on the bottom end of the small curve. The handle should be on the bnew extrusion curve. You will have to experiment with this because it is very tricky - and a test of your patience. But when it works you will have the bottom curved edge to the chimney surface.

Then it is a matter of generating a sequence of template curves (for Surface Connect) between points on the upper edge of the new surface and the upper red cylinder. You will need at least six curves for a quarter surface (90 degree arc) of the chimney skirt. The two end points of these template curves are one on the bottom edge of the cylinder and the other on the top edge of the extruded surface. Try different radii until the curves look right.

Use Surface Connect to create a surface grid over the new template curves. Shade it and see how it looks. If it is off a bit at one of the template curves change the radius a small amount and create a new grid surface. Repeat this at each template curve until the surface looks smooth without wrinkles.

I did this a while back with a much more complex surface. It took a month of evenings to finally get the one surface correct.

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Maybe someone else can suggest a better way.

Phil
DesignCAD user since 1987

paul craig

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Re: loco chimneys in 3d
« Reply #10 on: September 19, 2013, 02:54:37 AM »
thanks for that Phil, it was how I thought it might be  a PITA, but I do understand it was never going to be as easy as I would have liked 8)

It is such a useful skill to learn though. my biggest problem is deciding how to get the curves on the intermediate formers to accurately reflect the changing profile over the distance.

I did wonder whether, having changed the top and bottom lines, I could use f2 and create the next points on a horizontal basis by extension! Does that make sense, not really but I think you get the basic idea. a combination of the curve and the ellipse could then be made points with lines drawn vertically around the 45 degrees.

I had hoped it might only take two weeks, of evenings, not a month, but still once you know, it hopefully does get easier.

Paul

minstrel

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Re: loco chimneys in 3d
« Reply #11 on: September 19, 2013, 08:55:37 AM »
I had hoped it might only take two weeks, of evenings, not a month, but still once you know, it hopefully does get easier.

Everything gets easier with practice ;)

First I want to thank you, Paul.  I had been struggling with exactly this sort of complex 'fillet' for quite some time now.  Your post made me focus on solving the mystery [and enjoy some steam train research, too boot].  It may not be 100% what you're after, but very close.

Like I said, it's complex and I could never find the words to describe the technique [that's Dr Pr's gift].  Best I show how it's done in a 'screencast'.  It may give you some tips plus see the entire process, from start to finish,  done in 20mins or less!  That sounds much better than weeks and a month, now don't it?

Anyway, keep at it and I'll post a link to the 'screencast' when it's completed.

EDIT - Here's the 'screencasts' - Part 1 & 2 - "Choo-Choo Charlie": http://www.crossresolution.nl/3Dspace/premium.php

« Last Edit: October 01, 2013, 12:21:15 AM by minstrel »

paul craig

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Re: loco chimneys in 3d
« Reply #12 on: September 19, 2013, 02:09:39 PM »
thanks minstrel,
must confess I had not thought about using the fillet idea, because of the changing shape of the "skirt" as it goes round the chimney.  I guess it would be nice if there was a way of creating a fillet along a curve that changed shape as it went round ;D

still trying to find the best way to create the lower curve as a 1/4 of the whole.

Paul

Dr PR

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Re: loco chimneys in 3d
« Reply #13 on: September 22, 2013, 09:49:08 PM »
Minstrel's example is an excellent first pass.

Now use the original grid to create a bunch of new template lines on another layer. Use the Scale function to stretch these new lines until the top ends are all in the same horizontal plane. This is pretty easy - just measure the bottom to top height of the new template curve and then measure the vertical distance from the bottom of the curve to the horizontal plane. This will give you the scale ratio. Each template curve will have a different ratio.

After you have these new curves use them to generate a new grid surface.

NOTE: This method will stretch ALL of the curve, including the bottom short radius fillet. To prevent this break the template curves into two parts - the lower fillet and the remaining upper curve. Do this by drawing a new lower fillet curve and another curve for the upper part of the line. Scale only the upper part. Then, on yet another layer create another new set of template lines by gravity snapping to the points on the lower short radius fillet and the upper scaled curve (or just use "B" to combine the lower and upper parts). This will produce "stretched" template lines that all have the same lower fillet radius.

If necessary, use the newest grid surface as a template for drawing yet another set of template lines. You can mess around and waste a lot of times trying to guess what an intermediate template line should look like. The "Surface Connect" function can draw dozens of intermediate lines faster than you can figure out how to do one. Generate a series of surface grids if necessary, each one closer to the desired result than the last. Use each as a template for create the curves for the next grid. Repeat until the result is good enough.

Phil
DesignCAD user since 1987

paul craig

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Re: loco chimneys in 3d
« Reply #14 on: September 23, 2013, 05:12:25 PM »
thanks again phil, will work my way through that and see how I can get there as quickly as possible.

I wonder whether I will remember to time it ::)

Paul