Drawing a loco steam dome. How to get the varing flare?

[Penrhos1920]

I'm trying to draw a steam dome flare which changes radius.  On the top of the boiler the radius needs to be 1.33mm (as in the right hand dome) but as it drops down it needs to increase to a maximum of 4mm (as in the left hand dome) at the bottom.  I've tried to do this in autocad, 123D design and blender but they all appear to only be able to do a constant radius fillet.  I can see two ways of doing it, but both are long and slow.  The first is to draw a series of profiles and loft them into a solid.  The second way is to split the dome into many sections and apply a different radius to each fillet before glueing them back together.  Neither method is elegant.  So is there an easier method I've missed.

 

[-missy-]

Hello Penrhos.

 

This is how I do similar in Inventor. I am guessing 123D isnt that different?

 

 

1. I create a surface which follows the contours of the boiler. I do this by projecting a circle onto the surface where the chimney (or done) is going, then thicken this to produce what you see.

 

 

2. I then extrude to the new surface a small step to thicken the chimney where I want the fillet to go.

 

 

3. I then fillet the join between the parts (1) and (2) which produces the radius above.

 

I hope that helps in some way?

 

Missy

[PhilH]

Brainbox...

 

 

You lot amaze me, talk about new frontiers and all that. Now, where's me pencil....

[Etched Pixels]

If you can import STL and work from it then ImplicitCAD supports automatic filleting of unions and can be used to spit these out. That also means you can automate them with a tiny bit of programming rather than sit in CAD tools mousewaggling each one individually.

 

http://www.implicitcad.org/

[AJ427]

Hi Penrhos,

 

I'm not sure there is a truly easy and automated way to do this in autocad but this is how I do it. I also use the loft function but there are different ways you can use it so this might differ from how you do it:

 

I do the top part of the dome (or chimney) seperately as it's a simple revolve.

 

The next step is similar to Missy's method in that a guide is created that runs around the circumference of the boiler at the intersection with the dome flare. I do this by creating an intersection with two cylinders, 1 for the boiler, 1 for the dome's maximum diameter. The time consuming part is to then draw a spline around the resultant top surface (snapping to nearest, a lot). Make sure that there's a proper snap at the four cardinal points of the ring.

 

Above this we need another guide - a circle which will be at the top of the flared part of the dome. Next create 2 cross sections, 1 for the front/rear elevation and 1 for the side elevation. These should touch both guides at the cardinal points. Mirror these so you have 4 cross sections. It should now be as shown, cross sections in red and guides in green. Note that the cross section includes for the lip where it sits on the boiler.

 

 

Next I use the loft command. Select the 4 cross sections in order and then use the guides option, selecting the top guide and then the bottom guide. You could almost get away with just a loft using the circle as a path but it's not quite right so the guide method provides a more accurate loft with the inclusion of the base spline guide providing even more control.

 

 

 

Inventor looks like it's a lot easier but I'm an autocad man by training so that's what I'll stick with!

 

 

[Penrhos1920]

Thanks Missy that works pretty well.  The trick is your step 2.  That little lip means that the fillet stops in the right place and now the fillet does not have to be tangential to the side of the dome.

 

Thanks AJ427 I'm also an autocad man having used it for 15 years on and off at work.  The problem is the cost of a licence for home use.   I'll give your method a try.  Have you tried exploding the dome base and deleting most of it to leave just the curve you need rather than trying to draw the spline?

[AJ427]

iirc I have tried that but I think that the loft wouldn't recognise it as a valid guide. Could be wrong there though so worth another try.

[billbedford]

With the right tools it's dead simple

[brack]

I use Rhino3D v4 and a very similar method to MIssy's - seems to work nice and easily. I often try a few different heights for the flare and compare them when done to see which looks 'right' (slot them in place, then render and repeat). I find the flare done as per drawings may not always look quite right so its worth trying a few combinations.

 

the name of the commands and the way to use them will vary between software, but the principles are the same.

[Penrhos1920]

With the right tools it's dead simple

 

Is that Viacad 2D/3D or Viacad Pro?

[billbedford]

2D/3D

[AJ427]

Hi Penrhos,

 

I'm not sure there is a truly easy and automated way to do this in autocad but this is how I do it. I also use the loft function but there are different ways you can use it so this might differ from how you do it:

 

I do the top part of the dome (or chimney) seperately as it's a simple revolve.

 

The next step is similar to Missy's method in that a guide is created that runs around the circumference of the boiler at the intersection with the dome flare. I do this by creating an intersection with two cylinders, 1 for the boiler, 1 for the dome's maximum diameter. The time consuming part is to then draw a spline around the resultant top surface (snapping to nearest, a lot). Make sure that there's a proper snap at the four cardinal points of the ring.

 

Above this we need another guide - a circle which will be at the top of the flared part of the dome. Next create 2 cross sections, 1 for the front/rear elevation and 1 for the side elevation. These should touch both guides at the cardinal points. Mirror these so you have 4 cross sections. It should now be as shown, cross sections in red and guides in green. Note that the cross section includes for the lip where it sits on the boiler.

 

variable flange1.jpgvariable flange0.jpg

 

Next I use the loft command. Select the 4 cross sections in order and then use the guides option, selecting the top guide and then the bottom guide. You could almost get away with just a loft using the circle as a path but it's not quite right so the guide method provides a more accurate loft with the inclusion of the base spline guide providing even more control.

 

variable flange2.jpg

 

variable flange3.jpg

 

Inventor looks like it's a lot easier but I'm an autocad man by training so that's what I'll stick with!

 

Reading through JCL's beginners guide to Blender which referred to this post and reminded me that I discovered a better way to create the interface guide or 'pringle' in AutoCAD:

 

As before, create two cylinders 1 for the boiler, 1 for the dome's maximum diameter. Then perform an an intersection with the two cylinders (actually they can be any boolean operation, subtraction, union or intersection).

 

 

Next use the Extract Edges command on the compound object. This creates splines around all edges and interfaces between the shapes of the object.

 

 

Delete the object and any splines you don't need. You will now have your base guide (shown here in yellow).

 

 

Proceed as before.

[JCL]

Erm, thanks for the mention, but it's more of a guide from a beginner than a beginners guide!

 

Is this just a difficult or complicated thing for software to do? It's the one real problem I've had with Blender so far, and it means I've been manually nudging vertices. It gets easier as I keep practicing, but it feels a bit of a bodge.

 

I'll have to look at Bill's method on a bigger screen in the morning.

 

Cheers

 

Jason.

[clarkis]

whoa, Jason...where you at? Update please. If you have transitioned from 'beginner', you need to tell us what the magic pill was...

Hoping to hear from you soon,

Clark Cone

[JCL]

Hi Clark

 

Right, here's my third go at writing this - it's been a long week! I still see myself as a beginner. I feel that I've still only just scratched the surface of Blender. I'm also still learning about the anatomy of locos and rolling stock, and trying to recreate them is helping me along. My thread http://www.rmweb.co.uk/community/index.php?/topic/91147-a-beginner-starting-in-3d-printing-with-blender/has been a diary-come-step-by-step rather than a proper tutorial - I've included the misses as well as the breakthroughs in there. (My first attempt at diary-come-step-by-step was censored...)

 

The first part of post details how to create the chimney itself

http://www.rmweb.co.uk/community/index.php?/topic/91147-a-beginner-starting-in-3d-printing-with-blender/?p=1623436

 

And this one shows how I eventually hit on a procedure to get a smooth flange on the bottom.

 

http://www.rmweb.co.uk/community/index.php?/topic/91147-a-beginner-starting-in-3d-printing-with-blender/?p=1707937

 

Of course, other applications will be able to do this much more quickly, but Blender is free, and at the time I didn't have the money so spend on software, but I did have the spare time to be able to work this out. I can do this now in about 15-20 minutes.

 

-------

 

So, here we go, this is how I created this chimney.

 

 

Setting Up

1. Delete the cube that is there in a new workspace by default
2. Change the view to Orthographic by clicking on View -> View Persp/Ortho
3. Change the view to Front. You do step 2 and 3 so that you can see the Background image when you import it.
4. Change the units to mm as described in post 30.
5. Click on the tiny + to the left of the workspace in the top right of your screen to show the panel.
6. Put a tick in the box next to Background Images
7. Click on the triangle to the left of that box to open up the Background Images properties.
8. Click on Add Image, click on the Open button
9. Do your calculations, again see post 30, to make your image the right size. The result is in position 1 in the image below.

 

All of the above I've been through before. This bit is new. Personally I found that it was easier to line everything up correctly if the centre of the chimney was over the blue line of the Z axis (denoted with a 2 in the above image). That is where Z = 0. If I had cropped the background image to just the chimney, and the chimney was symmetrical, then the blue vertical line showing z = 0 would correspond to the vertical line on the chimney drawing. As it is, I'll have to move the drawing slightly.

 

To move the drawing, I simply had to change the value in X near the number 3 in the diagram until the centreline of the image lined up with the blue vertical line. In my case, the Y value was -1.960.

 

 

I also wanted the top of the smokebox to correspond to 0 on the y axis, so I did this by amending the number in the y axis box. You can see in the above image that Y was 0.750.

 

So, now my chimney is the right size for 4mm scale and in the right position for me to work with it.

 

 

Next I need to move the 3D cursor shown in the image above to the edge of the chimney (shown as 1). This is where the new object will be centred, and I choose Add -> Mesh -> Plane as per the above image.

Now, I change the mode from Object to Edit (3 in the above image), which will give me a Mesh menu option.

From the Mesh menu, I choose Mesh -> Vertices - Merge -> At Cursor to bring the Plane to a single point.

 

Creating the Profile

 

From post #12 you will see how I set up the profile. In the previous post to this one, you can see that I did the fillet in three steps as a test. If I want to make a smoother curve I'll add more steps.

Creating the profile goes something like this.

1. Make sure your first point is highlighted (that single point we created just above)
2. Press the E button, then the Z button, and finally move the mouse up to send a line vertically upwards. Click on the left mouse button to finish this line segment.
3. Press the E button then move the mouse over the line showing the edge of the chimney, Click on the left mouse button to finish this line segment.
4. Do the same again until you want the line to move horizontally, then press the E button then the X button and move the mouse cursor along the screen, Click on the left mouse button to finish this line segment.
5. Keep doing this until you are almost done.

When creating the inner wall, you will be moving the cursor horizontally by constraining it to the X axis (by pressing the Extrude, Xaxis buttons. As you move the cursor, the

Your last point should be somewhere near your first point. I selected with the right mouse click my first point. This was at X=0, Y=0, Z=0, so I right clicked my last point again, and made sure this was also 0,0,0 using the "Transform" number boxes in the top right. See the image below for the pre-adjustment info.

 

 

I now have a profile that I can use to make the chimney. To make life easier for myself, I'm only going to create 1/4 of the chimney, and then mirror this so that any changes I make in that quarter will be echoed around in the mirror images. Paul Hobbs does it this way, but it took me a little while to work out why I couldn't get this working. Here goes:

 

Spinning

1. First of all I changed the View to Top. Note, only the profile changes direction, the Background Image stays the same.
2. Move the 3D Cursor back to 0,0,0
3. Pressing the A key twice selected the whole profile.
4. Change the pivot point to the 3D cursor by pressing the spacebar, type origin, choose Set Origin from the list, Click on Origin to 3D cursor.
5. Click on the Tools tab at the top left of the screen.
6. Click on the Spin button with a setting of 90 degrees, and 12 steps (the more steps you have the smoother it will be, but the more work you will have and the larger the file will be). See the image below for more details

I now use 25 steps.

 

Spin Properties

 

Mind the Gap

 

There is one problem with this, which is that, although the first and last point on the profile shared the same space, they were still two separate points, and therefore, if I tried to edit the points a gap will open up. See the Mind the Gap Image. To stitch this edge together;

1. I selected all (A button, then A again until your object glows orange).
2. Then clicked on the Remove Doubles button underneath the Spin button.

Now I create my smokebox using a cylinder. Because everything is centered at 0,0,0, it's easy to make sure that the X value of the new boiler is the same as that as the chimney. I also move the boiler up until the top just touches the 3D cursor at 0,0,0. My boiler is 22mm in diameter, so it needs to be 1.1mm below the central point, so X = 0, Y = 0, Z = -1.1cm

 

Mirror

 

1. To create a full chimney:
2. Change the view to Top
3. Your chimney should already be selected from before, so click on the spanner (1)
4. Add Modifier (2)
5. Choose Mirror (4)
6. Click on X and Y, but don't click on Apply. Not just yet.

 

Since writing that post, the thing that I've I've changed is that that I now include a sizeable cylinder at the bottom of the chimney so that I can complete the steps below. I have also increased the number of vertices (or points) in the profile to make a curve that is a lot smoother than that in the first photo above.

 

---

This is the second post

---

 

Each time I write up how I do a chimney I find a new step that (hopefully) makes a better version. Therefore, my method now isn't revolutionary, but is based on the work I wrote up a few weeks ago. The only part I'll not go through again is the creation of the profile as this is the same as before. I will also show you how I made some adjustments after the chimney was created.

1. So I created the profile, then moved the 3D cursor to the inside edge of the chimney as represented by the profile by copying the X, Y and Z location values from the vertex closest in the middle to the location boxes for the 3D cursor (red arrow on the right in the image below)
2. I changed to the top view, and clicked on the spin tool. I changed the number of segments to 25 and made sure the angle was 90 degrees.
3. I clicked on the Mirror modifier and clicked on X and Y to mirror the quarter chimney in both directions. So making a whole one. The great thing about this is that I can then just edit a quarter of the chimney, and the other three quarters will automatically update. This is why only a quarter of the chimney contains the mesh.
4. Next press the A key to select all, and then in the toolshelf on the left, choose Remove Doubles. This will get rid of any vertices you don't need, tightening up the mesh.
5. Now, going around the edge, pull down the outer edge of vertices only by clicking on each one and dragging using the manipulator or by pressing G and Z.

A lot less work, and a guarantee of symmetry. Of course, what the symmetrical chimney looks like in practice is the bit that does require some work. Hopefully though, the rest of the steps below should show you that it's not that difficult (I hope).

 

 

Next, I applied the Smooth Vertices tool, also on the toolshelf on the left.This slowly smooths any errant vertices. Creases become bumps which eventually become straight lines. I can do one of those animated GIF files if anyone's interested.

 

 

Interestingly, because this is a "smoother" and not a straightener, the curve over the top of the boiler (image 2 below) stays put.

 

 

When I'd finished, I realised that I had a create in the chimney where I wasn't quite as accurate with the profile as I thought I was. Actually, it was because I ought that have added a couple more loops of vertices.

 

 

I had to do something about it, so I added a two more loops and resized them until the base was smooth. First of all, I selected all of the vertical edges around the whole chimney using the B boundary select tool. I had to do this three times, turning the chimney as I went around.

 

 

Then I pressed the Subdivide button. This puts a new vertex into the middle of each vertical line, so creating a new ring of vertices that are themselves joined horizontally around the loop. Have a look below.

 

 

Now, this is still a straight line at the moment, so I deselected everything using the A key, then pressed the Alt key and right clicked on a horizontal edge on the new loop. Pressing that Alt key selects the whole loop. This is incredibly useful doing domes, chimneys or boilers, etc.

 

 

On the left in the toolshelf you'll see there is a scale tool. Click this or press the S key and then move your cursor towards and away from the chimney until you get the curve you are looking for (the image below shows I went in towards the chimney a bit too enthusiastically!)

 

 

And when you're happy with it, let go of your mouse button. If you are still a little out, the scale properties are on the left hand side, and you can change them in the X, Y, and Z axes. You must change both the X and Y if you want the chimney to remain symmetrical.

 

Before I'd finished with the chimney, I widened the aperture at the top a little, narrowing the ring around the top, by again pressing Alt and right clicking an edge before using the S scale tool, and I pushed the base within the smokebox up using Alt+rightclick on an edge on the base and then G for grab and Z to move the base vertically along the Z axis. I also made the lip a bit narrower. The rivets I copied from the tender file.

 

Hopefully it'll still go through the Shapeways check.

 

 

That might be a bit more detail than you were asking for!