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curved, hollow pipe.

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curved, hollow pipe. Edmundajw 2/10/12 5:35 PM
SketchUp Version: 8
Proficiency: Beginner.

Hi, I'm wondering if anyone can help me with a problem I'm having while trying to create a pipe with a 90 degree turn. I've achieved it by drawing a circle, drawing a smaller one inside it, drawing a line up from the centre, and then a arc to a line at 90 degrees. (If that makes sense), and then using the follow me tool.
The problem is that the first section of the pipe extends through the curve so it half covers the inner of the second section, adjacent to it. This is much easier to see in the attached picture. I have also attached the sketchup file so you can see clearly.

Can anyone tell me how to change it, or even how to start again to achieve what I want?

Thanks in advance for any help.

Re: curved, hollow pipe. Gully Foyle 2/10/12 6:45 PM
I think your problem is not really with SU but with the design of your elbow, which has a bend radius smaller than the diameter, causing the pipe to turn in on itself. Also, the bend is not tangent at the straights, making it more of a mitered elbow than a bent elbow.

Are you sure of your dimensions?

Re: curved, hollow pipe. Bestistmate 2/10/12 6:54 PM
hi edmund , Rather than putting your follow me path at the center of the circle move it to the outside of the outer circleand it will work then . if you want it in the center then you must increase the radius . check out skp file 

Re: curved, hollow pipe. Edmundajw 2/11/12 7:52 AM
Hi, thanks for the replies. No I'm not sure of the dimensions. I just kind of made thisd to get an idea of what it will look like, and how to do it, with the intention of doing it with the right dimensions afterwards.
I will try your suggestion Bestistmate, thank you.

Re: curved, hollow pipe. Edmundajw 2/11/12 8:53 AM

I'm probably just being stupid, but I still can't get it to work. And I'm not sure how to make sure my path for the curve is the same diameter as my circle. I create the arc by first drawing the line it's going to, and then putting the start and end point of the arc, and then just making it rounded... but I'm not sure it's right...
Here's a couple of pictures to show how I attempted to construct it..but it didn't work. I did the path on the outside of the circle as you suggested, Bestistmate, but I still get the same problem. I've looked at your examples, but I guess I must not understand how you've done it, as I can't replicate them.
I tried drawing a vertical line up form the centre of the circle, and joing to arc to that, to make sure the diameter is the same. I don't know whether this would work, but it looks right. But the final result is still funny..

Here are some pictures.


Re: curved, hollow pipe. Gaieus 2/11/12 9:09 AM
Your radiused path is on the outer radius of the curve. Put it into the inner radius (and then you can make it much smaller, too).
Re: curved, hollow pipe. Gully Foyle 2/11/12 9:22 AM
I just kind of made this to get an idea of what it will look like, and how to do it, with the intention of doing it with the right dimensions afterwards.


If you'll pardon my mentioning it, that's kind of a backwards approach, since the dimensions are not just an incidental detail: they determine what the thing looks like, not to mention making the difference between possible and impossible geometry. The reason your elbows look peculiar is that they are using impossible geometry. The bend radius is way too small. It couldn't be fabricated in the real world any more than it could be in SU.

Standard dimensions for pipe fittings are not a well kept secret; there are published standards, and dimensions are shown on commercial web sites. Standard short throw weld neck elbows have a face to centerline dimension (or centerline bend radius) of 1.315 D. If you use that ratio, you can make your elbow easily using the centerline as the Follow Me path.

Re: curved, hollow pipe. Edmundajw 2/11/12 9:35 AM
Thanks Gully. I'd say I'm only a beginner so am always learning. So thanks very much for that. I'm not entirely sure how to do various things, but I'll try constructing it with that value.

Thanks again.

Re: curved, hollow pipe. Gully Foyle 2/11/12 10:53 AM
That's okay. I just wasn't sure at first whether you had special design requirements or fit-up constraints forcing you to use a very short radius. I'm also not sure what medium you are putting through the pipe. I some situations. like air ducting, you could use a mitered elbow, wyhich does have a square inside corner.

Re: curved, hollow pipe. Edmundajw 2/16/12 6:28 AM
Hi guys. I've been trying to do it based on your suggestions, but I still can't get it to work. Gully, when you say the center line bend radius, do you mean the path, from the centre of the circle, has to have an arc of a radius of 1.315 times the diameter of the circle. My circle is 3m in diameter, so a 3.945 radius for the bend? This seems massive. And I'm still not sure how to actually construct that, if that is right- I don't know how much higher the line at the end of the arc has to be from the vertical line... There's probably set methods to do this sort of thing...but I don't know. I've of course experimented quite a bit before coming back here.. but... failed.

With regards to purpose, the design is for a rough design of a fuel surge tank for a university project. So the intended medium is fuel, most probably kerosene (theoretically). The important bit was getting the dimensions of the tank and outlet right to drain a set amount in a set time (worked this out by hand, am and also checking with cfd software). So for the purpose of this project I could just close of the top, and put maybe just a hole in the top. But I thought it would be better to put in a pipe to represent the inlet. But actually, I don't know what's a realistic size. Also, we're thinking of sending the design to a 3d printing company to make a simple prototype. I know sketchup really isn't the best for this purpose, but it's only a relatively simple design, and I've found a plugin to export to stl, which seems to work (Viewing the stl in Blender). Printing it with a elbow coming out at the top rather than just a hole would be cooler :) ...
With regards to how feasible the printing is, I've contacted the company and they've said to call and he'll give me some design pointers, so I'm ok with that.
Re: curved, hollow pipe. Gully Foyle 2/16/12 11:51 AM
Okay, Edmund. I'm slightly embarrased to confess that I misread the dimension table (hey, I'm old). Short-throw elbows can actually have a 1D bend radius, not 1.315 D. Here; see for yourself:

So, attached, I've included a short tutorial on making the elbow. I have covered one other complication in the process, which is: because curves in SU are segmented, unless you make provisions to accommodate it, 90 degree elbows will not have square ends. The elbow will actually cover less than the full 90 degrees. For this reason, you have to run the extrusion slightly (or a lot) past the point of tangency and then cut it back to where the ends are square. This will make better sense (I hope) when you see the example. In any event, weld-neck elbows often have a short straight section on the ends anyway to keep the weld off the radius. And, of course, if your elbow has a socket end or a flange, these are also outside the radius.

See what you think.