Aligning two circular tubes

I am wasting way too much time trying to align a stovepipe chimney with the top of the fireplace. I can’t seem to pick the centers by inference. Someone here must have an expert trick.

Ortal Fireplace.skp (1.5 MB)

I am by no means an expert… actually a VERY new user.

But I did this:

  1. Explode the group into the three components
  2. Draw two lines over the two circles in question to make it very easy to grab the ‘center’ of either
  3. Turn On xray.
  4. Select the top chimney and new crossed lines…
  5. Move the center of that cross onto the bottom cross until they snap together
  6. Deselect, and then hide the top chimney’
  7. Erase my cross lines.

I can try and make a video if this is helpful, but I’m sure someone else actually knows the trick you’re hoping for. :wink:

Ortal Fireplace.skp (1.5 MB)

First I would switch to a monochrome view, then switch the back faces and eliminate some or all of the nesting. Realistically it would have been faster to model the upper pipe in place.
I would draw a short line marking the center of the lower pipe. Next I would find the center of the upper pipe using the move tool, click to start the move. Hit the up arrow key. Move the mouse to the end of the line marking the center of the lower pipe. When the endpoint is indicated hit the up arrow key again. Click to finish the move.
I would do a gif if you wish, might take a bit.

I referenced the tape measure tool to an edge where you place the stovepipe and that gave me the center. Then staying on the blue axis (PgUp arrow) I drew a line. You can see it in X-ray mode. Then I used that to center the stovepipe and move down on the blue axis using the
PgUp arrow key. Similar to the Danimaupin method.

Stovepipe.skp (1.6 MB)

Change to Monochrome so you can see what you are doing, then use Inferencing to grab the chimney by the centre, then use inference again to place it on the centre.
Centre infer

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Here is doing it with inferencing, without any drawing. I select the pipe, use the Move tool , and get an inference for the center of its circle, and then click. After that I inference the edge of the other circles, to find the centerpoint to drag to.

As you see, the same way Box did it!

OK, I guess I should explain how this came about. I am changing the original fireplace to a different model. The stovepipe is already positioned correctly in the overall model and it goes up through a cathedral roof. I just cut a pasted the parts into a new drawing for the sake of sharing in this forum. I am not going to move the stovepipe. Instead, I will move the fireplace to the correct position beneath the stovepipe and then extend the stovepipe length to the top of the fireplace. It was helpful to be reminded to change the style temporarily to hidden line so I can more easily see all the parts. (Black is nearly impossible) I will follow Box’s example, but in reverse. Thanks to you all!

This shows a good example of why it is best to create circles on axis, if the chimney was aligned so the vertices were on axis you could simply use the midpoint of the stove, and move on the green axis to align.
Here I have drawn in a ‘midpoint’ to align to. (not accurate if the circle isn’t either on axis or exactly half a segment off axis, a useful place to be in certain circumstances)
Mid ref
As a side note you should correct the face orientation on the stove.

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Once I add a material, I never even think about whether a face is reversed or not. Does it really matter? As for drawing circles on axis, that has never occurred to me to be important, but I can see now how it can be useful sometimes. I created this fireplace by roughly tracing over a 2D CAD file and then extruding it.Very rough.

In many render engines back faces are ignored, so you get holes in your renders. It is also how 3d printers know what is material and what is air. There are many models in the 3d warehouse where people have ignored the face orientation, they are basically bad models. If you wish to be known as a bad modeller you too can ignore face orientation. If you keep on top of it as you work it isn’t an issue.

Circles should always be on axis so you have a chance of joining them up. Draw two circle the exact same size but differently off axis and try to put one on top of the other.


+1 for all circles on axis, all the time unless for a very specific reason.


The fluke rotation method:

I have found helpful an additional good practice for SU circles (regular polygons) in addition to drawing circles on axis, and that is to utilize a quantity of edges divisible by 4 (four quadrants and two axes).

Normally, i input 96, 48 or 24 depending on radius size, level of smoothness desired and memory considerations.

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I usually use a multiple of 12. Makes the circle divisible by 2,3, and 4.

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