Fitting parts togther accurately



I am currently trying to model drain runs, and have found various components in the component warehouse, like these here by Stuart Patterson:

In real life one (eg a pipe part) would fit into another (eg a bend part). The components look like they are designed to fit togther in this way, but I cannot work out how to do this accurately

Conceptually the problem amounts to fitting one cylinder of a certain diameter into another of the same or lesser greater diameter.

One might imagine that a tool to do this might allow you to select one component, select the move tool, select a face on the component with the move tool, move the mouse to select an identical or smaller face to abut it to on the second component, then move it. Or one might do the same thing with edges that define a face. If one face were smaller (but the same shape) as another, it would by default be abutted symetrically within the other.

Does such a tool, procedure, or add-on exist? I have Sketchup Make 2017.

I have seen this discussion.

But the best solution seems to lie in the last post and I am not sure I understand it. THe video goes too fast and does not appear to be of a type where speed can be varied.

I would be very grateful for any help you can give.

Kind regards



Depending on how the components were created, often there is geometry used to create them that can be purposed for placement. I usually position components for DWV in xray mode.


Into a lesser diameter would be a problem in real life.

In general you’ll need to grab the object that needs to be moved at a certain logical location.
Here a center point on the center line is probably missing. You can add them to the (bend and pipe) components Inside their editing contexts to make things easier.
It may also help to work in X-Ray face style to make inner vertices accessible for reference or to snap to.

p.s. also turn on ‘Hidden Geometry’ to see all the geometry you need.


If you are doing a lot of these types of alignments, you may want to add “snap connectors” to the components.


The explanations in that discussion are a solution.
Mouse, where do you block yourself and you can not align the pieces?


And if you need to rotate the pieces…


Yes sorry got that the wrong way round - now corrected.

Thanks very much for the explanation.

Re central point missing, I see so the cross hairs or something like them are the solution. I was mislead by the fact that it did not solve the OP’s specific problem.

I will change to ‘Xray face’ style and ‘reveal hidden geometry’ mode and try it.

Kind regards



I see, thanks very much - I will look for that, or create some if there is none I can use.

Kind regards



A very neat tool - thanks very much for programming it. Will consider buying!

Would be nice to see it as a standard SU feature as well

Kind regards



Thanks very much for the animations - they make it clear.

I was trying to move a point on a selected circular edge to a point on the corresponding circular edge, but the result was out of alignment. I will try using or creating a centre and moving it to a centre.

Kind regards



I personally, would use this extension only if I was using these parts continuously in many different projects. The manual method, shown by @mihai.s , would be my first suggestion. As you learn how to manipulate and align the parts correctly, the skills you develop can be utilized in other ways.



Couple of suggestions: One, turn on hidden geometry (View>Hidden Geometry). This can make it easier to find a point on the edge of one piece that aligns with the mating piece. Two (a technique from Dave Richards): Change the axis orientation so that the axis origin corresponds to an insertion point. This may not always work, given the different shapes involved, but it may help in some instances.


If your component fittings have the built in reference geometry its really just a matter of toggling on back edges and snapping to the proper reference points. The only issue with having the built in geometry would be in the rare occasions it would be visible.


Many thanks again for all your help.

I have just tried the solution in your videos, and with the particular components I am trying to use it does not seem to work unless I misunderstand the video. The object ends up off centre and rotated along two axes. I think the problem may lie with the components maybe. As far as I can see, in Xray mode with hidden geometry revealed:

  1. There is no reference geometry as far as I can see.
  2. In one component the circle has no centre. At least hovering over the circumference does not reveal it.
  3. The components seem misaligned wrt to two dimensions on import so locking the movement in one dimension which I think maybe you are doing (?) does not work without two-fold adjustment of orientation - which I don’t find easy to get right.

I have referenced the components I am using in the first post. Is there a better set of drainage/pipe components I could use? Metric is ideal, but I guess I could scale US/imperial measures.

Thanks for your clarification about back edges. Are these what make up the front and back faces that Sketchup has?

It’s possible that there is something fundamental I don’t understand here. So could I ask a fundmental question. In principle to align two 3d objects in 3d you would need to match up three points on one object with three points on the other. How is SU working out how to align the two objects when you drag a single point to another single point?

Sorry if I am being dumb.

Kind regards



Thanks very much. Trying this now!

Kind regards



Thanks very much David for your thoughts. Obviously still missing something here. I can see that it’s critical to match points, but my understanding is that, to get a 3D match you should need to match three points on one object to three points (with the same distances between them) on another. Or, equivalently match a face on one object with a face of the same dimensions on the other.

I am afraid I don’t understand how the origin trick works, as it is still (if I understand it correctly) matches one point to one point.

Kind regards



Mouse, if it’s complicated to align those 3D models, then it’s easier to redesign them to your needs.

However, with the exception of detailed plans, you can probably use the low-poly 3D models without difficulty. The inside of those pipes is not visible anyway, so instead of 50 (or 102) segments, as they have now those circles, you better redesign them with maybe 6 segments interior, and on the outside probably 9 (12) segments can be enough. SketchUp presents pretty well those curved elements made of fewer facets.

So, redesigning, you can also create your own crosslines in the middle of circles right from the begining for easier handling. And you can hide them in a layer after.

It all depends on the result you need. But you can increase the number of segments of a circle as needed (only in 2D).


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