# Making clean intersections of non-solid objects in 2015 SUMake

I’m pretty new to SU, & am having trouble making clean intersections. I’m intersecting 2 circular tubes to create of equal diameter & wall thickness, perpendicular to one another, like a pipe tee. I make each tube a group before intersecting them, then explode to clean up the internal parts which should not be there. Every time, odd faces & edges appear which cannot be cleaned up without deleting attached faces that are needed. I’m sure there’s an easy solution to this, but I’m at my wit’s end. Any help would be greatly appreciated!

How big are these ‘pipe-tees’ ?
How segmented is the circle defining the pipe ?
SketchUp has an inbuilt tolerance of 1/1000" so it cannot create edges that are shorter, because it assumes the start/end points are coincident.
Thus faces relying on such an edge are not made either.
If this is the case scale up what you are working on - say x100 - then ther intersection works OK.
Delete the unwanted parts and finally scale done x0.01 so it’s back at the right size.
Tiny geometry can exist but you cannot create it initially…

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The tubes are 1.5" OD, made from 24-segment circles.

TIG is right but there might be something else going on here because you say:

Depending on how the two tubes intersect you might get some edges in one group crossing corresponding edges in the other group by less than 0,0255mm, say equal to or less than 0.001".
By exploding the two groups these edges “snap” to each other slightly distorting the model. And new edges are formed as well, to triangulate the slightly distorted faces.

Scaling up may temporarily help in the scaled up version. But as soon as you scale down to actual size you still get these extra diagonal edges in slightly distorted faces.

Take extra care in positioning the tubes correct so facets around both tubes match.

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This makes sense & seems to describe what I’m seeing. If I upgrade to Pro & make these tubes solid entities rather than shells, will this simplify the removal of unwanted internal geometry without generating new edges?

What I said also applies to the Pro version, no difference there.

The Pro version does have ‘Solid’ tools that make cleaning up an automated process.
But still both tube groups need to be positioned right.
And cleaning up in the Make version is not that difficult here.

Try to work with a grouped vertical tube and a copied version that is rotated 90 degrees. Intersect both tubes (=one through the other, not yet SketchUp’s intersect…) and than explode both groups. Does this make a better tee without extra edges? It should. Clean up inside.
But now if faces are missing see TIG’s advice above: temporarily scale up first > intersect > clean up > scale down.

This statement indicates you may believe that Pro is a solid modeler. It is not. Both SketchUp editions are surface modelers. Pro just has a few more native tools, and many more import / export options.

Creating a clean intersection of the identical tubes requires their corresponding geometry be perfectly aligned. The process of alignment begins the moment you draw the first circle.

Be sure the Inference Tool Tip indicates the tool is on-axes before you click to complete the circle.

Positioning extruded shapes is much easier when you’re able to see all the geometry within.
Click … View > Hidden Geometry to reveal all the Soft/Smooth (hidden) edges of the extrusions.

When properly aligned, the geometry should appear symmetric, something like this.

Notice the resulting lines of intersection are equally as neat.

Slightly misaligned geometry, like this, will yield a jagged intersection with a considerable number of unnecessary tiny edges.

In a smaller model, such as your 1.5" OD tubes, those tiny edges and the faces they support may fail to form or refuse to heal while cleaning up the intersection.

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Thanks, Dan. Good to know!

Thanks so much, Geo. This is a very helpful guide. I’ll be trying this out today.

Geo, your guidance was right on. Your technique produced a nearly flawless intersection, just 3 very small stray edges to clean up. Thanks again!