I’m trying to create this design. You can see ONE edge of the diagonal line starts at the corner of the top rectangle, and THE OPPOSITE EDGE of the diagonal line ends at the corner of the bottom rectangle.

I feel like this is a simple geometry problem, and I can’t figure it out.

Can anyone show me how to do this? I want to know how to approach it.

I’ve got to say, this was a little more of a brain bender than I was expecting. I think the best solution is going to be the line tool, and a simple matter of connecting the dots.

You are close but. Your angled part is a bit narrower than the material in the rectangles. Maybe thats OK. Otherwise move the points out on the ends of the diagonal piece. Guidelines could be your friend on this one.
good Work.

I recognize this as a geometry problem I’ve faced before, but it was using PowerCADD which solves it well. It could be done in SU if there’s a good plugin to accurately draw the tangent to a circle. I think there may be one, but I don’t have it.

In principal, you draw a circle centered on one of the starting corners with a radius equal to the thickness of the bar. A tangent line off the circle to the opposite corner is one starting line. Parallel offset and extend finishes the job.

Anyone have a good extension for tangent line drawing?

using circles for geometrical construction in sketchup won’t be precise. It’s something that has to be done in autocad or equivalent.

In this case, I would group everything, create a new rectangle to extend the existing thickness, and do a two steps rotation, first to find the reference point and then to snap in the corner, cut and paste into group and finally extend necessary lines and clean unecessary ones as follow :

There may be cleverer ways, but here’s one that works with built-in tools and is easy to do:

Off to the side, draw a rectangle the required width of the diagonal piece and somewhat longer than necessary. Make it a group.

Move the group so that an interior point on one of its sides is at the corner of one of the existing rectangles.

Draw an arc from that corner with radius to reach the corner of the other rectangle and with enough sweep to cross the group.

Rotate the group about the first corner using the crossing point of the arc and the group as the other point of the rotation so that point lands on the corner of the opposite rectangle.

Open the group for edit, trace edges across it where it meets the edges of the two rectangles. Erase the extra stuff. Explode the group and if desired, erase the portions of the edges where it meets the rectangles.

I was thinking that might work. I’ve seen arc & line intersection work before, but know that arc & arc intersection is problematic - which is why you wrote a tool for that, right?

Yeah. If you stop the arc at the edge of the group, it will be exact. In my video I ran the arc across to the opposite side, which could have produced a tiny error. In practice I would likely have used my circle intersect extension (or perhaps TIG’s true tangent) to get an exact crossing point but I wanted to show using only built-in tools.

If the arc is stopped at the upper edge of the long thin rectangle instead, the rotation will be more precise. I use a similar method for connecting the linkages in my steam engine models.

Which is what I noted in my reply to @RTCool. You need to stop the arc at the top edge of the group. When you do that, the final point is a vertex of the arc and is at the exact radius of the arc. In my haste to create the video I missed that, producing the tiny error you see.