Create an arc on an arc at a specific location

I’m drawing the sanctuary of the synagogue I work at and I’m drawing the bema at the moment. In the drawing below, you can see the outward arc of the first step of the bema but there are two inward arcs for the steps up at the middle of the bema. I need to draw the inward arcs starting a very particular point on the outward arc but I’m at a loss for how to do that. If anyone could point me in the right direction, I’d appreciate it.

I think we need to know more. What is stopping you? What is the specific point and why can’t you use it?

First, I don’t know how to measure along an arc. Second, I don’t know how to drop a point at the spot I need without drawing a line. I tried drawing a straight line but I can’t get it to land on the arc and I can’t rotate it to land on the arc without changing the shape of the bema. I’m sure it’s a simple fix but I’m not super knowledgeable in ketchup .

You still aren’t telling us enough to be able to show you what to do.
Can you upload your model and tell us what measurements you have to go on.

That’s the problem. I’m not sure where to get started. In the picture, you can see roughly where the inward arc will go but I want to measure exactly where it should go. How to I measure along an arc in sketchup? How do I drop a point at a particular location on the outward arc so that I can draw the inward arc? It’s not obvious to me.

At any rate, here’s the file.

Arkfrontfloor.skp (131.7 KB)

But what sizes do you have? What information have you got to determine where?
Just saying a specific spot is meaningless. What have you got to work with?

I don’t see how the measurements are material to what I’m asking, but here’s what I know.

  1. The apex of the inward arc is 88.5" from the apex of the outward arc.

  2. I wasn’t really sure how to measure the points that I needed for the other two points of the arc, but I know that if I draw a straight line from the 90 degree point on the far left to the exact spot where the inward arc begins on the left, it’s 15’4".

So how do I drop a point at each of those positions on the left and right side to start the inward arc? If I measure physically along the outside of that arc in the bema, how do I translate that distance along an arc in sketchup? Or am I on the right track using a straight line?

What is the 90° point on the left?

If you know where the endpoints and the apex of the arc lie, use the 3 point Arc tool to draw an arc that passes through those three points.

I think I figured it out. I used the tape measure tool to drop points where I needed them and then used the arc tool to draw from there.