Radius Corners on a 2D image

I have an image that I am trying to create smooth corners on. I will be cutting this design on a CNC router so I need to have a minimum radius of 1/16" because my smallest end mill is 1/8" diameter. I imported the image as a .dxf file that was sent to me from the person wanting me to cut the project.

I need to put the radii on the corners in the 2D image because then I can extrude the image so I can cut the inside part then I will go back and extrude the exterior so I have a positive and negative image. The image will be cut in oak and the interior will be cut in Walnut.

I hope this makes sense. I am learning sketchup as I go and am getting frustrated.

Every time I try to draw an arc or put a circle in, the lines all snap to parts of the circle and then if I erase what I don’t want, it deletes extensive pieces.


An Image is always an un-editable rectangle.
I can be resized, moved, rotated etc but little else.
But you can Explode it and it becomes a rectangular face using the image as a material-texture, with its four edges.
You can then take that selected geometry and make it into a group or component.

To edit/change the geometry you need to be in the same context as the geometry.
So if it’s now a group or component edit it first.
Now you will be able to draw new edges or arcs over the face and erase edges and bits of face etc as you desire.
However, remember that a face needs a continuous loop of edges - so ensure and new lines are snapped together.
In your Model Info > Units do NOT tick the snap box, as this might mean tiny gaps in what you draw.
Also make sure you are always inferencing onto the face in question - lines shooting off in 2d do not intersect the face as expected.
If your Style is set to have lines and profiles both showing, and with thicker profile set it’s easier to see when a loop is made, as its thick profile lines turn thinner…
Remember that geometry ‘sticks together’ in the same context, so get used to the advantages of this.
If you have some edges that you want to move but they are ‘stuck’ onto other stuff, then you can always select them, make a group to separate it from the rest, move that group, then explode it as needed to place those edges in the new location…
Note also that all ‘raw’ geometry like edges, faces, surfaces and curves should be made on Layer0 [which should always be the current layer - and you then assign other layers to ‘containers’ [groups/component-instances] to control visibility…

OK. I am still working on this. The file I am trying to edit is not specifically an image. It is a sketchup file that has been converted from a .dxf file. It has an outline that allows me to push/pull the surface but it is not allowing me to edit the corners.

What I am doing is this.

I have the file that has the outline on it. I am trying to put 1/16" radius corners on all the inside and outside corners. I thought I could draw a 1/16" radius circle and then simply copy and paste this in each corner with the circle tangent to each side. Then I thought I could then take and clip the outside corners leaving the radius for the corner.

Every time I try this and get the circle tangent, it re-shapes the circle with two flat sides. Then when I delete the outside corners, it cuts the circle further into a triangular shape.

I tried to group the original image and put the circle on but then when I try to clip the outside corners, it deletes the entire original, leaving just the circle.

This is what it looks like when I have the circle close but not touching the edges.

I will put the next two images in the next two replies. This only lets me put one image per post.

Once I let the circle touch the edges, this happens:

Then, once I clip the corner, this happens:

I know i am doing something very wrong but I don’t know where I am making the mistake. Can you point me in the right direction?


The sizes you are working with are too small for SketchUp. Once the circle touches the bounding edge (where you say: "Then, once I clip the corner, this happens: …) you see that the edges snap to the nearest end- (or mid-) points of the circle segments.
If you would do the same operation on geometry 10x as big this would not happen.
How many segments are there in the circle you applied?

I have 100 sides on the circle. That has been my default because when I
have less than that, I can see the sides of the circle when I cut the image
in wood.

Good eyesight! But I don’t buy that. Maybe for larger circles, yes.

** Wrong statement, see below!! (SketchUp converts the copy of a 24 sided “circle” into one with 12 segments when the radius is 1/16".)

You only may get away with working on such a scale when working in a component’s editing context in a scaled down component. Otherwise you have crossed SketchUp’s limitations on edge sizes and distances between endpoints.

** That statement is wrong. I was working with a much smaller circle at the time.

I have not cut circles this small in wood. You are correct in that. The
reason I have defaulted to this is that when I have cut prayer circles, say
approximately 1" in diameter, I could see and feel the 24 sides.
Therefore, I have been putting large numbers of sides so I can avoid this
in the future.

I did not think about the fact that this might be too small of a scale for
sketchup to handle.

These experts are right. It’s worth it to copy your whole component/model and scale it up by 100 or 1000 and then work on it. You will have far less problems. I’m learning this since starting Sketchup about a month or so ago.

I also use a lot more lines for my circles. But you might want to make it a number divisible by 6 for doing radial arrays in the future. When my circles are 100 lines, I had trouble spacing out radial array items on it. But if I use 96 lines for a circle, I can more easily radial array and evenly space out things around it.

Just something to think about.

once you scale up to a sensible size, the ‘Arc Tool’ can be used to auto-trim your corners…

BTW: @Rick, multiples of four, drawn on axis, offer the best outcome because they retain the primary ‘Cardinal Points’ on axis…



Yes Rick the multiple of six was because you had six sailfish circling your ring.

I had not thought to scale up and then do my editing and then scale back down. I will try this later today when I have some time to play around.

On this, will it work to proportionally scale up the radius of the circle? For example, I want to have a radius of 1/16" to match the radius of my 1/8" diameter endmill on my cnc router. If I were to scale up my drawing by say a factor of 20, would I need to created a radius of 20/16" (1 1/4") for my curves and then that would scale back down to 1/16" radius when I go back to my original size?

I hope you don’t think I wasn’t listening to the experts. That is why I am here. I was simply trying to provide all the information on what I am working on and show pictures of what is happening. I am new to this program and am learning all the ins and outs of working with it.

Thank you for your help and the suggestion to scale up then back down.

The arc tool looks like something that I am looking for. A question on the arc tool. In your example, the arc tool is working on 90 degree corners. Will this work on other angles say something that is more acute or more obtuse of an angle than a simple right angle?

If this would work on other angles, that would simplify my life greatly.

I am already planning to try scaling this up and then adding radii to the corners then scaling back down.

Thank you.


Really dumb question (I’m full of these) where do I find the arc trim tool? I found arcs but then I have to manually go in and trim the excess corner off. In the gif you have going, it seems to automatically draw the arc and then trim the excess leaving the nice radius on the corner.

Thank you.

watch for the magenta color change before the second click and it trims…
when it completes once hover the next corner looking for the blue square, then click, and on to the next…
works best in straight on view…
before you scale up you can add a guide line at 1/16" to use at 100X scale…

The magenta double click.


Thank you for the knowledge on the trim and also for the suggestion on the 1/16" guide line. I had thought of doing the circle at 1/16" radius and checking that but just a straight line would be incredibly useful to have there as well.

This is making more sense to me. I will try this a little bit later today and make sure this is working for me.

you only need the one guide…

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