Can I have two circles on different planes within the same sketch?
right. Any geometry not on the sketch plane is considered "3D geometry", and loses some functionality, like having dimensions. I would put the two circles on two different sketches.
BTW, what you are describing is something that we are working on improving right now...
Jeff Strater
Engineering Director
Your title question and your modeling description are not talking about the same issue. You are modeling a section of a cone, which is called a frustum. The issue you having are probably being caused by sketch constraints which you have in place. Take look at the screencast where I show how to manipulate two sketches to make variations of a frustum.
John Hackney, Retired
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Many thanks @jhackney1972 for your video. To be honest I was finding it difficult to put into words what my problem was. (I originally wrote "I am not exactly sure how to express what I'm trying to do" then deleted it for brevity.)
My question to you would be: how can I achieve the frustum in the first place? I watched this short video (how to loft) which describes creating construction planes onto which I can sketch different circles. Since watching that, I have managed to create two planes (one seems to be the same as the starting plane, although I admit I don't fully yet understand the concept of planes, and the other is 13.5mm "higher"). However when I start drawing my circle on one plane, the origin is not exactly the same as the origin shown on the other. Does that makes sense?
It was only about an hour later that I realised my cone wasn't truly symmetrical, as one circle has a slightly different origin to the other.
Is that how you created your frustum? If so, how do you make it so that the construction planes have the same origins, so I can reference one to another?
Again apologies if my terminology is not quite correct. I started my first 3D design yesterday so I'm very new to the concepts, as such it's difficult to identify exactly how to ask questions.
On a separate note, here's the print of my first attempt; this is the one where I wanted to go back and change one dimension, as the top larger circle needed to be 2mm wider in diameter. This is the version where the centres of the circles were properly aligned. But the sizing was slightly wrong.
Origin Planes and Construction Planes (sometimes called Workplanes) allow you to sketch in different locations. There are so many ways to create construction planes, the video you watched used Plane at Angle, I used Offset Plane. There is no wrong way to model just one way may be more efficient than another.
As you begin to model, make sure you follow good practices. All sketches should be fully constrained. An easy way to tell this is that they change color when they are fully constrained, most of the time. This is the answer to you question on how to relate one sketch to the other. You can project geometry from one sketch to another and use it for sketch constraints and dimensioning. In my screencast I am using a Coincident to the same Origin point so I did not have to project any geometry between sketches. Another good practice is to model about the Origin Center Point or relate to it with constraints and dimensions. I illustrate this in my screencast.
Also, Please, Please Please do not try and model complex objects until you master the basic concepts of the CAD application. You will become very frustrated and develop bad habits. Do a few basic tutorials and you will quickly find new terminology and methods.
John Hackney, Retired
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