How does one move a specific point on a sketch to a quadrant point on a circle?

[Anonymous]

As a newcomer to Fusion 360 I am having problems with things that are probably easy once you know how!

I am trying to draw some boiler fittings for a steam locomotive with a view to getting them 3D printed for making a small scale model. One item is essentially a part cone with the hollow flared top. I managed to draw the conical bit and then I used the sketch tool to draw the cross-section of the flare with the intention of revolving this round the axis of the cone to form the finished shape. My problems are as follows.

1. The plane of the sketch did not correspond to an obvious position on the cone. How should I have specified a plane on which to draw - for simplicity it should have been on the cone axis?

2. I assumed that it would be easy to move the sketch into the correct position using the sort of techniques common in 2d CAD programs,but I failed. I need to move the bottom outside edge point of the sketch onto a quadrant point of the upper surface of the conical part.

[HughesTooling]

Here's one way to get a plane on the centre line of a cylinder. 

First use Point at center of Circle from the construct menu and pick an edge.

Then turn on the origin and select offset plane again from the construct menu, first pick a plane then pick the point.

If you roll the history back to before you made the sketch and define the new plane then roll to the end of the history again you can use Redefine sketch plane and move your existing sketch to the new plane.

Mark

Edit read through your post again think I misunderstood, this might help.

To get reference geometry from the model look at Project on the sketch menu, pick the circle at the top of your part and it will project a line, you can use the end point to position your sketch.

[Anonymous]

Thanks for the reply, I'll have a go later.

Regards,
A. J. Nummelin

[Anonymous]

Mark,

     I'm still having problems. I think I must be approaching this program incorrectly.....

 

1. I struggled for over a day to find out how to turn on the origin - there seems to be no command available to do this and searches of the help system failed to find anything in any way relevant. Then by chance I found it a few minutes ago in the browser.  (Probably blindingly obvious to most users of the program, but not to someone used to pen and paper or 2D drawing programs.)

2. I followed the instructions to make a construction point at the centre of the circle, but there was no visible mark. So I tried drawing a new circle on a blank part of the drawing and putting a construction point at the centre: as nothing was visible I assume that construction points are not shown on the drawing. Have I missed something obvious again?

3. I selected the construct offset plane command, picked the appropriate plane visible at the origin, zoomed in to be sure I was in the right place, and tried to click on the centre of the circle. Nothing happened and the dialogue box only gives a distance option (not useful as I still haven't worked out how to measure the distance between two points on a drawing). See offsetplane.jpg attached.  I couldn't capture it on the screen shot, but hovering the cursor over the centre of the circle brings up a box containing: "select plane, planar face or sketch profile".

 

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4. I also tried your edit. I used, Sketch, Project, selected the top circle. The screen switched to show a top down view with the circle highlighted in blue and the Project dialog box. Clicking OK resulted in nothing more than the highlighting being cleared.

 

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5. I then thought I could make progress by drawing a line from the centre to the relevant quadrant point of the circle and using this. As far as I can see it is not possible to snap to a quadrant point, it seems that snap works with any point on the edge of the circle. So I drew a line at zero degrees and then extended it to the edge. Zooming in to the area of interest, I thought I should be able to move the sketch but I could not select the plane. I zoomed out, selected the sketch elements, zoomed in and managed to move the sketch to the desired place. Success at last!
Fortunately I had no difficulties in revolving the sketch around the central axis and thus creating the top lip of the safety valve cover. (See safetyvalve2.jpg attached)

I've now reached the point I was aiming for, but I feel this was more by luck than by learning and understanding. To reduce the chances of my needing help again I prefer to find out what I should have done differently and why.

Now it's on to the next stage...

Regards,

Andrew Nummelin

[HughesTooling · Accepted solution]

Here's a short screencast to demonstrate constructing the offset plane at the centre of a cylinder. It also shows how to project the edge of the cylinder to use as a reference.

As for a way of making this easier, for something like this it would have been a lot easier to draw the part centred on the origin. You could have drawn the profile for all of the cylindrical part in one go and revolved around the origin. The complete part could have been done with only 2 sketches one revolve and one extrusion.

2 sketches like this drawn at the origin.

Then revolve and extrude. I've attached the file, it's not done with any accuracy but it should give you an idea. To open the file use New Design From File on the file menu.

Here's the screencast.

Mark

[Anonymous · Accepted solution]

Mark,

      Thank you very much indeed for the excellent tutorial - I've watched it twice. Next stage will be to play it very slowly on one machine while ensuring I can copy what you have done on another.

      I agree that it would have been easier to draw this item centred on the origin but I did not do this as it is only one bit of the final item, and the origin is located in relation to that. I did wonder about sketching the whole of the cylindrical part and rotating that as you suggest - it would indeed have been the better approach. I didn't do it because I started with the saddle and extruded bits on top of that - now I have two "skills"!!!!!!!!!!!!!

     Again, many thanks for taking the time to help a novice - very much appreciated.