Extend sketch arc command changes the placement of the extended arc

[summerson1990]

Hi! I don't understand why when I try to extend the arc it changes the placement of it. I tried to apply the coincident constraint to it before extending but that doesn't work, so the same is when I try to add the coincident constraint after extending the arc in order to align the points - it doesn't work.

Could you please say what constraint should be applied here or what I'm doing wrong? .f3d file attached. Thanks!

[g-andresen]

Hi,

1. activate the design history.
2. I suspect that a 3-D sketch is not necessary, so I ask you what you want to achieve in the end.

Please show a real existing object.

günther

[barry9UDQ6]

There seem to be a lot of posts recently with people using unnecessary 3D sketches.

Maybe they are being mislead by a tutorial out there?

The process of building up a model from a series of simple 2d sketches, and getting to a solid asap seems to be slipping through the cracks.

[summerson1990]

Using 3d sketches in Fusion 360 makes a sketch wrong, not so precise as 2d sketch or what?

[summerson1990]

Here is .f3d file with history enabled. There is no real need in my sketch the arc to be extended as I described it in the topic. I'm just interested in why this generally happens.

[g-andresen]

Hi,

For example, if you show with pictures how you want your design to look, we can show you alternative methods to achieve that goal.

Afterwards you decide which way you like best.

günther

[g-andresen]

Hi,

This could be about it

Screencast

günther

[summerson1990]

Thanks but in your example you did these angles equal. But in my design they should be different. Maybe I'm not so good in F360 "draft tool" and it could make these angels not equal.

[barry9UDQ6]

3D sketches are used very seldom, and only when using 2D sketches is impossible. Perhaps having 2d and 3d sketches in one environment is misleading.

By using a sequence of fully constrained 2D sketches you minimize the chance for unintended errors creeping into your workflow, And any sketch errors that do creep in are much easier to spot.

Making use of Fusion as a parametric modeler - having the ability to go back and edit your commands (when the design history is enabled) is a big part of Fusions functionality. Allowing you to change lengths, thickness and so on.

Even if you think you don't need this functionality, I think you will be surprised by how often you actually do.

Those of us who have used modelers that are not parametric are possibly more aware of how necessary this functionality is.

I think what is most important is to have a user-friendly workflow that keeps errors and frustrations to a minimum, where they are the exception and not the norm.

This workflow is also a lot more conducive when it comes to either exporting your geometry, or toolpath programming/3D printing preparation inside of Fusion.

I think your reason for posting this issue is well spotted on your part. Struggling with these 'small' issues may not seem to impact on your model now, but may impact your workflow as you take your model further.

[g-andresen · Accepted solution]

Hi,

Look at the construction in the attached file.
When looking at the angles, you must of course pay attention to the plane in which they lie.
In your 3D sketch, the skeleton on the side does not result in a flat surface, but in a curvature.

günther

[rpweaverTTHVX]

But my sketch is all on the same plane and this still happens. Does an arc center point not get constrained to that point and if not, why not? What is the purpose of specifying the center of the arc if it can move unexpectedly and only discovered after many editing steps? Is there a history that can be edited in a sketch to correct this where it happens? Or can I specify that the center of an arc be constrained automatically? I can't count the number of times this has happened to me and in very complex sketches that need to be reconstructed, sometimes from the beginning. These points used to all be at the origin and when I try to move them back, they seem to have a mind of their own.

[davebYYPCU]

Image has limited information.

The black lines are already constrained somehow (unless they are dimensions), the white points are not, they will only go back to the origin, when the lines effected are permitting such a result.

Might help...