topic Betreff: Contraining Arcs/Splines in Fusion Design, Validate & Document Forum

Contraining Arcs/Splines

Anonymous — Fri, 14 Jun 2019 01:02:12 GMT

I've been practicing free sketching using lines/arcs/splines. I'm running into an issue where I can't figure out how to constrain a 3 point arc properly. The shape it's attached to moves as one, but the arc itself distorts due to not being constrained correctly. Any tips or advice is much appreciated.

I deleted all of my original dimensions to start from scratch.

Thanks!

Betreff: Contraining Arcs/Splines

g-andresen — Fri, 14 Jun 2019 07:29:00 GMT

Hi Kevin,

1. 3 point arc : coordinates of start and end point + radius

2. spline : fit point spline > coordinates of each controlpoint and defined tangent handle (up to 4 dimensions per point > depends on vertical or horizontal constrained handles)

control point spline : coordinates of the control points only

günther

Betreff: Contraining Arcs/Splines

mfyater — Tue, 01 Mar 2022 16:07:04 GMT

Hello, I'm struggling to get my splines and arcs constrained. I've tried constraining the handles but I'm having no luck. Any help you have on constraining my arcs and splines would be much appreciated.

I've attached a public link. Not sure if that's the correct way but let me know if not.

https://a360.co/3Hx7ZgP

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TheCADWhisperer — Tue, 01 Mar 2022 16:17:20 GMT

@mfyater

Where are your spline nodes located in space?

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mfyater — Tue, 01 Mar 2022 16:23:25 GMT

They're located at the tip and of the bottom length line and at the end of the arc at the top. The dimensions of the spline node line lengths are defined. Is that what you mean?

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TheCADWhisperer — Tue, 01 Mar 2022 16:28:40 GMT

1. There is no arc in your file.

An arc has a specific meaning in geometry - part of a circle.

You have a spline curve.

Where is the top node of the spline curve in space?

You left that position undefined?

Did you not observe that I dimensioned it's location (where you had it)?

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mfyater — Tue, 01 Mar 2022 16:33:55 GMT

I see. I guess my problem is that I built the arc by drawing a two point circle from the center of my line and then trimmed the rest of the circle away from the arc. I see now what you mean now. I have assigned a dimension for the length of the spline that I thought was an arc.

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mfyater — Tue, 01 Mar 2022 16:36:01 GMT

I do still however am not sure how to constrain these lines from there. I followed a video on constraining splines but I can't seem to get them to work.

Betreff: Contraining Arcs/Splines

TheCADWhisperer — Tue, 01 Mar 2022 16:52:26 GMT

@mfyater

My mistake - I missed the arc - it was there all along, but you did not have it dimensioned so I thought it was one continuous spline.

You need to dimension your geometry.

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mfyater — Tue, 01 Mar 2022 16:55:59 GMT

Thank you. Yeah, sorry. I'm new. Still have a lot of green around my gills. I've added the radius dimension for the arc and so now I believe I have all the dimensions you have added but my lines are still blue. Have I missed something?

Thanks again for the help.

Betreff: Contraining Arcs/Splines

TheCADWhisperer — Tue, 01 Mar 2022 17:05:34 GMT

@mfyater wrote:
I have all the dimensions you have added but my lines are still blue. Have I missed something?

Can you File>Export your new *.f3d file to your local drive and then Attach it here to a Reply?

Sometimes Splines can be finicky.

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mfyater — Tue, 01 Mar 2022 18:06:33 GMT

Absolutely. I've just attached it. Thanks again.

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davebYYPCU — Wed, 02 Mar 2022 00:30:51 GMT

Have I missed something?

Some constraints.

I deleted the angle dimension from the tangent handle and replaced it with a Tangent constraint.

Dimensioned the Y direction of that Tangent point, and

A Perpendicular on the construction line.

Might help....

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mfyater — Wed, 02 Mar 2022 15:47:40 GMT

Thank you for your help. I managed to get everything constrained. However, when I mirror the sketch to try to complete the body, I can't seem to get it to constrain the rest of my parts. Any help you have with this is greatly appreciated.

Also, If you have any advice on making the nose and tail more snub rather than long and skinny, that would be great. I'm not sure how to fix that with the spline nodes with this many constraints without messing up other dimensions. Is that possible?

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g-andresen — Wed, 02 Mar 2022 16:08:10 GMT

Hi,

Fit point splines require 4 determinations per control point, which requires significant effort when there are multiple c-points.
In contrast, the use of control point splines (2 determinations) is much simpler.
Basically, from my point of view, it does not make sense to follow the requirement of still fully specified sketches.

günther

Betreff: Contraining Arcs/Splines

mfyater — Wed, 02 Mar 2022 16:35:03 GMT

Gotcha. Thank you. I was able to extrude without being fully constrained which was my goal. I didn't know you could extrude unconstrained parts.

I have one last question for you. It might be better suited to another thread but I'm trying to set a trace tool path on this design so that a 5/8" router bit will trace the outline of this board and leave 1/16" of the piece alone at the bottom. I believe it is called an axial offset. I however am not sure if I have it done correctly. A simulation seems like it is not going that deep. I'm very new to CAM so any information/ help you have for that is appreciated.

Betreff: Contraining Arcs/Splines

g-andresen — Wed, 02 Mar 2022 17:49:39 GMT

Hi,

what you need is an axial offset (negative)

günther