Offset Limitation

[simon63091]

Hi 

I am trying to design something to be 3D Printed in multiple parts. To allow for a little room so that the parts can fit into one another I wanted to make a small offset of the inner part. Fusion though for some reason when making a very small offset does not recognise the new slightly smaller surface as a separate surface and still only lets me select the entire surface. In my test example I added bellow the cut of seems to be somewhere in between .3 mm and .4 mm. Setting the offset to .4 mm resulted in two surfaces while at .3 mm I only got one. This seems to be a relative limitation because with a 10 times upscaled image the limitation lies between 3 mm and 4 mm. A .4 mm offset would probably still work for my Print but I was still curious if any one could explain this to me maybe for possible future use cases. 

Thanks,

Simon 

[Drewpan]

Hi,

While I understand what you are trying to do I think you are wasting your time with such a small offset. If you try to

3D print it is unlikely you will get that kind of precision unless you are using the immersion in liquid printing. Standard

extruded plastic printing will shrink and deform and can make a mockery of such small tolerances.

My advice is use the offset that fusion recognises and take your chances on the print. Any fabrication method that has

any kind of potential shrinkage like extruded plastic or metal casting will be an issue to you and is difficult to predict

accurately.

Sorry for the bad news.

Cheers

Andrew

[simon63091]

Hi Andrew thanks for the answer.

I absolutely agree. .3 mm or .4 mm will make absolutely no difference in the accuracy of a FDM printer. I was more interested in the reasoning why Fusion does this because when scaling the model to 10 fold I still have the same issue. And 3 mm or 4 mm is a resolution that is well inside the specs of a 3D Printer. So I am just interested in what the reasoning is for the cut off in Fusion. It's more of an academic interest to learn for the future. 😊 

[laughingcreek]

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@simon63091 wrote:...Setting the offset to .4 mm resulted in two surfaces while at .3 mm I only got one. ...

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can you post the file with these surface in it?

[simon63091]

I attached the F3d file to my Original Post. Is it not visible?

[laughingcreek]

that file just has a sketch.  not any surfaces.  

[simon63091]

Ahh sorry Surface is maybe the wrong word then. The left snake with the .4 offset basically gives me two areas I could extrude into a Body (the core Snake and the boarder) whilst the right one with .3 offset only gives me one area to extrude. So I couldn't just extrude the boarder for example because I can not just select the boarder. This is what I am confused about. Why is there a minimum offset that has to be set before I get two distinct areas in the sketch. 

[laughingcreek · Accepted solution]

this isn't a limitation of the offset distance, but of using offset on a spline.  offsetting splines lines will generally result in a degraded curve.  it doesn't help that this is an imported curve, which frequently have rather poor curvature quality from the start.

in this case, if you delete the offset constraint, you can see that there is an unconstrained point in the loop-

you can use window select to apply a coincident constraint to close the loop.  see attached.

better would be to use surfaces, and offset those instead. see attached.

even better would be to use native geometry, and not imported geometry.

.

[simon63091]

Thanks for the answer and the work arounds. I am used to working with Inkscape and vector graphics. And since vector images are scalable I would not have expected such issues compared to a native geometry. Will take this into consideration for future work. Thanks again. 

[etfrench]

Actually, a .1 or .2mm difference in a 3d print can make a difference in how well two items will fit together.  One common place that this occurs is in threads.  Often offsetting 3 of the 4 faces of a thread by .1 or .2mm will allow them to fit together.

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@Drewpan wrote:

Hi,

While I understand what you are trying to do I think you are wasting your time with such a small offset. If you try to

3D print it is unlikely you will get that kind of precision unless you are using the immersion in liquid printing. Standard

extruded plastic printing will shrink and deform and can make a mockery of such small tolerances.

My advice is use the offset that fusion recognises and take your chances on the print. Any fabrication method that has

any kind of potential shrinkage like extruded plastic or metal casting will be an issue to you and is difficult to predict

accurately.

Sorry for the bad news.

Cheers

Andrew

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