topic Re: Offset work not correct in Fusion Design, Validate & Document Forum

Offset work not correct

Dmytro.Mukhin — Sun, 02 Jul 2017 20:03:29 GMT

Hello!

@Anonymous wrote at our Russian Fusion 360 board that his Offset tool working not correct.

Info about system and PC:

OS: Windows 8.1

Video card: AMD HD6570

CPU: AMD A6-3600

RAM: 4 GB

Screenshots with results:

Screencasts with actions at topic: https://forums.autodesk.com/t5/fusion-360-russkiy/problemy-s-instrumentom-offset/m-p/7198666

Re: Offset work not correct

Dmytro.Mukhin — Sun, 02 Jul 2017 20:05:54 GMT

I tried make the same with similar models and dimensions, but my Offset tool working correct.

I have no idea about reason of this action.

Re: Offset work not correct

TrippyLighting — Sun, 02 Jul 2017 20:15:38 GMT

The third image is a legitimate concern, but the design file would be needed (as in almost all cases !)

The first case is obviously not going to work as the radii would have a 0 diameter. I am sure that such cases could be caught by the code if it was more mature, but I would say it exhibits a certain lack of understanding of basic geometry on side of the user to expect that this to just work.

The second case I personally would never attempt. Offsetting from the edges created by filleting and assuming that these are all tangential across all the NURBS patches created by the filleting algorithm is wishful thinking at best. If there is one golden rule in mechanical design it's fillets last wherever possible. I'd offset from the un-filleted edges and apply solid fillets to the extrusion created from the offset profile.

Re: Offset work not correct

Dmytro.Mukhin — Sun, 02 Jul 2017 20:41:17 GMT

Already asked about file. I am waiting for it.

Re: Offset work not correct

Dmytro.Mukhin — Sun, 02 Jul 2017 20:56:02 GMT

File is attached.
I'll send for author yours advice.

Re: Offset work not correct

cekuhnen — Mon, 03 Jul 2017 00:44:28 GMT

@Dmytro.Mukhin Bugs in the sketch engine I would say.

@jeff_strater you might want to look into this too - another issue with the sketch engine

I would clearly say that the offset sketch command is bugged here.

but it seems that there are possibly some fillet surface issues too possibly making the sketch offset bug out

however in case it is connected also the surface offset command produces disastrous surface offsets from

fillets

few observations:

1. this model when making a sketch on a face slows down the PC noticeable when rotating the view.

zooming into the model makes the screen refresh so slow it even lags Win10

This happens on both MacPro GTX 970 Win10 and surfaceBook performance base Win10

2. offset preview is not what the result will be sometimes

3. with his fillets it seems that there is a gab between the surface edges making the offset chain command option fail

selecting everything

https://drive.google.com/file/d/0Byzv_NlyKp_2THd0OVBJekNyblk/view

Re: Offset work not correct

TrippyLighting — Mon, 03 Jul 2017 02:13:47 GMT

Yep, now that we have a model to get a hold of this looks a little different.

The code that projects sketch element into the new sketch creates segments that are not recognized by the other code (that is supposed to detect a chain), as a chain.

This is still far from robust. If you try to do this from stitched surfaces you'll have the same problem.

I am wondering if some of this has to do with the rather small overall scale of the model.

The bounding box of the main body is just this:

Re: Offset work not correct

TrippyLighting — Mon, 03 Jul 2017 02:37:52 GMT

Actually when trying to offset the projected profile I can elect one chain or the other, but I cannot set both. The purple points pointed at by the red arrows are also bigger than the green arrowed dots. That's exactly where each chain ends.

I tried to re-create this in another model but was not able to. The code that reduces the radii to sharp edges when the offset gets too small worked there.

Re: Offset work not correct

cekuhnen — Mon, 03 Jul 2017 13:21:06 GMT

@TrippyLighting @Dmytro.Mukhin

interesting point about scale.

here is a screenshot when I zoom in closely with a sketch it gets too choppy to work with.

https://drive.google.com/file/d/0Byzv_NlyKp_2NmVUdXZEY0dTVkU/view

regarding the sketch project edge issue I am close to say this is a sketch engine issue only as all my geometry checks worked in Fusion as well as external apps.

stitching works till a very precise level

quite funny is how the STEP export is done for the G1 fillet. This are trimmed tubes !!!

Just G2 fillets are blend surfaces

but the sketch issue happens with both G1 and G2 fillets!

piping the trimmed face works well.

piping the projected sketch does not

piping the secondary surfaces works well.

on a side note this models shows some pretty ugly fillet ball corner design.

the left fillet looks fine while the right fillet in 2 of 3 positions shows clearly deflated blend shapes.

Re: Offset work not correct

jeff_strater — Mon, 03 Jul 2017 15:03:29 GMT

I will log a bug with sketch offset for this model. I do think that @TrippyLighting is at least partially correct: The overall tiny size of this model may be contributing to problems you are seeing with it in general. Is there a reason for this model to be quite this small?

Jeff

Re: Offset work not correct

cekuhnen — Mon, 03 Jul 2017 15:23:48 GMT

@jeff_strater

I think they tiny scale is an overlook.

Two more observations:

1. STEP EXPORT and IMPORT

Exporting as STEP and re importing it allows you to do a chain select of edges but the offset still is wrong.

Scaling the body 10 times and then doing a sketch project and offset works fine

also the disastrous screen refresh rate seems to be linked to zooming into tiny objects. this does not happen with the scaled model!

Fusion RAW file Scale

Scaling the body and then adding the sketch and doing the offset still fails chain select and also the offset skips other elements when the offset has a certain

value but should work. the image shows the right edge being skipped! this is not a fillet that is being condensed down into a corner!

this begs the question if this is sketch or body. but when step files work fine then I assume it again is rather sketch engine related.

here is a screencast showing the issue.

https://drive.google.com/file/d/0Byzv_NlyKp_2bHhJN3BEeThKUFU/view

Re: Offset work not correct

Dmytro.Mukhin — Mon, 03 Jul 2017 20:51:55 GMT

I don't know about reasons of sizing the model. Author wrote us at Russian F360 board.

It look like it must work (at preview look fine at some parts) but it didn't work.

Re: Offset work not correct

cekuhnen — Mon, 03 Jul 2017 21:23:02 GMT

@Dmytro.Mukhin

It happens with other tools as well that the preview works yet the execution then still fails.