Offsetting complex, closed shapes made up of arcs.

stephen_dewing

In sketch mode, I am trying to offset a closed, complex shape with lots of arcs but keep getting any one of the following messages "Offset could not be created at this distance" or "Sketch can not be solved" or "Can only offset a single chain at once."
No matter what closed shape I make with arcs, how big or small, it will not offset either inwards or outwards.  
Can anyone help me please?  Is this a problem with the program or just my understanding?  Desperate!

owen_sparks

OK, lets hit the issues one at a time.

Is this the type of fillet you're after?

If so you need to join the individual parts together before the fillet. (Using the boolean tool.)

Owen S.

owen_sparks

Not quite.  In your last example you extruded a line which will give a surface.  We want to extrude "sketch regions" to make a solid part.

To boolean two solid parts there is no need to select faces, we just select the parts we want to join together.

To end up with a .45mm thick wall we have a few options.  We can either extrude it solid and then use the shell feature and tell that feature we want a .45mm wall, or just start with something .45mm and extrude it up.

Cheers, Owen S.

NeilCooke

Hi @stephen_dewing - welcome to Onshape!

Please post a link to your document as detailed here: https://forum.onshape.com/discussion/9107/forum-post-checklist-read-this-first#latest

It is likely that either the sketch is not closed (area is not shaded) or the arcs are too small. Select the offset tool and click/drag one of the entities to get a smaller offset (your arcs may be smaller than the default 5mm). 

owen_sparks

I had a similar issue this morning.  The sketch offset was happy when when creating it.  I was even able to use the drag arrows to get exactly the offset required. At this stage all the geometry was in the correct place and shown in black.  As soon as the feature was committed though it blew up red and failed.

As a workaround I've found it to be more robust to extrude the base sketch region into a new solid part, and then use the "Move Face - Offset" feature to get the required geometry/

Hope that helps,

Owen S.

stephen_dewing

Thank you Neil.  Here is the link.  https://cad.onshape.com/documents/7911a70ce5cdf73827c8d990/w/7ff3e5206ffd618ada34723f/e/22cb13049b00771b754ffcebI'm trying to make cookie cutters which are relatively small.  I may have to use another program, sadly, unless there is a way around it. The 4mm offset is the rim of the cutter.

owen_sparks

Any good?

https://cad.onshape.com/documents/0a6291890e1bc3f2c1ca275f/v/d5a2e18527bf1c1392bf42d4/e/cdb269dfe40fc288b09b0d0f

Owen S.

stephen_dewing

Wow Owen.  That's exactly what I want.  Just got to work out how you did it.  Hopefully it is a relatively quick process, as I want to do it to multiple shapes.  Thank you so much.

owen_sparks

Hi Stephen, no problem, it's like that on this forum

You should be able to grab the roll back bar and step through the features in the linked document above to see how it was done.  If it doesn't make sense then please shout.

Cheers, Owen S.

stephen_dewing

Thank you so much.  You are a legend. I think I have worked it out.  Can I trouble you for one last thing? I extruded the middle and hollowed that to form the cutter.  I am now trying to put a concave fillet on top of the rim into the wall of the cutter.  It seems to do a convex fillet on the rim but I want to do a concave fillet on top of the rim if you know what I mean. https://cad.onshape.com/documents/7911a70ce5cdf73827c8d990/w/7ff3e5206ffd618ada34723f/e/22cb13049b00771b754ffceb

In this link, I haven't taken out the bottom and the wall is way to high but it will suffice for this illustration.  You can see what I mean I think.  It added a fillet on top of the rim but it is convex not concave.  Thank you in anticipation.

owen_sparks

Sure thing, ask away.  I'm a bit lost as to which edges we're filleting.  Can you use paint to scribble on a screen grab just so we're all on the same page?

Ta, Owen.

stephen_dewing

 I obviously still have so much to learn.  https://cad.onshape.com/documents/7911a70ce5cdf73827c8d990/w/7ff3e5206ffd618ada34723f/e/22cb13049b00771b754ffceb
I'm still struugling. Wasn't able to colour the parts so just done another part without the fillet.  You will now see the top of the rim/handle of the cutter is flat.  I am trying to put a concave fillet on the top surface of the rim rising up the surface of the cutter blade. This is to strengthen where the cutter wall intersects the rim.  The other problem I have now is I am struggling to protrude the whole of the cutter wall.  At present, as you can see, I have part of the rime protruding into the centre of the cutter. It is meant to be right on the edge.  Hope you understand.  

owen_sparks

OK, lets hit the issues one at a time.

Is this the type of fillet you're after?

If so you need to join the individual parts together before the fillet. (Using the boolean tool.)

Owen S.

stephen_dewing

Yes, that is perfect. So do I select each section of the wall and rim then use the Boolean tool? The cutter wall also need to be .45mm. I tried to hollow it out to that thickness but I'm still struggling to extrude it at that thickness.  I only seemed to be able to extrude the inside of the wall.  Hence the protrusion inside now.

owen_sparks

Not quite.  In your last example you extruded a line which will give a surface.  We want to extrude "sketch regions" to make a solid part.

To boolean two solid parts there is no need to select faces, we just select the parts we want to join together.

To end up with a .45mm thick wall we have a few options.  We can either extrude it solid and then use the shell feature and tell that feature we want a .45mm wall, or just start with something .45mm and extrude it up.

Cheers, Owen S.

stephen_dewing

Hi Owen,  Thanks for your help so far.  Much appreciated.  No hurry, but are you able to give me a link to the diagram you posted above with the fillets, using the boolean tool.  Just don't seem to be able to create the fillet yet I'm sorry.  Thanks.

stephen_dewing

Here is where I am up to so far.  Just still not sure about the fillet.  Thanks.
https://cad.onshape.com/documents/7911a70ce5cdf73827c8d990/w/7ff3e5206ffd618ada34723f/e/22cb13049b00771b754ffceb

owen_sparks

Hi Stephen.

New file here:- https://cad.onshape.com/documents/f5d652a37beab9a608b3691f/v/01e35370794e0924574bc629/e/6687b516bf125553f0084f2c

"Edit 1" is a boolean feature to join all your parts into one.

The other three "Edit" features are different fillet options for you to have a glance through.  You'll need to turn one on at a time.  Just right click on the feature in the tree and select suppress or unsupress to turn them on or off.

BTW there are a bunch of great tutorials in the learning center https://learn.onshape.com/ and the free webinars are an awesome way to dig into the basics.

Happy CADing,

Owen S.

stephen_dewing

Thank you Owen.  That looks fantastic.  Even better, with fillets on the edges as well.  For some reason though the link isn't working.  I keep getting the message   "Failed to load document for version. Resource does not exist, or you do not have permission to access it."  Do you happen yo know why?  
I also wondered if Onshape allows you to make a small program, whereby I could insert any shape with all the dimensions and it automatically extrudes, adds rim and fillets etc?  From what I have read, it seemed that you might be able to, but not 100% sure.  If so I presume there would be tutorials on how to do it.  Thanks again so much for your help.

owen_sparks

Sorry, my bad, I didn't make it public.  Try this link please:- https://cad.onshape.com/documents/f5d652a37beab9a608b3691f/v/e06d0a083fdc2840c1caba98/e/6687b516bf125553f0084f2c

Yes on your second question, the onshape features are open source so can be edited, and there is a language called "featurescript" that allows stuff to vbe written from scratch.  I'd start with the basics though.  FS isn't easy for non-programmers.

Cheers, Owen S.

stephen_dewing

Great. Thank you.  Mmm! Not having any luck with the boolean fillet.  Not sure what I am doing.  Are there any tutorials on it?  I don't seem to be able to find any that are directly related to fillets.  Sorry Owen, I keep bombarding you with questions.

stephen_dewing

I think one of the reasons I can't work it out is because the suppress and suppress is not working on edits 2 and 3.

NeilCooke

Have you tried the learning center?
https://learn.onshape.com/learn/course/fundamentals-part-design-using-part-studios/creating-basic-part-features/fillet-and-chamfer

BTW Boolean is one type of feature and Fillet is another

owen_sparks

stephen_dewing said:

I think one of the reasons I can't work it out is because the suppress and suppress is not working on edits 2 and 3.

At a guess you're looking at "my" document.  If you want to be able to edit ti you need to make a copy of it.  I believe there will be a "make a copy" click-me in the top left-ish part of the screen when you open the link. 

If you'd care to send me a private message with your email address that you signed up to onshape with then I can share my document with you and we can then both work in the same one, rather than making copies all over the place.

O.S.