Why can't OnShape generate "oversize" chamfers? (Question/Feature Request)

aidan_fraser

Hi all, sorry if this is a repost/resurrection of an old topic but I couldn't find much discussion about this.

Often I find myself wanting to use a sweep shape or chamfer distance that onshape doesn't accept. It's "too big", it has self-intersections around tight radii and I get an error message about self-intersection.

Another post by an onshape employee on another thread suggested this was to avoid generating bad geometry. I understand that we want to avoid bad geometry, but this isn't a satisfying explanation for me.

I'm trying to understand the rationale for the restriction. There are reasonable cases when a sweep or chamfer intersects itself. Often, increasing the sweep radius, or reducing the size of the sweeping shape can be a good workaround, but often it's an unacceptable compromise.

One common case I find quite a bit is trying to model a routed cut along a curved edge that has some radii/details that are smaller than the routed shape. I think it's a reasonable thing to want to do, because it's easy to imagine and describe the part. And manufacturing it can be really simple with a standard router. 

I accept I may being totally naive here, but it feels like OnShape could accept "oversize" chamfers, at least in some simple cases (e.g. circular radii), since manually modelling these cases usually doesn't require a lot of thought, just lots of clicks and extra planes and sketches.

Thoughts?

Evan_Reese

I think I get what you're asking. If I do, then I think it's not because it's not possible to do, but it's a lot more math and coding to get it to work and the use case is niche or at least not main stream. Of course I could be wrong because I don't do a lot of router work. Perhaps there will eventually be a sweep with a body as an input so you can simulate the exact path of a cutting tool like a bit. I know Solidworks has something like that.

nicholas_radzykewycz

The best way I have found so far to do this is to make use of the slot sketch tool. Create your cut path, then go into the sketch and use the slot command and go down the path. You will then be able to set the diameter of your end mill to whatever you want, when it intersects your slot it will temporarily show an error, but once you click submit on the sketch it will resolve itself and clean up all the unusable sketch regions. Select your entire newly created sketch of intersecting slots, and extrude downwards to your depth of cut.

See Example contrasting the sweep approach with the slot approach:

https://cad.onshape.com/documents/b69d02e2fb6a21f644c95b14/w/9c791d33ceaf0c34a71ebe9d/e/ff94bfe49a468bd29bd3d460

@NeilCooke Any chance we could get skSlot into featurescript? I really want to make a featurescript for this milling function but I don't see the already existing slot command in the sk commands and I'd rather not re-derive the Slot sketch function from first principles if you are willing to give up it's secrets.

NeilCooke

@nicholas_radzykewycz unfortunately, the slot tool is not a FeatureScript function, but a server-side routine that adds all the offsets, arcs, and constraints.

aidan_fraser

A picture tells a thousand words? 

Hopefully this explains what I mean. (Check out the source doc if you like)

aidan_fraser

Hate to resurrect a zombie thread like this, but I continue to run up against this issue. Wondering if anyone, especially staff at Onshape, can weigh in on this definitively. 

This "over-sized chamfer" feature would make OS more expressive, and parameterized models would be more robust (bigger parameter space). Maybe I'm a weirdo? Wouldn't be the first time! But it's hard to imagine this not helping a lot of OS users.

I am pretty naive to the way OS is implemented, but I imagine it's possible to detect intersections in the swept chamfer and internally split the chamfer into two separate chamfer operations. 

Maybe I should try to make a prototype FS feature?