Variable Radius Fillet Problem

[JackJohnson321]

Hi there, I'm having a problem getting the variable radius fillet to work with the component shown in the following picture:

...The edge marked 'A' is 4.085mm in length and the edge marked 'X' is 4.958mm. I would like to make a variable radius fillet cut so that the radius at the corner joining A and B is 4.085mm and the corner joining X and Y is 4.958mm, so that the curved edge runs the whole length of sides A and X respectively. Unfortunately I am unable to do so as I get the following error message when entering the value for the second radius:

 

I can't enter a value higher than 4.3...mm for the second radius without prompting the error message, that's not to say that it won't work at all, just not to the desired length:

Any ideas what could be going wrong, or any alternatives for creating this feature? Thanks.

[TrippyLighting]

The problem is likely this corner. Once the fillet would eliminate it Fusion 360 complains.

[laughingcreek · Accepted solution]

because of the scale you are working at, and the relative large diameter of the object, it's hard for you to see what is happening here.  a few comments and questions-

-line A and X are not straight lines, they are arcs.  so are the measurements of 4.085 and 4.958 the length of the arcs, or the cord length between the end points of the arcs?

-doesn't matter.  The radius for a fillet is computed on a plane that is normal to the edge being filleted.  You wouldn't notice this on the edge of a cube, where everything is 90 degrees to each other.  in your case it does matter.  the radius needed to reach perfectly to the corner is going to be less than the distance between corners, because our edge is at an angle.  the numbers your putting in is causing it to fail because they are to large.

The first half of the screen cast below illustrated this.  I used a tighter radius and large dims so it is easier to see what is going on, but the result is the same.

You could compute what the exact measurements should be by applying some geometry, but it probably isn't worth it.  considering the scale, and the tolerances involved with making such a small object, I think you can get away with a work around similar to the one shown in the second part of the screen cast below.  you wouldn't even necessarily need to delete that small sliver of surface like i did.  Because of the small scale, and the fact that your looking at a hugely magnified version of it on your screen, you should be able to get to within a few .001 mm of the exact solution just by eyeballing.  you have to decide if that is close enough, but not many manufacturing methods are that precise.

also attached is sample file used for figuring out all this.

[laughingcreek]

the forum seems to be screwy right now, I can't do anything with screen casts.  here is a link to the screen cast referenced above-

https://knowledge.autodesk.com/community/screencast/41f85124-46b1-463b-b950-64e20c7c5117

[JackJohnson321]

It didn't occur to me that A and X aren't actually straight lines, I guess the measurement is whatever is taken with the measure tool when you click on an edge. Thanks for the explanation, the method you've shown in the screencast should do the job.