I know that fillets are pretty darn important cause it helps prevent cracking or stress, but are they necessary in every case? If not, when would it be okay to have 90° angles in an aluminum structure (other than because of predetermined specifications)?
Also, do you have any suggestions if a fillet is creating an interference with another part? Should I try making the fillet smaller, and if that does work, okay to remove fillet?
Can you attach your model?
If you can't apply fillet on every sharp edge / corner, put some chamfer please.
I can't attach a model due to confidentiality reasons, but here is a small snippit of the edges and corners I'm wondering about.
How will this be made & from what material?
Don't forget that it is standard practice for machine shops to have end mills with small radii ground into them - like .010" or .020" (or whatever you need - they get them custom ground). That way it's easy to get an inside radiused corner on a machined feature. If that part is cast or printed, than inside radii are even less of an issue.
The inside radii shown in red below are a concern, and begs the question asked by Evan - how are you making this? I am assuming you know better than to put the outside radii shown in blue in there for strength/fatigue reasons. Also - you started out asking about fillets, but then go into asking about 90deg angles - do you mean sharp corners, or 90deg angles?
Hi Evan and Chris,
I assume the contractor will be using a CNC mill, but I can make sure of that too.
So you're saying DO NOT fillet the blue parts? I'm not familiar with fatigue and strength analysis yet so that's why I'm not sure where or how often to fillet edges. Also, I'm not sure of the difference between sharp edges and 90°; sharp edges as in sharp but not necessarily 90°? Well, I'm pretty sure that everything in my assembly is 90°.
What about the black lines (essentially all the 90°s inside the part; picture below)?
thanks for all your replies
That information helps. The next thing to consider is the function of the part. Will these corners be under a moment force? Shear? Compression? Static? dynamic? That will tell you a lot about whether or not you need to radius your corners.
It would be very easy for a CNC mill to radius the red lines. It wouldnt necessarily add any steps depending on how you dimension your print and what notes you give your contractor. The black lines on the bottom of the large pocket would have a slight radius because of the radius on most end mills as someone mentioned. The black lines at the top of the large pocket and the blue lines would add a step for your contractor if you asked for a radius.
Its hard to say what SHOULD have a radius without knowing the function of the part. My guess (without knowing the function) is that if the part is going to fail it would be at the thin section. That being said if I were to say anything needs a radius it would be in the bottom of that pocket where the thin section meets the thicker sections.
Wether or not a fillet is needed depends on the geometry and load. If a fillet is not possible, an undercut can be a solution.