I used to make 3d models and it's clear usually where you are asked to make the fillet
but when I make this part (2D) I was confused how to determine fillet areas?
I am not sure that I understand the question...but here goes:
You can add fillets at any point in your process.
In my opinion, then best time to add them is as late in the process as possible, preferably as the last steps (sometimes that is impossible).
I very rarely use sketch fillets in a 2D environment.
Can you attach your *.sldprt file here?
Are you familiar with machined castings?
Every edge on the casting (before machining) that does not have an explicitly dimensioned radius on the drawing will have a R6 fillet (no sharp edges).
After machining some of these fillets will be cut off.
So if you start from a casting point of view - you should be able to figure out the problem from the given information.
determining from the drawing where all the fillets would go you could add 2 more projected views. one to the left and one that shows the depth of the part. There is also a nice little thing that lets you insert a isometric view so that you can get a 3d looking view on your drawing that would help determine what the part should look like when it is finished. Sometimes I would add a note to this view saying to fillet or chamfer all sharp edges with a given dimension..
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