fillet problems

 From:  Michael Gibson
2510.2 In reply to 2510.1 
Hi Armin, I'd recommend scaling your object up by some amount, for instance by a factor of 10.

Currently when you get to small fillet radius values like that (basically less than 0.05), they can get to be too close to the fitting tolerance of 0.001 units, and when the fillet rails and such are calculated to a tolerance close to the fillet surface size itself it can make for sloppy results.

I do have an improvement to this coming for the next v2 beta so that it will automatically reduce the fitting tolerance for the fillet to be a fraction relative to the given radius if necessary, which will handle small fillet radius values much better. But for the moment you need to scale your model up to avoid it.

To scale your object up, select it and then run Transform / Scale, type in 0 <enter> to use 0,0,0 for the scale origin, and then type in 10 <enter> to scale up by 10 times.

When you perform your fillets on the scaled up object, you should see some better edges in there.

However, one of the things that you seem to be asking about is the issue of fillets not necessarily matching up in width where they intersect one another, which is a normal thing that can happen when doing a constant radius rolling ball fillet between several things that meet each other at all different angles.

Usually if you want things to match in such a situation you need to also select the other edges that are going downwards so that a corner patch can be made to make a good blending between the different fillets.

Here is a bit of an exaggerated example to illustrate a bit more. Here I have a block which has surfaces which meet at different angles:



Now if I fillet the entire block (all edges), I get this result:



Notice how the fillets are different widths - that is a normal thing because an arc of the same radius is smaller or longer in size depending on the angle of 2 lines where it meets, here is a little demo of that to make that more clear:



Both of those arcs in yellow there are tangent to the 2 lines, and they are each of the same radius, radius = 5. But you can see that they are of different lengths due to the different angles that they cover - the exact same thing happens with a fillet surface between surfaces that meet at angles as well.

So if I produce a fillet on my block there and only choose to fillet just the top 4 edges instead of all edges, I will get this result:



You can see there the kind of different fillet widths as they run into each other. This one now does not have any corner patches since not all of the edges coming from the corner were filleted.

That is not a bug, that is a normal way that fillets function.

To make fillets meet up more nicely you usually have to incorporate more edges into the filleting process so that there will be a corner patch made as the juncture between the different pieces.

Does that make some more sense for what you are seeing there?

- Michael

EDITED: 24 Mar 2009 by MICHAEL GIBSON