Hi,
Why won't these edges fillet (highlighted yellow on image)?


MoI file attached.

Hi bisenberger, it's most likely having some difficulty with this juncture area here:




You probably don't want to have this other edge here at all:




It's probably having some problems trying to form a good corner patch in that area while trying at the same time to deal with the presence of that other edge - you probably want that piece to be one single larger surface and not have an edge there and that will simplify the corner condition for filleting.

- Michael

Hi bisenberger, also the scale of the object numerically is pretty small, being less than 1 unit in size, small scale of fillets can sometimes make additional complications so it would not be a bad idea to scale up by say 10 times in size.

- Michael

Hi bisenberger, I've attached an edited version that has that edge removed:



The key to getting rid of that edge is forming this curve as one single segment (used your original segments and then did a Rebuild on it to fuse them into one long single piece):




The attached 3DM file will now fillet ok in these areas here:






However, you've also got another type of thing that is also problematic for filleting which looks like a surface which is very close to being tangent to surrounding ones but possibly off by just a few degrees:



It's going to be difficult for the filleter to deal with things that cross over that edge - for filleting it would probably be better if that was actually a sharp edge instead of trying to build a smooth feature there - if it was sharp then you would include it along with the other edges during the filleting to smooth it out. A lot of times it can actually make things easier on the filleter if you let it smooth out some edges like this rather than trying to build a smooth surface manually there - when the filleter would smooth it out it can actually make it easier for it to form corner patches in the junctures where fillets collide into one another. In this situation it will be more difficult for the filleter to form the corner junctions.

- Michael

Hi Michael,

> also the scale of the object numerically
> is pretty small, being less than 1 unit in size,
> small scale of fillets can sometimes make
> additional complications so it would not be
> a bad idea to scale up by say 10 times in size.

I noticed that too but then I saw the unit measurement was in meters, I thought it would be okay seeing the 0.012m radius is actually 12mm, which is quite an aceptable size for a fillet.
Doesn't MoI take the unit measurment that is being used into consideration when calculating?

-Danny

Hi Danny, no the unit system is just a label, it has no part in general calculations. If the numbers you are dealing with are say 0.012 then that's the actual number that's being used.

Otherwise if it tried to base things only really in mm (which I guess is what you're kind of asking about?) it would not be very feasible to use some kinds of units like kilometers for instance if you wanted to sketch out a racetrack or whatever.

Basically the numbers that you enter are the numbers that are used - if you enter in large numbers then you're using large numbers. If you enter in small numbers that have a lot of decimal places in them, then you're using small numbers. This makes things pretty easy to know what to expect - whatever coordinates or numbers you enter is what gets used, it doesn't get a whole lot more straightforward than that. There is the exception of course of entering in something with specific units attached to it which will then convert it at that point like if you have units in meters you can still type in 5in and it will auto convert it to 0.127 meters and that's the number that is then used in that particular case. But if you just type in plain numbers those are the numbers that you get...

It's generally good to pick a unit system that will let you enter in numbers that are not either too large or too small, more like a range of 1 to 100 or so instead of having features of your model at small numeric values like 0.001 units and also it's not so great to be using large numbers like 500000000 or things like that either.

But if you enter in a fillet radius of 0.001 units, MoI will try to make a 0.001 radius fillet, it doesn't matter what the current unit system is set to for that. There is some stuff in place to try and automatically refine the fitting tolerance downwards to be some fraction of the value being used in an attempt to kind of make small numbers still work ok. But tuning that up is a kind of ongoing process and for best results it just tends to be better to use a bit more "regular' numbers more like 20.2 or 50.22 or 2.2 instead of a lot of 0.001, 0.00025, 0.0006, etc...

- Michael

Thanks for the concise explanation Michael, so what you're saying is that there should be some pre-thought in what units should be used in relation to the scale of the design/model you're going to do.
Most likely why SketchUp has preset environments for the same reason.

~Danny~

Thanks Michael,
Some good explanations here.

The model started out in Rhino. The template I used was small objects meters: Units: Meters Absolute tolerance: .001 m.
What would be the best unit and tolerance setting in Rhino for bringing stuff into MoI?
Bill

Hi Bill,

> What would be the best unit and tolerance setting in Rhino for bringing stuff into MoI?

It depends on the size of the object that you're building - but if your object is going to be less than 1 meter in size it's probably best to use centimeter units for it instead of meters.

- Michael

Hi Michael,
Most of the stuff I build is the size of a building, but usually there are a lot of associated small elements like the one that started this thread.
Thanks for your help.
Bill