Full Version: Fillets again

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Hello Michael and Anthony

Thank you very much for your comprehensive replies.

I will read the replies in detail this evening and I think I will then be able to get a model that we can use to machine a prop mould from.

I create the blade surefaces with a network surface using two aerofoils, one at the root and one fairly close to the tip and with a wire for the leading and trailing edge.

I think my aerofoil might have been a little crude and rustic at the leading edge, I will get an elipse onto the leading edge.

Burrman is a clever guy, I think he is still around, I bump into him on the Bobcad forum sometimes.

Many Thanks

Barrie

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I went back and tried fixing that model shown in the screencast. I've tried before but didn't have success. I think I found the problem. Basically the model with the airfoils projected onto cylinders will only allow a root fillet radius of .08mm while the model with the airfoils not projected onto cylinders will allow a radius of 1mm. You can actually see where the fillet breaks in some cases. I just kept trying different fillet values. Basically, I tried a lot more values than I did in the past. The thing is, .08mm is really small and undesirable. That's why I never went that low before. This was all done with Rhino 5, but in the past it seemed to work almost exactly like MoI v2 trial. I've been waiting for MoI v4 to come out, so I can switch from Rhino to MoI.

I don't know if MoI behaves the same as Rhino wrt fillets. Rhino will create invalid fillets with no warning. Calculating volume is how I check to see if the operation was actually valid. As mentioned before, with Rhino 5, I have had some models calculate a volume but still have an invalid step file exported. So this whole root fillet thing is a giant pain in the butt.

But the main thing is that you have to experiment with root fillet radius values. You also get limited by the te radius. So it's a lot of trial and error, even if you created good geometry up to this operation. One other thing I've found as far as model quality. When you go to fillet that edge, it should be one curve when you select it. If the model has you selecting multiple edges, chances are it's not going to fillet correctly. I also found the blend edge was no different than the fillet edge.

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Hi Anthony, do you have the model from the screencast posted somewhere?

- Michael

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Hi Michael,

I just made changes to the file to get it to fillet. I can work on it some more so there is a solid prior to filleting. I don't want to hijack this thread though. I'll create a different thread. I was just trying to share what I have learned with doing the same thing the original poster is trying to do. For me, it's been hit and miss with Rhino 5. This is one of the main reasons I want to switch to MoI. I haven't used MoI since the v2 trial. I went with Rhino because it had some features I needed that MoI didn't have. But it looks like MoI v4 will have those features, so I'm looking forward to switching.

I think what goes on is that, for a given geometry, there is an unknown max radius for the rolling ball fillet. So you end up having to manually iterate. It would be very helpful if there was at least some feedback saying that a good fillet can't be created for the specified radius. Instead, Rhino just puts in a bad fillet and corrupts the solid. Ideally, it would be great if the software told you what the max fillet radius is. That would solve the problem completely. Also, if you know why having a seam in the area you want to fillet is a problem, I'd love to know.

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Hello Michael and Anthony

Thanks for your help with the spinner prop project, I have got a result that I think I can forward to tool production with.

I used a blended surface, I trimmed a cut out in the cone to 0.75mm bigger than where the blade joined and then trimmed the blade out by 0.75mm and then blended between the two.

I can see that my modelling skills need refining somewhat going forwards.

Best Regards

Barrie

Image Attachments:
fillet.jpg  fillet_trailing_edge.jpg 

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