How to round off an object

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Olle
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How to round off an object

Post by Olle »

I'm trying to round off the end of an object by using a 2 rail sweep contour, but I cannot make it work properly. The first object was created by doing a two rail sweep, then it was trimmed by "cookie cutting" it with a perimeter vector. Then I did another 2 rail sweep to create the roundover, and used the very same perimeter vector to trim it. For some reason I end up with some garbage around the edges (see pictures). I have also tried to generate a vector boundary around the object, but it got even worse when I used that. It's just a matter of small fragments, and it seems to be caused by a slight misalignment somewhere.

I'm beginning to think that I'm going about this the wrong way, so is there better way to create the roundover?
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Garbage 1.jpg
Garbage 2.jpg

cac67
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Re: How to round off an object

Post by cac67 »

Set the combine mode to merge and add base height to the one you want on top to get rid of the thing sticking up.

Also, look at these pictures. See if you get some ideas.
vectors.png
components1.png
components2.png
With added base height.
With added base height.

Olle
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Re: How to round off an object

Post by Olle »

To make it more clear: I want the edge to be straight, but with a rounded bevel. The operation I want to perform is similar to what you would get when you run a roundover bit along a straight and square edge.

If you look at the picture below, you'll see objects I created (with object 2 moved out so you can see it). The end of object 1 has a square end, and I want to round it off like on object 2. I can "kinda" do this by lining up the right hand edges of the objects, trim 2 to follow the perimeter of 1, then set object 1's combine mode to "merge" and object 2's combine mode to "low". The problem with this is that the outlines of the parts need to match 100%, and the "wedge" you see in the previous picture is simply a piece of object 2 sticking out too far. It's just a sliver, probably no more than a thousand of an inch or so, but enough to screw it up entirely when I run the tool paths.

I'm sure there would be a better way to create the whole thing, but this is kind of an afterthought. I left it square in the model, and the plan was to simply run a bevel bit across the edge and then hand sand the roundover. However, sanding end grain gets kinda old when you have 30-40 pieces to finish. Tool paths and prototypes are done and I'm ready to hit the "run" button, so I'd hate to go back and redo it all.
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cac67
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Re: How to round off an object

Post by cac67 »

Have you considered just hitting it with a smoothing brush? That tends to round the edge down on a vertical. You could also run your sweep the other way. That would give you something like this:
components5.png

Olle
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Re: How to round off an object

Post by Olle »

cac67 wrote:Have you considered just hitting it with a smoothing brush? That tends to round the edge down on a vertical. You could also run your sweep the other way. That would give you something like this:
components5.png
Nope, can't do that. This is the lower edge of a pistol grip, so it needs to have a rounded bottom with sharp, crisp edges. If you know what the grips for 1911 look like, you'll get the idea.

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Re: How to round off an object

Post by cac67 »

I just did a google image search for 1911 grips and most of them either have flat bottoms or beveled, I only saw a few rounded. That being said, if that's what you're working on I think create shape from vectors may be your friend here. Outline the grips, extend the top a little bit so you can chop it off and get that vertical and create a rounded shape with the height limited to whatever thickness a grip is supposed to be. Like below. Note that I'm making no attempt to get the shape right, I'm actually supposed to be making an F16 right now.
components6.png
components7.png

Olle
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Re: How to round off an object

Post by Olle »

I just took 1911 as an example, the ones I'm working on are going to be a reproduction of the grips for Femaru 37M (Hungarian pistol from the WWII period). You don't have much wiggle room when you're making reproductions, they need to be correct or they won't sell. In other words: I can't wing it at all. The overall shape is more complicated than it looks, had to change the curvature and the taper from top to bottom several times and had to make 5-6 prototypes before they fit and looked right, but now they're within less than 5/1000" of the originals. I'm afraid that I will waste a lot of work if I screw up, so whatever I do to them at this point needs to be done in "the least intrusive way possible".

In any case, here's what I'm doing right now: Just a straight run with a bevel bit. Imagine this being cut with a slightly rounded bit instead, and you'll get an idea of what I'm after.
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Img_0847.jpg

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Re: How to round off an object

Post by cac67 »

If I were doing this for a one off I'd probably just chuck up a roundover bit in my cnc machine and use it as an overhead router feeding by hand. If I were doing this for production I'd go ahead and model it using the last technique I suggested, just not in exactly that way. Probably make a dome and cut a sliver off to stick on the end.

Olle
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Re: How to round off an object

Post by Olle »

cac67 wrote:If I were doing this for a one off I'd probably just chuck up a roundover bit in my cnc machine and use it as an overhead router feeding by hand. If I were doing this for production I'd go ahead and model it using the last technique I suggested, just not in exactly that way. Probably make a dome and cut a sliver off to stick on the end.
In this case, it will be more of cutting a piece off the end. It took a while to get the bottom edge to line up perfectly with the bottom of the pistol frame, so I don't want to mess with it. I was thinking about taking a roundover bit and modify it (I have done it in the past by grinding off the bearing end), but a bit with the radius I need would swing awfully close to the fixture I'm using.

I didn't want to redo everything for every prototype I made, I thought it would be easy to fix as a last cosmetic touch and that's why I saved it until now. Hope I can figure out a way to do it, I'm kinda tired of sanding... :mrgreen:

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Re: How to round off an object

Post by dealguy11 »

Olle - Here's one way to do it.

1. Here are the vectors
Gun Grip Vectors.JPG
2. Use a 2-rail sweep to create a component with one end rounded to the radius you want. The thickness of the component is the radius:
Gun Grip Component 1.JPG
3. Use another 2-rail sweep to create a curve for the first component to sit on top of. The height of this component is the overall height of your part minus the thickness of component 1.
Gun Grip Component 2.JPG
4. Place Component 1 on top of Component 2, with a combine mode of "Add". Voila!
Combined components.JPG
Steve Godding
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dealguy11
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Re: How to round off an object

Post by dealguy11 »

If you want your end to look more like the last example you showed, with the bevel, but with a radius instead, here's another approach. I'm going to assume that the radius needs to go to zero on each of the ends.

1. Here are the vectors
Vectors example 2.JPG
2. Here are the components.
a. The first is a flat component ("create shape from vector") with a thickness of the flat base
b. The second is a 2-rail sweep of the main curve on top. Set its combine mode to "Low"
c. The third is a 2-rail sweep of the curve on the end. Be sure to turn on "Scale Cross Sections with Width" for this sweep
Components example 2.JPG
3. Put the second component on top of the third. If they don't look right, you may need to set the combine mode of the third component to "Low"
Combined top component.JPG
4. Bake the second and third components together

5. Put them on top of the flat component.
Combined components v2.JPG
Steve Godding
D&S Artistic Woodworking http://www.dsartisticwood.com

Olle
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Re: How to round off an object

Post by Olle »

Guys,

What you're describing is basically the way I'm doing it, so I guess I'm half way there. Or rather "close, but no cigar".

The wedge you see is a small piece of object 2 sticking out from the side of component 1. You would think that the method would work if I generate a new "cookie cutter" as an outline of object 1, but it won't. The problem seems to be that the alignment is not perfect, and I suspect that the "cookie cutter" I'm using has been distorted just a hair after being copied, split, rejoined etc a few times over. I have all the profiles and rails I used for the sweeps, so I'm beginning to think that I have to start over to get everything aligned correctly.

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dealguy11
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Re: How to round off an object

Post by dealguy11 »

Could be. I have better luck with these kinds of issues when I'm not splitting and trying to rejoin components, because Aspire has to make a decision about where to split the pixels, there often seems to be some issues when you try to rejoin them. Much better to sit one component on top of another and use the combine modes to make them melt into one another.
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Olle
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Re: How to round off an object

Post by Olle »

dealguy11 wrote:Could be. I have better luck with these kinds of issues when I'm not splitting and trying to rejoin components, because Aspire has to make a decision about where to split the pixels, there often seems to be some issues when you try to rejoin them. Much better to sit one component on top of another and use the combine modes to make them melt into one another.
Yeah, after more experimenting I suspect that the problem lies in a slight inaccuracy in the objects. Combining them in different orders seems to make a difference, and baking them between the combine steps appears to change the outcome as well.

I just tried another type of grip panel (a block shape with roundovers around the perimeter) and ran into the very same problem. I tried it 3-4 times, each time in a different sequence, and finally ended up with everything but one corner being clean. I rigged it by shaving 3/1000" off that edge, which made that pesky triangle disappear.

It made me think that it would be very neat if you could make it ignore fragments like that. Is there any way you can get rid of them by changing a setting somewhere, like "ignore object parts smaller than X/1000"? This is one of those situations where you want to reach into the screen and tweak the model with your hands. :evil:

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