Blending artifacts question

I set up a flat vertical surface that forms a u-shape to be blended with a flat horizontal surface. (See pix.) I made a two rail sweep were the lower rail was modified to pass through the quadrants of the desired profile curves so that when I used the tangent blend option I could apply the same adjustment to all three sides and the added shapes at the corners. This seems to give a fairly clean surface but I get some little anomaly. When I turn on points to inspect the surface there’s always a few points that seem out of place - not where they’re expected to be. (144.9 KB)

Hi! You can try to run RemoveMultiKnot on your blend to see if it helps. I don’t know exactly how you built the upper surface, but I am sure this kind of input is likely to cause you trouble:

Yeah, that section and the other corner are a conundrum as in order to get them online vertically with the upper rail I have to use the pull function and it creates a lot of points. If I clean them up it seems the line goes out of alignment with the upper rail. If there’s any misalignment whatsoever then I can’t get a the simple surface I need to blend with. I’ve tried selecting a row of points with the UV selection tool and doing a smoothing to them but that’s not quite getting it either.

SetPt may be a better tool than Pull to use for aligning the section. It can be used on an object or on selected control points.

How many hours have you spent over how many weeks on trying to model this not very complicated object? Perhaps it is time for a complete restart, starting with the creation of a simple set of curves which satisfy the desired continuity conditions and have zero alignment issues…

You seem to assume that this is the only project I’ve been involved with. Not so. I’m watching and completing tutorials online with Lynda as well as things I find on the web. Thanks for your help and encouragement!


Rhino is likely performing the blend properly based upon your input. Rhino is simply displaying the results of the tiny variations of your input geometry. Try to be very deliberate and balanced in your use of control points, having an abundance of control points is not the way to go about it and will typically leave you with inflexible and very difficult/impossible to control surfaces like you see here.

Are you working from an image reference? If so I would recommend scrapping the model and starting from square one, concentrating on creating and aligning your curves keeping in mind to create them with just enough control points to define the surfaces, no more. One thing that helps me is to create and align my lines and curves first before thinking about surfacing anything. You cannot make those surfaces work if your input curves aren’t proper. Your input curves are less than ideal so you will not be able to get your surfaces to behave.

I take the images I’m using don’t export with the file. I know there’s a way to imbed them. Maybe I’ll include them to make what I’m trying to accomplish more clear. I want to reproduce the object as closely as possible to the original and this is why I’m wrestling with this model. I could make do with what Rhino puts out easily but I want to be able to meet future demands of clients.

I’m trying to blend cleanly three and four different radius edges and the bottom must match the top which has a different set of radius edges that must be blended. I’ve been editing control points and its then I’m noticing a lack of regularity in the placement such that I have to set points with the gumball.

Would you be interested in a file with the images included?

Hello JKayten,

Sure, I’d be interested in taking a look at it. I’ve found that there is often more than one way to model an item and sometimes it’s good to rethink the model if you start to encounter progressively larger issues within the process. Is this an Argus camera?

Okay, I’ve made a new copy with the images included. (I think). I also included radius specs for quick reference. The lines are the actual dimensions of the camera that I want to match. I’ve been through at least three different approaches to this task, all of which are sound, but I’ve not been able to get the smooth zebra I want. What I’ve found dismaying is that even when pulling the edge of a curved surface along parallel rails the resulting surface doesn’t match it’s original edge.

I also have an ongoing issue with unwanted multiples of curves being generated. I think it might be a logitech thing - I’m using a performance mouse, or it’s some errant setting I’ve made. I used a standard template to make this copy to avoid any unnecessary problems. (1.2 MB)

Hello JKayten,

The first thing I’d investigate is how this camera fits together physically. Do you have the actual camera in your possession? I managed to find some additional reference images that seem to indicate that the camera itself was put together differently that you’re trying to model it. I suspect this modeling project will get much easier if you examine some additional images, e.g. model the back/bottom of that camera separately, it isn’t a contiguous surface between the back and sides.

Unless you are reimagining the camera it also looks like you won’t have to deal with much over G1 on this model, there are visible seams present throughout. I think some of the issues you’re experiencing are simply because you’re trying to model and hold continuity on surfaces that aren’t present in the physical camera itself.

Green Mountain Camera has some good pictures of an Argus 75 that clarify this. Now that I am able to see the reference I would go about modeling this item as it was manufactured, not as a monolithic block. I should have some time over the next few days to figure out exactly how I might go about this. Thanks for the additional info.

I actually have one of these cameras and that’s why I think its a great learning project as it involves a variety of modeling tasks. The photos of it were taken with an iPhone so the images are a bit distorted. The model I sent you does have the viewfinder and top portion of the body modeled to a nominal degrees of accuracy. I’ll look up green mountain camera and have a look. In any case the measurements were taken from the actual camera. The model I have opens in the back with an L-shape cover that’s hinged at the bottom.

Yep, that’s the one