Mind blown by modeling task. HALP!

Hey all, I have a modeling question that has my mind in a pretzel.

For lack of better modeling means where I’m currently studying abroad, I’m making a final model of this personal items storage box, thing I’ve been designing, out of foam core and paper.

What it is, is pretty irrelevant. What I’m trying to figure out is if I can in fact make this particular edge feature out of a single piece of foam core (for all intents and purposes, out of any flat inelastic material.)

Importantly though, I want the surface to be uninterrupted, as in no actual cuts, just scores and bends, because considering the low-fi material for a final model, I need the execution to be very clean.

It’s a tapering filleted edge.
Here’s a simple image just showing the feature itself:

I know it’s certainly possible to make a tapering fillet with something like foam core, but what I can’t say for sure is if you can do so and out of the same piece then project out two perpendicular planes (in the picture, the top and side faces.)

I’m pressed for time and don’t actually have a suitable material to effectively test it out at the moment, but I’ve been trying to figure it out with some drafting and mind gymnastics.

But I’m getting stuck, and I want to know if the feature and/or my material of choice will work before I go to buy supplies.

Anyone have an idea? Am I completely dumb and over thinking this?

Thank you!


I might have just figured it out in a brain blast and I’ll feel very stupid if it’s as simple as I’m thinking right now, but I’ll still post this just in case!

I generally would never use the words “Foam Core” and “Very clean” in the same sentence. Foam core is great for a fast prototyping material. To get a clean surface will require a lot of bondo, sanding and TLC.

It can definitely be done though. Since your shape is a rectangle, if that model is what you actually want to build then just get a block of yellow foam, cut it down to the correct dimensions, then mark the tangent lines of your radius and start sanding. Once you’ve got it pretty close if you want a good surface finish then cover it with bondo/body filler and start sanding like a mad man to get it smooth.

Personally I never bothered trying to fill or polish up foam core…it’s a great exercise in manual labor, but chances are once you get out of school you’ll have the luxury of CNC machines, model houses, and rapid prototypes.

If you had more money to spend, then you could call local model or machine shops and see how much it would cost to CNC that radius out of a piece of Renn Shape (high density foam). That paints and cleans up much easier but its fairly cheap to machine (compared to plastic or other materials)

Rhino has a feature called unfold (or something like that), that pretty much flattens surfaces - it’s great for creating nets. I would then export it to illustrator, make sure the sides line up with the tapered fillet, and print it. I would then cut foam core according to that net, removing the 2nd layer and foam at the inside of the fillet so that it can be bent.

This can be done with foam-core, I’d just source some of the pale yellow stuff that’s denser, and cuts, sands, and super-glues far better than the blue stuff.

Or, make a hollow form from mount-board or foam-board and skin the top, radius and left side in thin white card, trimming the excess off afterwards.

Simple. :wink:

if you want to do foamcore or a paperstock type of material, I would do what hiower suggested
The command is in the Surface menu and is called:
Unroll developable srf

seems like it would be really simple to do in other materials as well as suggested

If you go to Home Depot and look at the sheet metal ducting aisle, you’ll see some of these, where you have an adapter to go from a square section to a round. You just make radial score lines out from the corner. Doing it in foam core would be tough I think, you need a thin material.

Here you go, took 30 seconds:

There’s definitely an art to making conical bends in sheets. I’ve seen it done on 1/4" steel though!

Guys today I am proud to be part of this helpful forum.

Well done everyone!

(and I can still sit back in my armchair :wink: without bending a finger.(or paper))


Thanks for all the responses!

The image I included was just an example of the edge feature. But in the model it’s applied to is a shell like form not a solid block like that, so doing this out of one of the various modeling foams is not an option, unfortunately. Originally I’d wanted to do some sort of thermoformed acrylic or styrene for most of the parts, but there’s not adequate facilities at my school here to do that properly. Foam core will always be rough around the edges (lol) but I think you can get a dignified outcome if you are diligent and precise. For this particular class project at least, it’s sufficient.

This is roughly the actual thing. All pretty self explanatory except for those tapered fillets!

I think that unroll feature is exactly what i needed though! Looking at the result, it makes sense from some of the drawings I’ve been doing, and confirms my suspicions that there are some very subtle angle deviations with how the planes extend from the fillet that allow everything to remain square once it’s bent to shape.

It’s a strange feeling that for once, the analog approach has proven confusing and complicated, and the 3D modeling software has a simple self explanatory solution just sitting there waiting for someone to tell me about it, hah!

Thanks again all :sunglasses:

What Scott showed is the way to go. You score the foamcore on the ID and you can create a radius. I have done plenty of times making prototypes. And believe it or not, you can make it “very clean”. If I have a chance to go through my archives, I will dig out some examples.

But beware that your front and back edge lengths will be different.

Back vertical + back horizontal > front vertical + radius + front horizontal

You will need to adjust accordingly.