Fill in negative space

[rrossenautodesk]

Hi all,

I am having a problem that I recon CAM designers also deal with, so I chose this subforum. Please let me know if I'm in the wrong place.

I am designing a 2-part mold (positive + negative) to 3D print. I am using an existing 3D model to make the mold for. The problem I am having is that I can not have negative space in the positive side of the mold. Or overhangs in 3D-printing terminology.

I recon this is a problem in CAM as well if designing for a 3-axis CNC instead of a 5-axis. What I am looking (hoping) for is a way in F360 to somehow fill up all the negative space in my model. To illustrate this more clearly; Imagine a 4-sided pyramid upside down (i.e. the tip is on the floor) - then I want all the negative space to be filled from object to floor. In this case resulting in a cube, as the top shape of the pyramid is a square. 

Does the question make sense? I have tried to google it quite a bit, but I think I'm either using the wrong terminology or it's to ubiquitous - "negative" + "mold" just yields tons of 2-part mold tutorials.

Kind regards,

Reinier

[engineguy]

@rrossenautodesk 

Hmmm, not 100% on exactly what you are asking for but if it is to create a shape within a solid block then when I do Mold jobs I find that it is usually easiest to turn the original shape upside down (What would be the Core of the MOLD) as you describe your Pyramid and then create a block to the required size and simply subtract the first shape from the block you have created and the shape (MOLD Cavity) will be in the block, here is your inverted Pyramid shape cut out of a cube, if this is what you want to do then it is simply a matter of using the "Combine" facility under the "Modify" tab in MODEL and setting it to "Cut", see image below for the Pyramid example

Fusion file attached

Regards

Rob

[johnswetz1982]

What you are calling negative space or overhang also go by the name undercuts. Generally you cant do molds with undercuts unless you are using cores as well.

[rrossenautodesk]

Hi everyone, Apologies for my late reply. I got caught up in some other things over the week. "undercut" was indeed the term I was lacking. I think I phrased my original question too vaguely. So I know you can not have undercuts, which is the problem I was hoping to solve "quick and easily". Say you have a shape with undercuts in relation to the "bottom" plane of a mold, I was wondering if there was an easy way in Fusion360 to fill / "make solid" the space of the undercut. I have added an example now. So the chin of the skull has a large undercut. I would need that to be solid all the way down to the ground plane. In my mind its something like "extrude all faces with the normal facing down all the way down to the groundplane" but I have no idea of and how I can do that in practise. Thanks again for your fast replies and I'll try to be faster next time, haha. Regards, Reinier

[johnswetz1982]

Without actually seeing your model you probably want you machining boundary set to silhouette. That should give you a projected outline of your features.

[HughesTooling]

This is not a problem for CAM as the cutter will not go into an undercut. To add to your problem you seem to be using a mesh so it's going to be difficult to create\add surfaces to cover the undercut. Don't really have any advice for working with a mesh apart from Fusion's probably not the right program. Fusion has some mesh tools but not a beginner job.

Mark

[johnswetz1982]

Working with a mesh should not be too much of a problem. There are some operations that you cant use, but I managed to make this lion head from a mesh model. It has undercuts too, but was done on a 5 axis machine.

[daniel_lyall]

@johnswetz1982  He is 3D printing it.

@rrossenautodesk  If you can get a solid model it will be a lot easier to do it in fusion.

[johnswetz1982 · Accepted solution]

Try this for a work around. Program the Features like you were going to mill it.

Simulate it. Where you would have an undercut you will have that contour be going down to your lowest level. Right click while in simulation mode and pick save stock. That will give you a new stl file with the undercuts eliminated so you can print.

[rrossenautodesk]

Hi John,

This looks like it will give the outcome I am looking for. I am not familiar with the CAM simulation, but I suppose I just select a toolsize roughly equal/smaller than my printer nozzle with for the proper resolution?

I will accept your answer as the solution for now as it comes as close as I think it gets before (as someone else commented) becoming the wrong tool for the job. Thanks!

Regards,

Reinier

[johnswetz1982]

You can actually use any tool or even make one up that would not exist like a .001 diameter endmill 5 inches long. That will get you the tightest resolution to the model. Since your not actually machining it only simulating it to get the stock for printing.