# Hollow wing for rc plane

I am trying to print a wing for a rc plane with my 3D printer. In order to make the wing as light as possible I need to hollow it (and afterwards put some stable structure there). I've tried the Blender Solidify modifier to do this but without success. The material on the sharp edge on the rear part of the wing gets thinner and thinner although the "Even Thickness" option is checked (see picture). When preparing this for printing, the slicer puts only one line of filament there instead of two. What I need is a brim on the inner side of the stl file with a constant spacing.

I've also tried the Meshmixer Hollow and Extrude modifiers. They both had problems with those sharp edges (see picture).

The third program I've tested was FreeCAD. But it crashed at all :-(

Can someone please help me? I would appreciate any suggestion or other programs which can handle this problem. Remodeling is no option for me as I have even more complex objects to hollow for example the fuselage.

The stl file of the wing can be found here: https://files.fm/u/5futezwj

Thanks so much for your help!

• have you tried simply using a solid STL and then choosing "0% infil" in your slicer? – Trish Oct 30 '18 at 21:46
• This will be very hard to accomplish with FDM printing as you are limited by the nozzle diameter, the slicer is cutting off the parts that your current set up cannot print – Perplexed Dipole Oct 30 '18 at 21:46
• @Trish yes that works but I want to add some stable structure to the hollowed part with two holes for a carbon tube and wires – fuxT Oct 30 '18 at 22:01
• @PerplexedDipole that is no problem for me if the slicer is cutting off a small part from the rear part of the wing. My main concern is to get a constant thickness of the brim. – fuxT Oct 30 '18 at 22:16
• Would you outline your design process, as in which way you took? There are many ways to the same outline, some are easier to do this than others. – Trish Oct 30 '18 at 22:42

I am sorry to inform you, that the answer to "How do I fix the thickness" is "Remodel them" - especially in this case as the whole design is... awkward.

But you don't necessarily need to resign them from scratch, if you can fix it... But beware, fixing does only work sometimes...

First of all, Blender is NOT a good modeling software for designing parts that shall be printed, Blender is a 3D Artist program, not a CAD program. It can serve its course, but it can and will ruin your day. I suggest grabbing Autodesk Fusion 360, since it is mighty and free for small makers.

# Step 1: Transfer into CAD software

For our first step, we want to take the surface of the Wing and export it as an STL. To do this, remove all interior vertices. ALL. Save as a work-project. Look for "BAD" areas - try to have as little vertices as possible. If several are in the same flat area feel free to remove some. The simpler, the better - compare these two pictures - left the bad side, right the good.

Export via File > Export > .stl.

Open Fusion 360 and import via the process outlined here: Insert > Mesh.

Now we need to turn our Mesh into a BRep like described here:

• Deactivate the pickup of model history by right-clicking the project in the left, then "Don't capture design history"
• Modify > Mesh > Mesh tp BRep
• choose your object and OK
• reactivate the model history by right-clicking the project in the left, then "Don't capture design history"

# Step 2: assigning Thickness

We got a surface now... or rather several that are stitched together. We want to give them thickness...

• create > thicken
• click on one area, choose the thickness as a negative value. For example -1 mm
• click on the body's lightbulb to make it visible again
• rinse and repeat for each area not yet thickened
• Hint: rightclick opens a context menu that offers repeat ..., where ... is the last used operation, in this case: thicken. This considerably can speed it up.

# Step 3: Combining thickened parts

Now, we have several thickened parts, all of them intersecting or touching. like, what usually looks like this...

actually is these different parts (which I colored for showing only - it is totally unnecessary!)

It's easy to see these all intersect. And luckily, intersecting parts can be easily merged!

• Modify > Combine
• click one, then another. OK.
• rinse and repeat as much as you can - some pieces will throw an "inconsistent edge-face-relationship" error. If these crop up, you need to start over, fixing the Mesh.

To state it clear after wasting 2 hours on this:

# Your files needs to be done again from scratch.

In a proper CAD modeling software. Because what you have there is not fixable easily.

Don't design your part as hollow. Make it solid. Then put it in the slicer and chose the infill (i recomment cubic pattern in cura) you want. So you have a mainly hollow wing with a nice structure in it.

• Why the negative vote? – Greenonline Nov 2 '18 at 14:22
• @Greenonline maybe tactical downvote. saw this so often, that I have no more desire to even post answers in the future. – Horitsu Nov 3 '18 at 15:13
• I upvoted you. Please don't be discouraged. We all have bad days, sometimes :-) I think that you were downvoted, because instead of a hollow wing, you suggested a clever alternative. I wouldn't have thought that it was a tactical downvote, tbh. – Greenonline Nov 3 '18 at 15:27