Filling 3D prints with filler material

Do you have any experience doing so?

I have a project coming up where I would like to print a large object and fill it with sand and resin.

Sand, as we all know is coarse, rough and irritating and it gets everywhere. So it's good filler material.

Afterwards I want to solidify it by adding resin, hoping that it gets everywhere as well.

What other materials are usable? Perhaps concrete but it can't really dry inside a printed object right?

The infill should be Gyroid with 10% with at least 3 perimeters IMO. Would something like tree infill work as well? Or removable infill? I'm not sure how to get a slicer to do that though.

I intend to build parts for a CNC machine so I value weight and rigidity in this project.

lime 15 points 7 days ago

there's a guy on youtube who has a whole series about filling 3D prints with concrete.

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brown567 2 points 7 days ago

Came here to mention him!

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grue 13 points 7 days ago

Perhaps concrete but it can't really dry inside a printed object right?

Concrete doesn't dry; it hydrates and cures. It can harden underwater, let alone inside a container.

If anything, the potential problem with concrete is that curing is exothermic, so it might heat up and distort your part. It'd have to be a pretty big print for that to happen, though.

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myplacedk 4 points 7 days ago

Concrete doesn't dry; it hydrates and cures.

It does both. Once it's cured, you might want it to dry. Not sure if that's important here though.

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brisk 8 points 7 days ago

Concrete doesn't dry, it cures. It is quite possible to fill 3D prints with it, and it has been done.

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Bluewing 7 points 7 days ago

Clean sand does work. But what you probably want is granite resin for this project. It's very popular with machine tool hobbyists and even expensive manufacturers like Hardinge.

Here is an explanation of how to use the stuff

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Zomg 4 points 7 days ago

Careful of sand. If you use it, don't run the fan until you cap off the void. Otherwise you're going to blow sand all over

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Good4Nuthin 4 points 7 days ago

I’ve used BBs, miscellaneous old nuts/bolts/screws, lead shot. Split shot fishing weights would work as well, if you can source them cheap enough.

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Reven 4 points 7 days ago

I filled a print with pennies, and it worked out better than I expected. They didn’t get everywhere, though, so it might not be what you’re looking for. 🤣

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username_1 6 points 7 days ago

Look that rich guy boasting. Pennies... Shame on you, multiple pennies owner. I bet you stole them!

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Rolive 4 points 7 days ago

I think it's cheaper than using resin haha.

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Schnipp 2 points 7 days ago

Maybe try ball bearings? Might be slightly heavier than a penny and at a given quantity slightly cheaper. Then you can fill it with resin. It might flow better through them than the rough and coarse sand, which gets everywhere.

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Reven 2 points 6 days ago

And ball bearings have the advantage of meeting OPs requirement: they will try to get everywhere.

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Reven 1 point 6 days ago

🤣🤣

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Lampenoel 4 points 6 days ago

I would be careful with resin as filler material, 2 component epoxy for example gets really hot due to the polymerization process (around 70-90°C in some cases) and could deform a PLA shell easily just because of the heat. They also suffer a lot from shrinkage, wich might be problematic too.

Maybe, as already mentioned in this thread, concrete would be a safer bet.

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mcavoya 3 points 6 days ago

I use casting plaster from a local hobby store. A little messy, but easy cleanup with water.

I use the gyroid infill and leave a 25mm hole in the bottom. Slightly over-fill then sand flat after it dries.

Adds a pleasant heft and is super easy to use.

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BrrdShrrmp 2 points 7 days ago

I sometimes fill the bottoms of smallish boats with hot glue to get them to float well.

Pros: Glue spreads easily, fits crevices, and is pretty cheap and easy to use.

Cons: Bit messy, not particularly heavy (though does make the prints feel more solid), bit of a pain to sort out how much glue to use and at what intervals while printing.

Can't say whether glue would be a good fit for CNC machine parts though.

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ExcessShiv 2 points 7 days ago

I have my doubt's that resin would distribute evenly throughout all the sand in the model. I also have some doubt's about the sand, maybe you can shake/vibrate the model so the sand distributes well, but it will probably be hard to get into all the small smaces depending on model shape and how dry the sand is.

Why not just straight resin as filler?

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Rolive 2 points 7 days ago

I thought of that a well. The resin will likely not get everywhere. The idea was saving costs as resin is kinda expensive.

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ExcessShiv 1 point 7 days ago

Sand by itself doesn't add much to rigidity I think, it only adds weight. With only 3 walls and sand you'd probably be lacking in rigidity in the areas without resin.

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ouRKaoS 1 point 6 days ago

I've had good results using table salt to add a bit of weight to a chess set.

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CHOPSTEEQ 1 point 7 days ago

I watched a video a year or two ago about a guy printing a lathe, which he filled with concrete.

It ended up being kinda shit iirc

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brown567 2 points 7 days ago

If you're thinking of the same guy I am, he revisited it with everything he learned from the first one and still uses it for his projects =)

https://youtu.be/6Js8erWbsDQ

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CHOPSTEEQ 1 point 7 days ago

I think that’s it. My original comment probably came off as judgey/rude, any functional machine from scratch is a triumph

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lemmyman 1 point 7 days ago

Ives tried to use resin to fill prints and it ended up leaking all over and making a mess. I'm sure with the right geometry and enough perimeters it can be done, but keeping the walls sealed is an important consideration.

My preferred approach to weighting models is to design in holes for bearing balls and press them in, with optional (and lightly applied) adhesive.

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