# Newbie to 3-D printing, looking for critique/help on one of my first models?

This is my first foray into 3-D printing and I would appreciate some insight on if there is any way to make my model design better in any way. After many unsuccessful attempts and wasting a couple hundred dollars trying to replicate and hollow my original hand-made clay design using silicone and resin casting, I am kind of at the end of my rope for patience. I have decided to try out 3-D printing as recommended by a friend as I need the piece to be hollow and clear to translucent, and preferably resin based. However, I am clearly not very familiar with many of the materials that can be used, the methods for printing, and etcetera. I have ordered two test pieces so far, and am waiting to get the results using two types of resin; formlabs clear resin and another that just said clear UV cured resin. However, since I am going to be getting about 8 of these designs, I want to ensure I am using the best type of material for what I need structure and finish wise, as well as cost-wise. I am willing to put time into the sanding and buff and polish of the exterior to give it a nice glossy finish, but the interior needs to be hollow so that it will be lightweight, and also use less material and be cheaper. This piece also needs to be clear to cloudy-translucent as I will be shining a LED through it to give it a glow. Because the interior is glowing, it does not matter to me if the hollow interior is rough on the inside, as that should help diffuse the light, but the exterior I will want to make smooth. If I can’t sand the object due to the printed material, I would like to add a thin layer of clear epoxy if it is chemically possible. The model is not going to be supporting anything and have any pressures on it save for its own weight so structurally, I do not think it will need to much “infill” in the walls at all. I have seen that my model can also be printed in translucent or transparent plastic as well. Any suggestions or recommendation on that or other materials that I may not have considered? Thank you for your assistance, and as a last note, If it helps with your suggestions, I am really trying to get these piece printed less than $20 each, as I’m going to be needing around 24 different pieces. Feel free to modify my model if you have any physical suggestions that would improve it. hornf.stl (18.9 MB) First problem is your STL is not a solid. The bottom has a hole. See attached picture. To 3D print a part you need an STL file that makes a sealed volume. I sealed it up and uploaded it. You can print a hollow solid part by changing the settings on the slicer to zero infill. The part will however have a closed bottom that you will have to cut out. If you do not want to cut it out you will need to create an inner surface offset from the outer surface and then merge that with the bottom edge. Now the bottom edge is not flat and so you will need some support. Also the part needs to be rotated about 45 to 55 degrees to make printing easy. This may cause some bottom surface distortions where the supports attach. Printing at a .3mm layer height print time looks to be maybe 5 hours or so for my printers. Printing with white would give a nice milky white appearance but transmit light well. The PLA can be epoxy coated to give a smooth outer surface, however because the epoxy is crystal clear you will still see the build ridges. Not a bad look but maybe not what you are looking for. You could add some white pigment to the epoxy to make the epoxy milky to kind of hide the build lines. Is each part of your 24 different or just 24 parts of the same design. Also does your$20 price target include finishing?.$20 for just the printed parts might be reasonable leaving all the finishing to you completely finished that would be low depending on what you want. I only have FDM machines. SLS could give you a finished part in a nice tough white milky texture. However I expect they would be more than$20 each. Have you thought of a rotomolded part? I have a roto molder for hollow balls that could make hollow horns however they would need to have the bottom hole cut out. Making a mold though is kind of expensive If you were planning on making a hundred parts it might make sense but if they are all different no way that could be economical.
hornf_solid.stl (3.47 MB)

1 Like

Thanks for taking the time to respond!

First, I did actually *want* the hole in the bottom, as its a hollow cup-like base that narrows at the base of the shaft and the hole should continue up inside of it. Is there a stability reason or something that would require the base to need to be solid? I am okay with dremmeling the bottom off is needed, but I feel like just printing it without the bottom would be easier in general. I was thinking the shape would be similar to am upside down hollow ice cream cone, where the walls are a certain thickness, and the interior is hollow with the “base” being wider and the hole narrowing as it continues up the shaft. I understand that my bottom portion is very wobbly and uneven as well, and that’s not by design, but because of my poor 3-D modeling skills honestly. I originally was trying to build up the horn shape from the base shape I’ve attached that was originally made using another program that was a lot more even. I tried to warp the shaft portion from that base shape as I needed the width dimensions at the bottom to be about even.

This specific model I am only going to be needing 8 of actually. The attached portion however, I will be having 8 of, and then 8 of a similar model to the attached model, but slightly bigger. So far, I have been able to find someone that was able to make me a test print of the model I originally made, and his images are looking fairly great save for a few defects due to support portions. I think it may have a filled in base like your model suggestion, which again I can hopefully just dremmel out, but I won’t be for sure until I receive the piece. This was printed using UV curing resin, and seems to have come out fairly translucent as well, and he’s recommended I can paint them with a UV curable gel as I need them to actually be different solid colors at the end of my project.

I have never actually heard of a roto molder at all, so I’m not actually clear on what you mean by that at all.

Thank you for your insight on the printing techniques!
tinker1.obj (66.5 KB)

It’s possible to print with a hole in the bottom however the STL file is just a surface with no thickness. See the HornSection.jpg picture. You need to have both an inner and outer surface to establish a thickness.Like shown in the HornSectionWithThickness.jpg picture. This can be easy or hard to do depending on the software and the way the model was built in the software. In the slicer program the part can be printed without infill. The sections will be made hollow with a specified wall thickness however it needs a closed volume to work. Could your part work if it had a uniform wall and perfectly flat bottom like in the attached picture?

A rotomolder is a machine that rotates a mold in all axes to continually coat the inside of the mold with the plastic resin.

You need a mold of the outside shape of the part. Pour a small amount of resin in the mold close the mold and turn it on. Two part polyurethane is a common resin. The mold rotates and the resin clings to the inside and constantly coates it while it cures. Once it is hard open the mold and you have your part. https://www.youtube.com/watch?v=yzxlBrcn2Fg Most commercial stuff is done with metal molds. I use silicon molds on mine.

My machine is more like this.