Put a hole in it (Make your 3D Prints useful)

Many 3D Printed models that we make are pretty useless. Things like logos, name tags, even models of objects like buildings or vehicles or cartoon characters. I've found one little change I can make to most models to make them at least semi-useful.

Put a hole in it!

I've gotten into the habit of adding a loop or a hole in my models so that at least the object can be hung from a backpack, used as a zipper pull or put on a keychain. This is especially meaningful when teaching a beginner or a group of younger students, as it gives beginner 3D printing enthusiasts a way to show off their work and start a conversation about their new hobby ("Yo, what's that plastic bulldog hanging from your backpack?").

The first time I did this was with the first model I ever printed on my printer. I found a great simple set of Minecraft (tm) tools on Thingiverse. They were cool, but very useless. I simply added a keychain hole to the handle of each of the four tools and they definitely became more useful - or at least displayable.

How to do it

There are two simple methods to achieve this.

First, you can actually punch a hole in the model by subtracting a round circle from the main model with a cylinder. This is the best method for the flat models. I've found that about 4mm is the right total diameter to make it easy to get a key ring into the hole - but it also matters how much material you leave around the hole. It seems that 2-3mm is about right to get enough strength with not too much width to get a keyring around the material.
I try to pick a corner of the model for the hole to give more clearance for the keyring. Sometimes you can get lucky and the hole can become a natural part of the model - like in the Twitter bird name tag examples in the post about name tags.

TinkerCad Torus shapes

Second, you can add a small ring of plastic at the edge of your model - which is the most useful method for wide models which are not really flat enough to allow clearance for a keyring. The two shapes which work for this method are the torus - which is a rounded-edged ring, or a flat cylinder with its center removed. Again, you want to have approximately a 3-4mm hole and 2-3mm of material on all sides - so either of these shapes should have a total outside diameter of around 7-10mm depending on how much strength you need and how thick of a keyring you expect to use.

If you use the second method, remember to add the ring (torus or hollow cylinder) to a place which is conducive to successful printing - not floating out on the side of the model which will require supports or just fail to print right.

Doing this in TinkerCad or 123D

In TinkerCad - you're either using the "cylinder hole" object - aligning the hole object with the place you want the hole - or using a torus, which is offered in a few different ways in the Geometric Shapes category.

In Autodesk 123D Design - you've pretty much got the same options - using a Cylinder and subtracting that from the main object to punch the hole, or using a torus and adding it to the model in a position which will let it print successfully

Sometimes, the hole can be part of the model (birds eye)