Overhangs - A Christmas Story

So, this story starts around the time I decided to descend into the rabbit hole that is 3D Printing.

I had recently purchased the Adventurer 3, without properly informing the significant other. As everyone should know, this is an epically bad idea.

Luckily for me, M is ultra rational for 3.5 weeks out of every month. The rest of the time she is a normal person, both of whom I am rather fond of, so I'll take it.

Anyway, getting back to M.

In a burst of ultra-rationality, M resolves to get her money's worth from this contraption and into my Google Drive pops a shared folder containing about 50+ models, downloaded so fast, I swear, I could see the Fibre Cable glowing.

One of these models is a countdown to Christmas. No, I am not trying to be political or whatever, it is what it is, ok.

It's a great model, thank you Elproducts, unfortunately I am an “Engineer" therefore nothing quite comes up to my “Standards". Even a Rolls-Royce can have more features and be built better, in my opinion.

With this in mind, I set about completely redrawing the entire model. Why, pray tell, would I do such a thing? Am I a Masochist with a superiority complex? Probably, but that’s not the reason here.

No, no, dear reader, the reason is the most insidious, most devious and most unstoppable force devised by Mother Nature, Gravity.

Gravity will get you in the end. It moves the immovable and will find you, no matter how small, or far away, you may be. It is the bain of the 3D printing world and the source of tears and pain for many, check out OzzyManReviews on YouTube for more.

Anyway getting back to the topic at hand.

Overhangs are unsupported areas of a 3D print. They are closely related to bridges funnily enough, sort of in the same way a Rock Hyrax is related to an Elephant. However, unlike the mighty Hyrax, an overhang can, magically, transform itself into a bridge if it is short enough or supported on both ends.

Yes, yes, yes, cantilever bridges are a thing and can be made from Meccano, if James May is to be believed, but these are not what I am talking about here.

In order to successfully print an overhang, the print head must extrude into free space for a period of time. This does work for short periods, if supported on both ends, ie a bridge, with some droopage expected towards the centers. A pure cantilever is likely to collapse and really ruin your day.

The same is true of bridges, both plastic and concrete. Due to the insidious nature of gravity, any structure must be supported if its internal structure is incapable of supporting its weight in an acceptable manner.

It's why a piece of string does, actually, have a finite length and so does a 3D printed bridge.

So getting back to the model …….

The top edge, cleverly hidden from view, is a long, unsupported bridge which I would classify as an overhang, and will not meet my “Standards" in final print.

Unfortunately, as with most most 3D printing models, the original CAD files were not included. Therefore, in order to correct this, the entire model must be reverse engineered, in the best Chinese tradition, and “improved” with the addition of a chamfer to the top corner, thus generating integral support material for the top edge and ensuring dimensional security for the ages.

For those readers unfamiliar with ridiculous engineering jargon, a brief explanation follows below. I swear people came up with these names after too many down a’the pub.

Anyway, a chamfer is a (typically) 45° flat edge added to, or removed from, a part thus removing a sharp edge. Consider the image below from www.engineering.com:

This should not be confused with a fillet, which is the rounded version, or a bevel which removes an entire face, leaving a knife edge.

See what I mean, only a drunk Aristocratic, Victorian, engineer could have come up with these names.

I digress.

Once chamfers are successfully deployed, every edge, in creation, was filleted and the model exported to the Adventurer, the finished product was spat out about 4 hours later.

It was at this point when I realized I had messed up. The number blocks no longer fitted, without which, this is a Festive sweetie holder.

No matter, have CAD, will Fix.

Later that day, 2 new number blocks, resplendent in red, awaited my approval on the Adventurer's print bed.

Overall, the jobs a good'n.