Its magic. Pure magic…
3D Printing is the Best Kind of Printing
I find 3D printing to be a very satisfying way of producing parts. Okay, its not fast. Okay, its not very precise. Okay, it is finnicy, prone to faliure, and usually has more reasons not to work than it does to work. Yes. But its cool. Very cool. And has a unique feature that other methods of fabrication do not! It allows one to manufacture impossible geometry! (Albeit by making it possible, its not really impossible anymore…) Anyways! That is exactly what we are going to do here. Print an object that would otherwise be impossible to manufacture.
The Object, and its impossibility
The object in question, is very simple. It consists of a hex nut which rotates, trapped inside a bolt, that is capped at both ends. The impossibility being, how did the nut get there? The bolt is capped and formed of one solid part, so how did the nut make it into the screw?
Its a trick question of course. The nut never made it there. It was created there. Using the wonders of 3D printing, we can create the nut and bolt simultaneously, with both already in place!
The object was obtained from Thingiverse, at the following link:
https://www.thingiverse.com/thing:4193497
Below is a picture of what the model looks like, from the object page:
Printing Methods are not Created Equal
As per the requirements, I selected two distinct printing methods, on two respective machines:
- FDM (Fused Deposition Modelling) – On a Prusa i3 Mk3
- Stereolithography – On a FormLabs Form 3
FDM is your standard classic “ol’ reliable” method of printing, via deposition of fused plastic filament. Each layer is deposited on top of the last one. Stereolithography on the other hand is magic. Thats it. Just magic. Okay, actually, it is a method of printing that consists of hardening a liquid resin using a laser. Each layer is hardened onto the part via the laser, and slowly pulled from the pool of liquid resin.
FDM
This process was very straightforward. No problems whatsoever. The original model was scaled down a little to fit inside the capsules, and one test print was made, in bright orange PLA. Once that was finished, and I confirmed that it worked as intended and fit inside the capsule, I printed the other three copies, also in orange PLA. Again, no problems, and no issues. Sometimes it behaves, I guess…
The end result is shown below:
Stereolithography – Liquid Magic
This one took a bit more pre-processing, since I had to manually create the support structure, but it did not take too long. I printed the same exact model on the liquid resin machine, using the resin it had installed at the moment, called “Tough V5” with a teal-aqua kind of color. Watching the print complete slowly was pretty amazing. Its like an object was being pulled out of a pool of liquid, and forming magically as it was pulled. I’m telling you, its magic.
The print completed successfully, and by the time I got back to the OEDK, a lab tech had already washed it, and cured it. I took off all of the supporting material, and filed the stubs, and tested it. The nut was not moving. It seems the nut was slightly fused to the screw. I tried applying precise, surgical forces (Whacked it with a piece of wood pretty hard) to see if the nut would come loose, but it did not.
Undeterred I tried several other things. I tried printing it upside down. Printing it tilted. I tried editing the model to make the inner screw a bit smaller. Tried making the nut a bit bigger. And every time, the nut would not turn. Upon more destructive inspection of these failed prints, I discovered that even though the rest of the model was washing and curing properly, the spaces between the threads of the nut, and the threads of the screw were not. Liquid resin still remained there despite washing, and when that resin partially cured, it stuck both parts together, binding them into one.
Despite my best efforts, I was unable to figure out a way to wash that tight space, or to prevent it from hardening and binding both parts.
On the bright side though, the translucent properties of the resin make for some very interesting light effects!
Cost of Production
Material cost:
Thanks to the wonders of digital software, its really easy to get a measurement of how much material these parts required.
According to 3DPrinterOs, used for the FDM machines, each screw required 6.25g of filament. Which amounts to 0.13$.
According to PreForm, used for the Stereolithography machines, each screw required 7ml of liquid resin, Tough V5, which amounts to 1.23$ (Significantly more expensive than FDM)
4 copies of the FDM screw, and one copy of the stereolithography screw therefore amount to: 1.75$
Tool time cost:
Each screw took 1hr on the FDM machine, and 2.5hrs on the stereolithography machine.
Most eastimates place $/hr at around 5$/hr. Which for 6.5hrs, adds up to 32.50$
LabouR Hours cost:
The average pay for a workshop worker (similar conditions to the OEDK, not a factory) seems to be 25$/hr
Between setting up each print, staying to watch the first layer, and post processing the stereolithography part, I only had to be there for about 2hrs.
This brings labor cost to 50$
TOTAL:
All five screws together thus add to: 84.25$
This sounds very expensive, compared to what the material is actually worth! In this case, the material was only 2% of the total cost!
