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Hack Chat Transcript, Part 2

A event log for Resin Printing Hack Chat

Do you do the goo?

Dan MaloneyDan Maloney 10/13/2021 at 20:110 Comments

anfractuosity12:19 PM
Is the minimum layer height you can achieve dependent on the resin used (i assume different resins may be more sensitive to the UV light?) along with the stepper motor?

Andrew Sink12:19 PM
Absolutely!

Andrew Sink12:19 PM
That's a great question, with a LOT of variables

Andrew Sink12:19 PM
I use car analogies a lot, so hopefully this makes sense!

SimonAllen12:19 PM
What entry level machine would recommend?

Andrew Sink12:20 PM
But it's sort of like asking "What's the fastest you can go?"

Grant - 3D Musketeers12:20 PM
One of my biggest hurdles and one that is not taken into consideration enough is how toxic resin is for not only humans but the environment @Andrew Sink But with proper precautions and making sure everything is cured, it can work out well and safely

Andrew Sink12:20 PM
It depends on the car, how many people are in it, what road you're driving on, etc!

Dan Maloney12:20 PM
I think my obstacle to adopting MSLA is the mess, but we've already seen that can be managed. I guess the odor might be next -- I have a small shop, can't really ventilate it well.

Andrew Sink12:20 PM
But basically, with layer heights, a widely accepted standard is 50 microns (.05mm)

Andrew Sink12:21 PM
An interesting fact is you can print a thicker layer using a translucent resin, as the UV light is able to penetrate deeper through the resin itself!

Andrew Sink12:21 PM
Using a thick opaque resin, this would be more of a challenge!

Thomas Shaddack12:21 PM
The Lambert-Beer law.

Andrew Sink12:21 PM
@SimonAllen, I'm VERY partial to the Elegoo Mars 2 Pro

Andrew Sink12:21 PM
It's inexpensive, and it provides reliable results

Grant - 3D Musketeers12:21 PM
same^^

David Geller12:22 PM
@Dan Maloney I haven't found the odor to be too bad. In fact, I print in my office, which is a room in my apartment.

Andrew Sink12:22 PM
It's also heavy enough to not worry about tipping over, and it's a popular-enough model that there is a large user base online to bounce ideas off of!

controlmypad12:22 PM
Since SLA printers have a smaller build volume than Filament printers, is there a way to fuse smaller SLA prints together into a larger piece?

Andrew Sink12:22 PM
@controlmypad, GREAT question!

Nicolas Tremblay12:22 PM
I have the Mars Pro and it's great with the seperate air purifier.

Andrew Sink12:22 PM
There are MANY options for fusing parts, the easiest is by creating models as an assembly (think dovetail joint) to assemble after printing

alexkollen.edu12:23 PM
@Dan Maloney a god carbon filter and HEPA filter goes a long ways.

Thomas Shaddack12:23 PM
Assemble together with mating surfaces wetted with the printing resin, before the final curing.

RichardCollins12:23 PM
The material used for 3D printing is not as important or critical to learning this, as the basic 3D design and compiler (to convert to instructions. Cost and time management, knowing the market or need, having a good application that helps people or groups. On Mars and the moon, they will use molten materials, electrochemical and plasma separation, and the tools will start with "3D". The chemistry, physics of materials will be critical to making things that last. Keep in mind the needs of the rest of the century for reliable tools and methods for other worlds.

Andrew Sink12:23 PM
You can also add a bit of UV-curable resin and cure it with a UV light to permanently bond two parts

Andrew Sink12:23 PM
Great question, @controlmypad!

Andrew Sink12:24 PM
I agree with @Nicolas Tremblay, the built-in air filter on the Mars 2 Pro is another great feature!

Thomas Shaddack12:24 PM
When we do the gluing-together-with-resin step before the final curing, we have a lot of unreacted acrylate groups left on the surface and we can achieve higher bonding strength.

Brian McEvoy12:24 PM
I made a UV laser holder for tacking parts together.

http://www.24hourengineer.com/2021/04/2021-04-05-m-uvlasermodule-completed.html

Andrew Sink12:24 PM
I used a tower fan put on its side, and open my window just enough to lay it sideways!

Andrew Sink12:24 PM
This blows air outside, while another window allows air inside the room

borelli.g9212:24 PM
hello, is there any real cleaning liquid alternative to IPA? :)

Andrew Sink12:24 PM
It's basically a VERY low-tech air exchange system!

Andrew Sink12:24 PM
@borelli.g92, that's another great question!

controlmypad12:24 PM
Thank you, it sounds like it could fuse nearly seamlessly and also work for clear prints?

David Geller12:25 PM
Negative pressure ventilation works well. Stick a fan in the window blowing out.

Andrew Sink12:25 PM
I haven't used it, but I've seen Simple Green used to clean parts

Andrew Sink12:25 PM
It's a solvent that should break down the resin, but it's something I haven't personally tried

Thomas Shaddack12:25 PM
I disabled the chamber fan, and just leave it form saturated vapors. Limits the total amount of evaporated material, if the vapor pressure at the printing temperature is sufficiently low, which is easily the case with the big-molecule reactive diluents. (The oligomers don't contribute to the vapor pressure, nor the photoinitiators.)

Andrew Sink12:26 PM
IPA is definitely not something you want to be careless with, but it works great for cleaning parts!

Andrew Sink12:26 PM
@David Geller, great point!

Andrew Sink12:26 PM
@controlmypad, yes, you can use the resin to fuse parts together! However, if there is any resin that is uncured, it will be visible through the clear surface

borelli.g9212:26 PM
@Andrew Sink yes. that's right. A friend of mine who is a chemist suggested me to find the right dilution of acetone. That should work as well. Any feedback on that? :)

Andrew Sink12:27 PM
Making *fully* clear parts that are made from multiple pieces is difficult, and at a certain point, it becomes more attractive to move to a casting process

Andrew Sink12:27 PM
@borelli.g92, I don't know that I would use Acetone

Thomas Shaddack12:27 PM
Note on side. The curing reaction is fairly exothermic. I spilled a little bit of the resin on myself, wanted to peel the drop off instead of smearing it with a tissue, and lit it with UV LED. OUCH. Got a nice drop-shaped blister (and scar).

Andrew Sink12:28 PM
@Thomas Shaddack is correct, you don't want to spill the resin on yourself!

Grant - 3D Musketeers12:28 PM
NOPE!

Andrew Sink12:28 PM
I saw a picture of someone who spilled the resin on their leg before walking outside; once the sun cured the resin it led to a particularly nasty burn

anfractuosity12:28 PM
eek, didn't realise it was that dangerous. are the fumes bad too then?

Andrew Sink12:29 PM
@anfractuosity: the short answer is: "It depends"

Andrew Sink12:29 PM
Some people are very sensitive to the smell of UV-curable resin, and some aren't

anfractuosity12:29 PM
ahh

Andrew Sink12:29 PM
If you've ever been to a nail salon, a UV printer smells almost exactly the same

Andrew Sink12:29 PM
In fact, the same principles used to create a resin 3D printed part are used to make UV-curable acrylic nails!

Andrew Sink12:30 PM
They even use the same wavelength UV LEDs that we do!

Thomas Shaddack12:30 PM
It's relatively harmless, the oligomers are big molecules that won't get through skin, the reactive diluents are the biggest concern (they can be nasty irritants and some people can get allergic to them, but there are some that are fairly good - I chose the one for my mix that didn't make my skin feel itchy after exposure, it has one of the lowest irritation indexes).

RichardCollins12:30 PM
Thanks. I have been working since 2 am and have to get back to it. Best to everyone.

Andrew Sink12:30 PM
These are all really great questions!

Andrew Sink12:30 PM
Bye @RichardCollins, thanks for stopping in!

Andrew Sink12:31 PM
Ok, so, let's talk about washing / curing!

borelli.g9212:31 PM

Thomas Shaddack12:31 PM
for postcuring, one nasty thing to deal with is the oxygen inhibition. The presence of oxygen interferes with the radical polymerization. Major issue with printing inks.

borelli.g9212:31 PM
Another nice usage of UV-based 3d printers is to make PCBs.

Have you ever tried?

Andrew Sink12:32 PM

Andrew Sink12:32 PM
Here's an example of a resin 3D printer, next to a Wash / Cure station!

Andrew Sink12:32 PM
This station has two functions: 1) wash the part, 2) cure the part!

Andrew Sink12:32 PM

Dan Maloney12:32 PM
Looks like the washing step generates a far amount of waste. What's the best practice for disposing of that?

Andrew Sink12:33 PM
After printing, the part is washed in IPA to rinse any excess resin off. Printing models hollow is a great way to reduce material usage as well as minimize the wear and tear on the part!

Dan Maloney12:33 PM
*fair amount

Andrew Sink12:33 PM
Great question @Dan Maloney!

Andrew Sink12:33 PM
It actually generates *FAR* less than you may think

borelli.g9212:33 PM
You can use IPA multiple times

Andrew Sink12:33 PM
The IPA is heavily reusable

Andrew Sink12:33 PM
So, for instance

Andrew Sink12:33 PM
I filled this wash station with 3 liters of IPA, several months ago

alexkollen.edu12:33 PM
What is your experience with dunk tanks, vs agitated tanks (with magnet string), vs ultrasonic cleaning?

Andrew Sink12:33 PM
and it is still potent enough to remove the material from parts!

Andrew Sink12:34 PM

KC2FRH12:34 PM
@Andrew Sink - That's the same cure station I have. It's been the difference between me using my mars elegoo, and not. The cleanup was just not fun. I've had the same experience with my IPA, and have not replaced it yet.

Andrew Sink12:34 PM
It does this by inducing cavitation (making little bubbles) and actively rinsing the parts!

Thomas Shaddack12:34 PM
My favorite is ultrasound. Improvised setup with eyeglasses cleaner with water, and in it a beaker with alcohol.

Andrew Sink12:34 PM
This way, instead of just soaking, the uncured resin is actively removed!

Andrew Sink12:34 PM

Andrew Sink12:34 PM
Once the part has been washed off, it can then be cured after the support has been removed!

Andrew Sink12:35 PM
The UV lights in the chamber will fully polymerize the part, turning it into a completed model!

Andrew Sink12:35 PM
From there, you can paint, sand, post-process to your hearts desire!

Andrew Sink12:35 PM
An interesting note, once the part has been fully cured, it will be significantly stiffer (and more brittle) than it's previous semi-cured state

Andrew Sink12:36 PM
If you take a part pre-curing and tap it on a desk, you will hear a "thunk"

Andrew Sink12:36 PM
a post-cured part will make a "click"

Dan Maloney12:36 PM
Are there any dimensional changes after curing? Shrinkage perhaps?

Thomas Shaddack12:36 PM
Indeed. So some operations (thread-cutting, removing of supports...) can be better done on only briefly surface-cured part.

Andrew Sink12:36 PM

Involute12:36 PM
Any rules for determining how long to cure?

Andrew Sink12:36 PM
Great question, @Dan Maloney !

Andrew Sink12:37 PM
Dimensional change is a really hard subject to tackle, as the number of variables (including the geometry and features of the object) can influence the final part size

Andrew Sink12:37 PM
I rarely have parts that don't mate up, so I've never spent a lot of time chasing down the tolerance post-cure

Andrew Sink12:38 PM
@Involute, Not really, but it's worth noting that curing does generate heat in the part

Dan Maloney12:38 PM
So for practical purposes, not an issue.

Andrew Sink12:38 PM
So I'll typically cure for 1 minute

Andrew Sink12:38 PM
then let it sit for several minutes

Andrew Sink12:38 PM
then cure for one more minute

Dan Maloney12:38 PM
And to be fair, FDM prints have some dimensional issues too, after they cool.

Andrew Sink12:38 PM
That's true!

Andrew Sink12:38 PM
So, practically, again, the answer is "It depends"

Andrew Sink12:39 PM
It's such an unsatisfying answer!

Andrew Sink12:39 PM
Trust me, I know!

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