A bit of resin alchemy

I’m making an object that snaps together (it’s classified, so I can’t post the pics unfortunately), and has very tight tolerences (it’s got to create an airtight seal with a gasket squished by the pressure of the snap-fit), and has to be easy to take apart and put together repeatedly. A tall order for printed materials.

I’ve been hacking around, trying to get parts that are both very accurate, and also able to handle repeated snapping-unsnapping without fracturing. Clear by far produces the most accurate and detailed parts. Black is not too bad, and the details are easy to see in black, but the consistency just is not right for my application. Along came Tough, so I decided to give it a shot.

Reading here regularly, I could see a pattern of parts failing more than not when using Tough. It’s very thick, and I reasoned that its viscosity was one of the core reasons as to why the failures were happening. I hacked a resin tank heater together, and bought some tough to test my theory. I heated the resin to ~35C, and my first prints came out very nice, although I did notice a little less detail on some small holes in my part, e.g. the holes were undersize by quite a bit, with some almost closed up.

After testing the snap fits, it seemed like the parts were still slowly deforming under load, even after four hours in the lightbox and two hours in direct sunlight. This made the snaps a bit too sloppy for my liking, so I decided to try mixing resins to see if I could improve upon the behavior. I decided to try a simple 50/50 mix by weight of Clear and Tough first. Clear for the detail and low creep, and Tough to help prevent shearing under load.

First test, I heated to 35C, and used the Tough preform material profile. This worked well on the thinner walled parts, but made the thicker parts very brittle. I reasoned this was overcure of the Clear component, because the Tough needed more exposure than the Clear, but honestly, I’m just winging it here… I have a great exposure chart that @JoshK created, but it does not yet have tough or flexible in it, so I’m really not sure where Tough fits in with respect to the chart. My guess is that it’s North of Black somewhere, but that may be incorrect.

Second test, I decided that Black might be a reasonable Preform exposure profile to try next, as it’s a bit more heavy-duty than Clear, and not as heavy-duty as I suspect the Tough profile would be. Again, the resin was heated to 35C. This pretty much nailed it. Really nice layering and the detail is totally back in the small holes. I did do a quick wipe of my main mirror in there too, so that may be having some effect, but I think the Black profile might be the one for a 50/50 Clear/Tough resin mix. It’s still post curing, so this may be a bit premature, but looks great so far.

I’ll keep documenting as I learn…



Thanks for sharing

Can you share your snap fit design or is that part of the secret?

Sounds promising so far.

To continue on, the 50/50 Clear/Tough hybrid mix (which I’m calling Tuff) in conjunction with the tank heater, and printed with the Black material setting is producing the best prints I have ever done to date, and I’ve been using the Form1+ for over a year, every day, and I’m on my third printer… Knocking stoutly on some hard, fiberous plant material :smile:

Here’s a pic of a control stick boot done in Tuff @ 100um. The object has a 0.5mm wall throughout, is fully cured, and can be completely compressed and will spring back to original position, albeit a bit slowly. The point is it does not crack or break, and it keeps it’s dimension much better than Tough. This print was a test, but the finished version of the obejct will be a positive for a silicone mold to be made from. The final part will likely be cast in urethane.


Great work. It sounds like you are taming that printer even better than I did. I read you were thinking of casting it into urethane. I was wondering if you could print a mold, then cast a part from ‘mold making’ silicone?

Thanks @JoshK. I could, but undercuts are a bitch. I was just sitting here pondering, and I’m just about ready to try a 33/33/33 Clear/Tough/Flexible mix and just print the part and use it directly. What do you think about that? I’m using Black profile to print ‘Tuff’, any ideas about what flexible in the mix would want for laser profile?

I never got my hands on tough or flexible, so I’m not sure what the mix would do. As far as laser profile, comparing the estimated print times actually reveals a lot about the power needed to cure it. It seems they use a similar or same brightness, but change the travel speed. It might give you a starting point at least.

1 Like

I dumped the Tuffer mix out of the heated tank and weighed it. Then I weighed in half as much more of flexible to that, stirred it for 5 minutes, and put it back in the tank. Voila! :new:Tufflex-33. I pushed my finished boot to that material @100um/Black/98-105F and wow! I do not need to make a mold now - this will function well.

I used lots of .4mm points, maybe too many actually, and it printed the 0.5mm wall perfectly everywhere. Nice sharp edges and smooth layering. All I had to do after cleanup and two hours in the lightbox was grab the support matrix and rip it off the model in literally one go. It was like velcro meets bubble wrap if that makes any sense… Minimal sanding with an emery board removed the sightly harder bumpies very quickly. It’s practically as good as a cast urethane material, like say a Simpact 60A, but without making the mold! It feels quite a bit stronger and tear resistant than Flexible. I can’t imagine trying to print 0.5mm walls with Flexible.
Plus, the Flexible profile enforces ridiculous point sizes that destroy whatever you’ve printed anyway. If you need anything like this boot that needs to flex repeatedly, not tear when bent over itself, and be very thin, this might be a good starting point in your own experiments.


Awesome! So the final mix is about 50% Flexible, 25% Tough, and 25% Clear printed at 100°F using the printer’s black setting?

Not quite. My description was a bit confusing. I had 125g of Clear/Tough left in the tank @ 50% each. I added half of that weight (62.5g) in flexible, for a total amount of 187.5g. Or, a 33/33/33 percentage mix of each component.

Here’s a quick video of how this Tufflex-33 resin mix looks and behves in action:


Wow, that looks amazing. If that stands the test of time everyone is going to be mixing that! Keep us posted on any property changes and how long they took.

Great work, I especially like the Tufflex-33 name. =] Recovery is a bit slow but overall it looks great.

Getting that thin of a wall to print well is a tall enough task, glad it also has the performance you were hoping for.

It’s funny. It never dawned on me you could mix Form resins with different properties to get new properties. Thanks for sharing and opening my eyes to possibilities. The boot looks great in the video.

It is. The result is more plastic-like than rubbery. It bends well, but it has very little elongation. It feels like it has pretty good tensile strength, but I need this part, so don’t want to find out :wink:

It’s not just mixing resins, there’s colorants out there as well that I have added to clear to get deep colors (albeit only using the resin in it’s liquid state for surfacing some stuff). I have not tried the colorants in the tank yet, as I was afraid they may tint the PDMS too. Before I resurface this tank I’ll try that. Hopefully it will not affect the PDMS, and we can have any color we want just by using the primary color colorants (+ black) at this link. Then, I can make the boot black like I want it to be.

@Formlabs This kind of thing is why we need more knobs and gauges. That, and a bit more transparency on the differences between the hard-coded material profiles in Preform. An expert mode that parameterized everything would seriously be awesome, and would empower the community to get stuff done. This will only help you in the longrun.




Just make us sign a disclaimer and agreement that we won’t come crying to you when we muck everything up. Your printers/software are brilliantly easy to use, but we want to tinker!

Unfortunately there isn’t much value added in spending the time adding these features to the interface. Form2 is launching with open resin mode so this concern is at least on the radar.

1 Like

Update: after a couple of days, the Tufflex-33 has gotten quite stiff. Too stiff really for it’s intended purpose. Recovery was slow, and now it’s r e a l l y s l o w. I’m going to make up and test a batch of Tufflex-50 (50% Tuff, and 50% Flexible) and see how that goes. I may end up having to mold this part after all…

Thanks for the update. So good for prototyping, but not stable. When something is printed in Formlabs Flexible, do you notice a hardening within a few days too?