Need advice on strength of material for snap fit

I am having trouble designing a snap fit with the clear resin. Any advice? Anything I can do to strengthen it? Right now its 4mm at the base in thickness and tapers down to 2mm at the top. I’ve tried much thinner without success also.

Are any resins stronger than the others? I’m using clear (version 1))
What about affect of resolution on stregnth. I usually print at 0.1mm. (i.e. does curing more layers add strength or just add more points for the part to fail)

What about post-curing. It sees to become too brittle with any post-curing and any flex causes it to break off at the base.

All SLA resins are brittle.
That’s simply the nature of the beast.

Some (by other brands) are marketed as usable for load-bearing parts, and they are slightly less brittle, but even then - they are way more brittle than FDM thermoplastics. Even the flexible resins are brittle - they break easily if you stretch them (although they are compressible).

Yes, they are more brittle than I expected. However, formulas notes material properties such as tensile stress and stiffness that are greater than injected molded ABS. This can be found under tech specs.

There tech specs refer to 50 um and (green parts?).
It seems to me they are more brittle with increased curing???

Is there any difference between the different resins in regards to stregnth?

High tensile strength is quite probably not what you need (judging by the application) and neither is stiffness. Your application requires the exact opposite - low stiffness and high shear strength.

Yes, curing makes things worse, as does further exposure to UV.

For all intents and purposes, methyl methacrylate is pretty similar to cyanoacrylate (and other acrylates for that matter), as far as physical properties are concerned. While it’s nominally a thermoplastic, it behaves as most other “resins” do.

No clue about differences in resins, i imagine they aren’t that different (apart from castable and flexible) and differ only in pigment and activator.

your prototype parts will necessarily be of a different geometry if the material types are different. you need to reduce the flex of the arm there, by what looks like reducing the undercut - like in half probably.

– OR –

make a mold of it, and cast one in a more appropriate material.


They are right, the resin is no good making decisions like this if you intend to use injection molding for the final part. The best advice would be to probably print it, and use your imagination while playing with the parts. But actually assembly will probably break it. The next revolution in 3D technology will be in practical materials, but that’s not today.
One risky idea you can try is to lower the exposure of the part. It should at least allow you to snap the assembly together without breaking it. It does work, but if you go too low the parts are just jelly. If you want to try this, choose a resin color setting that is lower power than the correct setting:

I see that maker juice has SF resin for the form1 and made solid has Vorex. Both state they have good flexural properties which would be good for snap fit while remaining tough. What about formlabs flexible resin, I just imagine the flexible resin by form labs is probably to flexible for functional mechanical parts.

The flexible resin is not all that flexible. Like a hard rubber. “Superball” rubber but not as high a durometer. It’s shear strength in tension appears to be fairly poor (it parts easily if bent), but it tolerates a lot of compression without a problem. I’ve only done a few test prints, but am getting ready to try a part that needs some structural rigidity, has to hold a shape.

I’ve used both grey and clear, and both are pretty stiff and brittle. Not sure if one is better than the other. For parts that need to tolerate mechanical shocks or bending moments, particularly larger parts that have to take a higher load, I’m still printing with ABS.

Not the best metaphor, but the Form1 prints need to be treated more like glass where my MakerBot prints can be handled more like they’re plastic (which of course they are).

1 Like

Yep, FFF is good material and SLA is good quality, and that’s the wall 3D printing technology seems to have hit and stopped at.