Tough resin constant load application

I notice Formlabs explicitly recommends against using Tough resin for parts which will be under constant load.

My question: Why is that?

e.g. Will the part deform over time even under small constant loads?

My scenario:

I’m printing a replacement part for my articulating keyboard arm. I don’t know how much force it’s under, but the old one is made from ABS plastic and snapped after ~10 years of use. I suspect the plastic got more brittle as it aged, and even though I reinforced the vulnerable portions when designing the replacement, I’m wary the standard materials may be too brittle for the task.

The tray is quite large; it’s a custom piece of veneered MDF (or similar) material, and together with the keyboard, mice, my arms when I’m tired, etc. will hold let’s say up to 15-20 lbs. Due to the angles and force moments the strain in the part is more than it would be just holding that weight straight up, although it will have some metal reinforcement pieces (inherited from the original part) to help.

It’s not a big deal if it the part bends / stretches a little over time, as long as that eventually stops and I don’t have to constantly readjust it for years. Is there a point in time where deformation due to constant load will eventually “peak” or balance out and it will stop deforming any further?

Are there other considerations I’ve missed?

I’ve also considered mixing in some Standard resin with Tough, like these guys have done, to get something that’s got a bit more stiffness than Tough but isn’t as brittle as Standard.

Tough Resin was recently re-formulated to have much lower deformation than previous versions. Given sufficiently low load, there should be very little deformation especially if you’re reinforcing the part with metal beams. The Young’s Modulus (stiffness) of Tough V3 is actually very similar to that of our Standard Resins so “a bit of resin alchemy” shouldn’t be necessary :wink:

Ah, so you’re now mixing clear and tough and calling it v3 :slight_smile:
Cool. Glad I could help :slight_smile:

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They didn’t copy your formula… Yours is much easier to remove from the build platform and they added turquoise dye that turns green when post cured…

To simulate ABS Smooth-On has Task21 Urethane you may want to check out. You will have to print a part, make a mold and cast duplicates.

I use the Clear resin for pretty much most of my mold making and wasn’t all that impressed with the tough for my applications. I found in general the printed parts tend to lose memory, some quicker than others.