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…