[Doxin]

> without being injection-molded with an extremely durable plastic, it will not make good strike.

I wonder how true that actually is. A properly 3d printed ABS part isn't really much if any less durable than an injection molded part. It's mostly just worse with respect to feature resolution.

[ProllyInfamous]

>Mostly just worse with respect to feature resolution.

Inclusive to my injection-molded comment, but could be mitigated (e.g.) with an acetone bath (to "smooth" the layers/resolution).

The stress fractures will most-definitely grow parallel to the layers, though... watch a Selectric's mechanism (rotational; linear; impact), in slow motion:

https://www.youtube-nocookie.com/embed/RTtKaqIpOJc

https://www.youtube-nocookie.com/embed/izZ02t2UEGc

https://www.youtube-nocookie.com/embed/1ctlRduNCn4

[Doxin]

Ah yeah, you would probably get stress risers along the layer lines. Hadn't considered that failure mode. I'd still expect wear and "mushrooming" of the type to be a problem before stress fractures are though. Plastic is pretty soft and gummy when you get down to it.

Interesting to see the timing on the mechanism too. It looks like it's already getting the rotation set up for the next character before the return stroke even happens. I suspect in normal use the ball would bounce off the page, avoiding smears.

EDIT: worst case you could always make a silicone mold and cast the type ball in an engineering resin of one kind or another. That probably fares better over the long term than 3d printed plastic.

[ProllyInfamous]

>I suspect in normal use the ball would bounce off the page, avoiding smears.

>Plastic is pretty soft and gummy when you get down to it.

I don't think most people could break the typewriter ball with their bare hands, either by pulling or compressing ("squishing"). Just tried this with my least-favorite font — 275lb blue-collar electrician can't break it (barely any deflection).

Not sure what the plastic's composition is, but it is absolutely RIGID (as it must be). The thing can fly letters onto the page (I can do sustained 80wpm, with bursts into 100+ — thing could go twice my output rate on a clear-headed day, mechanically).

Selectrics are just absolutely modern marvels (still)!

>engineering resin

The ball's plastic is harder than cured JB-Weld™ (standard 2-part mixture).

[Doxin]

Oh yeah on a human scale there's plenty of VERY hard plastics.

It's still pretty soft and gummy when compared to a LOT of materials. It's all relative and whatnot. You'll often find machinists using descriptors like "chewing gum consistency" for stuff like copper. On that scale plastic is pretty soft and squishy.