Quoted from zacaj:
In my experience ABS is more flexible, which is probably good. There's also PETG now, which I've heard is much stronger than PLA. I've got a spool here but haven't had a chance to use it yet
Hey Martin and everyone else, I stumbled onto this post while trying to research from what type of plastic real drop targets are made. I'm 3D printing my own and I've run into reliability challenges.
I've got a special project - I'm bringing a discarded Black Knight playfield back to life. When I acquired it, many of the playfield assemblies were missing, including one of the four drop target banks.
At the time, I couldn't find any 3-bank Williams drop target assemblies anywhere, new or old, good or bad. Instead, I took a gamble on an Alvin G drop target bank (think I found it on PinballLife) that was a good price.
Luckily the drop spacing was correct, and the overall dimensions fit the playfield. The only problem was the targets themselves didn't match the look of Black Knight. So I decided to model my own drop target, using the stem of the Alvin G target, and the head of the Williams target.
I've gone through several iterations of my design. I think I'm getting closer to a working design, but pinball life is rough (for parts, at least) and they keep breaking.
I attached a picture showing my design iterations, starting with the original Alvin G drop (white on the left).
My v1 design, in red ABS, mimics the Alvin G stem as closely as possible, even down to the thickness of the walls. It has some flex to it, and I had high hopes for it. The bottom lip, which keeps the target retained in the assembly, broke quickly on all 3. Not sure if it would have developed breaks in other areas had I resolved that issue, but I did notice some hairline cracks about midway up, so chances are it would eventually break in multiple places.
My v2 design is in black PETG (2 left black targets). I switched to PETG because ABS is smelly and dangerous to your health, and PETG supposedly has similar toughness. Using the original design as a starting point, I set out to make it stronger. I thickened up all the walls, and even made the stem larger in thickness too, as there was a lot of slop in the mechanical assembly so plenty of room to make the part larger (and hopefully stronger). Unfortunately, I left some design details in from the original Alvin G, like those 3 vertical grooves. I knew those were going to be a problem, just on how these features caused the 3D printer to print side-to-side instead of top-to-bottom - a part like this needs vertical strength. Sure enough, it broke pretty quickly right in the middle. I'm still confused by this, as I didn't think that section would get so much force as to cause a break, even though it was an obvious weak point in the print.
My v3 design, also in PETG (2 right black targets) is a no-holds-barred, maximize solid areas and eliminate any unnecessary cutouts. It only has openings for the switch arm and the return spring. I'm going to start testing it this afternoon, but I'm sure it's going to fail too. I've come to the conclusion that PETG is just too brittle for pinball life.
I'm also thinking that my efforts to make it more robust by adding more plastic are backfiring. I compared it to the original Alvin G target today, and the Alvin G has a rubbery, flexible quality to it. The PETG v3 drops I've printed are so thick and solid, they don't really have much flex anymore. So they'll likely resist for a while, then break spectacularly. I think these parts need to have some flex to give it robustness - bend don't break.
I'd love to know what kind of plastic the Alvin G's are made from. I don't think it's ABS, as my original red ABS targets that mimic the original design even down to wall thickness feel very stiff compared to the springy Alvin G's. Maybe it's nylon.
I've ordered some Nylon 6 to try that next, which is probably my last hope. Nylon 6 has good qualities for impact strength and good flex, which should work in this application, plus low enough temps to actually be printable on my Prusa Mk2.5S. Nylon printing is hard(er), mainly because it is extremely hydroscopic so you have to dry the filament right before you use it. I'm continuing to develop and test in PETG, as I'm hoping whichever design works best in PETG should work really great in Nylon.
If that doesn't work, then some glass fiber embedded nylon is my absolute last step. But those abrasive glass fibers will wreck my hot-end, so if I have to go down that path I'll probably farm that print out to a service.
Of course, that's where my solution gets a bit crazy. I only did this because I couldn't find a Williams 3-bank assembly, and I'm starting to realize that going down the Nylon path is becoming too expensive. If I paid a service to do this, I'm sure that would be ridiculously expensive. It's probably smarter to start hunting for a Williams drop bank instead.
Anyway, thought I would share my experience in case this is helpful to anyone. I won't have the nylon for another week or two, so the story is unfinished. If anyone's interested, let me know and I can share the final result.
PaulDrop Target Iterations (resized).jpg