The Challenges of 3D Printed Pinball Parts

Life for parts inside a pinball machine is rough.  Literally.  Anything that comes into contact with a speeding ball of steel is in for some abuse.  Look at some of the metal components that have been in service for decades, and they will often be deformed or broken.  And even more destructive are the super powerful solenoids.

This makes life incredibly tough for 3D printed plastic pinball parts.  Is survival even an option?

Most of the 3D printed parts I've designed do not come under any direct stress.  Things like electrical connection mounting brackets, or decorative toys.

For example, here is a 3D printed Monty Python Black Knight toy on top of the upper playfield's shooter lane ball ramp.  I was finding that balls would bounce and get caught on the metal hood.  A 3D printed flat-topped cover solved that problem, and provided a perfect place to mount a toy.

A 3D printed cover (black) prevents balls from getting stuck, and made a perfect spot to mount a toy

But one of the 3D printed parts I designed for The Black Knight Rises are some drop  targets, to make an Alvin G drop target assembly cosmetically match the Williams drop target style.

Designing a drop target doppelgänger was easy.  Coming up with a design that would survive has been the real challenge.

My original prints were in ABS.  They broke.

I also tried PLA, which broke even faster.

I upgraded to PETG, which lasted longer, but also broke.

I modified the design to be more massive, in hopes of making it more robust.  And that broke even faster.

Original Alvin G drop target in white.  ABS red and PETG black design revisions all broke.

Surprisingly, the target head itself never broke, even though it takes direct hits from the pinballs.

Click through to learn the rest of the story.

Rather, the stem is what kept breaking, and it would break on reset.  The original Alvin G solenoid was too weak to successfully reset the bank with a 38v power supply, so I replaced it with a more powerful solenoid.  Now it seems it is way too powerful.  Sometimes the drop would break in half in the middle.  But most often the very bottom lip, responsible for keeping the target from flying out of top of the playfield, would shear off.

Ironically, the more robust I made the drop target, the quicker it would break.  I finally realized that what I was doing was adding mass, making the job of stopping the drop target on reset harder and harder - basically it's easier to stop a lightweight bicycle than a heavy train.  Once I figured this out, I went back to one of my original lightweight designs, and only added reinforcements sparingly to strengthen the bottom lip.

I also tried my hand at printing nylon.  Nylon is one of the most challenging materials to print with in a home environment.  You need to dry the nylon for at least 8 hours before printing, you need high temperatures, you need an enclosure, and you need special build surfaces to allow for both adhesion and release.  And you need lots of printing experience.  Luckily I had all of that, but it was still extremely challenging.

Though the color isn't a perfect match, my 3D printed nylon drop targets on the right look great.

So far, my nylon prints have done the best, though I have been able to break those too, often in just a few days of play.  I finally wised up and lowered the power for the drop target reset, setting the PWM level to about 30%.  With the reduced bank reset power and optimized design in nylon, my latest nylon drop targets have been working fine for over a month.

But knowing that my consumer grade printer (Prusa Mk2.5s) was far from the best for printing nylon, I spent the big bucks and had a few printed by Shapeways.  These cost about $16/ea, so not exactly cheap, but also not exactly expensive in the world of pinball.  In hind-sight, it would have been cheaper to source a used Williams 3-bank drop target (something I might still end up doing).

My home printed nylon drop target is on the left, the Shapeways nylon print on the right

I've noticed that the nylon drop targets that I printed have a good amount of flex to them, very similar to the flex of the original Alvin G drop target and similar to a flexible filament.  The Shapeways print is quite a bit stiffer.  I'm a little concerned it may be too stiff.

I did change the design slightly for Shapeways, as the Nylon material will print 100% solid, vs the 20% infill I'd been able to do at home.  Since the Shapeways part was solid, I carved out more material to keep weight down - similar to the original Alvin G injection molded design.

The difference in print quality is huge, an easy victory for the Shapeways print.  Of course, they are using a printer that easily costs over $100k, which fuses powdered nylon with lasers, so you'd expect nothing less than perfection.  I'm most hopeful that the layer bonds are stronger than what I can achieve at home.

The difference in print quality is more apparent from the back.

I've not tried the Shapeways parts in The Black Knight Rises yet.  The current drop targets that I printed myself are still working fine, and I was thinking about keeping these Shapeway targets for spares when one of those break.

Outside of being twice as stiff, my only other complaint regarding the Shapeways prints is that the surface texture is slightly rough, similar to 600 grit sandpaper.  Shapeways offers polishing for certain nylon colors, but not for red.  Cosmetically it's fine, but I might need to polish the target head to make it smoother for better sticker adhesion.

My Thoughts on 3D Printing Pinball Parts

I've seen a lot of DIY pinball projects lately, and more and more I see 3D printed parts, made at home on consumer gear, being used on the playfield as ramps and diverters and targets and toys, where they will come into direct contact with pinballs.

So, are these parts up for the challenge of pinball life?  Probably not.  For prototyping, I think these parts are fine, but eventually a pinball will find a way to destroy them.  

Designers can make an effort to protect these 3D printed parts with both careful design and also by using more robust parts like metal posts to take the brunt of any impacts.

Any plastic parts that will take direct hits by pinballs need to have some type of shock absorption to allow them to flex a bit and dissipate the force.  Using nylon is probably a better choice, too, as more accessible plastics like ABS, PLA and PETG are more fragile.

In general, it's probably best to limit 3D prints to parts that won't see hard, direct impacts. 

Myself, I plan to keep 3D printing pinball parts, mainly because it remains one of the best solutions when original parts cannot be obtained.  My next project after The Black Knight Rises is Centaureon, based upon Centaur, and it has a lot of very unique under-field mechanical assemblies that I probably won't be able to source.  

I've purchased a CPR Centaur playfield, and I've already discovered the ball trough opening is unlike anything else I've seen before, plus it auto-launches balls from beneath the playfield, rising through a ramp halfway up the playfield.  I'll be extremely lucky to even find these parts for sale to build my Centaureon from scratch - more likely I'll have to 3D print some entire mechanical assemblies.

Fingers crossed it actually works...