3D printed bolts?

[DavidBoren]

Not screws, obviously... but the piece that moves back and forth, loading/firing paintballs.

Is it possible/wise to do print a bolt for a STBB?

Clearly it is possible to print the shape, but will it hold up to repeated blasts of pressurized air, AND being yanked around?

I am intrigued by the air passage possibilities available for a printer, but could never be machined (as one piece, at least... never dismiss a competent machinist, they always have a boxer's chance).

[ReconSWS]

Haven't tried it yet but I think it could work depending on the design.

What air passage possibilities? I would do a spiral WAVE inside the bolt lol not sure what else you'd do. I think if you constrict the flow trying to control the air it might not hold up to the pressures, especially if you allow expansion before it hits those features.

[DavidBoren]

I was thinking of a continuously expanding internal cavity, opening towards the front. The rear opening would be as small as reasonably possible... probably matching whatever the port between the upper and lower tube is.

Right before the exist, it would reduce to about 63% of its largest internal diameter, maintaining a sweeping radius... the cross section would look like a teardrop. The tip of the bolt would be rounded, and look similar to the TechT Hush bolt, just open.

This reduction in diameter of the bore at the front would provide enough material for an external O-ring to seal the breech of the barrel.

Incorporating some sort of spiral, or scales, or threads, or dimples, or whatever would be cool... but completely unnecessary for the first go around.

[Paintzapper]

You could do SLS or MJF out of GRN.
I typically use JawsTech for that kinda stuff as they have a polishing/finishing service as well.

[JonM]

It's theoretically possible, but I wouldn't even attempt it with an FDM printer. Depending on how it's oriented on the bed, I'd be concerned about layer separation or stepping.

[DavidBoren]

I was thinking it would be a horizontal print, that way the layers run the full length of the bolt... and the pin connection to the striker would, hopefully, be less likely to rip the rear third of the bolt free from the rest.

And a vertical print just seemed to be tempting fate for some stupid leaning tower of PLA nonsense.

[JonM]

I was thinking it would be a horizontal print, that way the layers run the full length of the bolt... and the pin connection to the striker would, hopefully, be less likely to rip the rear third of the bolt free from the rest.

And a vertical print just seemed to be tempting fate for some stupid leaning tower of PLA nonsense.

The pin connecting the bolt to the striker couldn't be printed horizontally or else the layers would fail at that point. You would certainly need to use a steel pin in this case. Even so, you'd likely start getting deformation with repeated cycles where the pin meets the bolt. You'd also get a stepped surface since you'd be printing a round object horizontally. In my opinion, it's an interesting thought experiment, but other manufacturing methods would be vastly superior to 3D printing in this application. It's kind of like using a screwdriver as a hammer. You can drive a nail with one if you wack it hard enough, but there are much better tools for the job.

[DavidBoren]

I honestly thought that the layers would be stronger stacked, versus having a vertical bore between vertical layers... I figured you are begging for layer separation at the bore for the pin. The widest point of the vertical bore will have nothing more than the bonding between the layers holding the bolt together when the striker/pin yank it backwards and the front two thirds of the bolt are perfectly content being at rest.

In juxtaposition, horizontal layers would literally be stacked with a vertical bore through all of them... the widest point of the vertical bore would literally have to tear every layer in order to fail. This seems less probable than the bonding between two layers failing. To me, at least.

The stepping associated with printing a round object horizontal is the least of my worries... as the steps literally affect nothing, because they run lengthwise along the bolt. Oh no, less contact/friction. It will have O-rings providing any and all necessary seals, so it looking pixelated is literally a non-factor. And, if anything, the steps within the internal cavity would probably help airflow.

[JonM]

You'd be risking layer separation in either print orientation. If the bolt is printed vertically, it could potentially crack in half as the bolt is repeatedly slammed forward & back. If the bolt is printed horizontally, the striker pin would likely snap off if it's printed or else repeated firing could potentially loosen the material around a steel pin, causing it to deform.

[DavidBoren]

I probably should have specified that I intend to use a steel pin to connect the bolt to the striker.

Would a solid infill that spreads lengthwise around the vertical bore be enough to mitigate deformation? Looking down at the vertical bore, the solid infill would form an eye-shape, with the vertical bore being the pupil. If that makes any sense.

This SHOULD spread the stress along the length of the bolt. I think...

[JonM]

I probably should have specified that I intend to use a steel pin to connect the bolt to the striker.

Would a solid infill that spreads lengthwise around the vertical bore be enough to mitigate deformation? Looking down at the vertical bore, the solid infill would form an eye-shape, with the vertical bore being the pupil. If that makes any sense.

This SHOULD spread the stress along the length of the bolt. I think...

I suppose that would depend on the material it's printed in. I certainly wouldn't use PLA since it would be more likely to shatter. PETG could be an option, but it's a pretty malleable material. You could try PLA+ and see how that holds up. I know Ty uses it for combat robots.

[DavidBoren]

Combat robots...

[JonM]

Yep. He's involved with a 3D printed mini robot combat league. He brought his bot down to Flounder's place earlier this year and I got to see it in action. Scary little bugger when it gets running.

[Spider!]

There have been bolts that are aluminum in the back and delrin in the front, pinned together. I used one to graft the front of a timmy bolt on for a pump.

I've considered venturi profiles or flow-tabs, but I think that first turn out of the body might be the important spot. I was thinking about an oring bolt to avoid surface issues.

[grendal50]

I have a 3d cocker bolt, I haven't used it at all, but it seems strong enough. There isn't a lot of mass moving there and it has the bore of the gun to keep it from expanding from the air pressure. I suppose I can put it in a gun and put a couple hundred rounds through it for "science." I printed it vertical like it shows in the picture and my original intent was to use it measurements to make a custom halfblock bolt.

I think the design is up on thingiverse, labeled as "Bruizer"

https://www.thingiverse.com/thing:590906

[grendal50]

Here's the Bolt, I put it into a Trilogy and dry fired it ~25-30 times. Both upside down(quieter) and right side up with my hand in front of it to keep the noise down and provide some back pressure. I'll put some paint through it tomorrow when it's not raining and see if I can make it fail.

[jerryjjackson69]

I printed a midblock cocker bolt that worked fine but was nothing special... I'm still tweaking it to make it special though!

It seemed to work ok, but it wasn't being subjected to the violence of a STBB. I did design it with o-ring grooves that still need some adjustments.