3-d printed material strength: A/C back block?

[Sharkytrav]

Can something be 3d printed with enough strength to withstand the rigors of an auto cocker ram's action?

[ChoSanJuan]

Probably... Print it horizontally and you'll not experience snapping from sheering forces on the z axis. You might still get a bit of deformation but depends on how much psi you are using to sling that ram.

Funny you mention this since I was going to model one up and test it in my STO.

[Sharkytrav]

hmmm... it sounds like the other part I was thinking about might have trouble in that case.

What about an Inception style eye cover that has a mount for the ram? If a back block needs special consideration then a small ring hanging off the bottom of an eye cover seems pretty sketchy, no?

[Law]

I would think the weak point would be the pump arm threading, adding a threading insert might be a good idea depending on the material and print quality.

[JonM]

It also depends on the material used. There are a lot of options out there with different properties that make them better or worse choices for use in paintball. I'll do most of my prints in PETG for the strength and temperature resistance it provides, but it has its drawbacks too. I used to print in PLA, but it can be too brittle for use in paintball and it can warp in the heat of a locked car. Professional shops like Shapeways print in a variety of materials that are better than anything my printer is capable of using. I recently had them do one of my Emek bolt caps in PA12 and it looks and feels almost like the GRN used in the stock body. Since then, I've moved all of my designs to them since they are able to produce a superior product to anything someone with a hobby grade printer can create.

[boarder2k7]

I'd expect it to do fine. Like Law said though, I'd put in an insert for the pump arm threading. JonM raises a valid point about in car temperatures, so PETG would probably be the best choice of easy to print at home materials.

[Sharkytrav]

I don't think I have the time or connects to make it happen, but I am envisioning a bolt-on reverse kit for inception designs cockers. something that doesn't require a new 3-way or ram to be manufactured.

My thought is:

an eye cover that a ram can be mounted to

A skinny insert that fits between the frame and body with a 3-way mount

new front block with a backward facing hole for the LPR that lines it up next to the bottom tube and grip frame.

Ideally everything would be aluminum, but proof of concept for the 3-way and ram might work as 3-d printed.

[Rainmaker]

Edit: only talking about the back block here.

Ok hear me out, but I think this could be a good opportunity to use annealed PLA+.

When annealed, PLA has greater strength and heat resistance than PETG. The big issue with annealing is that it causes some warping and shrinkage during the annealing process. This would probably affect the holes in the back block a bit, making them shrink or go out of round. But since they are probably all standard drill sizes, you could probably re drill them after annealing.

The initial design would probably need to be beefier than a regular back block, scaled up ~3%, and other optimizations to limit annealing warpage as much as possible. It sounds like a lot of work, but it wouldn't be too complicated.

Also, I'd probably try a version WITH a threaded insert for the rod, and another version WITHOUT an insert (just tapped into the plastic).

[JonM]

On the subject of threaded inserts, I've tackled this issue when designing my PGP pump handles. Modeled threads do work in a case like this. The thread pitch is even the same. The problem would likely be with longevity. The question would be how long the threads would hold up with repeated cycling. This would also be affected by whether or not the Cocker was properly timed with an appropriate gap between the back block and the body. An improperly timed Cocker would likely rip out the threads sooner than a properly timed Cocker would since the back block would be continually slapping against the body. Speaking of the gap, there's also the question of deformation over time. As a 3D printed part is cycled over and over, I expect that gap would eventually change as the threads start to deform under repeated stress. I expect the insert would help with this. Although, as you can see below, the insert requires additional material around the hole which would affect the overall dimensions of the part. In other words, you'd need to make the back block chunkier to compensate for the wider hole for the insert.

[Bulldogr6]

Does carbon fiber PLA inneal the same ? I haven't experimented with any of the engineering stuff yet but I imagine carbon fiber nylon would handle it.

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[nobbie333]

I wonder if you print it without the outside walls then fill it in with epoxy

[ChoSanJuan]

https://youtu.be/DyAKtS1b3SQ

There are a few videos on how to anneal 3d printed parts using a salt pack. stephan seems to usually overdo it in a great way. Worth the watch. Tldr... Your pla will come out super tough and feel like ceramic.

[Rdav]

If you make it with a good layer alignment and a fair few walls it can probably survive 'most' of the rigors of use, however for fine shallow depth threadings you'll need threaded inserts,
In addition you can also design the model to have studding embedded into the print for strength in certain axis, you don't need threaded insert for this.

As a side note for deep threads smaller than m8, I find its a lot more effective to not model the threads into the part and merely tap a warm bolt into it, the friction generated from the tapping process tends to selectively melt and form the plastic very well around the bolt so for studding embedding this works pretty amazingly for high strength axial reinforcement.