Nerf Caliburn U - Simplified Edition

by captainslug Nov 17, 2019
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Design Flaw
an issue I see with the U-Channel Caliburns, is that the U beams are located Below the boreline
as in, they are off-center from the main spring forces
which means the beams are constantly under torque trying to bend them downwards
You get away with it because they're so darn stiff, but it would be better engineering to have them centered so they don't have to deal with that additional stress...

-different schools of thought I guess: do you overbuild to handle stresses? or avoid them?

They can't be placed at the bore axis because they would obstruct the ability to attach the base foregrip. They're placed where they are to avoid making the assembly any wider, in a location where the hardware that can be used to attach to them has space to exist within all the printed parts that attach to them. The stresses are somewhat triangulated as each piece that attaches to the u-channels also rests against the top surface of both sides of the u-channel. I had originally designed this with a third u-channel up top, but that has its own downsides. Namely that it wouldn't provide for any way to attach picatinny segments up top without having to drill and tap screw holes in that one piece.

Yeah, I can see that
Though it means each part has to deal with twisting forces where they 'tab' into the channels; a spot already a bit stressed by having screws driven through them.

I just think that your original threaded rod design is superior.
It was quite elegant in that all the printed parts experience Only Compression, which is great since there's no shear or tension that might try to separate layer lines.

I do understand that stiffness was a goal, and U-channel beams are stiffer than threaded rods. Though I don't think I'd have taken the same approach. I've been thinking about adding tapered interfaces to the parts; so that instead of butting against each other flat they interlock. That should let the compression from the threaded rods counter side to side wiggle.
Will be experimenting with remix.

No, the shoulder that's resting on the top side of the u-channels is preventing the screw bosses from seeing any twist. It could be even more of a truss structure if each piece were deeper to help triangulate any offset loads. The only designs I've produced that see only compression are the Esper and Wspr designs. The normal takedown Caliburn sees several different kinds of stress, but they're subdivided across multiple parts. The rev2 Caliburn with the monolithic magwell had more of a truss structure to it than the current version.

Comments deleted.

Hi, I was just looking at your Etsy and saw the listing for the build-at-home kit for this. Is the link to this page mainly for if I need replacement parts?

Or assembly instructions.

The NamePlate (which the assembly instructions say you need 2 of) file does not appear to be in this file set.
Where can I find it?

Reuploaded to the file set

This is exactly why I love giving you money. Thanks, Captain Slug!

You just keep coming up with the GOODs.
Well done again Cap.
You are a true All Star of the Nerfing Community.

Where can I get an AR grip?

There are a few on thingiverse that you can print out and I might add a plain one to the file set soon. Otherwise there are injection-molded ones available from a lot of online retailers at varying price points.

I've added two printable options to the file list.