Has anyone tried to 3d-print a collapsible stock? It seems a viable undertaking, considering the materials used in a simple a2 style collapsible. Sadly, my Google-Fu has failed me and standard members can only search through the past 30 days.

Honestly, I'm considering building a pistol lower with an arm brace similar to the SB-15, but I'd rather use the lower I already have- with a standard buffer tube. The problems are:
1)The SB-15 is expensive
2)The SB-15 doesn't appear to be able to fit on a standard buffer tube because of the track used for the stock length adjustments on a mil-spec buffer tube doesn't exist on the pistol buffer tube.

The good news is that the arm brace is simply a modified collapsible, so reinventing that modification while retaining the adjustibility would be simple, given an existing autocad file. Does anyone have, or know someone that has, any such files?

Try Google site:ar15.com 3D print stock

The arm brace is NOT just a modified collapsible AR stock.  It looks like a standard AR stock from the side.  A hard plastic arm brace may not fly w/ Tech Branch.

No, 3D printing is what you use to finger fuck an idea before going into production.

As for actually using it?  It'll fall apart before you get to the range.

an SB15 is authorized and cheap compared to unknown on a rifle buffer tube

Come again?

BTDT.  Just because you can squeeze a few rounds off for the camera doesn't make it anything you'd want to use for any period of time.

I've 3D printed and installed a prototype handguard, doesn't mean it's anything anyone would want to use if they had a choice.

Careful, you'd be getting into NFA territory by using a rifle or other collapsible tube on a barrel under 16".

I've seen plenty of people wrap para-cord around their collapsible tubes, but that is a no go in the eyes of the ATF.

Got a source for that statement?

https://www.atf.gov/files/regulations-rulings/rulings/atf-rulings/atf-ruling-2011-4.pdf

Okay, so you're safe if you don't own a collapsible stock at all and never get your pistol near one or a riffle lower for that matter.  I may be leaning on the safe than sorry side here, but for $50, I'd just buy a pistol tube.

Here's BigBore's letter from 2004 - you can use any buffer tube you like:

http://www.ar15.com/archive/topic.html?b=3&f=122&t=483410

You can definitely use any tube you like and printing a Sig brace like stock seems really dumb when you can buy one that has ATF's approval.  Yours will not nor will it be as durable.  You are correct that the Sig brace will not fit on a standard carbine tube.  There are several pistol tubes to choose from and they are not expensive. [%|

Any receiver extension is fine.

The Thorsden Buffer Tube Cover is BATFE approved and it is made exclusively to fit a standard carbine receiver extension.