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Kopsis

@ Kopsis @forum.guncadindex.com

Posts
3
Comments
130
Joined
3 mo. ago

  • Water treating PA6-CF20

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  • Unless you need extremely high impact strength, there's little reason to choose PA6-CF over PPA-CF. If you do need extremely high impact strength, then you want PA6-CF to absorb moisture because that's what contributes to it.

    There's this perception that moisture absorption is some kind of continuous and unending process that eventually turns PA6 into goo. That's not true. Without immersion, PA6-CF is going to max out at around 5% moisture content. At that point it's still 3 times stiffer than PETG.

  • Metric TAXIDRIVER

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  • General Discussion @forum.guncadindex.com
    Kopsis

    Franken 9 Issues Sorted Out

    With Unseen Killer's help, I was able to determine that my Franken 9 problems were entirely due to using printed Sten mags. There was a different problem that affects only milsurp mags, but that's fixed in UK's latest drop. If you're using milsurp mags, print the latest frame and you should be good to go.

    The problem with printed mags is that the dimensions deviate significantly from production magazine drawings. Every design I checked was wider at the feed lips and flared more steeply than specs call for. Most are also about 1mm shorter font-to-back. As a result, they won't seat deep enough to reach the mag catch or feed correctly (or at all). To be clear, there's nothing the Franken 9 can do to fix this -- the incompatibility is with the Glock slide itself.

    I didn't want to print new mags just for this build, but curiosity got the best of me. I remixed a "spec-ish" version of the DMB Sten v1.1 and squirted a test print in PLA Pro. With that the Franken 9 is able to feed 100% reli

  • DEAR 22 Question

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  • The AR22K stuff just adds a couple of minimalist handguard options for those running really short barrels. Whether to use one of those or one of the SG22K handguards really just comes down to style/ergonomics.

  • OKB-69 Project Venera Update

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  • Good to know my Krizantema stamp last year is benefiting the proletariat :)

    For anyone curious, Krizantema doesn't really compete with commercial 9mm K cans and certainly not full-size printed 9mm cans. But it is surprisingly good as a flow-through 22LR suppressor (despite the hugely oversized bore). I suspect the 5.7 version would have even better performance and is definitely worth considering for a 22LR, 22WMR, or 17HMR host.

  • Giving up on the Franken 9

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  • Don't worry, I'm actually pretty bad at giving up :) It tends to last about 2 days before I'll think of something new to try.

  • Finished testing PET-CF; it sucks

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  • In the firearm space, PET-CF works well for some handguards that are bolt-in-place designs (I used it for the handguard on my Urutau). The high-stiffness, low-creep, low-cost is also good for magazine bodies (as long as they don't need to survive drops). Stocks and braces are another application where PET-CF shines, again due to high-stiffness and low-cost. If you ignore cost, PET-CF/GF is always a bad choice. But if the idea of paying $60+/kg to print a pistol brace bothers you, PET-CF/GF at $35/kg starts to make more sense.

  • Giving up on the Franken 9

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  • You're close. It's not an easy problem to describe. Here's a photo that might explain it better (DMB Sten left, DMB Glock right):

    This is with the DMB Sten mag, but the UK and DB9 are all very similar. I could probably mod the mag to make it work, but I think remixing with a Glock magwell would be a more robust solution.

  • Giving up on the Franken 9

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  • You got it ...

    Front rail pocket:

    Front rail pocket w/ rail:

    Slide on:

    I should mention this is the pre-fix frame. I just printed a small part to fill the gap in the guide rod stop and glued it in place so I could finish function testing before I re-printed.

  • Giving up on the Franken 9

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  • Thanks, but at this point I'll wait and see if Unseen does a Glock mag version. I mentioned surplus mags just to be clear that the problems I've had may be entirely due to printed Sten mags and not an issue with the design itself.

  • General Discussion @forum.guncadindex.com
    Kopsis

    Giving up on the Franken 9

    After a week on the struggle bus, I think I'm going to throw in the towel on the Franken 9. I love the concept and there are some really clever design elements. The problem is that I just can't see how to get standard printed Sten mags to work reliably. With a modified mag catch, I was able to get my build to accept a printed DMB Sten mag and feed dummy rounds. But it's hard to get the mag to lock in (because it has to be held right up against the bottom of the slide) and it's very easy to induce a failure just by bumping the mag.

    The fundamental problem seems to be that printed Sten mags present the rounds about 0.8mm lower than Glock mags. That means the feed protrusion on the slide just barely catches the rim of cartridge in the magazine. It can work, but there's no margin. Mag fit relative to the slide has to be absolutely perfect. It might work better with surplus magazines (I don't have any to test). It also wouldn't be too hard to remix the printed mags to be a little more comp

  • Finished testing PET-CF; it sucks

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  • With my PET-CF/GF settings I've found that chamber temps over 40°C don't improve layer adhesion. And running it much higher forces me to boost the cooling on bridges and overhangs, resulting in worse layer adhesion for complex parts.

    It's definitely possible to print too hot. For Siraya PET-CF/GF, 320°C is within spec. For Polymaker it's a little high and for Bambu it's a lot high. I generally don't go over the recommended max without quantitative strength tests showing it actually helps. I'd also suggest dropping speed by 30 - 40% and doing some flow ratio calibration tests. Nothing kills layer adhesion like under-extrusion.

    All that said, PET-CF/GF does have some significant limitations. It is extremely brittle and won't tolerate any significant flexing or bending. Getting good layer adhesion doesn't change that, it just means the break will be less uniform. For parts that need some flex (like an AR style handguard that clamps to a barrel nut) PET-CF/GF is generally a poor choice.

  • Finished testing PET-CF; it sucks

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  • Moisture doesn't cause creep. Moisture in PA6 reduces bending modulus and increases impact strength. Moisture in other nylons like PA12 doesn't have much effect. In all cases, nylons only absorb a limited amount of moisture and don't lose any more strength/stiffness beyond that point.

  • Finished testing PET-CF; it sucks

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  • PET-CF isn't the perfect material, but it's a lot better than what you're seeing.

    First off, printing Glock frames in any orientation other than horizontal is a failure waiting to happen. Rails-up vs. rails-down doesn't matter but if you want the best strength, you have to print them level. Layer adhesion strength is directly proportional to layer surface area. When you print at any significant angle, you get really small layer surface area around the pins and the locking block -- the most highly stressed areas on the frame. If you had printed level, the layer would run the whole length of the frame and the layer area would be several times greater and several times stronger.

    This looks like a combination of bad print orientation and poor settings. It's not the material. I have a PET-CF Glock 26 frame that's seen 800 rounds of hot 124gr NATO 9mm and it's still in perfect condition. I'm testing PET-GF now and it's just as strong as PET-CF for all practical purposes. I typically run PET-CF/GF 310°C nozzle temp, around 60mm/s print speed, no cooling, enclosed chamber at 40°C. If your settings aren't very similar, you may want to make some adjustments.

  • Franken 9 Fixed - Build Complete

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  • I've been able to get remixed magazines to retain and feed dummy rounds, but that's just not a good solution. The last thing anyone needs is yet another "almost Sten" mag that won't work in anything else.

    Instead, I came up with a re-designed magazine catch that should work with standard printed and/or surplus mags. I have a DMB Sten mag on the printer now. I'll fine tune the mag catch dimensions with that and then post the STL (hopefully tomorrow) for anyone that wants to try it.

  • Franken 9 Fixed - Build Complete

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  • The UK-RR Sten mag should work, as should your surplus mag. I just pulled a UK-RR mag off the printer and I'm seeing the same problem. Feed lips hit the slide before the mag catch can engage. The location of the mag catch in the frame seems off. With the slide off and the mag fully inserted, I measure 78mm from the bottom of the magwell to the top of the feed lips. But with my slide there is only 75.5mm from the bottom of the magwell to where the mag hits it, so I'm getting 2.5mm over-insertion. I'm seeing the same thing with three different slides (one Glock and two aftermarket) so I can't see how this is supposed to work.

    Fit in the magwell with the UK-RR mag also seems pretty sloppy. The magwell is 24.2x39.3mm. Sten mag specs I've seen put mag size at 23.1x39mm, so surplus shouldn't be a bad fit (I don't have a surplus mag to test). But the UK-RR mags are only 22.6x38.1mm, so over 1.5mm side-to-side play and 1.2mm front-to-back. I'm going to remix the UK-RR mag with slightly larger dimensions and a higher mag catch slot to see if I can get something that will at least feed.

  • Franken 9 Fixed - Build Complete

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  • I won't be able to test mine until middle of next week, so I look forward to hearing how it runs.

  • FTN.5 PA6-CF Annealing Recommended?

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  • Yes, the greatly improved heat tolerance far outweighs the small loss of impact strength. And even annealed, the moisture conditioned impact strength of PA6-CF will be higher than most other materials.

  • Chortex + Kaewon 10/22 Receiver

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  • I tell anyone who asks that my stuff is 3D printed. It's completely legal where I live and I figure if people see someone using 3D printed firearms responsibly, it helps counter the media stereotype of "ghost guns are for criminals". It's to the point now that when I arrive at the range, the first thing the ROs ask is if I have any cool new printed guns to show them :)

  • Officially here… Removed Reddit from the phone today…

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  • Mods are trying to keep the 3D2A sub alive while under the Reddit censorship microscope. Reddit isn't interested in keeping the sub compliant, they're trying to find any excuse to kill it. Reddit is psychotic about encouraging people to use other platforms. That predates the current rule 7 crusade and goes back to the API lockdown.

    So Reddit doesn't want us there but also doesn't want us to tell people to leave. The only way to win is not to play.

  • Replaceable Suppressor Wipes

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  • Printable TPU is much too hard and doesn't have much heat resistance.

  • Franken 9 Question

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  • Never a waste when you learn something in the process.

  • Show Off Your Builds @forum.guncadindex.com
    Kopsis

    Range Day with the Urutau

    My Urutau was a big hit at the range today. ROs and shooters alike were all very interested in the build and how it performed. I've been slowly working to get the firing pin length dialed in and I think I'm finally getting close. I didn't run a lot of rounds, but it ran the two 20-round factory CZ mags and the two 30-round ETS mags I brought without a single failure. Some slow-fire, some doubles, some Bill-drills. I even ran the last 30 rounds with a 3D printed can (OKB-69 Khrizantzema). Note that this is with a remixed lower receiver since the ETS mags do not properly fit the lower in the official release. If I have another successful range session with this lower, I'll release it.