I printed a Orca 15 upper in Polymaker PET-CF and the clamshell barrel mounts slide in/bottom out inside the upper easily with just gravity, no pushing or hammering. Seems like the hole in the upper that the barrel mounts go into is slightly too large.

I've calibrated everything and I'm using the barrel mounts from Hoffman's kit. I previously printed the upper in PLA and that one had a nice snug fit, but this PET-CF one is quite loose.

Any suggesstions on what I should try or settings to adjust if I have to re-print the upper? I'm using OrcaSlicer if that matters.

It might need a higher flow rate, I've observed Polymaker PET-CF having looser fits as well.

Just for clarity (I'm seeing the same issue), are you saying higher flow rate for the clamps or the upper? Or both?

    Bolo556

    I re-printed the barrel mount clamshell pieces with 0.05 higher flow ratio in Orcaslicer and then they fit perfectly the way Hoffman said in the docs. To do it properly I should probably print the upper scaled down slightly, but the mounts with higher flow seems to work fine so far.

    I didn't want to print the upper again because it's a 25+ hour print plus the cost of filament vs the mounts are just about a 4 hour print.

      a month later
      2 months later

      I printed the clamshell pieces about a month ago, have been waiting on parts. The clamshell is too small ID to fit over the end of the barrel and fit inside the upper. I am going to reprint, maybe after sitting for a while they shrunk? not sure but I will reprint with PET-CF again (I ended up buying .5 kilo so I have a bunch left still. Hopefully they fit this time. Mine are not too loose though, I have had the opposite effect, too tight to fit around the barrel, there's about ooh 3mm gap between the clamshells.. maybe 2mm, I'm in the US I am terrible with metric.
      Edit: The OD of the clamshells fit inside the printed upper (I used Sunlu Pla Plus 2.0, it's GREAT) and they fit together nice and snug about 3/4 of the way in, I do NOT want to push them all the way in, might be impossible to remove safely, so just the ID of the clamshell seems to be a little small for my barrel. Things have gone together so well until now, but that's ok this is a learning experience. I will reply with an update after I reprint. Thank you for the hard work sharing all this great info with us.

        jinko421 You can just use inches 😉

        The gap between mounts should be about 0.020. You observed 0.080 - 0.120, which is a lot. 0.020 is the theoretical value, often times 0.030 is observed, and function is fine.

        Seams, small blobs, and even stringing can hold the barrel off. Including these formed in the groove. A bit of sanding and a little scraping may be all that is needed.

            hoffmantactical
            This is a follow up so I know you know what I know.
            I printed the clips and barrel mount using Siraya PET-CF filament 209c hardened 6mm nozzle, 80c bed, on an Ender 3 s1 pro with a bigtreetech pad 7 klipper screen. No major modifications to the printer, just about 8 months of learning. Prusaslicer, latest version, my favorite slicer by far.
            What I found to be MY issue - and maybe others will find this and it will help:
            I reprinted after fooling with the original prints, really cleaned out the groove and made certain there were no boogeys or bumps anywhere, sanded very lightly to really smooth out the insides. No joy until I removed more materail than I was comfortable removing from the groove. Your VERY exact with your files and measurements and all, This should have fit. Yeah maybe there is a machining tolerance issue with my -not the cheapest barrel but it's not the most expensive either, but I doubt that. -
            After I had an IDENTICAL experience with my 2nd print of the mounts, I decided to look a little further into possible shrinkage of PET going maybe from the 80c bed or even cooling from the 290 nozzle temp, so I set the XY shrink to a measly 0.5% in the slicer, printed at 0.16 layer height, used your support modifiers as always, I slowed the print down about 15% to be certain there would be less 'blobs' (there were still a few tiny ones but that's ok)
            Anyway.. with a little cleaning up I didn't even fit them without the barrel, I wrapped them around the breech of the barrel, and it, I won't say 'slid' right into the upper, but I goes in about halfway before I don't want to push it in any farther until I'm ready for the final install, fully seated and sure this is the time. - I test fit a LOT.
            I appreciate you humoring my post and replying kindly. Thank you, seriously, for all the hard work, time and I'm sure money you've spent building and maintaining Hoffman Tactical and the community we are all part of.

                jinko421 Great that you got around the issue! I would suspect a steps per mm issue rather than shrinkage, even with annealing above 100 C, PET-CF exhibits very little shrinkage. The small amount of heat from the bed will certainly not have an impact.

                There is also the possibility that it was over extrusion / wide lines due to the larger nozzle and fiver filled material. The XY Size Compensation can help fix that.

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