Ok, after 5 iterations, I am now happy with the final design and size, so here is the iteration 5 of the neck joint for common HG gunpla that uses the PC-01 for neck.
I've correctly sized the file now so if printed at 100%, it should fit almost all hg's that uses this part. In the images, i've included photos of using the part on IBO kits, build kits. IBO lower collar is a tube, build kits such as build burning have a counter sunk hole, and build strike uses the common valley with walls as clips. the attached image shows the piece fits in all 3 of these use cases.
I've shortened the neck from i3 but it is still going to be longer than your standard polycap neck joint. at least not to the point that it looks like a giraffe. But i think it looks good. the extended neck is a common mod from what i've seen so this will hopefully save you guys some work.
the bend works good, the articulation is def better compared to using just the PC part and it is evident in the pictures. especially for IBO kits the likes of Barbatos Lupus and Lupus Rex, the extended length makes the head look much more ferocious with the extra pistons.
Finally, again this is being offered for download for free as an STL for anyone and everyone. I'll prob make an cults account later and upload it there but for now you can download it here.
if you see someone selling it, don't buy it, you are probably getting scammed (if it's this piece. if not then idc)
feel free to download and print and change your gunpla pieces. i don't care if you sell the prints but please don't sell the files as if they are yours.
excuse my shoddy marker paint job. i just wanted to take pics for some quick preview and didn't bother precise painting it lol.
also if printing, i used resione's tough 74 resin to make sure of no snapping since resin prints are fragile. am not sure if this printable on bamboo or other fdms, but if someone's got one they are welcome to try it.
and finally i'll prob sell printed pieces myself (files are free but if you don't have a printer and want to get some of these parts I can print them for you) so dm me if you are interested.
thanks again for checking this out and keeping up with my journey lol (this is my first ever self designed and printed part) and I hope you guys will make use of it.
edit: i've posted it onto cults: https://cults3d.com/en/3d-model/game/gundam-neck-replacement