155mm Howitzer Shell UPDATE now with scale diorama accessories

prusaprinters

For model makers (dioramas) see the exciting addition of accessories belowThis is the standard 155mm howitzer shell in use by the US army since around WWI. This model was inspired by @sbeecroft's models on Thingiverse; this is not a remix, but a ground-up CAD model off the US Army's 1994 procurement specs. However his model doesn't fit on the prusa (if you have a gMax sized printer I recommend his, or if we ever get our i3max!!). Also note, he sells pre-made ones of these, which look amazing.. I glued the sections together using 3D Gloop for PLA.Note: Unlike @sbeecroft's model I was never thrilled with how the screw threads on the fuse worked, (likely due to the issue of the fuse being SLA printed and the shell being FDM), so I made the fuse glue-in (I used epoxy)The painting was complex, and I used a variety of paints, including the flat-army-green spray which matched the spec'ed color, along with the flat-yellow (CAT yellow). For masking I used the included mask which I laser cut is laser safe masking material (laser safe critcut sheets) which I use movable spray adhesive to place (note make sure it sticks well if you don't want to be doing hand touchups). Krylon makes a nice copper spray paint I was able to get at Home Depot for the copper rifling band.I have included the reference artwork I got for the fuse painting. I used acrylic red with a very fine brush for the next and screw indicator. To be honest I needed to touch it up with a red fine-point sharpie for it to work.I ended up putting about 15lbs (6kg) of cement in the base as it kept tipping over. The fins are designed to grip the concrete so it doesn't shift around. When you glue each section together (I used 3D Gloop for PLA) you will need to use model putty to get a nice smooth finish.Diorama Accessories [NEW]I was making a diorama using the Trumpeter 1/35 scale M198 howitzer and the shells in the kit are garbage (the 777 isn't available yet) for someone (they are based at a muddy location so not the usual sandy location everyone does, and it just needed some other stuff to make it realistic. I added some cool (or I think so) handy accessories which will probably be stupid at full size (well the charge storage rack would be like 200kg of filament at full size so no), which I needed when I made the diorama at 1/35 scale = scale 0.03 (resin printed) where I just made the shell as a single piece with the fuse separate (that was a really stupid idea since the fuse at 1/35 scale was around 1x1.5mm in size (there are a lot of them on my floor I can tell you). Anyway the parts are as follows:Propellant Chargemodern howitzers used separate fabric wrapped propellant which are chained together to create the zone of fire (1-6 bags = zone 1-6 distance); bags used in zones 1-3 are teal green and 4-6 are tan, the carrier above is set up for a zone 2 fire. I could have made some clever locking thing but honestly at that scale a tiny dab of CA glue was equally good (see the photo). Note the inset on the end was to make the red (primer area that faces out the breech - “All Clear, Red to the rear”) acrylic paint stay in the circle (for some reason in the photo it looks like it is coming up the side but it's not. Note the propellant fits into the rack (which is slightly oversized to fit the clearance at that tiny scale). . Obviously if you are FDM scale printing it you would be doing a diorama in something like 1/16 scale or something as 1/35 would probably not look very good at 1/35. Note I didn't bother with the black stripe around the side as it would be really hard to put on smoothly since the line would be like 0.3mm or so at that scale.Charge Rackone of the major advantages of NATO artillery systems is their logistics for storing the propellant. The Russian army is currently using wooden crates (welcome to WWII style) while the US uses a modular rack that locks the tubes that hold the propellent into a grid system. (see the photo of the detail) You see the rack with one charge bag sticking out of the tube (it's a diorama I took some artistic license) and yes I am aware that the HESCOs would not be cocked like they are given they are soft-sided and weigh hundreds of Kg, but the grout I had used as “dirt” I hadn't worried about stacking before it dried so didn't worry about the flatness.Solid capped single shellWhen printing the tiny shells for the pallet in the back I ran into the problem that at that size the walls were too thin even for a resin printer. So quickly realize I needed a cap to make the slicer print it as a solid part (I guess you could do this full size on a really big printer this way too). This prints as a single part as gluing the multi part at that scale would be terrible.Print instructionsEach section is designed to have a print surface (the one with the holes, not the alignment spikes. The bottom obviously prints base down. Note, I printed the fuse on a SLA (Form 3) as the lettering and screw won't show on FDM most likely, in a gray resin (although since you are priming it doesn't really matter).Note even though you may be tempted to just use the army green PLA as is, it's too glossy and you need to sand the model to get rid of layer lines anyway; and if you use putty for the joints it won't work anyway: I used Tamiya model putty. To me the advantage of the army green PLA is if the paint gets scratched it will reveal green rather than some random color.I used the stock Prusaslicer 0.15mm Prusament settings, with 15% gyroid infill...CAD ModelsI added the STEP and SOLIDWORKS model files for those who wish to modify them.