Ahoy folks! I was bored while waiting for parts for my Big Gun cannon project, so I decided to do some CAD modeling. Nine hours later my parts finally arrived. Anybody care to identify this ship? Click the thumbnail for full size. BTW my plans were a little hazy on the details. The number/shape/location of funnels, masts, fighting tops, flying bridges, secondary guns, tertiary guns, quaternary guns, ventilation scoops, and anchor decks may not be 100% correct. I'm not even sure if the barbettes should be circular or pear-shaped. What I can tell you for certain is that it has twin 12" main guns, two shafts, one rudder, and a very prominent ram bow. I hope that helps.
Yes, it is the battleship Mikasa. Or the Asahi, or the Formidable, or any of a couple dozen predreads built in British yards. Turns out they were all built to basically the same hull, with only minor differences like compound vs harvey armor, fire-tube vs water-tube boilers, old-pattern or new-pattern 12" main guns, or an extra set of secondaries or tertiaries. My goal is to turn this into a printable Big Gun battleship that can wear a variety of paint schemes and flags. I am also working on a printable Big Gun cannon sized for predreads and early dreadnoughts.
I was thinking Formidable too...the notched bow is a giveaway from that whole series of cookie cutter but internally improved ships
I spent a good chunk of this week playing about with the Mikasa model. It is getting close to ready for an initial test print. A lot of internal detail isn't determined yet. I won't know those details for sure, however, until I actually get a physical model that I can play with, flex, and float-test. The cannon design is pretty much done, too. I'll post photos of that when it's ready. The prototype is working very well, though. My shop compressor can put out 120PSI, and at that pressure it's clocking around 150FPS. You'll notice that certain details have been omitted. The thick balsa used by Big Gun can be difficult to work with, so I am doing my best to make this hull easy to sheet. That means the hull curves aren't quiet as complex, and the complicated anchor decks have been eliminated. Furthermore, rib spacing is fairly broad, with 3/8" ribs and more than 3" wide penetrable windows. The hull will meet WWCC hull construction requirements. Unfortunately this means it cannot be used for Fast Gun, but I could find no good way to meet both rulesets. Thanks to the small footprint of the cannons, I will be able to fit a 5oz CO2 bottle in there. It's also getting standard-sized servos for rudder and firing. I'm not completely sure about turret rotation yet. If I use standard gear-motors, I'll be able to use an ant-weight combat bot board (1.5" x 1.5", two fully reversible 10A ESCs and a non-reversible 15A ESC) for control. That would make the wiring extremely simple, and it's easy to waterproof. The down-side is I'd only have velocity-control for turret rotation, not my preferred position-control. That position control has proven extremely important in the past. So I'm not sure yet. At least I don't have to decide yet.
Her? You mean THEM! Why settle for one when you can spend a little more time and money and build at least FOUR of them? MWAHAhAHAHAHAhahaha! I've already invested the design effort. Unlike previous projects, I won't have to glue several sheets of plywood together before cutting, either. I can just press file-print a few extra times. So much easier. Predreadnoughts have so many delightful options for color schemes, too. I'll paint the first pair in Vickers Yard colors. As for the next pair, maybe I'll do my favorite East Asian white-and-buff, or perhaps Home Fleet black-and-buff. The French, Germans, and Russians had some interesting period-appropriate paint schemes, too. The first couple test pieces came off the print bed this evening! This test hull will primarily be for test-fitting and ballasting. While I know approximately where all of the major parts go, I still want to do a proper float test with all major components, so I can ensure ballast is properly placed for optimum stability. I suppose a CAD master would just model everything, tell the computer how much each part weighs, and let the computer determine the ballast, but honestly I find it easier to work with real physical objects. I can feel things and move things, and also check ergonomics. How easy is it to remove this cannon for maintenance, and how will that change if I put a cross-brace there? Does it even need a cross-brace there? How easy is it to perform post-sink maintenance? These are all important things to consider that I can't figure out from a CAD model alone. I'll also find out all sorts of details I forgot to include the first time around, like deck hold-downs and alignment holes. Speaking of physical objects, these are prototypes for the cannons I plan on using. They use a standard 1" copper tee fitting from my local hardware store, which gives approximately 3 cu.in. of accumulator volume. The valve and endcaps are 3d-printed, with o-ring seals. That means they are removable and re-arrangeable. The flat tee accumulator will go in the bow, while the vertical tee accumulator will go in the stern, to better fit between the drive shafts, but they use the exact same parts. The magazines are 3" OD, currently with a single-layer magazine and sliding pistons to close the breech. The chronograph reported an average velocity of 150fps at my compressor's limit of 120PSI. A single layer holds approximately 110 rounds, or about 55 shots. There is enough height for at least 3 layers overall, but I don't know if I'll actually put that many in due to stability concerns with that much steel high up in the boat. I'm also not sure about a depression mechanism - it's a lot of extra complexity, and this ship may not need it in the first place. If I do include a depression mechanism, I'll have to get creative to fit the servo, since the magazine is so small. I ran A LOT of garage tests with a variety of different valves, accumulators, and magazines before settling on this design. Hooray for 3d printing! I learned so much from this development process, I'll have to see about writing up a summary of lessons learned in the future.
Printing of the prototype continues apace. Now that I'm on the largest sections, a fearsome old foe has reared its ugly head: bed separation and warping. My printer is just about the best setup you'll ever get for printing ABS. Heated PEI bed, heated enclosure, and settings carefully dialed in over hundreds of prints. Unfortunately these prints are at the very limits and I'm getting a little bit of warping. The first big section had built-in bilge keels. The starboard bilge keel warped badly, so the next big section I printed without the bilge keel. Still had warping, as you can see. While it's unacceptable for a final product, this little warping won't prevent me from completing the prototype. It'll still be good for ballast- and fit-testing, and it's really helping me find those dumb mistakes. I've still got another trick or two to try and eliminate this last little bit of warping. I noticed that the warping is consistently on the side with the most open seams. I'll be going over all the seams with tape to prevent cold air leaking in. And if that doesn't work, I'll try some relief cuts, so whatever shrinkage does happen puts less strain on the print bed. I'd have to fill in the relief cuts later for strength, but that's fine. And if, in the end, it proves impossible to print full hull sections, I'll split the troublesome segments in half. That will unlock additional options for me like a nice fat brim for maximum bed adhesion. Well here is what I've printed so far. Five of eleven segments printed, and test parts starting to go in. The stern cannon nestles perfectly between the shafts, down in the water channel. Motor mounts are not designed yet, because I don't know exactly how far aft they need to be for proper ballast. If I can push them further amidships, that'll leave a nice space for a bilge pump just forward of the accumulator. I'm also not sure about turret rotation yet. Gotta finish printing the ship so I can test-fit and find a satisfactory arrangement for both bow and stern cannons. If you look closely at the subdeck near the copper accumulator, you'll see a hole. That is for attaching one of the 6-inch casemate guns after sheeting. Hopefully that'll be easier than trying to fit balsa around a permanently-installed casemate. I forgot to keep the solid backing, though. One more detail to add back in. I've also modeled the hooded barbettes. As you can see there's a lot of barbette and not much hood. Only the turret and the small flat bit around it actually rotate. Everything else is fixed from the sloped portion on down. I might have to fudge that a little, if I want to fit a depression system in. There's plenty of space belowdecks for the servo, but there's very little room for the hardware in the turret. I'm already planning to change the orientation of the depression system from the standard arrangement. That portion of the design is still classified, though. So no pics yet.
Youve got to tell me your secret to getting ABS to stick to heated PEI. I use the same sheet at 110c and one part will stick and the next will slide all over. I have had a lot of success using thick ABS slurry on glass though the surface finish is pretty terrible.
I use a heated bed 110C as well. I regularly clean the PEI with isopropyl alcohol. And for the prints I'm really worried about, I will very lightly scuff the PEI surface with a greenie. Actually it's isopropyl-scuff-isopropyl, to ensure maximum cleanliness. This gives me better results than ABS slurry, air spray, wolf bite, kapton tape, or any other surface I've tried. It's still not perfect though, as you can see.
I've had luck with textured beds, well cleaned with alcohol, running 113C on the back face of the bed. I've had to put stress relieving slits in larger ABS models to handle warp gracefully.
Well this is interesting. I finished the last big midships section, and the use of relief slots has stopped the bed separation. Even the bilge keels, the most susceptible item on the list, stayed put. It's taken some experimentation, and I' still have to determine the best relief slots for each section, but the theory has been proven quite effectively. However, a new problem has reared its ugly head. See those lines? Those are a problem with the X axis. Something has been causing inconsistent travel on the X axis. Most curiously, it appears to shift almost exactly 0.45mm each time it shifts, and it always alternates directions, for an overall X-axis error of 0.9mm no matter the size of the part. This has been a very rare but on-going problem for the last year, but it's been getting more frequent lately. Today, every single print was squished. Compare my latest cannon valve body (center) to one I printed three days ago (left): I spent most of today troubleshooting and testing and browsing forums for similar problems. I had given up and was writing up my symptoms in a trouble ticked for Lulzbot when I realized that the circles on the botched valve body look weird. It's not a smooth, squished circle. The circles are flattened off, almost like the X axis wasn't moving for the first few seconds or so after each direction change, and then it would start going. I then gave the print bed a little push, and noticed that it slid a little without the motor moving. Aha! I checked the setscrews on the pulley for the stepper motor, but those were tight. Then I removed my heated bed, and wiggled it some more. Finally I saw what was happening. The screws connecting the print bed to the X-axis belt had worked themselves loose over the last few thousand hours of printing, and now had about a half-millimeter of play. I have now tightened down those screws, and checked tightness on many of the other screws in the printer. I've got two test cubes printing now, and if they actually measure 10mm each then I'm back in business. I still have about 1/3 of my plastic spool left, so hopefully I'll be able to squeeze out the rest of the hull before I run out. If so, that means the entire hull requires less than 1kg of plastic. In other news, parts are starting to arrive. Last week the regulators arrived. Today, the 5oz CO2 bottles arrived. I already have stacks of motors suitable to the task. I have bushings, screws, and other hardware on order from Mcmaster-Carr. As for pumps, well... I still have some CAD modeling to do.
Nice. I've had good luck keeping the slits within 1.5 inches of one another. another big thing is to keep the slits normal to the surface to keep from making areas prone to cracking.
I am unfamiliar with the use of "relief slits" - can you illustrate/explain their design and function?
Literally slits one nozzle diameter wide, they are put in throughout thicker sections, always staggered and never full height. Makes part more flexible, reducing overall warp. Brush of acetone seals them right up. Let me find a picture See bow section and zoom in https://rcwarshipcombat.com/attachments/img_20211117_233112-jpg.27023/
Aaahh, I see - thank you for the explanation! At work we send ABS print requests to another printer lab - we are set up for mainly PLA for prototyping, and PETG/TPU for finished parts. PETG doesn't exhibit a lot of warping, but the relief slits would be useful for wider parts. We'll have to experiment with solvents to find one usable on TPU, because that definitely experiences warpage.
I have no issues printing entire hulls in ABS 100c bed purple glue stick. No relief slits necessary. I have 7~ ABS cruisers in my garage right now and an entire Queen Elizabeth class. If you are having warping/bed adhesion issues you need to enclose + insulate and add enclosure heating.
oops. Good thing this first hull is just a test, not a final product. Will, how extensively sealed and insulated is your enclosure? What temperature do you maintain inside? My printer has a very nice aftermarket enclosure, with a temperature-controlled heater. It can reliably maintain around 115-120F (49C) in the enclosed area. Even if I could go hotter, I'm not sure I'd want to. The idiots who designed my printer put the "cold" side of the main board's heat sink on the inside of the enclosure.
