Armory Sponsor
81mm Mortar barrel/tube/build info (Page 14 of 15)
The reloaded fuzes worked great.  81MM mortar spotting charge Shot it without the windscreen, and no visible damage. The striker moves freely so I think I should be able to reload it again. Might have to clean the channels where the springs and pins go but should work again.   
|
|
Got my sight from Bowman today. Pretty neat to complete a piece of history, even if my Vietnam-era sight is more user friendly. Attached File |
|
Congrats, if you're not going to 3D print shells, then make those a priority. They don't come up for sale often, but people out there will have some gems when they do. When doing load data, it's easier if the shells are all the same model because of weight, fins and fuze threading. Also have a clean impact area/line so you can find your rounds easier. When working on load data, place your tube at the highest elevation possible between, 85-89 degrees and then lower your angle on the tube till the rounds land in your designated target area. |
|
Originally Posted By Kornbread: Placed my order. This will be my first so any and all advice is appreciated! Have a full machine shop at my disposal so if there is anything that needs to be made for these, shoot me a message! Congratulations. This thread cost me money 2 years ago. I think I documented everything I did here, but when yours gets in feel free to ask any questions. |
|
Originally Posted By MHIDPA: Congratulations. This thread cost me money 2 years ago. I think I documented everything I did here, but when yours gets in feel free to ask any questions. Yeah...I need to start doing some research but I've been wanting to upgrade my 07/02 for awhile. This is the excuse! I appreciate it! |
|
Originally Posted By walkinginadangerzone: Congrats, if you're not going to 3D print shells, then make those a priority. They don't come up for sale often, but people out there will have some gems when they do. When doing load data, it's easier if the shells are all the same model because of weight, fins and fuze threading. Also have a clean impact area/line so you can find your rounds easier. When working on load data, place your tube at the highest elevation possible between, 85-89 degrees and then lower your angle on the tube till the rounds land in your designated target area. I can 3D print or machine if necessary. Any recommendations on where to look for originals? Anything else I need to look for? |
|
Originally Posted By Kornbread: I can 3D print or machine if necessary. Any recommendations on where to look for originals? Anything else I need to look for? A sight (not mandatory) Bowman has some Italian ones available, but you'll have to fab an adapter to work with the Yugo bipod (not difficult). |
|
Originally Posted By Kornbread: I can 3D print or machine if necessary. Any recommendations on where to look for originals? Anything else I need to look for? Originally Posted By Kornbread: Originally Posted By walkinginadangerzone: Congrats, if you're not going to 3D print shells, then make those a priority. They don't come up for sale often, but people out there will have some gems when they do. When doing load data, it's easier if the shells are all the same model because of weight, fins and fuze threading. Also have a clean impact area/line so you can find your rounds easier. When working on load data, place your tube at the highest elevation possible between, 85-89 degrees and then lower your angle on the tube till the rounds land in your designated target area. I can 3D print or machine if necessary. Any recommendations on where to look for originals? Anything else I need to look for? I've found mine from random users in gunbroker and ordnance.com |
|
Originally Posted By Sonoran_Tj: I ordered a 3D printer last night. I have a pile of those tail fin sections from a few pages ago. It's time to start making projectiles. Are any of the 81mm projo drawings open source yet or do I need to start from scratch? If you have Solidworks or a compatible 3D CAD software, I can send you my stuff to play with. |
|
Originally Posted By MHIDPA: If you have Solidworks or a compatible 3D CAD software, I can send you my stuff to play with. Originally Posted By MHIDPA: Originally Posted By Sonoran_Tj: I ordered a 3D printer last night. I have a pile of those tail fin sections from a few pages ago. It's time to start making projectiles. Are any of the 81mm projo drawings open source yet or do I need to start from scratch? If you have Solidworks or a compatible 3D CAD software, I can send you my stuff to play with. After work today I'm going to download the free version of autodesk fusion. If that works then send them on over. If I'm not happy with fusion I'll pay up for solid works, its only $20. |
|
Originally Posted By Sonoran_Tj: After work today I'm going to download the free version of autodesk fusion. If that works then send them on over. If I'm not happy with fusion I'll pay up for solid works, its only $20. Look like the free version of Fusion doesn't take Solidworks files. Shoot me your email address and I'll send you STEP files that you can play with. |
|
Many thanks to @MHIDPA I used his mortar design as a baseline and inspiration and have my version 1 3D printed round. Modeled after the practice rounds I got from Bowman, and uses MHIDPA's fuzewell and fuze. Rear threads accept the U.S. tail fin sections from Sir Plus surplus. I did redesign the solid fuze/nose cone to be hollow as well, I want more internal volume for weight. The threaded fuzewell and fuze are brilliant, thank you for that design. Hopefully, these will be strong enough that only the fuze needs to be replaced after impacts and the bodies are reusable. I printed it with 5 walls, 20% cubic infill, .2mm layer thickness. There is essentially no infill due to the overall wall thickness. Feels really sturdy. Internal volume is 400cc, empty round weighs 1 lb 6 oz, with the solid fuze.I'm going to run the numbers next to see what filler is cheapest and heavy enough. If there is interest, I can upload these files somewhere to share. Attached File Attached File |
|
I spent the week toying around with a 3D printed spotting fuze and got a prototype to work today. I used generally the same form factor from MHIDPA's design. The spotting fuze is made up of two parts and fully 3D printed. The main body is designed to hold a 209 primer and has a cavity sized to fit 100 grains (<.25 oz) of black powder. The nose cone contains a 3D printed firing pin and is designed to crush on impact. I printed up a few versions today and drop tested them off a 6' ladder. They're working well from that height. I also confirmed my mortar body design is heavy enough with concrete fill to fire a lift charge primer. Attached File Attached File Attached File Attached File In the last picture you can see what's left after the drop test. The nose cone broke, allowing the firing pin to compress into a channel leading to the primer in the body of the spotting fuze. The spotting fuze itself also broke, the bottom part is in the background of the picture. I suspect this is preferred as it'll allow the smoke and gases to vent better when it goes off. The firing pin is still in the fuze body in the picture. The firing pin was strong enough to detonate the 209 primer and didn't break. I'm loading up some lift charges and will hopefully be able to shoot some test rounds in the next few weeks. |
|
Originally Posted By walkinginadangerzone: Neat, does your design blow up the fuze? Or do the gasses travel into the mortar body and vent from there? The design intent was to vent out the front of the fuze. I haven't tested it with a black powder charge in it yet. In a drop test off a ladder with just a primer, the fuze body broke in half and that should vent just fine. I may refine the design to have vent channels in the fuze body. I don't want the gases to vent into the body. The bodies are concrete filled and will hopefully hold up well enough to be reusable. Same as MHIDPA's design, the bodies have a threaded top cap that accept the fuzes. They are sealed units. |
|
FINALLY got my unit in this week. Bowmans 7-10 day ship estimate was more like 20-25! Can someone walk me through the proper set up on these Yugo kits? I guess thats a good first step. Mine has a painted line all the way down the tube and base plate. I have found that those have to be lined up and the tube needs to be around a 45 degree angle in order to install and remove the tube from the base socket. Do they also need to be lined up when firing? Or does it need turned? Looks like the demill process was severe. A welded in bolt at the muzzle - which I already removed. A large hole at the base of the tube. A smaller hole in the cup and it appears the firing pin is gone and possibly welded over? |
|
Nice, congrats. Set up is fairly straight forward for shooting. Digging in your base plate should be considered as a must, don't want to your mortar to slip during firing and injure you or probably mess something up on the system as there are almost no replacement parts. (even if your not using full power loads, makes great practice)  I like to set the triangle base plate with the flat bottom facing the target but either orientation is fine, and the handle facing back like in the pic. Also makes it easier if you align your safety to face outwards, this way you can always see it at a glance. Sucks going to fire a round, only to realize you forgot to remove the safety, then having to go through unloading procedures, and ruining a lift charge.   Before your clamp in your barrel, make sure to orient the clamp in the right direction. The recoil shock absorbers should be facing down the barrel. Like in the below pic. Bi-pod set up is easier for the gunner if you face the crank handle inside, that way you can lower or raise the barrel, and the cross leveling mechanism should be to the left of the system. This way the gunner has an easier time making adjustments while looking down the sight.  The white line is more for armory stuff, like zeroing the sight, or sighting in the mortar with the compass. Before you key in your barrel to the baseplate, you might want to clean up the weld at the bottom of the cup ball so it fits better and to not gouge up the socket in the baseplate.  The cup ball has a flat ring on it, so you need to stand the barrel straight vertical it'll drop into the socket, might have to angle it just a few degrees to a certain side.  45 degrees is where your max distance is going to be depending on lift charge load. But IME the rounds were too light to use 45 degrees on the tube effectively, probably had like a 60% dud to fire ratio. Depending how much powder you want to use on your lift charge, it'll depend on your tube angle. Personally I like a higher elevated tube so I could use more powder, for a bigger bang/recoil impulse and it also helps the rounds fall faster down the tube thus setting them off more reliably. (for newly produced barrels) I've also found that cleaning and swabbing your barrel with oil/CLP a day before range day helps in the rounds sliding down the tube easier. And when firing as well, swab after every 5 rounds or so. |
| walkinginadangerzone covered most of it. I'll add that the white line is helpful for rough aiming especially if you don't have a sight. Depending on how your cup is demilled, I would unscrew the plug in the bottom and look to see if the firing pin is there. If it's just welded in place you can probably free it by grinding away the weld at the tip. If it is missing, I can make a drawing of mine for you to make a new one. |
|
Tested my printed mortars this morning. It was not very successful. I shot three rounds, all three failed the same way. I did not get any data for the fuzes. The body broke off at the top of the tail fin threads in the tube. The tail fins stayed in the tube and the body went flying end over end about 300 yards. It looks like layer failure just above the threads. I'm not sure what I need to do to reinforce that area. 100% infill may fix it, or more material. Possibly a different material, PLA+ isn't the strongest out there. My guess is the area above the fin threads compresses when the mortar hits the bottom of the tube, then tears as the body is propelled forward. The fin section is heavy enough it just rips off and stays in the barrel. Attached File Attached File Attached File |
|
Originally Posted By MHIDPA: I don't think printed threads are going to work for fins. Everyone I've seen either uses a bolt or a piece of all thread going through the bottom of the printed shell. The threads themselves aren't failing. Its the plastic just above the threads that fails. I'm going to try a couple things. For the next model I'm adding width in the threaded area. I'll also print with 100% infill in that section. In another version I'm going to model in 6 holes to insert metal rods for structure. I may also try printing in other materials. PETG may be better suited as its less brittle. Or ABS, but that starts to get more expensive which I'd like to avoid. |
|
Originally Posted By Sonoran_Tj: The threads themselves aren't failing. Its the plastic just above the threads that fails. I'm going to try a couple things. For the next model I'm adding width in the threaded area. I'll also print with 100% infill in that section. In another version I'm going to model in 6 holes to insert metal rods for structure. I may also try printing in other materials. PETG may be better suited as its less brittle. Or ABS, but that starts to get more expensive which I'd like to avoid. I'm surprised that you aren't already printing in 100% infill. How are you getting the spent shells out without drilling a hole in the tail for a punch rod? |
|
Originally Posted By SGT-Fish: I'm surprised that you aren't already printing in 100% infill. How are you getting the spent shells out without drilling a hole in the tail for a punch rod? I'm not sure why I didn't print 100% infill. The body around the cavity is functionally 100%, 5 walls inner/outer make up the whole width of the plastic there. The infill created voids just above the threads which was bad. I put the shells through a washer and then into the tail fin. The washer gives me a point to lever off of with a screwdriver to pull the spent shells out. They're ASME narrow 3/4" washers, McMaster-Carr pn 90474A158. Attached File |
|
Originally Posted By Sonoran_Tj: My guess is the area above the fin threads compresses when the mortar hits the bottom of the tube, then tears as the body is propelled forward. The fin section is heavy enough it just rips off and stays in the barrel. Same failures ive had with my fully printed designs. Its happening because the thing is whipping in the tube causing the layer lines to shear on pla+. PLA+ layer adhesion is insufficient and honestly too low. PETG is more flexible but honestly too weak. PCTG will do a lot better, you need materials that are as close to isotropic as possible. No fiber fill either in any of these as it will retard layer adhesion more. You can also experiment with punching a hole in the middle of your thread stack, drilling a hole in the tail section and then bolting the entire thing together to allow the bolt to act like compressive rebar. Ive made some progress on mine but have been too busy teaching to get out and hang em, all in good time. A fully printed round is 100% possible. 
|
Ended up having 3 fin adapters made. They're a little longer than they should've been, I'll get them shortened next time I get more. But at least now I can use atleast 3 of my practice rounds.  Originally Posted By MHIDPA: Bump to stay out of the archive Thanks for that. |
Two rounds fire for effect. Lol 81MM Mortar practice rounds |
| I just received a bunch of Bowman Yugo M69B 81mm sets. I haven't even opened them up yet, as I have 87,000 things happening right now- without me digging through the whole thread did anyone ever determine if there is in fact enough meat left to cut the tube above the hole and rethread for the cup? Or the consensus ended up being weld or get a new tube? |
Twitter/Instagram: benunsuppressed
https://americanpioneercorps.org
https://americanpioneercorps.org
|
Originally Posted By Ben: I just received a bunch of Bowman Yugo M69B 81mm sets. I haven't even opened them up yet, as I have 87,000 things happening right now- without me digging through the whole thread did anyone ever determine if there is in fact enough meat left to cut the tube above the hole and rethread for the cup? Or the consensus ended up being weld or get a new tube? You can't rethread the tube, it is smaller than the minor diameter of the threads. What I did was cut the tube off above the demill, then I turned down the tube about .050 and press fit a threaded sleeve. It shortened the tube down to the length of a US 81. I think this solution is safer than a reweld but much cheaper than a new tube. |
|
Originally Posted By MHIDPA: You can't rethread the tube, it is smaller than the minor diameter of the threads. What I did was cut the tube off above the demill, then I turned down the tube about .050 and press fit a threaded sleeve. It shortened the tube down to the length of a US 81. I think this solution is safer than a reweld but much cheaper than a new tube. What OAL was the tube prior to adding the press fit piece, and what were the details on the threaded sleeve you used? Unfortunately my shop is completely inundated with making FRTs right now and I seriously can't even entertain retasking anyone or any machines, so I'll be needing to go to a friend to have this done unless I wait til we bring more machinery online. I also don't have a lathe in my shop that can thread an 81. |
Twitter/Instagram: benunsuppressed
https://americanpioneercorps.org
https://americanpioneercorps.org
|
It's 50" after being cut down and faced. This post is where I showed making the sleeve. I can't remember the thread dimensions off the top of my head. It's a proprietary major diameter and 11tpi (I think) anyone you would trust to make it can figure that part out and fit it to your cup. |
Perhaps try this instead of a machined adapter. Separate the main body from the tail fin adapter for print orientation, use 100% infill on the tail fin adapter, and use an epoxied stud and hole to mate them back up after printing. Use a thread tap to manually tap the threads instead of printing them in place. |
|
Originally Posted By MHIDPA: Just this one for now. A buddy blasted and powder coated it. I want to make sure the thickness of paint doesn't affect firing before I do them all. The fuze well threads are 1 1/2-12 as far as I can tell that is standard across US mortars. I got a tap off eBay to chase threads in the rusty M880 bodies. Any updates on how the powder coat is holding up? |
| It holds up better than regular paint, but it still cracks/flakes in impact areas. I think coating them then having a matching spray can for touchups is probably the way to go. Plus realizing that launching a 7lb metal egg a couple hundred yards is just not gonna stay pretty. |
81mm Mortar barrel/tube/build info (Page 14 of 15)
Armory Sponsor