7.62 x 39 mm round

by clintkc, published

7.62 x 39 mm round by clintkc Jan 4, 2012
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7.62 x 39 mm round by clintkc is licensed under the Public Domain license.

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This is a 7.62 x 39mm round. This is NOT my design (downloaded from a 3D CAD resource on the net with no designer's name).

I wanted to print it out to test the Thing-O-Matic's ability to print objects that are much taller than they are wide or deep. I printed it with a raft, no support, 20% infill (mainly for weight than stength), and 2 shell layers.

The print went very well, up until about the end of the "casing" section. Since I designed my filament guide, I don't have to baby-sit my TOM nearly as much...so I let the print run while I ate dinner. I visit to my upstairs office found that the base of the bullet was rocking back and forth, fore and aft during the print. My nozzle seemed extra close to the printing object, which caused drag and probably caused this error.

Anyhow, this object printed just about how I expected. The TOM shakes about quite a bit, and I wondered how well it would do with tall, narrow objects like this. ANSWER: Not very well.

I'm relatively new to the MakerBot scene (had mine almost a month now), but very familiar with CAD and CNC. My belief is that objects such as this (if not all objects) should be printed with a moving extruder, not a moving build platform. (I could be wrong... I was once before, back when I believed I was mistaken... heh heh.)


Print (at your own risk) with your own settings, and see what you can do with it. Please note that my print was NOT successful. I have no further ambitions with this design, other to mark it up as a learning process (i.e. "do not print tall, skinny things").

Please note that the STL file name is wrong... on my SD card, it was "7.62..." not "62..." No, I'm not an idiot. :) I did my time as a Marine infantryman, and I definitely know my weapons & rounds. This is NOT a 62mm round! :)

Best of luck! :)

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LoL i would be embarrassed to put a picture of that on the interwebs

Thanks so much to everyone who posted photos of their prints, and to those who made comments... many of them very helpful ones. It's clear to me that I need to explore my Skeinforge settings... something I've been afraid to do, because I've had a very hard time finding any sort of meaningful documentation about what all of the settings mean.

Yes, I've found a few helpful posts in the User's Group, as well as a lot of helpful info on various searches done with Google and Bing. However, I am an extremely detail-oriented person, and have found no complete Skeinforge information. I found and printed a nice page that half-way describes e
ach section of the Skeinforge settings, but not in NEARLY enough detail for my tastes.

In most cases, it doesn't describe exactly what each setting does, how it effects your prints, what the risks are with adjusting certain settings, doesn't recommend settings for medium, regular, or high-quality
prints, and basically left me feeling empty.

I have found the MakerBot documentation to be poor, at best. Bre and the gang at the BotCave have truly revolutionized the 3D printing era, that's for sure... but I expected MUCH better documentation from such a truly remarkable
amp; complex device. So far, I've found myself searching blog after blog, forum after forum, and doing basic internet searches for everything I've felt a need to know. Otherwise, I've learned by trial-and-error (truly the best method for learning anything, although there are always better (and faster) methods).

And I apologize to those of you who have suggested that I seek my information elsewhere (i.e. groups, forums, sending smoke signals, carving messages into stone for my ancient ancestors to find, et cetera)... I apologize for using Thingiverse as I do Facebook (saying whatever is on my mind, and wh
enever it happens to pop into my mind)... but I've gotten MANY more positive results from this.

I apologize to whoever owns Thingiverse, and is paying for the storage space there. It's still not clear to me who owns Thingiverse, as I constantly see designs for Mendels, Prusas, etc, etc, etc. In f
act, I see more designs for those 3D printers than I do for any MakerBot product (and it's my understanding--or so I thought--that MakerBot pretty much started Thingiverse (I could be wrong).

I don't have ANY problem with Thingiverse hosting designs for other 3D printers. In fact, I find it very h
elpful and informative. However, I do have 2 issues with Thingiverse (see next post):

(CONTINUED)... 1) I would highly appreciate it if designs were categorized by:

       a)  Printer the designer owns (some posters do not even own a printer)

       b)  Printer the design was printed with

2) I would appreciate stronger posting protocols. I'm seeing many designs that are not 3D printer capable, and usually have no comments or actual build photos attached. And usually several in a string from the same person. I understand that it would require a dedicated staff-member (or several
) to screen posted designs for quality and/or printability... however (as a successful businessman myself) I also understand the need for consistancy, quality, and eliminating wild-cards.

So far, I hear myself as the only one complaining. And that's fine... MakerBot is a fairly new business, and s
eems to be overwhelmed. They've done some great advertising, made a great product, and can't seem to keep up with the demand. Their shipping times are terrible, at best. Their documentation is sparse
amp; inconsistent. And their customer support refers me to Wiki pages that give very vague answers to my questions.

It's a great product, but needs improvement. I realize this is an "open-source" based product... however, if MakerBot doesn't take it to the next level, they will be over-run by another company with the balls to make real things happen.

And I hate to say that. MakerBot could make it. But they'
d better take some huge steps forward. Otherwise, they'll not last long.

My 2 cents. And 2 cents ain't worth much these days, I know.

The picture above shows the result of the "cool" settings, I mentioned below.

I like your "cool" settings comment. I have not tweaked the "cool" settings, only noticed that the "cool" portion of Gcode compilation do not take very long. Like I said earlier, I definitely need to learn
amp; adjust my Skeinforge settings.

I like the Corsair you're holding in your profile pic... are you an R/C guy? I've been building R/C planes since I was about 10, but my current inventory only consists of a SIG Kadet Senior with an O.S. 46 (extremely basic, but I still love to fly it... I modified the wing dihedral so that it's a
lmost flat, and it performs very well for what it is) , a Hangar 9 Aresti 40 with a 4-stroke Saito .72 (this thing will move and dance), and still in the process of building a Top Flite Cessna 182 Skylane kit that I bought over 10 years ago (with the full interior kit), etc. I got married since I b
ought the kit, and have moved it from 5 different houses. (I'm a general contractor and insurance adjuster... either I'm 5 states away from home for 6 months at a time, or I'm too busy designing and building homes. And I'm also waiting for a suitable gas engine to put into my Cessna 182, as well a
s re-designing a lot of things (especially the paint scheme) to look like a more modern version. I have a vinyl printer (and now a 3D printer) which should help scoot things along. The wing is built, the fuse is 1/2 built, the tail feathers are complete, and I"ve been packing these build parts aro
und for 8 years. I haven't worked on this model for 9 years. I want the fully-functional "fowler" flaps, I've got the LED lighting kit from RAM (even the rotating beacon), and I plan to make this look like a real Cessna 182. I've been around 'em all my life. I've flown planes, designed model air
planes, designed jet aircraft in conjunction with Lockheed-Martin for a private investor... I basically live my life in 3D. Kinda sad, really. My wife stares at the back of my head. :( I tell her it's better than staring at the front of my head. :)

There, I added an image of it printed on a printer with a moving head rather than platform like you were thinking about.

Not the greatest print (or picture... whitebalance? We don't need no stinkin whitebalance!) since my belts are loose, but it gives an idea.

I'm not trying to be negative here but I thought I should provide some correction on the information provided here. The 7.62 x 39 is not the .308 caliber nor the standard NATO round. It's actually a russian cartrage from the 1940's. The NATO 30 cal round is the 7.62 x 51mm, which is also the .308 in USA. The 7.62 x 51mm is somewhat longer than the russian round and has a higher pressure/ muzzle velocity. I use the 7.62 x 51mm military surplus ammo frequently in me .308 for cheap target shooting.

Just wanted to make sure there wansnt any confusion.

Anyway thanks for posting the file.

Have a great day.

You're right. My bad. :-[

I wonder if these will feed and extract properly...home-made snap caps, anyone? I'd love to try other calibers, do you remember where you found this one?

UechiMike - in reply to

It's definitely not 7.62x39 - Mine's pictured next to one for my Mauser. But I like the idea of making "snap caps" in different calibers.

Hey... I downloaded it off of some free CAD server, and that's what the author called it. I didn't pull shells out of my SKS and spend an hour miking everything to make sure it was a 7.62 x 39mm round. It looked like one, and I printed it.

Poor results in my print, and poor results in my feedback.

Sorry to disappoint anyone. My results have very rarely resulted in this much negative feedback. Next time I'll pull a full background check on whoever designed the file.

Better yet, I'll just post my own friggin' designs from now on.


clintkc - in reply to

I use a lot of different CAD providers. Couldn't tell you where I found this one... sorry. But yes, snap caps was the idea.

I printed this on my Emaker Huxley. The only change I made to your settings was to turn on Cool in Skeineforge and set minimum layer time to 10 seconds. This will allow the layers to cool properly.


I think that while the previous layers have not set, the extruder pushes the model down and lays down a thicker layer. Another fix that lets things cool is to use multiply to print several copies at once. This may leave threads between objects though.


Brian. I just printed on on my TOM - and it's my tallest print yet. Temp in the room was 2-3* F cooler than normal and I got to ~35 mm tall before I got a glitch and around 40mm before it started looking a little ugly. Will allowing the "cool" to last longer help prevent the upper layers from "swelling" into the head? I've only been printing for a couple weeks so I'm still learning.

On another 3D printer, I had great luck using the "cool" settings to allow time for the layer to cool. I was printing the "do nothing machine" and the pins were coming out ugly. I used skeinforge 39. The key settings in "cool" were "slow down" and "Minimum Layer Time (seconds): 5.0". Hope this helps. :)

I'm currently fighting my Z axis as well. I build my makerbot last week and it prints smaller things beautifully but after about 25-30 mm tall the head drops down instead of moving up. I have a ticket open with maker bot. My Z stepper gets so hot I don't want to touch it and what I guess is happening the stepper board resets and lock in a full step when it does so...it just so happens that the full step pulls the head down instead of up.

Also I've noticed that the ABP belt is not a great printing surface - it has too much "give" resulting in the wobbling you described. Anyhow this will make a nice dummy round and I might just print one out.

Now, for a pneumatic linear accelerator to put these in...

I'm assuming you mean along the same line as a potato gun? I've already designed a pneumatic soda can launcher, but won't post it here due to the fact that A) it's a weapon, and could literally kill someone, and B) it's a weapon, and could literally kill someone, and C) it has nothing to do with 3D printing, whatsoever.

Sorry. But great idea. A projectile of this diameter (if printed successfully) would reach some incredible speeds, given it had enough mass (which my print certainly does not) and some sort of radial influence (similar to barrel rifling).

Nice thought.