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Thread: First Time CETME Build (Ongoing)

  1. #1
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    First Time CETME Build (Ongoing)

    I got my parts kit in from Numrich Gun parts today, my barrel will be in from Apex on monday, and I just ordered my CETME receiver flat from Robertrtg tonight. The unistrut will be in in about a week, so that I can make the Skridlow (spelling?) style jig to bend the flat. I've got an idea to that I'd like to run by everyone. So, I have enough 3/4 inch OD steel rod laying around to build a reinforced pressing piece (think 16 inch rod, with a 14 inch rod welding on top of it, kinda like an = sign). The second part of the idea, seeing that 3/4 inch rod isn't ideal for doing this, is to take some copper tubing I have which is exactly 1mm wall thickness, slit it lengthwise and wrap it around the bottom piece, thereby taking it's OD to closer to 20mm. Thoughts?

    Anyway, back to what I've done so far. I started the demill tonight. Thanks to a very helpful tutorial posted on this site, I was able to separate the cocking tube and extension, and the trunnion from the receiver stub with no problems. An 11/16 inch OD 1018 rod I'd bought in case I needed to straighten the cocking piece made life so much easier when separating the receiver from the cocking tube. I just kept it inside the cocking tube and pried against it and the tube stayed pretty much in round while I separated it all. I did pull two welds through the tube wall, so had to planish those holes back round and smooth out the inside of the tube with a file afterwards.

    I had lost some sleep recently thinking about how I would reweld the trunnion to the receiver, seeing as how those spot welds are supposed to be fantastic. I'd researched for days, thinking about how I'd replicate the quality of those welds.....Well folks, I did zero grinding on that trunnion. I just slipped a screwdriver in between it and the receiver and popped the whole thing apart, one side at a time. I mean I might have put maybe 30 lbs of pressure on it. The welds just ripped out of the trunnion walls on three of the welds, leaving rough craters. If that's not grain enlargement, I don't know what is.

    I have access to my arc welder, which is all that I ever really do, or my friend's decent flux core setup. I was originally thinking about doing a plug weld with 3/32 6011 stick to get good adhesion to the parent metal of the trunnion, and then tie into that weldment with the flux core. Now, I don't know if I should bother, seeing how weak the original welds were. Thoughts? I'm open to any constructive advice.

    CETME1.jpg

    CETME3.jpg

  2. #2
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    I had originally posted this thread on another forum, but have received zero feedback, so am moving it over to here. The following pictures will show how far I've gotten with the demill. I was afraid of grinding too far into the cocking tube, since I've heard that they're nearly impossible to replace. I accidentally ripped two of the welds out of the tube, creating holes. Luckily I was able to planish the outsides flat using the 11/16 OD rod, and filed and sanded the inside smooth. It does not seem to affect the charging mechanism's play up and down the tube. The entire process was actually far smoother than I had thought it would be.


    CETME4.jpg

    CETME5.jpg

    CETME6.jpg

  3. #3
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    So today was the barrel installation day. I'd seen a video where a guy froze his barrel and the heated up his trunnion and they just slipped together.......LOL! Yeah it helped me get it seated, and that was about it. I'd liberally coated it in Permatex NeverSeize so it wasn't a lubrication issue. I then proceed to attempt to install it by clamping the barrel shank in a vice and beating on it using a wooden block between the trunnion and my sledgehammer. I don't have a proper shop press, so after doing this for a while and hitting a point where it just wasn't going to go anymore, I had to rig something up.

    Did you know that you can use a hydraulic pipe bender as sort of an upside down press? Neither did I, until today. So after rigging that up and pressing the barrel the rest of the way in, I got it in a range where I can correct it.

    Once it was pressed in it was somehow easier to adjust with a big rawhide mallet. I'm talking a five pound mallet, though. The barrel is now about a millimeter proud of the trunnion. I can persuade it back and forth in the trunnion with a hammer and a piece of brass, so I'll be able to get the barrel where it needs to be.

    How proud of the trunnion should the chamber face be? I thought I saw about .03 in another post, but I'm not certain if that's correct.

    KIMG1863.jpg

    KIMG1866.jpg

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    After installing the barrel I realized that I did it exactly backward of the way everyone reccomends it. I hammered and pressed this barrel in from the front of the trunnion. Yes, the side that the handguard interfaces with.

    Did I just ruin this trunnion?

  5. #5
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    I read your post at 7 this morning (middle of my night) and went back to sleep thinking about it, so this morning I have some comments and a question.

    1. Good job getting the old sheet metal separated from the needed parts without too much damage! If you ever do it again, grind a little deeper into the existing spot welds and the sheet metal will tear around the welds instead of pulling off of the tube and trunnion.
    2. Barrels are pushed in from the rear so there is no chance of bending the barrel by pushing on the muzzle end and bowing the barrel. I have pushed on the muzzle end myself, but only on very heavy barrels that were too large in diameter to go in the other way (with less chance of bending).
    3. Oh yeah, Your welding rod idea for pressing the receiver flat into the trunnion was too confusing for me so it sounded bad. Do whatever you need to to get the push rod as close to 20mm as you can.
    4. I think you'd be better off using your buddy's wire welder than an arc welder. I'm sure it could be done but you'd need to be some kind of welding god to pull it off with a stick.

    Lastly the question, what is the bolt gap measurement you ended up with when you pressed your barrel in? That's the most important part of putting the barrel into the trunnion.
    Last edited by holescreek; 08-29-2018 at 10:40 AM.

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    Thank you for your compliment, sir!

    1. Thank you, sir!
    2. I was hammering directly on the trunnion with the barrel supported as close to the trunnion as possible, at all times. The final adjustment after pressing was done with a rawhide mallet tapping on the muzzle. I stressed heavily about bending the barrel so it was foremost on my mind. While pressing the assembly together the barrel shank was supported, and not the thinner portion of the barrel, so doubt I have any barrel warpage from that. Barrel seems straight as an arrow and passes the roll test I use for pool cues, lol! I'll stop worrying about having destroyed my trunnion, now.
    3. Thank you for the advice, sir. The copper tubing wrapped around the 3/4 OD solid bar will bring the overal OD of the bend bar to close to 20mm, if my math is right. Low-tech Redneck, here, I use what I've got.
    4. Note taken. I will only use the wire welder. I am no welding god. I'll just smear the area outside of my weldments with vaseline to make the spatter easy to remove. (I know, I know, it's redneck, but it works)

    I tried gaining a bolt gap measurement, but am running into an issue. The bolt assembly that I received in my CETME kit from Numrich is stuck in the locked position. I tried prying it apart from the bottom with a screwdriver, but only succeeded in stabbing myself. It's stuck pretty good. I'm certain I'm not the first person with a stuck bolt assembly. Once I get it unstuck I'll gladly take my feeler gauges and get a proper bolt gap reading. The bolt gap and the cocking tube gap are things I'm keeping foremost in my mind, sir. I most certainly don't want my new rifle battering itself apart because I didn't give it the proper tolerances. I know about these things thanks to the incredible team of people I see kicking around.

    You, Nitegunner, GW11, R.Erichson (spelling?), and Bladeworks are all the reasons I'm comfortable tackling this. More info is always a good thing, which is why I'm documenting all of this for other newbies. Don't do it the Yeti way, do it the smart way, lol.

    Oh,and I know what you mean about 7 being the middle of the night, Bartender here. There will be alot of 3 am posts from me.

  7. #7
    holescreek's Avatar
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    Squeeze your rollers into the bolt head with your vise. The bolt is guaranteed to unlock.

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    Just saw this, am walking straight out to the garage to try this.

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    It worked like a charm. However, it takes the vice to get the bolt to unlock each time. Is this normal for an uncleaned CETME bolt, or am I looking at a damaged piece? I've got to find a tutorial on how to disassemble this thing in case it's clogged with cosmoline.

    CETME8.jpg

    CETME7.jpg

  10. #10
    holescreek's Avatar
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    Yes, it's normal to be that hard to unlock. Typically you would insert the bolt into the receiver backwards and slam it in to force the rollers inward for reassembly.

    You can see me doing it starting around the 4 minute mark here:



    A slim flat blade screwdriver works well too, just gotta keep it off your flesh.

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