Mounting the Cocking tube during a build

[vista461]

I seem to remember reading there was something about a spacer or something like that to make sure the cocking tube was mounted right. Anyone know what the heck I am talking about?:o

[cimmaronkid]

There should be approximately .020" gap (about the thickness of a dime) between the round piece that the cocking handle is on and the solid stop in the tube. Set this gap AFTER you have established the bolt gap so you won't have to redo everything. This gives you the right dimension so that the cocking handle can cam open the action, but when it is fired, it wont force the round piece of the cocking assembly into the end of the stop.

[SSwee]

Yes. After pressing your barrel and getting your bolt gap of .018" in example. You make a spacer from shim stock or similar material the same .018" thick. This spacer is placed on the end of the carrier, with double stick tape or the like, where it contacts the cocking piston. It should be slightly smaller OD than the end of the carrier you are putting it on. Install the cocking tube and making sure it is indexed correctly and tack into place. This should set your cocking handle gap at the same measurement as your bolt gap.

If I have left anything out, please chime in.
SS

[drhall762]

More great information for the first build.

Thanks,
Dave:)

[New2HKinAZ]

This was posted on cetmerifles.com after it came back up after the hacker attack. I don't remember who posted it to properly cite the source, but there is a couple paragraphs about the mounting the cocking tube and using the shim.


if you want a g3, or hk91, buy a g3 kit, receiver, and start there
youll be FAAARRRRRRRRR ahead at that point.
The G3 has NEW parts readily available for it
the G3 has US MADE compliance parts readily available for it

by making your cetme into a g3, you are causing yourself soooooo many problems youre not even aware of yet


building it is easy on paper

install trunnion into receiver until it bottoms out on the rails - ensure trunnion is installed square, plumb, and true to the rails of the gun (look through the back of the receiver with a flash light and look for a trunnion installed not square with the rails)

weld trunnion into receiver once its straight

cocking tube is next, but this presents its own set of problems. If the cocking tube is not installed correctly, youll either have VERY hard problems cocking the gun, or your gun will destroy itself. There must be a very small gap between the end of the carrier tube, and the inside of the cocking sleeve. this gap decreases with wear the same amount that your bolt gap decreases with wear. Therefore, if you set your bolt gap to .010 you need .010 gap in the sleeve. If you set your gap to .020 then you need your sleeve gap to be set at .020
lets say you are aiming for .015 bolt gap which is a good number, then you want .015 gap in the sleeve too.
cut a small disk out of a .015 feeler guage. Cut it so it fits on the end of the carrier tube with tape or light epoxy, elmers glue, etc. It must be under the diameter of the carrier tube just barely.

with appropriate sized shim installed to carrier tube, insert complete bolt set WITH SHIM ATTACHED into the receiver and let it lock into the trunnion. the carrier tube will protrude out of the front of the receiver where the cocking tube normally goes.

insert the cocking tube with complete cocking mechanism installed (sleeve, cocking handle, pin, and spring) into the receiver and over the top of the carrier tube until it bottoms out on the end of your shim. make CERTAIN that your shim isnt bound up inside of the cocking sleeve and that the shim is squarely pushing the cocking sleeve against the sheet metal stop built into the inside of the cocking tube. Align the cocking tube to your likings (make sure the cocking slot is where you want it), clamp the tube to the receiver with a LONG wood style clamp and tack it in 1 spot - light heat, just enough to hold it. unclamp it and insert a copper rod inside of the cocking handle to back up the thin cocking handle - this prevents weld burn through and acts as a heat sink. weld the cocking tube to the receiver now.
one thing to know before welding the cocking tube. if when fitting the cocking tube to the carrier with shim you notice that it does not butt up squarely with the receiver, you need to measure how much gap is present in between the cocking tube, and receiver - this is a precision measurement. you should remove the same amount of material from the end of the carrier tube with a precision machine tool like a lathe, mill, or surface grinder. If your tube buts up squarely to the receiver with the shim installed to the end of the carrier tube, you should turn off a small amount of the shoulder on the cocking tube until it doesnt butt up to the reciever - go small amounts here until it clearly doesnt butt up - a .010 gap welds up nicely.

ONCE THE COCKING TUBE IS GAPPED AND INSTALLED CORRECTLY, REMOVE THE SHIM OFF THE END OF THE BOLT CARRIER. THAT SHIM IS ONLY TO GAP THE COCKING TUBE AND YOU DONT WANT TO SHOOT WITH THAT SHIM ON IT CAUSE IT WILL DESTROY YOUR GUN


so, now you have the trunnion installed and the cocking tube installed, now to the barrel

insert the bare barrel into the end of the receiver and through the trunnion until it bottoms out on the trunnion - press the barrel in from the rear of the receiver. press it in until its close to where it needs to be, remove the gun from the press, install the carrier and check bolt gap - if gap is too much press the barrel in a little more until gap is right. if gap is not enough, press it back out and start over. one thing you need to take account for is that the gap shrinks a bit after you first shoot it - how much?? thats a guess. if you press your barrel until it gaps at 20 thou, it may end up at .017 after you shoot it - may end up at .015 after you shoot it?? who knows?, but take that into account, you can always get undersize rollers to accomodate too much gap.
once your barrel is gapped right, drill it through the barrel pin hole with a 5mm drill bit and drive in the barrel pin. you will probably need to locate the barrel pin hole in the receiver if its a century receiver, cause century doesnt drill the barrel pin holes.


now, you have the cocking tube, trunnion, barrel, and barrel retaining pin installed to the reciever

now to the triple front frame
flux the inside of the triple frame, and the barrel where the triple frame will rest. install the triple frame to your barrel and index it to your rear sight - once perfectly indexed, clamp it all so it cant move. heat it up with the torch (barrel area and triple frame) and silver solder the triple frame to the barrel from behind the triple frame. once cool, and set, and you are happy with the alignment, hold off before drilling and pinning it with the sling eyelet pin - more on this at the end of this post.

convert your trigger pack to semi auto only, and your grip frame
install the shelf to your trigger box by welding it, and install the shelf inside of the grip frame. install your us made semi auto trigger parts, and install this set of parts to your gun - assemble everything else too (buttstock, handguard, etc)

go shooting, but take a torch with you
if it shoots to point of aim, you are good to go
if it shoots badly to one direction heat the triple frame/barrel up to melt the solder and move it a little bit and let it cool back down
shoot again - once centered stop shooting for the day.

drill your barrel for the sling eyelet pin
insert a new sling eyelet pin from RobertRTG and peen over


refinish

done


it SOUNDS easy, but there is ALOT to it

it isnt an AK, but it is similar in build to one
there is a HUGE difference though
AKs you dont have to worry about bolt gap so you just install the already headspaced barrel and trunnion to the receiver - cetmes and hks you really do need to worry about bolt gap cause most kits wont gap anywhere desireable cause they are well used.
and you dont have a cocking tube on an AK that needs to be gapped correctly.


As i told you before, if this seems too much for you, you should get on big50s waiting list. I have watched him assemble HKs, and CETMEs before, and he knows his stuff, and he will build you something youll be REALLY proud of when its done.


i cant tell you how many times people have asked me to build there guns for them over the last couple of years. Most people dont understand that i do not have the proper FFL to accept a firearm from people so im posting this in hopes that other people who may read this will understand that i cannot do this kind of work for you - contact big50 at big50hk.com, he knows what he is doing with these guns, and will build you something you are proud of.


hope this helps

if you searched the forum and read through enough of the posts, you would find everything i just typed many times over, and much more. <!--[if gte vml 1]><v:shapetype id="_x0000_t75" coordsize="21600,21600" o:spt="75" o:preferrelative="t" path="m@4@5l@4@11@9@11@9@5xe" filled="f" stroked="f"> <v:stroke joinstyle="miter"/> <v:formulas> <v:f eqn="if lineDrawn pixelLineWidth 0"/> <v:f eqn="sum @0 1 0"/> <v:f eqn="sum 0 0 @1"/> <v:f eqn="prod @2 1 2"/> <v:f eqn="prod @3 21600 pixelWidth"/> <v:f eqn="prod @3 21600 pixelHeight"/> <v:f eqn="sum @0 0 1"/> <v:f eqn="prod @6 1 2"/> <v:f eqn="prod @7 21600 pixelWidth"/> <v:f eqn="sum @8 21600 0"/> <v:f eqn="prod @7 21600 pixelHeight"/> <v:f eqn="sum @10 21600 0"/> </v:formulas> <v:path o:extrusionok="f" gradientshapeok="t" o:connecttype="rect"/> <o:lock v:ext="edit" aspectratio="t"/> </v:shapetype><v:shape id="_x0000_i1025" type="#_x0000_t75" alt="" style='width:12pt; height:12pt'> <v:imagedata src="file:///C:\DOCUME~1\ADMINI~1\LOCALS~1\Temp\msohtml1\01\cli p_image001.gif" o:href="http://www.cetmerifles.com/forum/vb/images/smilies/frown.gif"/> </v:shape><![endif]--><!--[if !vml]-->file:///C:/DOCUME%7E1/ADMINI%7E1/LOCALS%7E1/Temp/msohtml1/01/clip_image001.gif<!--[endif]-->

good luck on your build

[Seattlefungus]

AN another good idea is to use a heatsink jig during the tube weld so you don't burn through!

[jfowl31]

That was Perro typing there... all good info.

[tomoshenko]

That was Perro typing there... all good info.
I re-posted that Perro post when CETMERIFLES came back up. I had saved that for my own "book of Cetme folder". Here is another one that may be useful that Mike posted:


first order of business - you guys were right, the virgin barrels are drilled for the barrel pin - my mistake - we wont be using them holes anyway

back to the build thread - i see that you already welded your cocking tube and trunnion in - im going to offer some advice on this since other people are following this thread

the cocking tube is THIN - get a piece of copper rod (forgive me for i dont remember the diameter and mine is buried - when i find it, ill get the measurements) and chamfer the end of the copper rod.
insert the cocking tube into the receiver, and then insert the copper rod inside of the cocking tube from the back of the receiver. this provides a heat sink, and it prevents you from burning through as bad (its so thin, its easy to burn through if youre not real careful)
weld the cocking tube all the way around - preferrably tig fused, but any method will work.


now - since you have your trunnion installed and welded into the receiver square, plumb, and straight to the rails, you are going to press your barrel into the trunnion from the rear of the receiver

you want to turn the old barrel pin slot 180 degrees from where it should be - this way when you drill the barrel pin hole, you are drilling into fresh meat on the barrel - this means the barrel pin slot is facing UP when you insert it into the back of the receiver

notice that the barrel is tapered right past the trunnion - this makes it self centering if you press it in from the rear of the receiver - insert the bare barrel into the back of the receiver and drop it down and through the trunnion until the barrel taper comes to rest on the trunnion on the inside

make a mandrel that fits inside the chamber a HAIR loose inside the chambeer and protrudes out the back of the receiver a bit - mine is made of 1 inch aluminum rod about 16 inches long - you want the part that comes to rest on the barrel face to be almost as large as the barrel face - you will be pressing the barrel in by pressing down on top of this mandrel with your press.

make a press plate with a hole in the center of it a hair larger than your barrels largest OD - your barrel will slip through the center of this hole and your trunnion will come to rest on this press plate - this lets you press the barrel in


press it in to where its close, then insert your bolt set into the receiver and check gap - if gap is too low, press the barrel out and start again
if the gap is too high, press the barrel in a little more and check gap

once you are at .020 (.024 if you can find -2 rollers, or .028 if you can find -4 rollers) stop pressing the barrel in

clamp the barrel to your mill table and locate the center of your barrel pin hole - drill through all the way through the fresh meat of the barrel with a 5mm drill bit - if you want to ream it, get an undersized reamer and ream it tight for a press fit - a 5mm bit works just fine though.
now drive the barrel pin in with a hammer - when it gets close, use a punch and a hammer.

be expecting the gap to drop a bit after you first fire it as things settle in

once you test fire it and you find that gap is good and it functions good, then install your triple front sight frame - plumb the triple frame to the rear sight, and solder it from the rear of the triple frame. test fire it again - if windage is not good, then reheat, move the triple frame, then resolder. once windage is good, drill for the sling eyelet pin (available new at robertrtg.com/g3.html)
peen the end of the sling eyelet, or weld it on the non eye end

[tomoshenko]

And another one a Welder posted regarding TIG welding the cocking tube....


I never built one of these but i do have some welding pointers for thin stuff.
Instead of trying to get the weld done with one bead, which can make it easy to burn through or warp it.
Make the weld out of a bunch of tac welds. Hold the welder just long enough so the filler metal flattens out, so you get good penatration , it should look like a like circle of weld, with a slight dome.
Then stop, Let the metal cool. Then do another one, over lapping the previous weld. Do this all the away around your seam. If you mess one tack up, you can easily grind it off, and try again.
If you do it right. It will look like one continuos bead. You can make welds look like a "row of dimes" Doing it this way.

This is a tryed and trued methood that a lot of body/custom shops use.

[vista461]

press it in to where its close, then insert your bolt set into the receiver and check gap - if gap is too low, press the barrel out and start again
if the gap is too high, press the barrel in a little more and check gap


So that I am clear on the pressing part, the bolt gap decreases as the barrel in pressed inward correct?








the cocking tube is THIN - get a piece of copper rod (forgive me for i dont remember the diameter and mine is buried - when i find it, ill get the measurements) and chamfer the end of the copper rod.
insert the cocking tube into the receiver, and then insert the copper rod inside of the cocking tube from the back of the receiver. this provides a heat sink, and it prevents you from burning through as bad (its so thin, its easy to burn through if youre not real careful)
weld the cocking tube all the way around - preferrably tig fused, but any method will work.

Also where do you guys find the copper rod to use as a heat sink?

[drhall762]

Thanks a bunch to all you guys that know what you are doing and have posted so much saved information. It is very useful to a guy like me doing my first CETME build.

Dave :sniper:

[rustypirate]

Vista,

You are correct, bolt gap DECREASES the further FORWARD the barrel is pushed into the trunion.

As for the copper rod, you can find a metal dealer in your commercial white or yellow pages. Just tell them the size and length of material you need, and they can get it for you if they don't have it in stock.

coppper rods are (or were before copper got REAL expensive) used for home and industrial electrical grounding rods.

[Seattlefungus]

ETgoddard@aol.com is a good sorce for an aluminum welding jig. Machined for the cocking tube & receiver, notched to stop at the joint while welding the the rifle pointed up. Last I bought one, a month a go, they went for $35.00. Nice work and Ed is retired Airforce. More than a few from CETME rifles bought from him. Good guy.

[jfowl31]

btw, the thickness of a dime is about .053."

I dont know where the idea that a dime is .020" came from, but Ive seen it posted here a few times, so I decided to look it up. According to the US Index List, a dime is 1.35mm thick.

That thickness is too much gap in the cocking tube, and it will be really hard to unlock and charge if you set your cocking tube gap to that.

[bullseye]

They were refering to a heavily circulated dime, not a new one. :1087:

[Perro]

a dime is too thick - the dime is used to troubleshoot a firearm that is hard to cock, and nothing more - it is a troubleshooting tool only. Century had a bad habit of never installing the cocking tubes correctly. Instead of fitting the cocking tube correctly, they ground the end of the carrier tube instead to create gap between the cocking sleeve and cocking sleeve stop - too much grinding and the gun is hard to cock - the dime closes that gap and if the rifle magically unlocks easy like its supposed to, then you 100% have a carrier ground too much by CAI. If you leave the dime in the gun and shoot it, it will crack the welds and self destruct.


solid copper rod can be found at mcmaster.com - it is where i buy mine - since copper is so expensive right now, aluminum is fine too - however a copper rod from mcmaster will be cheaper or same price as the one you buy from the guy listed here for $35.00, and copper wont melt as easily as aluminum. Copper is preferred, but aluminum works.

tig welding in dots?? itll work, but damn its slow - turn your tig welder down to the lowest setting and work your way around in a circle till it puddles up - then push the puddle around the gap - done. HK TIG fuses there tubes - cetme uses filler rods - either way works fine. It will be damn near impossible to burn through with the heat sink in there if you know how to weld - as soon as it puddles up, start pushing the puddle and you wont have any problems with it whatsoever.
another problem with welding in dots, is that welds shrink - it cannot be avoided, it can be minimized, but it cannot be avoided. If you are going to tig weld in little dots, i HIGHLY recommend alternating your dots or the tube will pull to one side too much. A dot on the left of the receiver - a dot on the right - dot on the left - dont on the right - dot on the left - dot on the right till you hit center - welding it all in one pass avoids the thing pulling to one direction or the other cause it all cools at once and pulls together.

using the heat sink has another added benefit - it helps to prevent bad warping of the thin tube by holding the tube straight.

ground rods?? those are just copper PLATED, they are not solid copper


my opinions only