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Posted: 6/22/2007 6:28:30 AM EDT
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I am building a Romy G kit. I had already installed the front and rear trunnions. After pressing the center support rivet in I tried to slide the bolt carrier in and found that it wouldn't slide forward as before. After looking at the receiver, I noticed that it is slightly curved in at the point of the center support, hence making it too tight. Has anyone else had this happen? Should I just file down the rails so that it will accept the bolt or should I remove the rivet and try again? Thanks. |
I've found that prying the top of the receiver open just a bit (~1-2 CH's) allows the bolt to slide again. it probably isn't the top rail rubbing on the carrier, it is probably the sidewall of the receiver "below the rail" that is rubbing on the carrier, so grinding off the rail won't solve your problem. ask me how I know  .
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Were you using an AK-Builder center support? |
That figures. His center supports are shorter than normal, and is resulting in receivers being pinched in more narrow in the middle, which is causing bolts not to slide properly. Don't bother trying to tell Curtis anything's wrong, because he will tell you (in a 45 minute long-distance conversation) that nothing he sells is defective, and you must be doing something wrong. We had the same problem using AK-Builder center supports, AK-Builder flats, AK-Builder rivets, and all AK-Builder jigs. We got several receivers that were drawn-in in the middle. Curtis refuses to believe that anything of his is causing the problem, even though his center supports are measurably shorter than Tapco and DPH center supports (which are both of the correct length). The rest of what Curtis sells is top-notch, but he needs to acknowledge that a batch or two of his center supports is apparently shorter than it should be. |
| Well, what do you know, someone who is actually stating the truth about things that I had a on and on oh and on coversation about on another post. Was warning a brand new builder on what to watch out for , what is optional with buying rivets, etc. because I have been through it, money wise, etc. Meanwhile all I got in return was a posting stating that none of the stuff you just mentioned is even close to reality. Don't be afraid to say don't like this or tried that. be honest don't just follow, thats what makes this forum awesome_ for the most part. |
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Makes sense. I opted to grind and drill it out and use a Tapco bushing that I had lying around. I had noticed that it was just a hair longer. After pressing the Tapco bushing in, my problems went away and my receiver is no longer pulled inward in the center. Build and learn. I will add - the Tapco center support rivet is insufficent in length (IMO). Curtis' center support rivet is longer and better for the task. |
The Tapco rivet is definitely too short, and the AK-Builder sleeve is too short. I'm buying the Tapco center sleeve ($3) and the AK-Builder center support ($7). I use the Tapco sleeve and just the AK-Builder rivet. It's not the cheapest way, but unfortunately, that's about the only way to play it safe and do it right. 
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Ok, so do the math on the center support length. Inside dimension of receiver 1.25" Thickness of right side rail .040" Thickness of ejector rail .062" Take 1.25" and subtract .102" from 1.25" and you get 1.148" which is what the length of the center support should be. What is the outside measurement of the receiver at the front trunnion, center of the receiever and the rear of the receiver? The only possible problem there could be is the material for the rails is being displaced by the hardened center support. Curtis |
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Well it would be nice if someone offered the whole package deal at a reasonable price. I too have found that Tapco Rivets are too short but so are AK builder Center Supports. I have a stash of Tapco rivets/center supports, same for AK Builder and DPH. No matter how you do the theortical math, the DPH & Tapco center supports tend to fit the best. I put in 3 center supports this weekend and would test fit each of the three center supports in each receiver to find the best fit, and it was never the AK Builder. If you like your receiver to be bow-tied then go right ahead and use the AK Builder. The Tapco's, likewise, tend to be too wide. Maybe Curtis could overbuild them so that all of us could grind them down to fit our particular receivers? Just a thought, because it's much easier to take metal off than add metal. Oh, and the three receivers I was working on were 2 Polish and 1 Hungarian (aka Polish) along with a Romy the week before. On a side note, I really don't like the idea of shoving a wood prying device into the receiver and turning it as to widen the lower and top rails because of a center support that is too short. |
I'm really hesitant to go into very much of a conversation about this, as I don't want it to turn into anything more than a factual dialog, but here are my theories on why the center support is binding the receiver in the middle: 1. Your center support sleeve is measurably shorter than your competitors. If you stand an AK-Builder center support sleeve upright on a flat surface, along with DPH and Tapco sleeves, you can see that the AK-Builder sleeve is slightly shorter than the Tapco and DPH sleeves, which are both the same length. 2. The flat bending jig that I bought from you is bending the flats too wide. When comparing a bent flat to the original cut receiver, it's very clear that the internal dimensions of the bent flat are wider. When the front and rear trunnions are slid into the bent flat, there's quite a bit of space between the trunnions and the side walls. In fact, once the front trunnion is riveted in, it pulls the top of the side walls in, while the bottom of the walls is wider at the base. This even causes the bottom of the bent flat to bow out and downward slightly once the trunnion is riveted in. With the sides of the bent flat wider, it makes sense that the center support, once riveted in, would pull the receiver inward. Again, these are my theories that have been discussed with you before. For now, we're using all AK-Builder tools and hardware. We're buying the AK-Builder center support sleeve and rivet combo, but only using the AK-Builder rivet, and then using the Tapco center support sleeve. That's because that's the only thing that works for us. Otherwise, the receiver pinches inward in the middle when the AK-Builder center support is riveted in. I hope that this issue can be constructively resolved, and I can get the center support sleeve and the rivet all at the same source, and save some money. |
We boxed them up and mailed those to you a couple months ago along with the trunnions, and your response was that there was nothing wrong with them. |
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Tonight I'll try to get some original and Curtis bent flat measurements along with the center support measurements. I'll measure the center supports if I can find them all. Obviously this in not an isolated case because multiple people are having the bow-tie issue. |
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Ok, nothing means anything dimensionally if the front and rear of the receiver outside dimensions aren't targeted to be in the 1.333" range. The trunnions dictate the overall width of the receiver at the front and the rear. The center support is what ties it together in the center. Even if the receiver is wider at the bottom the rivets will pull the receiver in at the top. A few thousandths here or there won't distort the receiver enough to cause major problems. I just grabbed a Hungarian AMMS rear trunnion and clamped it in place in the rear of a bent receiver. Measuring from the outside at the top it was 1.336". Then I took one of the center supports with a set of rails and clamped them together. This measured 1.334" on the outside of the receiver. Now... since the center support is harder than the rails at Rockwell 42-46 and the rails are annealed it could recess into the metal. I used to have the rails heat treated, but the quest of everybody to purchase less expensive flats led me to do that. So, if somebody can take measurements at these three places that are having problems and will post them I will make some different center supports for a different length if necessary. They are made to keep the center of the receiver at 1.333" which could be .005" more or less in reality. I have the receiver flat in my hands that was bent on the flat jig that was sent back. The measurements on the lower outer bends are 1.332" in the front 1.347" in the middle and 1.340" in the rear. The deviation from the theoretical dimension of 1.333" is .014" so even with that it will only draw in .007" per side. When I trim the rails on my receivers I clamp a piece of 1.25" flat bar which is probably more like 1.242" wide. Then CNC them out so they will be the same from front to rear once riveted together. Try to trim the top rail after welding in the bolt guide rails since it can warp with excessive heat after installing them. If it was a major problem then I would have hundreds of calls one one or two here or there. The thing I need to know is if the center of the receivers are the same as the front/rear after they are riveted. The receiver pieces sent to me that were riveted and cut up weren't prepped very well and that was the biggest problem with those cut up pieces. I replaced the flats even though the person other than you that supposedly riveted them together on an unknown tool was the one that messed them up. I said this over the phone and will post it in a forum on the internet since it is what I believe the problem was. I don't play games and actually have built receivers/rifles on these tools using the parts I have made. Ok, I've rambled on enough and hopefully will get feedback from nay sayers as well as others that have used those center supports without issues. I don't get on the forums much and the phone is the best way to contact me at my shop during the day 816-229-0804. Don't have free long distance... then call me and I'll call you back. Curtis |
Like I said, I'm not trying to turn this thread into anything other than a factual discussion. I'm not a "naysayer", and I have nothing against you. We have spent in excess of $800 with you, and will continue to buy from you. All I know is that using a different center support sleeve cleared up the problem, and it apparently did for the original poster as well. You should probably measure your latest center support sleeves against a Tapco or DPH sleeve to see what I'm talking about. I also stacked it against one of the cheap silver center support sleeves being sold by a member in the equipment exchange, and all three (Tapco, DPH, cheapie) were the same length, except for the AK-Builder sleeve, which was shorter by a hair or two. As for the rivetting, the pieces sent to you were indeed sloppily riveted on a bolt-cutter rivet tool, but I disagree that it caused the middle to draw in (since that didn't happen until the AK-Builder center support was riveted in). Since then, we have purchased your rivet jig, which is quite a well-designed tool. The fact remains that your center support sleeves are shorter than the others, and the others work well for me personally with all AK-Builder flats, all AK-Builder jigs, and all AK-Builder rivets. At this point, I don't really see this as much of an issue for us since we've figured out that buying a different center support sleeve is the answer. I was just chiming in to offer the same advice to the original poster so that he doesn't have to learn the hard (and expensive) way how to keep from binding the middle of the receiver, and apparently my advice did exactly that. P.S. Since I'm only using the rivet in your center support pair, I'd be happy to mail you one of my leftover sleeves if you think that maybe a batch of shorter sleeves slipped out, and you don't find one of them (shorter sleeve) in your workshop that was shorter compared to the Tapco or DPH. |
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I think other center support bushings, like Tapco's are 1.17". This is because flats like Tapco's use the 1mm sheet metal for both of the lower rails. 1.25" interior dimension - 0.039 left rail - 0.039 right rail Akbuilder flats have a thicker ejector rail, making the 1.148" appropriate for their flats but not Tapco flats. |
That may be the case for some. Here's the combo what works for us: AK-Builder flat (including lower rails) AK-Builder rivets AK-Builder jigs AK-Builder center support rivet Tapco or DPH center support sleeve |
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Guys, I've been reluctant to jump in here for several reasons, one being I'm not a professional anything, let alone builder. Also, I don't write so great, particularly about technical stuff. But I've worked with these parts and equipment enough to understand the issues a little. Bowtied recievers happen. This is beyond doubt. I've seen it several times, even posted about it here a few weeks ago. (the topic didn't get much traction, and I didn't pursue it) And then sometimes they try to "hourglass" on ya. I have some thoughts. Tweaking a bowtied reciever with a piece of wood jammed in-between the upper rails can work good. (my building buddy had a Rommy with a bowtie and he straightened his out with a hydrolic body and fender thingy, kinda like a mini "jaws of life" divice. It worked) I straightened out one by clamping the rieciever between two by fours in a vise, (gripping it down low, along the bottom edge, just above the trigger guard) then resting a piece of wood against the upper rail and smaking it with a hammer, first one side, then the other. But I have since learned that careful attention to prepping the reciever after bending the flat can totally avoid the issue. It seems to be about those bottom 9o dgree bends. Make em too sharp, yer too skinny and wind up with an hourglass. Do nothing, and they may bowtie. And of course if it's gonna hourglass, just shorten the sleave. Look, no offense to any one, (I think that these jigs exist is brilliant!), but compared to whatever equipment/tools are used in an AK factory, flat bending jigs are crude technology. You have to tweak (prep) the reciever after pressing. This aint plug and play. It took me a while to figure that out. The first one I did after pressing I thought the bottom 90's ought to be sharper. So I pulled the bent reciever out the jig, left the mandrel in and placed a long piece of heavy bar stock on the bottom edge, put it in the press and tried to make that lower 90 sharper. It just sprung back, so I put it on the concrete floor and smaked it with a sledge. Wound up with a great, sharp, 90 degree corner. Thought cool! But that reciever wound up too skinny, and the center support spread it out in a hourglass. Truth is, each one comes out of the jig a little different dimensionally. Sometimes they are too wide, sometimes too skinny. But then maybe I'm just doing the pressing wrong in the first place, how would I know? Then spot welding lower rails can change things too. Gotta keep up with it. It seems to me that these jigs, by there very nature are only gonna getcha close. That's what they're for. To get you close. If ya want a perfect ready to go reciever, buy one. I hear Nodak's are tits. I have not measured different center support sleaves or rivets. When I weigh the difference between waiting for UPS or the mail to bring me different parts, and the immediate gratification of just tweaking the reciever, I tweak the reciever, or shorten the center support tube. And I've yet to have any problems with FCG mechanics from these slight dimensional differences. Nothing wrong with mixing and matching center support sleaves and rivets to match whatever dimensions you wind up with, but for me it's just easyer to tweak the reciever to match whatever parts I have on hand. (which after trying Tapco and some others, are now always Curtis's, by the way.) So-------the above are just my thoughts based on my experience. No right or wrong way to do this. (unless your not having fun, or are unsafe, or your AK wont work, THEN your doing something wrong!) Build on! PCM "To my mind it is wholly irresponsible to go into the world incapable of preventing violence, injury, crime, and death. How feeble is the mindset to accept defenselessness. How unnatural. How cheap. How cowardly. How pathetic." - Ted Nugent |
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I would have posted this yesterday, but seemed the site was down. Anyways, I'd like to suggest this to people...it's seemed to work for me. After you bend a flat, clamp your front and rear trunions into the receiver and let it sit for a few days...this has helped me with riveting in the trunions a week later, due to the fact that the tops want to spring back out. The next time you rivet in a front and reat trunion in, try this. Put in a center support, try AK builder's, and hand push in the rivet. Then grab the center support and move it left to right, and you will feel play/slop in there, due to the lack of length. You can go ahead and use that if you want, but I'm not really up for jamming wood in the top rails and twisting to widen them out due to a stupid problem of too short center supports. We pay good money for these products and they should work. I measured the center supports and AK Builders came out at 1.150 DPH and Tapco's came out at 1.172, 1.174 and 1.176 The ourside dimensions of the two polish underfolders came out, this is with the trunnions riveted in. Front Lower 1.340 and 1.350 Front Upper 1.352 and 1.346 Rear Lower 1.351 & 1.356 Rear Upper 1.348 & 1.352 Center by the rivet (with the rivet installed) 1.348 & 1.380 The Romy which is also already assembled came out Front Lower 1.353 Front Upper 1.355 Rear Lower 1.359 Rear Upper 1.354 Center by the rivet 1.385 |
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I forgot to mention this, but here's yet another person who fully admits that AK Builder center supports are too short. pyroclayman uses AK builder center supports and his builds bowtie, as per his own admission. He is fine with this because he uses the "jaws of life on his builds" or uses a wedge to spread the top rails. I'd rather just put the damn thing in and have it be RIGHT! So what are we up to, person number 4, 5 or 6 that has the same bowtie problem with AK Builder center supports? All I want for Christmas is a resonably priced center support and rivet combo that work. |
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Yes, I may very well be added to the list of those who have had the "bowtie" issue while building, but bear this in mind: I don't know what hell I'm doing! I might very well be doing it all wrong! I just surfed the web, printed tons of info, read till my eyes were bugging out, and went for it. Zero proffessional guidance. I DID ask a few questions here on this board and a couple others, and got the help I needed. Every thing I said in the above post is just me theororizing as to why it happens sometimes. The truth is, I don't know squat. Well, I like guns and women, but other than that I don't know squat. PCM Oh, and I like sleep. And good whiskey. and harleys. |
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On all my builds, I've had to adjust/compensate when installing the center support. Were "building a rifle," not assembling an AR15. Since no bending jig works perfectly, I wait till the front/rear trunnions are temporarily installed and take measurements at those two points. I then make the center support area match those two measurements. Sometimes I need to added a very thin washer to the centersupport or remove metal from the support. The end result is that the receiver measures +/_ .003" end to end, which for me is very acceptable. Doing this has caused minimal problems with the carrier sliding on the upper rails. Also the top cover fits nicely against the sides of the receiver, no gaps are present. Before I do any riveting, the entire receiver is temporarily assembled and all parts are checked for correct operation. If any problems arise, I like it to happen "before" anything is permanently installed. |
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Well the next time you permanently install your front and rear trunions take a look at the receiver head on and from the back. If you used the AK Builder Jig and Flats, like I do, you'll notice that the receiver is now a trapazoid; with the lower portion of the receiver being wider. Which is more than + or - .003...so, not so good. Then take your AK Builder center support and rivet and put that in and look at how your receiver bowties. Lovely. I accept the fact that my receivers are trapazoids, because the wood usually hides that, but I refuse to accept that there is anything right about the center supports. They simply don't work. You know it, I know it, everyone knows it...hell I bet Curtis even knows it, but he'll refuse to accept that he is wrong and that his center supports are TOO SHORT. I have spoken to Curtis before and he's even told me that he doesn't even have time to build AK's...you'd think he'd take the info from the the "field" a little more seriously. Don't believe me? Call Curtis and ask him the last time he built an AK was...I think Reagan was president at the time. Oh, and fyi, built another Romy over the weekend and SURPRISE, the AK Builder center support rivet was too short...ended up using a DPH. |
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