AR Sponsor
Posted: 5/17/2009 7:51:22 PM EDT
| im building my own upper and i and have found through out builds that lapping the upper makes for smaller MOA;s how many of you guys out there lapp your uppers? |
|
I think what isu600rr is talking about is lapping the part where the receiver and the barrel meet. Squarring would be a better word to describe the process. The idea is to have the barrel perfectly inline with the bolt and bolt carrier. You can buy a tool like this one to do it.
http://www.midwayusa.com/viewProduct/?productNumber=810457 Some receivers don't require too much but you still can improve accuracy with this simple job. You can also use this to align the holes for the gas tube if you are way off. |
|
Quoted:
I bought one of the tools to use on my varmint build. Where can I find reasonably priced lapping compound though? Any hardware stores carry what I need? I don't know what size grit you need but any auto part store will carry grinding compound used to grind engine valves (valves job). You can find different grits and either water or oil based. They both work fine. |
|
I have done this exactly twice. The first one I did (Spike's) made me think this probably has some benefit. It was noticeably "out of square" for lack of a better description. I checked the "square" of the receiver using a glass surface and small finishing square, rotating the receiver to check my findings on several places of the glass. I questioned how flat the glass might be but used a mechanics straight edge to check the glass. It was pretty darn flat. I marked the receiver for the low and high spot prior to using the lapping tool. Once the lapping tool was inserted it confirmed my marks and that only about 50% of the receiver touched the lapping tool. It took about 20 seconds to spin the lapping tool with 600 grit compound and very light pressure using a cordless drill. After doing this it had virtually complete contact (Brownell's says you need 80% surface contact). The second one I did (DPMS) needed very little truing, I touched it up just because I was already there. Go figure, I would have guessed it may have been the other way around with these two brands of receivers. I used a light oil on the bearing surface of the lapping tool and was very careful not to let any compound touch any place but end of the receiver. I have read that some builders have reservations about removing the anodizing on the receiver. I too wondered about this and acknowledge that these concerns may be valid. Though I don't like the idea of removing the anodizing, I have read that in some instances it's actually the anodizing that causes the problem. I can definitely see where a painted receiver may have problems here. After a little consideration I couldn't see where the anodizing offers significant benefit in this area. After all once the barrel is on, it's on, or at least to my way of thinking. Brownell's has a short video on the process. It is neither expensive or difficult to do this procedure. For me the jury is still out. At this point, I believe that if you just want to squeeze every ounce of accuracy out of your rifle it's probably worthwhile. If it is a plinker and minute of paper plate is acceptable, leave it alone. Of course your experience may vary. I'm going to check a BushMaster that I have apart tomorrow, I also have 2 LAR's to work on in the next couple of weeks. I'll probably have a better opinion once I get there. |
| I do not see how the tool can accurately pilot the lapping tool to be exactly perpendicular to the boll face. May just be a feel good manuever. Lapping is something you do to smooth a machined surface not square it up.The receiver is probably soft enough that torqueing the barrel nut accomplishes most of this. You may find that if you torque a barrel extension on and then remove it , these imperfections are already gone.Quite a lot different situation than squaring the receiver face on a bolt gun where the center of the receiver is located and then the face machined perpendicular to it and the bolt face. |
|
This is one of those things that I never understood. If the barrel is properly secured in the upper how can a accuracy be affected by lapping the upper. If it isn't truly square/flat wold the barrel simply point slightly off to one direction or another? Does that make sense?
It seems that a square/flat surface on the receiver and the barrel would simply make the barrel point exactly straight in relation to the upper. If the direction the barrel points is slightly off I don't see how accuracy could be affected because it would still zero and still shoot consistently. If that make no sense I apologize for the poor description. Just one of those things I never understood. |
|
I understand about squareing sufaces but when the barrel extension goes into the upper it is a snug fit so i cant see how
when you tighten the barrel nut it would cock the barrel to one side if a receiver is off that much you would see it when you put the barrel into the upper ever one that i have checked is as square as it is going to get. |
|
It works on both centering the barrel as well as distribute/isolate/dampen harmonics: the more contact area, the more distribution of all forces. You may want to call it 'unitizing'.
Whether empirical data exists proving this to work, I do not know. For me, this is more mental than anything else. I know that the extension and upper are making 100% contact, and the barrel is as centered as I can get it. Thus, it is in my mind that rifle will shoot tighter, and it does. |
|
Quoted:
It works on both centering the barrel as well as distribute/isolate/dampen harmonics: the more contact area, the more distribution of all forces. You may want to call it 'unitizing'. Whether empirical data exists proving this to work, I do not know. For me, this is more mental than anything else. I know that the extension and upper are making 100% contact, and the barrel is as centered as I can get it. Thus, it is in my mind that rifle will shoot tighter, and it does. It does make sense maybe i will have to test it out on future builds. Mike |
|
Quoted:
The term "lapping" may not be the optimum word to use, but squaring the face of the upper so that the barrel is absolutely true and square to it, along with maximizing the contact between the upper and the barrel flange cannot help but improve the alignment of the barrel. A number of people have posted (in another thread) that they have used this tool AFTER correctly assembling their uppers and found that, even after properly torquing the barrel in place, the upper was not square.
I do not see how the tool can accurately pilot the lapping tool to be exactly perpendicular to the boll face. May just be a feel good manuever. Lapping is something you do to smooth a machined surface not square it up.The receiver is probably soft enough that torqueing the barrel nut accomplishes most of this. You may find that if you torque a barrel extension on and then remove it , these imperfections are already gone.Quite a lot different situation than squaring the receiver face on a bolt gun where the center of the receiver is located and then the face machined perpendicular to it and the bolt face. Whether the bolt face is square in the upper is another matter, related to how accurately the bolt carrier and bolt were milled. And that's really immaterial because an AR is nothing at all like a bolt gun. |
|
Just did this on Friday for the first time. I lapped/trued a DPMS Lo-Pro. Followed Brownell's instructions. After the first 15 seconds, I could see the anodizing was slightly affected near the top where the notch is for the barrel pin. After the second 15 seconds, I felt I was at the 80% mark and stopped. Still had some anodizing mostly intact near the bottom. I had a ton of CLP inside the receiver to lube it up. It was a very tight fit, the tool really had to be spun in and out because it wouldn't slide. I used Permatex valve lapping compound from Autozone. I would guess the grit at 150-180, I think Brownells recommends 180. The package isn't marked with a grit or fine/coarse rating.
I also used Brownells gas tube/barrel nut alignment tool. Very nice. It slips into the gas key and barely will slip through the hole in the upper. If the barrel nut is off even a little, it won't go through. I was installing a Badger handguard and when done, the top rail lined up perfectly with the DPMS rail. |
| I've been thinking about this, but I'm not sure I understand how you all are doing this. With my bolt gun, I put the compound on the lugs, applied a little pressure to the bolt face by a dowel rod and worked the handle until I was satisfied. This doesn't necessarily square the lugs, but it does make the lugs fully contact the receiver. Is there a write up on doing it for the AR or maybe some pictures? |
|
Quoted:
I've been thinking about this, but I'm not sure I understand how you all are doing this. With my bolt gun, I put the compound on the lugs, applied a little pressure to the bolt face by a dowel rod and worked the handle until I was satisfied. This doesn't necessarily square the lugs, but it does make the lugs fully contact the receiver. Is there a write up on doing it for the AR or maybe some pictures? Click Here... 
|
|
Consider it, blue printing a part. Your'e just assuring the reciever is as square to the bore as you can get it.
An added benefit of lapping is, it seems to make timing a barrel nut easier. Especially when you get one that starts pushing the upper torque limits. Using a different nut works sometimes as well. I use only aluminum oxide for lapping. It's said to break down and not embed into the parts. A word of caution. It might not be a good idea to lap bolt lugs once the barrel has been installed. That can only increase head space. 458 |
|
Couple of things. If the receiver face is not perpendicular to the receiver bore axis, then the barrel may point off in some other direction. The barrel is also slightly cocked vs the bolt face. How much these affect accuracy, I can't say for sure. I do know that a very experienced AR builder does face the receivers for top accuracy. However, he inserts a precision fitted mandrel into the receiver, mounts the other end of the mandrel into a lathe and spins up the mandrel/receiver assembly. The lathe then cuts the receiver face to square it up. This process eliminates any inaccuracies that could exist with use of the Brownells tool and the receiver, because of some necessary clearance between those tools spinning the mandrel inside the receiver interior. Most of us do not have access to a lathe, hence the Brownells or Midway tools look more appealing. As an aside, the AR builder indicated some of the most accurately faced out of the box receivers are SunDevil.
I do not recall the diameter of the receiver face, but if 1", and is tilted by .001", point of impact of a bullet at 100 yards is changed about 3.6". Given that, I would want to make sure whatever cutting I am doing is truly improving things! - Phil |
|
Quoted: I mean no offense with this reply, I hope it isn't received in this manner. This is one of those things where you can listen to other's opinions and weigh the pros and cons all day long. You won't know for yourself until you try and even at that point unless you do a before and after you won't know if there is an actual improvement.I would want to make sure whatever cutting I am doing is truly improving things! I'm pretty new to this process but I've done several of these in the past week. I worked on a Stag with/for my friend today. He had a canted sight and was considering changing the sight to a flip up with a set screw. He didn't really want to change sights just to correct a problem that his eye was picking up. I told him I thought we might try a couple of things before he spent the money on a sight. We tried re-torquing the barrel and even shimmed the receiver extension stud using shim stock (there wasn't much free play in the slot). It didn't seem to make any difference. We ended up lapping the receiver and the improvement was very evident. I don't think anyone looking down the barrel for the first time would have considered the sight to be anything less than correct. For me, I did enough screwing around making sure that I was actually seeing high spots and that what I was seeing was repeatable before I ever removed any material. I am certain that I have more complete/better contact on these uppers with the mating surface on the receiver extension. No hard sell from me on this you can do it or not but I don't think the concept is hard to understand. As far as cutting it on a mill, that may or may not be a better way to go, I don't know. I know when doing a valve job on a head I always use precision machinery to cut the seat but when everything is said and done I lap the valves with compound to finish the job. |
|
I used a piece of glass, a machinists straight edge, level and a square (actually a couple of them). Initially I questioned whether or not the glass was flat. The straight edge confirmed that the glass was pretty darn flat. I also checked the receiver on several different spots on the glass. I used the level to check the surface plane and then set the receiver on it's nose. I used the square running down the T-Rail and left side of the receiver to to look for a right angle (this let me look at the lean from over a 90 degree span). I marked the receiver once I found how the receiver tilted. I rotated the receiver to see if the "lean" consistently repeated itself. I then repeated this on several different areas on the glass. I of course recognize that there could easily have been flaws or unevenness in the T rail but to my way of thinking it is designed to be perpendicular to the end of the receiver. I did this several times and the same place on the receiver kept popping up as the high spot. I also just used a square running down the T rail and pivoted it across the end of the receiver and measured with a thickness gauge, this pretty much confirmed the same thing the other checks were showing me. I coated the end of the receiver with a crayon and spun the lapping tool in the receiver (the lapping tool is a tight fit and not something easily turned by hand, it needs to be heavily lubed, I used a drill with the receiver in a clam shell). The lapping tool removed the crayon in the same areas I had marked as being the high spots. These very non-scientific checks gave me enough confidence to move on and use lapping compound. In essence what I was seeing was a plane on the outside of the receiver and from the bore that showed high spots in the same place. One of the other receivers I looked at stood very straight, when I did the crayon test on it one small area showed to have a dip in it but not enough to cause the receiver to lean. At the end of the day if you trust the tool and it fits the bore well the outside of the receiver makes no difference. I just needed a little extra confidence before I used the tool |
|
Quoted:
Quoted:
I mean no offense with this reply, I hope it isn't received in this manner. This is one of those things where you can listen to other's opinions and weigh the pros and cons all day long. You won't know for yourself until you try and even at that point unless you do a before and after you won't know if there is an actual improvement.
I would want to make sure whatever cutting I am doing is truly improving things! I'm pretty new to this process but I've done several of these in the past week. I worked on a Stag with/for my friend today. He had a canted sight and was considering changing the sight to a flip up with a set screw. He didn't really want to change sights just to correct a problem that his eye was picking up. I told him I thought we might try a couple of things before he spent the money on a sight. We tried re-torquing the barrel and even shimmed the receiver extension stud using shim stock (there wasn't much free play in the slot). It didn't seem to make any difference. We ended up lapping the receiver and the improvement was very evident. I don't think anyone looking down the barrel for the first time would have considered the sight to be anything less than correct. For me, I did enough screwing around making sure that I was actually seeing high spots and that what I was seeing was repeatable before I ever removed any material. I am certain that I have more complete/better contact on these uppers with the mating surface on the receiver extension. No hard sell from me on this you can do it or not but I don't think the concept is hard to understand. As far as cutting it on a mill, that may or may not be a better way to go, I don't know. I know when doing a valve job on a head I always use precision machinery to cut the seat but when everything is said and done I lap the valves with compound to finish the job. Not sure why any offense would be taken, but none is. Good to hear your efforts worked out well. I may or may not try it on mine. I am curious, and that may get the best of me. - Phil |
|
Quoted:
Quoted:
im building my own upper and i and have found through out builds that lapping the upper makes for smaller MOA;s how many of you guys out there lapp your uppers? I dont believe it needs to be done. Mike I am eating my words.Just received the tool and did two receivers and it took the rockability out of the face of the receiver on both.Placeing both on a machinest plate before they would rock and after lapping no movement.I will be doing this to all uppers i build. Mike |
The last two before today got this treatment, after a rockabilly test on a granite counter top checked for flatness with a level's straight edge. The lapping tool is going to find the uneven part of the receiver face.
The one I put together today didn't get it as it passed the rockabilly test. If it zeroes without extreme windage adjustment and is consistent I'll be happy; if not I might take it apart and lap the receiver face. |
| Taking into consideration the number of shops putting out uppers and the varying dimensions of the I.D. I would think that if the pilot was the least bit undersized in relation to the bore that the results would be questionable. If you want to get good results the pilot would have to fit with minimal clearance to eliminate an orbital motion (wobble) of the tool. The Midway unit looks like pretty simple lathe work and you could custom fit the pilot to the upper. |
|
Quoted: I had forgotten about this thread. I've done a bunch of these since the time I first responded to this thread. I've become even more of a fan. I will tell you that I've never had one of these that would remotely be considered loose. It's not the kind of thing you can spin with your hand. Some are definitely tighter than others. I did one CY6 that took a serious corded 1/2" drill to turn it. Others I've done have been easily accomplished using an 18 volt cordless. Again, this isn't something I can really tell you to sway you one way or the other but I'm not concerned about "orbital motion or wobble" as you described it. I have done before and afters of these using a laser bore sighter. The improvement each time was positive and in a couple of cases significant. Taking into consideration the number of shops putting out uppers and the varying dimensions of the I.D. I would think that if the pilot was the least bit undersized in relation to the bore that the results would be questionable. If you want to get good results the pilot would have to fit with minimal clearance to eliminate an orbital motion (wobble) of the tool. The Midway unit looks like pretty simple lathe work and you could custom fit the pilot to the upper. |
|
Quoted:
I do not see how the tool can accurately pilot the lapping tool to be exactly perpendicular to the boll face. May just be a feel good manuever. Lapping is something you do to smooth a machined surface not square it up.The receiver is probably soft enough that torqueing the barrel nut accomplishes most of this. You may find that if you torque a barrel extension on and then remove it , these imperfections are already gone.Quite a lot different situation than squaring the receiver face on a bolt gun where the center of the receiver is located and then the face machined perpendicular to it and the bolt face. Very interesting topic. To the point made by Nightforce, has anyone checked an upper receiver, for square, after a barrel had been properly installed and torqued - more towards the 80lb high. It would be interesting to find out if an out of the box receiver actually was squared by the barrel installation process. |
|
Quoted:
Quoted:
I had forgotten about this thread. I've done a bunch of these since the time I first responded to this thread. I've become even more of a fan. I will tell you that I've never had one of these that would remotely be considered loose. It's not the kind of thing you can spin with your hand. Some are definitely tighter than others. I did one CY6 that took a serious corded 1/2" drill to turn it. Others I've done have been easily accomplished using an 18 volt cordless. Again, this isn't something I can really tell you to sway you one way or the other but I'm not concerned about "orbital motion or wobble" as you described it. I have done before and afters of these using a laser bore sighter. The improvement each time was positive and in a couple of cases significant.
Taking into consideration the number of shops putting out uppers and the varying dimensions of the I.D. I would think that if the pilot was the least bit undersized in relation to the bore that the results would be questionable. If you want to get good results the pilot would have to fit with minimal clearance to eliminate an orbital motion (wobble) of the tool. The Midway unit looks like pretty simple lathe work and you could custom fit the pilot to the upper. If you hold the tool vertical the wobble is reduced or nonexistent. Lube on the pilot will help as well. 458 |
|
Quoted:
Quoted:
It would be interesting to find out if an out of the box receiver actually was squared by the barrel installation process. The answer is no the two receivers i did had barrels on them before and lapping squared them up. Mike Yup... I did the same thing. Had just mounted a Shilen .204 bull barrel on a Mega upper. Took it apart and placed upper on the bed of my jointer. Took machinist square and found it to be off. Tested a brand new, unused, Spike's upper and it tested dead nuts. I'm not sure how people are applying the square to the receiver, but I used the of the picatinny rail (top); then the pivot pin lugs (bottom) and finally each edge of the picatinny (left & right). BTW - ordered the lapping tool and abrasives from Midway. |
|
DM
In your case only run the tool for a few seconds and continue to check for wear on the face. Bet you'll be surprised at it's wear pattern. As far as I can tell the tool is simple and if one had the dimension and a lathe you could make your own.. Nothing special. I would not use valve grinding compound with one. 458 |
|
Got the Stoner lapping tool today and took apart 3 uppers. It took a couple of hour to lap all three uppers (2 - Spike's & 1 - Mega) with most of the time spent on measuring and using machinist squares to check for straightness. I used Wheeler 220 lapping compound and I'm glad I did. Anything lower would remove to much material to fast for me. Besides it's next to impossible to keep the compound from wicking into the interior of the upper. Not much, but enough to put very light swirls on the tool. I would not have wanted 160 - 180 grit getting in there.
I learned very quickly that you should not attempt to support the tool and attached drill. In my case, I initially tried to relieve the weight of my 18 volt 1/2" Makita. I found out very quickly it throws off the evenness of grinding. I would run the tool at 200 rpm for 15 seconds and check the results. In the end, I chose to remove all the anodizing from the front of the threads. That way I knew the entire surface was squared, provided I didn't screw up along the way. My earlier mistake was easily rectified by letting the tool and compound do the job with no input from me. Once you get the picatinny rail square, everything else pretty much comes along with it. I was fortunate to have a machined surface to work from and an assortment of machinist squares to work with. I will say it was worth doing, because it removed any doubts lingering in the back of my mind. |
|
Quoted:
I hope everyone knows that this trues the receiver face to the bore and not to the rail. If the rail is out of line with the bore, a windage problem will still be there but no problem if it can be adjusted. +1 on that your trueing the front of the receiver face so it does not matter if you use a square to check it against the rail.Your making sure your bolt and carrier are running concentric to the receiver face. Thats like when you true a Remington 700 receiver your useing the bolt way as your guide so checking for squareness to the outside of the receiver isn't going to tell you much unless the rail is true to the inside of the receiver which it should be but not in all cases. Mike |
|
hdbiker & MGP - yup I agree even though I didn't specifically say so. I used the rail as a reference to check my work and overall progress of squaring the face of the receiver. As stated earlier, I decided early on to remove all the anodizing from the face of the receiver. Once properly accomplished, I did get more consistent and predictable contact between the machinist square and the rail.
|
AR Sponsor