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Ar detent mod question

warwickben

warwickben

bubba Kalashnikov
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I know some guys tap and thread the rear detent for a set screw . So it doesn't get lost Swapping put the stock.. Saw this happen Saturday lol.


What size tap you use . And how long of a set screw and how much do you cut the spring . My google skills lack today
 
For reference: the rear takedown pin detent hole in a mil spec lower should be 0.097" (#40 drill) so you shouldn't have to open it up (though, obviously I'd check first...breaking off a 4-40 tap in there would suck)
 
I have a bunch of the set screws on hand. Bought a bsg of 100 before the first build party. If you want one, come on up. You'll also need a .050" Allen wrench for the set screw.

Also, you need to tap the hole vertically. Do NOT let the tap go on an angle since you'll easily snap it. Just as Malodave if you don't believe me. [laugh] If you use two fingers (thumb and index finger) on either side of the tap that should make it easy. Even the weight of the tap handle will cause the tap to snap.
 
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What a great idea , I could have used something like this while I was fighting with the pistol buffer tube install , good thing I'll be taking it apart again
 
Golddiggie said:
I have a bunch of the set screws on hand. Bought a bsg of 100 before the first build party. If you want one, come on up. You'll also need a .050" Allen wrench for the set screw.

Also, you need to tap the hole vertically. Do NOT let the tap go on an angle since you'll easily snap it. Just as Malodave if you don't believe me. [laugh] If you use two fingers (thumb and index finger) on either side of the tap that should make it easy. Even the weight of the tap handle will cause the tap to snap.
Click to expand...


I have the Lower to show what I had to do to save it. Milling with a 5/64"
end mill was quite the task.

Malodave
 
Golddiggie said:
I have a bunch of the set screws on hand. Bought a bsg of 100 before the first build party. If you want one, come on up. You'll also need a .050" Allen wrench for the set screw.

Also, you need to tap the hole vertically. Do NOT let the tap go on an angle since you'll easily snap it. Just as Malodave if you don't believe me. [laugh] If you use two fingers (thumb and index finger) on either side of the tap that should make it easy. Even the weight of the tap handle will cause the tap to snap.
Click to expand...
can I come buy and do a couple 3 receivers in November?
 
The set screws are the hardest part to track down . I'm going to do the mod when you add a set screw to apply pressure on the rear take down pin.
I'm building this ar up to use with a scope. And a free float rail. Figure it can't hurt¿
 
What happens if you don't take 1/8 in off of the spring?

PS I thought messing around with the receiver was a bad idea at first, but the more I think about it the better it looks.
 
warwickben said:
The set screws are the hardest part to track down . I'm going to do the mod when you add a set screw to apply pressure on the rear take down pin.
I'm building this ar up to use with a scope. And a free float rail. Figure it can't hurt¿
Click to expand...

As I already posted, I HAVE a bunch of the set screws. I found them on Amazon months ago. Bought the 100 pack bag of them, and it came to under $10 with overnight shipping. AS I also mentioned, if you ever get your punk ass up here, you can have one of the set screws.

- - - Updated - - -

Gammon said:
What happens if you don't take 1/8 in off of the spring?

PS I thought messing around with the receiver was a bad idea at first, but the more I think about it the better it looks.
Click to expand...

Nothing bad happens when you trim the spring. You need to trim it so that it won't be pushing too hard against the detent. If you're really paranoid, just pick up a couple of replacement springs.
 
ivarr said:
any aubuchon hardware store has them as well
Click to expand...

^^This. I did all 5 of mine. You also might want to consider applying a little anti seize to the threads of the set screw as the threads are raw aluminum and there are now 2 dissimilar metals in contact. I did just for my own piece of mind. Maybe it will never be a problem, but with the luck I have, the one time I want to remove the set screw it probably wouldn't budge.
 
atilla said:
i can't believe i never thought of this. so simple, but makes shit a little more convenient.
Click to expand...

Seriously. I made a similarly simple discovery recently...maybe there should be an AR tips & tricks thread

Anyways, I was cleaning the bolt lugs and was having trouble getting my AA mag light to shine right where I needed it...then I realized the OD of the head of the flashlight looked about the same as the OD of a bolt carrier. The flashlight drops right into the upper and shines straight down the barrel while leaving room for you to clean through the open bottom of the upper.
 
Gammon said:
What happens if you don't take 1/8 in off of the spring?
Click to expand...

Detent pin won't compress (because you'll have fully compressed the spring with the set screw).
You'll only do this once because then the takedown pin will either be stuck in, or stuck out.
 
As for getting taps to run true and not break....
Take a scrap of ~1/2" aluminum. Drill hole in it that will JUST clear the tap.
Clamp this guide block centered over the hole to be tapped. Insert tap into guide block and proceed with threading.
 
Archilochus said:
As for getting taps to run true and not break....
Take a scrap of ~1/2" aluminum. Drill hole in it that will JUST clear the tap.
Clamp this guide block centered over the hole to be tapped. Insert tap into guide block and proceed with threading.
Click to expand...

Tapping block .... I use stainless , but that because 99% of what I machine at work is stainless.

I just use a drill press and a centering pin when ever I can .
 
Make sure and put a little Aeroshell 33MS grease on the set screw. Steel & Aluminum should have a little something on it, even though it's such a small application.
 
ntomsw said:
Make sure and put a little Aeroshell 33MS grease on the set screw. Steel & Aluminum should have a little something on it, even though it's such a small application.
Click to expand...

Mot much of an issue if the lower was anodized, or had Cerakote applied, after the hole was tapped. I anodized my first 80% lower after the hole was tapped (did it during the machining).
 
anyone local have a 4-40 tap? or know of anywhere locally that carries 'em. I don't think home depot, lowes, harbor freight, or ace hardware carry them............
I think I bought the right size set screws :)

To people who have done this, is it not smart to do with just a hand drill?
 
JCV said:
anyone local have a 4-40 tap? or know of anywhere locally that carries 'em. I don't think home depot, lowes, harbor freight, or ace hardware carry them............
I think I bought the right size set screws :)

To people who have done this, is it not smart to do with just a hand drill?
Click to expand...

No drilling, just run the 4-40 tap into the hole. I have several of the taps on hand (even after breaking some). You'll need/want to support the tap with your fingers, and keep it vertical. If you put it to any angle (even horizontal) you have a very high chance of snapping the tap (with a standard tap handle/wrench on it). We had that happen once already and it took a bit of work (and a milling machine) to get around the broken tap to extract it. You'll only need just over 1/8" of actual threads. So determine how deep you'll need to send the tap ahead of time.
 
JCV said:
anyone local have a 4-40 tap? or know of anywhere locally that carries 'em. I don't think home depot, lowes, harbor freight, or ace hardware carry them............
I think I bought the right size set screws :)

To people who have done this, is it not smart to do with just a hand drill?
Click to expand...

I can do it . Did mine
I just ran the right size drill with a tap handle just incase tho.
 
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My local ace hardware usually has tap and dies to match most of what they sell. Up to 1/2 inch. My local ace is very good. If they dont have it there quick on getting set. My 4/40 tap I have had since I was into Rc cars planes ectect. There mini Allen drivers are nice also. Don't know who makes them but has held up nice.
http://shop.dubro.com/p/4-40-tap-drill-set-qty-pkg-1
 
I got my tap and handle at Ace as well as some set screws. They're flathead instead of Allen key, but that's all they had. Might go back and see if they have the hexes.
 

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