AR drill/mill fixtures... have we been doing it wrong for years???

[clm2112]

Just thinking through the problem of how to clamp onto an AR lower (any AR lower, be it AR-15, AR-10, LR308, etc.) and it sortta dawned on me that perhaps all the jigs are going about this the wrong way.

Before throwing stones and rotten tomatoes at me for my heresy, hear me out...

How do nearly all the milling fixtures work now? They wrap around the outside of the lower and key off the take-down pin holes in order to locate the point where the safety selector and hammer/trigger pins are drilled. So, the side plates of the fixture have to be relieved for the various ribs and details a manufacturer chooses to add on the outside of their AR lower. And, the jig has to account for the different dimensions of where the take-down pins are on an AR-15 vs. AR-10. Lastly, the jigs all have some form of top plate bolted on that keeps the jigs sides from folding in when you try to clamp it.

Turn the problem around and think about what all AR's have in common regardless of model.

Well, they all accept the same injection molded plastic grip. It is so common that nobody even thinks about whether manufacturer X's grip is going to fit. People just buy it and bolt it on. And that grip is always attached with same size bolt in the same place.

Also, the relationship between that grip mounting point and the fire control parts is the same on all AR designs, so the centers for all the holes (safety selector, trigger pin, hammer pin, and the happy pin we are not allowed to talk about) can all be located off the safety selector detent hole and grip mount.

So... why the heck are we not making our fixtures to attach to the grip mounting point and indexing off the safety selector detent hole? It is low on the receiver, so it fits well inside typical vise jaws. It is a very solid chunk of metal that will take a lot of clamping force. And it is hidden by the grip after assembly so if you accidentally mar the surface, nobody will ever know it.

This is something I'd like to explore in detail.

 

[Branch]

You bring up a good point, and have my brain stirring now too. I have milled several AR-15’s on my Bridgeport vertical mill using a cheaper jig that I modified for forged versions, and I made my own holder for some billet ones. I have a 308 lower to machine yet, and have been thinking about how to hold it properly. I’m going to look into locating it off the grip mount as you are suggesting, it would certainly be easy to locate fore/aft off the detent hole.

 

[clm2112]

You bring up a good point, and have my brain stirring now too. I have milled several AR-15’s on my Bridgeport vertical mill using a cheaper jig that I modified for forged versions, and I made my own holder for some billet ones. I have a 308 lower to machine yet, and have been thinking about how to hold it properly. I’m going to look into locating it off the grip mount as you are suggesting, it would certainly be easy to locate fore/aft off the detent hole.

Yeah, it has been gnawing at me all day. My first LR308 lower arrived in the mail this morning and I spent the day at work sketching out various blocks to make to mount the receiver using the grip mount.

I'm kinda settling on a plan of attack using a block of aluminum the width of the receiver, with an angled slot to go around the grip mount. Put a steel pin in to go up into the detent counter-bore. Then attach it to the right half of my current jig to see how this will work using a commercially made AR lower.

If it works the way I am imagining it, I will lop off the font halves of the jig side plates. And finish by shortening the jig, which will remove the indexing of the rear takedown pin. Should end up like a "U" shaped cradle that goes around the rear portion of the lower.

 

[clm2112]

Giving it a go!

Spent most of this morning doing the core block to try this idea out. The basic idea is an aluminum block that bolts to the grip surface of the lower.

And it fits every receiver I've tried it on

Next step is to modify the side plates so this block is attached to one side in the correct orientation.

 

[clm2112]

Epoxying the block to one side of the existing jig. Pins that used to locate the receiver on the take-down pin holes have been removed. The shanks of 1/4" drill bits are keeping everything aligned until the epoxy cures. Once the block is permanently attached to the side plate, the pins will not be needed.

If this works, everything from the bolt catch forward will get cut off the sides of the jig.

 

[clm2112]

It works!

No pins, no top plate, just the clamping action of the vise on the internal block and the grip screw.

After I mill out the trigger pocket on this AR-15, I'll do a little more cutting on the side plates to allow the LR-308 lower to fit. Just a little trimming at the tops of the side plates for that overhanging shelf that serves as filler between the lower and upper.

 

[brian]

The mounting approach is interesting and certainly looks to take advantage of some existing holes in an 80% lower so hats off for thinking out of the box. I am using a 5D tactical jig which has worked fine for me for an AR9/15/10. I use their guides with a router, not a mill, so I am trying to figuring out how the mounting process you are exploring is a game changer as I am still going to rely on their "upper jig" which is more or less dependent on their lower. Their lower also gives me the markers I need to drill the pin holes for the trigger. Are you ultimately working toward a new jig for 80% ARs or just a different way to attach with a jig you are using?

 

[clm2112]

Not much use to you there Brian. This idea is really only relevant if you are using a mill or a X-Y table.

 

[clm2112]

One other thought that sort of bucks the trend...

What are you going to do when the gubberment cracks down on the sale of jigs to make 80% firearms? Or the jig just isn't available (hey we've seen that happen multiple times... where you can get the part to machine, but can't get the tooling to machine the part.... think JSD MUP-1's )

Similarly, what do you when you want to alter the inlet on your AR to something your current jig doesn't allow for? I've seen about six inlet styles used on the commercial AR... most revolve around cutting the inlet for components not normally found in Joe-Bloe's AR. The router style jigs typically only cut one pattern only.

The solution is to make your own.

What I just demonstrated is the bare-minimum bit of tooling needed to machine an AR. You don't need to buy it, you can make it out of scrap metal, just like I did.

It means upping your metal working game a few notches. But one thing I've noticed of late... used manual milling machines are getting cheaper. A fellow I know just bought one off Craig's list for the cost of the gas to go get it. It's a beat up and tired knee mill, but it works and the grand kids wanted pap's shed cleaned out.

 

[brian]

One other thought that sort of bucks the trend...

What are you going to do when the gubberment cracks down on the sale of jigs to make 80% firearms? Or the jig just isn't available (hey we've seen that happen multiple times... where you can get the part to machine, but can't get the tooling to machine the part.... think JSD MUP-1's )

Similarly, what do you when you want to alter the inlet on your AR to something your current jig doesn't allow for? I've seen about six inlet styles used on the commercial AR... most revolve around cutting the inlet for components not normally found in Joe-Bloe's AR. The router style jigs typically only cut one pattern only.

The solution is to make your own.

What I just demonstrated is the bare-minimum bit of tooling needed to machine an AR. You don't need to buy it, you can make it out of scrap metal, just like I did.

It means upping your metal working game a few notches. But one thing I've noticed of late... used manual milling machines are getting cheaper. A fellow I know just bought one off Craig's list for the cost of the gas to go get it. It's a beat up and tired knee mill, but it works and the grand kids wanted pap's shed cleaned out.

Trust me, I wasn't trying put down your effort just wanted to better understand the why. The idea of having CNC and milling knowledge is clearly beneficial to me - it is going to be pretty hared for them to outlaw a chunk of metal which is all you'd need to make a mup, your own 1911 frame, AR receiver, etc.

 

[clm2112]

No offense taken. I knew this whole idea wasn't going to make a whole lotta sense.

The ability to make your tools from raw materials goes against the trend of our hobby. I liken it to the same trend in other hobbies.... like model airplanes or model trains. Few people build anything from scratch, they just buy it ready to use, because the products being sold are really, really, good. But, what gets forgotten is the skills to make it from a box of balsa or sheets of brass. If fact, the skill are not just forgotten, they are never developed in the first place in people new to it.

Where the analogy diverges... nobody is going to be in peril if they can't buy a ready to use model of a Pennsy K4 locomotive. But I am worried about what can happen when we run out of professional gunsmiths and we don't have the skills to make up for the loss.

On the plus side, the trend to make the task of making a firearm easier has opened the hobby up to a lot more people who didn't think it was possible.

On the minus side, in making it easier, are the newcomers not learning key basic fabricating skills that will be needed later.

...and it is 4:00 am, I'm slurping coffee, and just rambling on incoherently.

 

[clm2112]

On a different vein, I'll throw a little challenge out to anyone with more skills in the 3D printing world...

Take the basic idea of a minimalist clamping and drilling fixture that attaches to the AR grip area and 3D print it in PLA.

I made mine out of aluminum, just because I had a handy block of scrap aluminum, but I can envision the same thing being made out of plastic. The layers should run parallel to the sides of the lower so the print is under compression while it is clamped in the vise for milling, or laid on its side for locating the pin holes for drilling. And, it can likely be printed in one piece instead of a block with two separate side plates.

That way, anybody can generate the minimum tooling to machine an AR from scratch and not be forced into purchasing a commercially made jig. (I've got nothing against commercially made jigs, I just see their potential lack of availability, and rising cost, as a risk to the activity.)

The same plastic jig could also be handy for doing repairs and modifications on finished lowers.

The long term goal... give anyone with the time, and motivation, the means to take a piece of aluminum bar stock and form it into a functional, durable, AR lower.... i.e. a true 0% lower.

 

[clm2112]

The moment of truth.... first cut using the grip block as the clamping fixture.

This is going to work. Pretty aggressive cut with a 3/8" end mill. No chatter, no change in depth down the length of the slot. The clamping force is sufficient to hold the lower in place while carving away on it.

 

[clm2112]

Couple hours later... the 0.445" deep layer is complete, starting on the 0.630" layer.

At this point I gotta press pause and get ready for work. I'll pick up tonight finishing the 0.630" layer and hopefully get into the 1.249" deep layer to finish it.

 

[clm2112]

Moving on... spent this morning relieving the side plates for the LR308 lower. Really, just carving the material away to make room for the extra material.

 

[clm2112]

What the inside of the sides look like when done. There is an extra block that goes through the trigger guard, this is a leftover from a previous modification to the jig and really isn't needed anymore (I just haven't gone to the trouble of removing it.)

The only other modification I am considering is to drive the steel drill bushings out of one side, and install them in the other side. So you would drill the safety selector hole starting from the detent side. This might lead to a more accurate hole. I dunno, I'm still pondering this.

The spare A2 grip is just a little quick test tool. I ground down a 1/8" steel rod to a point and drove it into the detent spring hole. This can be put onto a lower to check that the detent hole in the lower is in the correct location prior to loading it into the jig for milling.

I just found out that the AR-10 lower I got from RightToBear.com (Daytona Beach) was incorrectly machined. I'm waiting to hear back from them if they will replace it. I just sent the photos they requested yesterday to illustrate what is wrong. (They machined it about 1/8th inch too far to the rear of the receiver so it doesn't line up with any grip.) We'll see how this goes. I've never had a receiver show up with the hole in the wrong place before, but I guess there is a first time for everything.

Checking a Tactical Machining lower shows the holes perfectly aligned (the steel pin in the grip goes right down the center of the detent hole in the lower.

Same test with the RightToBear lower shows the mistake in the milling... the holes don't line up and the detent spring would never work... it would end up crushed between the grip and the lower during assembly. Safety Selector wouldn't work right either, since the other end of the hole doesn't intersect a properly placed selector hole through the width of the lower.

 

[clm2112]

In response to a private message sent through the forum I feel I should make it clear to everybody.

I am not selling this. I'm not going to make them to sell. I'm hanging this design idea out here for anybody to use. Take it and run with it. Incorporate it into you own jig design if you like it. If you have some free machine time and want to make a few to resell, go for it. If you are one of the 3D printer wizards, CAD the crap out of it and show how to print one. I am too old to go starting another business selling jigs and milling fixtures.

The sole objective I have is to ensure that the amateur gunsmith has access to the tools needed for the craft to continue. And if that same person is denied access to ready made tools, then he or she has the knowledge of how to do it starting from a chunk of metal and a drawing.

If I really wanted to be obnoxious, I'd mill a middle finger out of 6061 and point it squarely at the nanny state.

Hopefully, I'll make another one to simplify the design even further. I'm kicking around some ideas of what the simplest side plates should look like to do the task of marking the locations of the holes. I don't know if I'll get to that in the next few week, but I will post that as well when I do. And like the idea of how to grip the lower, how to mark the holes will be for anybody to do what they want with it.

 

[AZ-2A]

Very cool idea!I don't use jigs just my DRO and blocks to clamp whatever I'm working on this idea would make the process of clamping alot faster and possibly more consistent, after losing my shop (I used to be a 01,09,07,08 license holder) I gave up building or prototyping.... got back into it 4-5 years ago using the manual mill/lath I have in my home setup I built decades ago (basically a machine shop inside a semi trailer with a Colchester bantam2000 lathe and jet 16 mill/drill not enough room for a big knee mill) and just never thought about buying any jigs have got ALOT of blue prints etc... but fixturing can be a pain and very time consuming I frequently use the grip lug as primary clamping location but somehow never thought to mill out a block specifically for that purpose....

thinking maybe make it thick enough to be clamped horizontally from either side for cutting the selector hole etc.. then flip it around vertical for the pocket, possible make a set of vice plates so it could always be centered exactly the same... now going to have to

 

[clm2112]

Yeah, I'm thinking about doing another one myself. But using very thin, removable side plates that just mark the centers of the holes to be punched and drilled. The grip of the block on the grip tang is strong enough for the vise jaws to hold during the milling. I really stopped using the tops plates to guide the milling anymore. I just mark the centerline of the receiver and set stops for the X-Axis to mark the ends of the cuts.

 

[AZ-2A]

Well something to keep in mind.... I made my own side plates and a grip block like you did... got 3 RTB AR15 blanks and that other ar10 replacement to do... as I don't have any stripped lowers laying around I used an ar10 lower from another supplier out of oregon to mark where to drill the grip screw hole.. just dropped a layout punch through the grip screw hole a light tap.. figured better to be sure dead on in right spot etc.. drilled it and used end mill to counter sink outside etc.... went to test it on onea the RTB AR15 lowers and... the hole is off.. by about a 1/16th or better..... tried to figure it out... then put the block on the RTB AR10 blank... lines up almost perfect grip boss is thicker on the RTBAR10 so gotta widen the slot a lil etc.. then put it on yet another AR10 lower this one from 5D and it lines up perfect! put it on the one from oregon and again lines up perfect... it seems that not every 80% company actually has the grip screw in a universal location/angle still yet to be determined as have ALOT going on right now will try to get pics time permiting... just a heads up it might not be so universal... gonn slot the grip screw hole so can get it to work with the RTB AR15 lowers later