So I am getting ready to start my lower and trying to find a 1/4" end mill bit according to 80% Arms.  For there jig they recommend a 1/4" x 1/4" x 2 1/2".  My question is this they say that at least a 1/4" of the end mill shank needs to be touching the jig so that it doesn't cut into the jig. Anyone got any advice on what end mills to use?

This is the site where they discuss the finishing.

http://cdn.shopify.com/s/files/1/0218/5770/files/Jig_Manual_80_Percent_Arms.pdf?106

Either www.use-enco.com or www.MSC.com sell end mill bits.
You may have to grind the bit short to get the necessary shank exposure.  If you do need to shorten the end mill make sure to take the depth of the cut and mark it on the bit before grinding (and dunk in water often to prevent work hardening the bit!!!). Prior to using the end mill you will want to drill a pilot hole to make thing easier.   I would recommend using a finishing end mill as the aluminum is soft enough.  If you have any question just ask, I will help all I can.
Good luck and remember, measure twice and measure often!

Wow there is so much fail in this thread.
End Mill bits.  They are just End Mills.
Grinding on them will Work Harden them. What is that ? They are hard to begin with. Grinding on them and getting them too hot will make them SOFTER.
You will be tempering them.
I suggest you guys do a little more research.

I was a Tool & Die Maker for 30 years.
Damn.

Travers Tool co. is a good source for supplies.  Enco is cheap crap.

Glad you said it, i didn't have the heart to call them out since they are under post count of 3 each..

I'm new at machining and need all the help I can get. Since botching my first attempt at completing an 80% AR-15 lower I want to mark some critical points on the next one before starting. One critical point is the midline of the deck where I mill out the FCG pocket. What is the easiest/best way to mark a midline on a rectangular piece of Aluminum that is known to be square?

I'm haven't tested it yet but I'm pretty sure the edge finder I used is screwed up. Looks like my center line was of by .017.

Also, since completing an 80% AR lower is a pocketing operation, do you have any suggestions on where I can read up on best ways to do it?

Thanks in advance.

By mid line, I take it you mean the centerline of you work piece. I use a Starett edge finder. the one side is .200. You run the mill at around 1000rpms. with your edge finder in your drill chuck. There are few ways to do this.

1) Mike the outside of your piece. Divide that by 2. that will be your centerline measurement. Slowly come in against the edge of your piece. You just want to barely touch the side of the material with the edge finder. It will slide off to one side. Do it a couple of times if you aren't sure. Call that a temporary zero, move in .100. You are now on the edge of your piece.. You simply go in the distance you calculated before. You are now at the center. And your real Zero, as most prints will work off the centerline.

2) You can bump the edge finder off one side. this is your zero. Set your dial. now go to the other side and do the same thing on the other side. Divide the distance you have moved in half. That will be your centerline.

3) You can use a dial indicator in your drill chuck. Put your mill in neutral. Sweeping the indicator back and forth move in till you hit the piece go in a few more thousandths. Set your indicator to 0. You will notice that the indicator will only read 0 at the center of your swing. Do the same with your dials. Now go to the other side and do the same thing coming in slowly. when your indicator hits 0 on the other side. You divide the distance you have moved in half. This is really the most accurate way. But I believe the edge finder, will work too.

You can trash an edge finder by slamming it into the work piece too hard. A new edge finder is cheaper than a new 80% lower

Keep in mind that your lead screws will have slop in them. If you don't have a digital readout, to tell you when you are really moving the table. You need to know the backlash, and take that out, by turning your handles the same direction both times.

Personally I would plunge the most material out as I could in the pocket. Staying away from your finish dimension, by .030, sides and bottom, Then you can finish up in a normal cutting fashion. Keep in mind a small cutter can flex out. You will get a better finish on your part if you climb mill the last pass.

Really your going to criticize me about calling them bits?  As far as not having enough knowledge I agree, I don''t have knowledge about milling. That's why I am asking questions.  I don't have a mill and will be doing this on a press, can't afford a mill.  Thanks for letting me know where I can get some good supplies.

Thankyou for the detailed response.

I have ordered 2 new edge finders because I think the one I was using is screwed up somehow. I had used the technique you described in step 1. Did it at 1000rpm, and verified edge finder alignments from several angles. I was still way off, though.

Fortunately I have a DRO but it is only on the x and y axes but not the z, which kind of sucks. BTW, I know it's trashy but I have developed a nasty habit of using the "paper test" to set the z-axis zero and am getting very inconsistent results. Would I get more consistent results using a 0.001 feeler gauge or is there another technique that works well?

I have come to the same conclusion about plunging as much of the metal out of the pocket as possible and then running 2 to 3 finishing passes. I spent about seven hours on the lower I milled, but that includes the time taken to tram, transfer punch the safety selector hole and hammer and trigger pin holes, drill the safety selector hole, setup the piece in the mill vise, and all the cleanup. I think that at minimum, drilling a 7/16" pilot hole at all four corners of the main pocket, and the end of the middle pocket where that meets the shelf edge of the shallow pocket, could save some time and reduce the chances of overshoot.

On the first lower I drilled a 7/16" hole at one corner of the main pocket and then cut out the main pocket with 12 rectangular passes cutting 0.100" deep and then two finishing passes. Then did the middle and last pockets. That takes a lot of time and with that many passes, it is hard to maintain focus so the risk of overshooting a cut gets higher.

I do worry about smaller and longer cutters flexing. I have been using 7/16 end mills (except for the trigger slot, which requires a 5/16. Unfortunately because of clearance issues on the milling machine I am using I have to use a fairly long shanked end mill to cut the middle and shallow pockets. That's another reason why I would like to drill most of the metal out first and do very light cuts with the longer mill.
Thanks again!

Edited to add: Just occurred to me that I could plunge cut and do some cleaning passes down the centerline of the main pocket using a 5/8 center cutting end mill.  Since the main pocket is 0.690 wide. That would leave me a little over .037 on each side to clean up (which I would do with a 7/16 end mill to get the proper corner radius)  and doing the centerline cleaning passes at 1/2 diameter of the end mill would let me do 4 passes at 0.310 depth. The main pocket is 1.249 deep so that would leave me .009 on the bottom to do a finishing pass after roughing in the main and middle pockets. Is that a reasonable approach or would I be making a really bad newbie mistake by doing that?

All advice appreciated, whether worded kindly or not.

im pretty sure that was for the guy that responded to you he tried to come across like he knew what he was talking about and didnt

I re-read your post and would like to pass along some stuff I have learned the hard way recently. In my view there are two paths you can take with finishing an 80% lower and the path you take depends on what you really want out of it.

If, like me, your *primary* goal is to learn machining skills the completed lower is a bonus.

If your *primary* goal is to have the experiencing of building an AR-15 in a way that is a bit deeper than the norm, the quality and function of the completed lower is your focus.

No insult intended here, but I think that if either of the above is true for you, then you are asking the wrong question.

For example, if you want to learn machining, a better question to ask is for the equipment you have, what is the best strategy to use to complete the lower.

You can find a mechanical drawing of the AR-15 lower on the 'net and start looking at dimensions of the FCG pocket that you will be milling and asking yourself whether a 1/4" end mill is really the right tooling to use. Without going into detail, consider that the typical radius of the corners in the main pocket is 0.218. Doing the math, the radius of a 7/16 end mill = 0.4375 / 2 = 0.21875. That is not a coincidence. Now go look at the Enco catalog and see that you cannot find a 7/16" end mill with a 7/16" shank, so if you run the shank up against the jig top plate edge, the cut will be wider than you want.

Lots more issues than that, but it's just to illustrate the idea that *strategy* is a critical consideration.

Regarding the point of view that the primary desired result is the lower itself and the machining is more or less the price of admission to get there, then the question to ask (at least in my limited view) is that for the equipment and jig that you have, is the 1/4" x 1/4" x 2-1/2 end mill really the way to go or is there a better choice.

Again, please consider that I am very new at this but I can think of several obvious issues. One is that the main pocket is 0.690" in width. A 0.250 diameter end mill will take 3 cuts per "lap", so you cannot run the mill around the edges of the jig top plate cutout edges and cover the whole area of the bottom. Maybe that is not an issue because you will be drilling most of the metal out before you start milling. Or maybe it is--depends on your skill and equipment and the time you are willing to invest in completing the lower. Also, do the instructions you have recommend that you use that same end mill for all 3 pockets? If so, I would be very concerned about the possibility of  that 2-1/2" end mill not being long enough to clear the buffer tower and still reach 0.630 down into the metal for that last pocket.

All that being said, I think you will get the answers you are looking for if you say what you are trying to accomplish, what equipment you have, what recommendations you have been given, and ask if there is a better way.

Completing an AR-15 lower is an extremely cool way to learn machining skills but it is an effective way to learn because you will very quickly find that it is complex and not easy to do well.

Ok, so to answer your question consider the following:
* Rigidity in the milling system is critical. Longer mills/drills are less rigid and therefore not as precise. It may make sense to use mills of multiple lengths.

* LOC (length of cut) is a big deal. If you could find a 7/16" end mill with a 1.249" (the depth of the main and middle pockets) LOC, or slightly shorter, and a 7/16" shank so you could ride it against the jig top plate cutout, you would probably end up with a very nice result.

* Since the trigger slot is 0.312 (5/16 = 0.3125) in width, then a *long* shank 5/16 end mill with a short LOC will do the job for that.

Sorry for the rambling response, but my point here is that being more clear about what you are doing will make it easier for others to give you the knowledge you need. I'm a newbie, but a lot of the tripping points are still fresh in my mind so I can at least share that.

BTW. the jig you chose looks like a great choice. I am curious about their choices of end mills, though. I'm guessing their choices are strongly influenced by the fact that the jig will be used on drill presses.

Anyway, please keep this discussion going. I'm learning from it too.

Thanks for all the info, I should have posted more.

Here is what I am working with:
15", 12 Speed, 1hp, Floor drill press (can't afford a mill right now)
80% Arms Jig
I haven't bought or ordered any end mills yet because I am not sure exactly how I want to attack this yet.

80% Arms recommends using:
RecommendedBits:

1/8”DrillBit(0.125”)
17/64” Drill Bit(0.266”)
3/8”DrillBit(0.375”)
7/16” DrillBit(0.438”)
1/2”DrillBit(0.500”)
1/4"CarbideEndmill(0.250”)*Minimum2.5”long
3/8”CarbideEndmill(0.375”)*Minimum2.5”long

All holes are then pre drilled, and they they say to use the end mills to smooth out the sides and remove the remaining material.  Trigger pocket is created using the 1/4" end mill using the shank and the side of the jig as a guide like a router.  Would the larger end mill that is the exact size be a better choice?  I was originally looking for a 1/4" end mill that was 2.5" long with a very short LOC as they show in their manual but haven't found anything like that.  Any other directions other than theirs I would like to look at, an advise is welcome.  This project is both to start working with metal, as well as being able to create the lower.  Before this I have really only worked with wood, but have always been interested in learning more about working with metal.

Just for a reference these are the directions that 80% Arms gives.

http://cdn.shopify.com/s/files/1/0218/5770/files/Jig_Manual_80_Percent_Arms.pdf?106

This is for the guys I offended here. Sorry.
When actually asked for help I am more than willing to respond. I will say that I wouldn't attempt to make a lower on a drill press. The spindle bearings in a drill press aren't made for a side load.
I assume you have a 2 way slide attached to your drill press.
One can be bought at Travers. around 150 or so.
I have a drill press to, but no more access to precision machinery. I'm disabled now. Don't work anymore.
Ask me a specific question and I will be glad to respond.
Also the 2nd poster I responded to has left you some excellent advice. I would listen to it.
P

The best directions I have seen (and they could use a little work) are the DRO directions from Colfax Tactical. That does not apply to *your* situation, though. I honestly do not know enough about using a drill press for things it was not designed for to be able to make any intelligent comments, so I'll let others do that.

I do think you are wise in doing a lot of analysis up front. If you do not have the machine drawing of an AR-15 lower, go here to download it. Some of the measurements related to the FCG pocket are very difficult to extrapolate and the DRO directions cited above can be very helpful for that. Keep in mind that you need to add toolbit radius to those distances, though.

The Colfax Tactical directions for a drill press are very similar to the way I was looking at doing it.  It uses the press to remove as much material before using the end mill to smooth it all out.  I do like their directions a little better.  I down loaded the machining drawings as well.  I have a good set of calipers and will just have to take my time and use lots of WD40.  My jig should be here tomorrow, which means I probably wont get started till Friday.  If there is anything else you think of please let me know. Thanks

We are taking two very different approaches (you will be using a drill press and I will be using a vertical milling machine) and they are *very* different ballgames. I think the thing they have most in common, though, is that the "rough cutting" is where the most time can be saved. I will be doing it by plunge cutting with an end mill. You will be doing it with drill bits. I think it makes a great deal of sense to remove as much material by rough cutting as you safely can and leave the lightest possible work for the end mill.

As I have said before, the things that bother me the most about the idea of using a drill press are the lack of rigidity and the fact that the tool head is not designed for side loading. I'm not being a hater here--that's just the facts.

The result is that the horizontal cuts made by the drill bit can be bigger than what you are expecting. That means you need to be extremely careful around the edges. Along the back side of the main pocket are channels for the magazine release and bolt catch mechanisms. You will end up with a thin wall (a little more than.100 in.) between the main pocket and those channels. It is waaaaaaaaaay too easy for a wayward cutting tools to break through that. I would suggest approaching the cuts for that edge with extreme caution. Same for all the edges, but especially so for that one.

This is probably stating the obvious, but I would keep the tool lengths (i.e., drill bits and end mills) as short as possible while still giving adequate clearance, especially at the buffer tower.

Also, since the drill press is not designed for side loading, I would make extremely shallow cuts on the sides of the pocket.

Best of luck and please keep us posted.