Machining an AR lower from a forging - pic heavy

Good pic Kharn, but where is your MD Shooters glass?

Coinboy, I've got almost everything pulled co0mpletely apart right now, getting set to anodize it, but will definitely post when I get them done.

I've got black, gray, OD and brown anodizing dyes, might try something fancy if the first few turn out OK just black - gotta crawl before I try to run, LOL.

Through the process, you'd mentioned some issues with your mill. Are there any (relatively) cheap mills on the market today that you might be able to recommend as being adequate for the job, now that you've got some firsthand experience?

Wow! Great looking rifle Kharn!

Thanks E. I look forward to the pic's.

Dst said:

Through the process, you'd mentioned some issues with your mill. Are there any (relatively) cheap mills on the market today that you might be able to recommend as being adequate for the job, now that you've got some firsthand experience?

Click to expand...

The mill I have is probably most similar to this one:
http://www1.mscdirect.com/CGI/NNSRIT?PMPXNO=17766073&PMT4NO=0

They refer to this style machine as a "benchtop mill", but one would need a SERIOUS bench, since the mill alone weighs 600#, leveling is rather critical and vibration must be kept to a minimum or it will telegraph to the work's surface finish. Mine has a dedicated stand that is similar to the stand on this slightly more expensive model:http://www1.mscdirect.com/CGI/NNSRIT?PMPXNO=19058123&PMT4NO=46831071

It's not a bad machine, considering the cost, but there are some things that would make it more precise and more convenient to operate.

Operating strictly off the handwheel dials, it is very difficult to get repeatable accuracy due to the .015 to .030" of free travel when changing directions, referred to as "backlash". I have a digital read out ("DRO") on mine, which shows me my exact table location on the X and Y-axes and forgives many evils, since it allows me to work around backlash easily. With a little fiddling, I can return to the same place +/-.0005" every time, very good for an imported machine. No matter how nice the mill, it is always improved by a good DRO.

Vertical backlash in my quill's travel is the most difficult slop to work around, since I would be pushing down on a drill or mill, loading the gears upward, and when it cuts freely, it will drop to the downward side of the gear engagement. The Z-axis DRO allows me to "see" this slop, but does not allow full control of it, and the only way to get a repeatable depth of a bore or pocket is to set the stop

Getting around the lack of fine precision isn't too hard, especially since tolerances are relatively generous on "milspec" stuff like these lowers. The opportunity to make an error begs one though, and you must more closely watch the sloppier units for sure. A more expensive, precise unit would have substantially less backlash in all directions, which both allows simpler operation and greater precision.

The second feature a bigger, nicer mill would have is a larger table.

The advantage of a larger table is mainly that it allows more latitude and flexibility of setup, my biggest nemesis as far as lost time goes. Far more time is devoted to setup, clamping and truing work to the table and quill, and having to move a solidly mounted angle block or clamping fixture that has been painstakingly set up parallel to table travel is nearly heartbreaking. Excess backlash complicates these setup operations, so, we combine insult with injury and are forced to move our clamps and angle blocks more often than a bigger table, and as a result of lash, it's tougher and more time consuming to do.

The bigger table also allows larger projects, and there are a couple things I'd like to do that require more travel than I have. Even the AR-15 lower would have been more comfortable on a bigger platform, since I had to relocate the work at a 90o angle to be able to drill the trigger guard holes. Since I was able to turn the work, I could accomplish it. Not turning the work would have saved an hour or moving the angle plate, then moving it back for other ops in the next sequence. A logical sequence is necessary, to do the heaviest work while having the most meat to clamp to. For example, one needs to leave the magwell solid as long as possible to allow cross clamping here with a lot of pressure to enable other operations.

Similar to the advantages of a a larger table, a nicer mill will have a square column. The average quill, similar to a drill press quill, only moves about 5". Any more movement precludes accuracy and rigidity, so in order to reach further down or get above higher work, the head (or the knee/table) must move in the vertical axis. The square column allows one to move the head up and down to relocate the quill vertically without losing the lateral reference location to the table, which would render any previously located lateral locations useless. My inexpensive round column mill will twist slightly as I raise and lower it, and so if I need to simply move the head up by even 1/2" to access a larger cutter, I must go back over and re-find my locations.

All of these very desirable features jump the machine's price, weight and bulk up considerably, but at the same time makes operation much more convenient and makes better results easier to obtain. There is a LOT to be said for not wasting one's time repeating setups, and even paying yourself minimum wage, there is quickly a point reached where a bigger mill starts to save money/time. I do this as a hobby, between time at my regular 45-70 hr/wk job, so being time efficient is valuable to me in many ways.

A lot is determined by how serious one is about this stuff and how much space is available. I lacked much hands-on experience with machine tools, and needed to determine my aptitude for learning how to do tis stuff before sinking too much money and aggravation into it. I was quite pleased to get this machine and am still happy with it within the limits imposed by my shop size and budget. I have learned to look ahead and economize my setup moves, and am also doing several parts at a time in a mini assembly line fashion, while my first parts were made one at a time to avoid making the same mistake more efficiently on several parts in a row.

Now that I feel confident enough that I like doing this stuff and can turn out functional parts, I'm craving a bigger machine, but that's actually part of the disease, LOL. I don't have headroom for a full-size mill right now, but did see a beautiful (well, nice and gray and shiny) used Bridgeport at a local machinery broker's that would *almost* fit that would have been *almost* affordable.

Nice work! Impressive! Amazing!

If you dont have to register an 80% lower could you put a SBR upper on it?

I am going to assume the answer is no, but if you wanted to, how would you go about it?

BTW, great documentation on your build! WOW!!

crkakm4:
You'd have to Form1 the lower and engrave it with your name, city and state just like any other firearm you are doing a Form1 on. But then, the main point of an 80% firearm is getting it off-the-books so that kinda defeats the purpose. I chose to SBR a Bushmaster lower rather than one of my 0%s for that reason.

Kharn said:

crkakm4:
You'd have to Form1 the lower and engrave it with your name, city and state just like any other firearm you are doing a Form1 on. But then, the main point of an 80% firearm is getting it off-the-books so that kinda defeats the purpose. I chose to SBR a Bushmaster lower rather than one of my 0%s for that reason.

Click to expand...

Thanks Ripper & crfakm4.

You know what they would have said:

Bump for a buddy....

Is it possible, in your (highly respected by me) opinion as a machinist, to do this kind of work with a smaller machine like a Sherline?

What possible disadvantages would come with such a smaller machine? I've wanted to get one for years, but I've held off since the only things I ever see guys making with Sherlines are little tiny steam engines!

mudskipper... I have a Sherline lathe, as well as the milling attachment for the lathe. I have never done an AR receiver, but I can tell you there's no way you could possibly finish one on a Sherline. It's just too small, doesn't have enough travel, and is not powerful enough to hog out the metal involved. I'd venture a bet that with one of the big, heavy, cheap Harbor Freight mills, you could do it, however. And they're probably even cheaper than a Sherline. Sherlines are fine, small precision instruments, but their niche is in doing really small parts, not something the size of an AR receiver.

And in 10 minutes, someone will probably Google up a website that will prove me wrong.

Half-cocked said:

mudskipper... I have a Sherline lathe, as well as the milling attachment for the lathe. I have never done an AR receiver, but I can tell you there's no way you could possibly finish one on a Sherline. It's just too small, doesn't have enough travel, and is not powerful enough to hog out the metal involved. I'd venture a bet that with one of the big, heavy, cheap Harbor Freight mills, you could do it, however. And they're probably even cheaper than a Sherline. Sherlines are fine, small precision instruments, but their niche is in doing really small parts, not something the size of an AR receiver.

And in 10 minutes, someone will probably Google up a website that will prove me wrong.

Click to expand...

I doubt I'd trust the precision of the Harbor Freight mill for a receiver. disclaimer: I am not a machinist, but would love to learn the trade, therefore my opinion is based on previous experience with harbor freight tools and quality of forementioned tools.

Half-cocked said:

...It's just too small, doesn't have enough travel, and is not powerful enough to hog out the metal involved...

Click to expand...

I'd agree. The 8 x 18 mill I used for this was barely large enough, and we must remember that as we stretch out adjustments and increase load on the little guys, we get a poor product and premature tool failure.

And in 10 minutes, someone will probably Google up a website that will prove me wrong.

Click to expand...

Adams74Chevy said:

I doubt I'd trust the precision of the Harbor Freight mill for a receiver....

Click to expand...

It's a lot to work around when you have excess backlash, runout and end play. The mill I have would be almost impossible to use if it didn't have the digital read outs ("DRO") so I knew exactly where the tool was.

I did mine on a Grizzly combo and it was touch and go some times due to travel.

I'm terribly impressed by Ed's work doing a 0% in 10 hours...it took me at least 30 hrs and a lot of hand work and polishing to cover up my mistakes. I used an 80% jig to do most of the locating and that would have been a real bear to do without specific references from a complete lower.

If I were to sell them since I am a class 07 manufacturer, I'd look to get at least $3,000 eachfor the time I put into them...hard to compete with the big boys. 80% are not hard at all, but still not worth the work unless you just want one that isn't on the radar scope.

That's why I don't build suppressors for sale either....besides, I'm having too much fun with SBR's, AOW's and SBS's.

Wow that is VERY nice

this thread was referenced over on zombiehunters.org by a guy from st. louis...so damn e.shell you sure make it around

This thread was also referenced on weaponsguild.com

Hey Ed did you ever get it anodized? just curious how it ended up I feel like I got to the last 15-20 of a really good movie and the DVD player stopped working and you don't know how the movie ends

Adams74Chevy said:

I doubt I'd trust the precision of the Harbor Freight mill for a receiver. disclaimer: I am not a machinist, but would love to learn the trade, therefore my opinion is based on previous experience with harbor freight tools and quality of forementioned tools.

Click to expand...

It can be done, even on a HF mill. The little HF will do receivers with sufficient accuracy.

Mark

mudskipper said:

Is it possible, in your (highly respected by me) opinion as a machinist, to do this kind of work with a smaller machine like a Sherline?

What possible disadvantages would come with such a smaller machine? I've wanted to get one for years, but I've held off since the only things I ever see guys making with Sherlines are little tiny steam engines!

Click to expand...

Half-cocked said:

mudskipper... I have a Sherline lathe, as well as the milling attachment for the lathe. I have never done an AR receiver, but I can tell you there's no way you could possibly finish one on a Sherline. It's just too small, doesn't have enough travel, and is not powerful enough to hog out the metal involved. I'd venture a bet that with one of the big, heavy, cheap Harbor Freight mills, you could do it, however. And they're probably even cheaper than a Sherline. Sherlines are fine, small precision instruments, but their niche is in doing really small parts, not something the size of an AR receiver.

And in 10 minutes, someone will probably Google up a website that will prove me wrong.

Click to expand...

LOL, 2 1/2 years after I posted that, mudskipper goes ahead and shows the world how it's done.

I salute you - and BTW.... ---> Need pics!!! <---