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 Post subject: AR-15 "Off the books"
PostPosted: Sun Mar 18, 2012 10:09 pm 
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I had an interesting morning.
A local gun shop wants to sell more rifles and rifle gear so they teamed up with a near-by machine shop. They are offering the opportunity to mill out your own AR-15 lower receiver. No brand name, model or serial number.
Image

They only do it on Sunday morning to work around the normal working hours of the machine shop.
You bring your own 80% lower, or buy one they have available, pay $65 for the machine shop use/instruction and walk away with your very own, unmarked, AR-15 receiver.
About a dozen guys showed up this morning, but I managed to bully my way to the head of the line and I was in and out in less than an hour.
I'm thinking this receiver is going to turn into an AR-15 based pistol. Maybe .450 Bushmaster or .458 Socom.

:D



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 Post subject: Re: AR-15 "Off the books"
PostPosted: Sun Mar 18, 2012 10:17 pm 
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Fantastic! I can imagine the consternation in Sacramento when hundreds of these rifles are produced and start showing up at gun-shows.

Good job! I remember seeing one of these receivers milled out of solid brass,.....



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 Post subject: Re: AR-15 "Off the books"
PostPosted: Sun Mar 18, 2012 10:30 pm 
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If it "shows up at a gunshow" (for sale) it has to have ATF specified markings: serial number, model, maker, etc.
For personal use it doesn't need any markings.

One in brass would be awesome...and HEAVY!



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 Post subject: Re: AR-15 "Off the books"
PostPosted: Sun Mar 18, 2012 10:49 pm 
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so how long will it take for them to close the "machine shop loophole?" :roll:



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 Post subject: Re: AR-15 "Off the books"
PostPosted: Mon Mar 19, 2012 12:17 am 
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That is full of win. I'm certain that it's giving coronaries to all the hippies around. You can build your own machine gun there! Oh, the horrors!


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 Post subject: Re: AR-15 "Off the books"
PostPosted: Mon Mar 19, 2012 12:35 am 
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Yup. I expect black helicopters over my house tonight.

:(



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 Post subject: Re: AR-15 "Off the books"
PostPosted: Mon Mar 19, 2012 1:13 am 
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That's cool.


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 Post subject: Re: AR-15 "Off the books"
PostPosted: Mon Mar 19, 2012 5:25 am 
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Flintlock Tom wrote:
Yup. I expect black helicopters over my house tonight.

:(


If you get locked up, call me & I'll see what I can do to help bail you out (but I'm not putting my house up for bail!). Your lovely wife has our numbers, right? ;)



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 Post subject: Re: AR-15 "Off the books"
PostPosted: Mon Mar 19, 2012 8:00 am 
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Dinochrome wrote:
Good job! I remember seeing one of these receivers milled out of solid brass,.....



It's an AR-15 receiver, you could mill it out of walnut and it would work just fine. (maybe not for .458 SOCOM though :mrgreen: )



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 Post subject: Re: AR-15 "Off the books"
PostPosted: Mon Mar 19, 2012 11:55 am 
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So how does that work with the Gummint: owning, making, and/or buying a receiver without numbers?

SA



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 Post subject: Re: AR-15 "Off the books"
PostPosted: Mon Mar 19, 2012 12:07 pm 
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scipioafricanus wrote:
So how does that work with the Gummint: owning, making, and/or buying a receiver without numbers?


Owning and making work fine. Buying, not so much.



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 Post subject: Re: AR-15 "Off the books"
PostPosted: Mon Mar 19, 2012 12:37 pm 
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Netpackrat wrote:
scipioafricanus wrote:
So how does that work with the Gummint: owning, making, and/or buying a receiver without numbers?


Owning and making work fine. Buying, not so much.


Or selling, or taking across state lines.



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 Post subject: Re: AR-15 "Off the books"
PostPosted: Mon Mar 19, 2012 12:55 pm 
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CByrneIV wrote:
Netpackrat wrote:
scipioafricanus wrote:
So how does that work with the Gummint: owning, making, and/or buying a receiver without numbers?


Owning and making work fine. Buying, not so much.


Or selling, or taking across state lines.


The taking across state lines would be the thing I would be afraid of ACCIDENTALLY doing / having a family member do ACCIDENTALLY. But otherwise, super cool if only for the fact that you can.



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 Post subject: Re: AR-15 "Off the books"
PostPosted: Mon Mar 19, 2012 2:58 pm 
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Why would taking it across state lines be an issue? It complies with all ATF requirements.
It was purchased before it was a firearm, just a piece of aluminum. I built a firearm out of it. Home-built firearms are okay with the .gov as long as it is not an NFA firearm and not for sale (or transfer).

https://www.tacticalmachining.com/80-lower-receiver.html



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 Post subject: Re: AR-15 "Off the books"
PostPosted: Mon Mar 19, 2012 3:20 pm 
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Flintlock Tom wrote:
Why would taking it across state lines be an issue? It complies with all ATF requirements.
It was purchased before it was a firearm, just a piece of aluminum. I built a firearm out of it. Home-built firearms are okay with the .gov as long as it is not an NFA firearm and not for sale (or transfer).

https://www.tacticalmachining.com/80-lower-receiver.html


There's never been a test case to actually hit a court, but they have charged people with unlawful interstate trafficking in arms, conspiracy etc... for taking unnumbered receivers across state lines.

It's likely those charges wouldn't stick, but they'd bankrupt you and likely get a lesser felony in the process.



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 Post subject: Re: AR-15 "Off the books"
PostPosted: Mon Mar 19, 2012 3:29 pm 
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Thank you!
I DON'T want to be the "test case."



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 Post subject: Re: AR-15 "Off the books"
PostPosted: Mon Mar 19, 2012 4:48 pm 
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First, I'm assuming this would be verboten in my own state of NJ. Still, if one completed such a lower, what would you need to do, legally, if you moved to a new state? Destroy it?


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 Post subject: Re: AR-15 "Off the books"
PostPosted: Mon Mar 19, 2012 8:27 pm 
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Wide range of answers depending on the state.
If I were moving I would either add a serial number/markings to make it "transfer-able" and sell it or bring it along and comply with my new state's laws.



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 Post subject: Re: AR-15 "Off the books"
PostPosted: Mon Mar 19, 2012 8:36 pm 
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NVGdude wrote:
Dinochrome wrote:
Good job! I remember seeing one of these receivers milled out of solid brass,.....



It's an AR-15 receiver, you could mill it out of walnut and it would work just fine. (maybe not for .458 SOCOM though :mrgreen: )


The brass receiver was done for looks; maybe the guy wanted it to match his Winchester '66. :mrgreen:

If I were to build a wooden AR receiver, I think I would use something denser than walnut. Maybe ironwood or ebony with some bearing inserts for the thru-pins and metal reinforcement for the buffer-tube attachment.



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 Post subject: Re: AR-15 "Off the books"
PostPosted: Mon Mar 19, 2012 10:28 pm 
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MarkD wrote:
First, I'm assuming this would be verboten in my own state of NJ. Still, if one completed such a lower, what would you need to do, legally, if you moved to a new state? Destroy it?
Actually looked into it a while ago. It is not illegal to finish your own 80% receiver in NJ. The upper and butt stock must pass our B.S. assault weapons ban(no bayo lug/threads/flash hider/adjustable stock) and I believe it is recommended(even by BATFU) that you mark it in some way, usually your name, county or city of residence, date of manufacture and some sort of serial #(even if it is 0000000001).
CByrneIV wrote:
Or selling,
According to the BATFU it is legal to sell a home made firearm, so long as you're not building it for the purpose of selling it. But then again they are known to either make up rules or change their minds on a whim. I think if you were to build one, shoot it for a few years then decide to sell it in a private sale(don't think an FFL would be to quick to put it in his bound book) you should be fine. At least that was the answer several people got from BATFU over at homegunsmith.com. There were several PDFs posted by members on the forum to that effect.



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 Post subject: Re: AR-15 "Off the books"
PostPosted: Tue Mar 20, 2012 12:08 am 
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TheIrishman wrote:
MarkD wrote:
First, I'm assuming this would be verboten in my own state of NJ. Still, if one completed such a lower, what would you need to do, legally, if you moved to a new state? Destroy it?
Actually looked into it a while ago. It is not illegal to finish your own 80% receiver in NJ. The upper and butt stock must pass our B.S. assault weapons ban(no bayo lug/threads/flash hider/adjustable stock) and I believe it is recommended(even by BATFU) that you mark it in some way, usually your name, county or city of residence, date of manufacture and some sort of serial #(even if it is 0000000001).
CByrneIV wrote:
Or selling,
According to the BATFU it is legal to sell a home made firearm, so long as you're not building it for the purpose of selling it. But then again they are known to either make up rules or change their minds on a whim. I think if you were to build one, shoot it for a few years then decide to sell it in a private sale(don't think an FFL would be to quick to put it in his bound book) you should be fine. At least that was the answer several people got from BATFU over at homegunsmith.com. There were several PDFs posted by members on the forum to that effect.


And you missed a very important point.

The question wasn't whether it was legal to sell a home made receiver. It is, so long as you didn't manufacture specifically to sell it; at least federally. That wasn't in dispute.

The question was the legal status of a home made receiver that was not marked "properly" (which according to the ATF and GCA '68 means a unique serial number, manufacturers name, and place of manufacture).

According to the ATF you can sell a home made gun, and also you do not have to mark a home made receiver; HOWEVER you may not transfer a firearm made after 1968 unless it is "properly marked".

Further, the ATF has held that "transfer" does not mean sell or transfer ownership. It means that you have transferred CONTROL of the firearm to another.

Under this doctrine, they have SUCCESSFULLY prosecuted people for unlawfully transferring a firearm to a prohibited person, or a minor, by allowing those people to use the firearm; and even in some cases, for simply not securing access to the firearm properly when they knew those persons might be able to access the firearm (one of these cases was recently upheld in the federal circuit court of appeals, and will likely go to the supreme court).

Finally, several people who have made large numbers of unmarked firearms, or have transported unmarked firearms across state lines, have been charged with traffic in unlawful arms, or conspiracy to traffic in unlawful arms etc... etc...

The upshot is, if you're going to make a gun, MARK IT PROPERLY.



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 Post subject: Re: AR-15 "Off the books"
PostPosted: Tue Mar 20, 2012 12:22 am 
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If you mark it with a serial number, manufacturers name and place of manufacture, do you have to send that info into the BATF or are the markings sufficient in themselves?


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 Post subject: Re: AR-15 "Off the books"
PostPosted: Tue Mar 20, 2012 12:29 am 
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toad wrote:
If you mark it with a serial number, manufacturers name and place of manufacture, do you have to send that info into the BATF or are the markings sufficient in themselves?


Nope, no paperwork on the markings, unless it's a class III item or unless it is manufactured for sale in which case you need to be an FFL licensed to manufacture that type of regulated item, and you have to pay the associated taxes (there's an excise tax on all firearms).



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 Post subject: Re: AR-15 "Off the books"
PostPosted: Tue Mar 20, 2012 3:23 am 
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Pity Mil-Spec barrels cost so darn much. :cry:


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 Post subject: Re: AR-15 "Off the books"
PostPosted: Tue Mar 20, 2012 4:55 am 
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toad wrote:
Pity Mil-Spec barrels cost so darn much. :cry:


Ass opposed to what? The 4140 barrels? I know that upper wise you can get good deals on Mil-Spec uppers from a variety of places.


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 Post subject: Re: AR-15 "Off the books"
PostPosted: Tue Mar 20, 2012 3:32 pm 
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A good deal depends on how much money you have and how much you want to risk on the quality of certain "mil-spec" barrels and uppers. I admit that I don't research that stuff anymore, but I seem to remember from the past that their were only about three companies you could get actual, real, mil-spec.
I'd take Chris's word on what's what since he actually builds the dang things.
When I looked into building my own I found I saved no money because not just parts but also when I make holes in things and I want them precise I use reamers.in other words the tooling cost started eating into the budget real quick. I started adding up the price of the tools and parts that would satisfy me as to quality and it just wasn't feasible, at least for me.


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 Post subject: Re: AR-15 "Off the books"
PostPosted: Wed Mar 21, 2012 11:26 pm 
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 Post subject: Re: AR-15 "Off the books"
PostPosted: Thu Mar 22, 2012 12:21 am 
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A tech question--the receiver appears to be anodized, and the milling operations have exposed bare aluminum. Is that a concern?



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 Post subject: Re: AR-15 "Off the books"
PostPosted: Thu Mar 22, 2012 12:43 am 
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Darrell wrote:
A tech question--the receiver appears to be anodized, and the milling operations have exposed bare aluminum. Is that a concern?


I was wondering the same thing. Are you going to have to re-anodize the receiver after the milling, or is it not a concern?



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 Post subject: Re: AR-15 "Off the books"
PostPosted: Thu Mar 22, 2012 2:11 am 
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CByrneIV wrote:
The question wasn't whether it was legal to sell a home made receiver. It is, so long as you didn't manufacture specifically to sell it; at least federally. That wasn't in dispute.
The question was the legal status of a home made receiver that was not marked "properly" (which according to the ATF and GCA '68 means a unique serial number, manufacturers name, and place of manufacture).
According to the ATF you can sell a home made gun, and also you do not have to mark a home made receiver; HOWEVER you may not transfer a firearm made after 1968 unless it is "properly marked".
We're actually in agreement, you just went a little more in-depth of it. Some however, believe a "self built" firearm may never be sold. Properly marking it as even ATF recommends still keeps it off of the radar but provides you with a margin of safety and does allow for later sale.



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 Post subject: Re: AR-15 "Off the books"
PostPosted: Thu Mar 22, 2012 10:23 pm 
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Found a local Trophy Shop that will laser engrave markings for me. The counter guy is a retired Gunnery Sergeant. He wrote "left side of the mag well on an M16 receiver" on the invoice with me just pointing.
He was curious about the work I had done and if I was going to do any more.



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 Post subject: Re: AR-15 "Off the books"
PostPosted: Wed Apr 25, 2012 8:16 am 
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i am thinking about doing this,but there is no machine shop that i know of in vegas that offer this, what should i do?


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 Post subject: Re: AR-15 "Off the books"
PostPosted: Wed Apr 25, 2012 3:23 pm 
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bunkerguy wrote:
i am thinking about doing this,but there is no machine shop that i know of in vegas that offer this, what should i do?

Tactical Machining sells "jigs" for positioning the holes and cuts. They also sell the "non-firearm, lower, almost-receivers."
http://www.tacticalmachining.com/80-products.html
Presumably you can finish your receiver with just a drill press, if you're patient and careful.

Or, my suggestion would be to get involved with the local gun community and ask around if anyone has done this or knows of a machine shop with CNC milling equipment that would take on the project.
Here in San Diego we have a, sort of "hobby shop" where they provide equipment and training and turn you loose.
http://www.makerplace.com/
You might see if there's something like that in Nevada.

Also, I went ahead and had some engraving done: made-up manufacturer, made-up model, made-up serial number.
I think I picked a font too large and the laser engraving isn't very deep, but it gives me some peace-of-mind.
Image
Also, to answer Mike's question, I don't believe the bare aluminum will be an issue, but I'll keep an eye on it for signs of oxidation.
I still haven't decided what it's going to be yet, but, when I look at the .50 Beowulf barrel I get chills...



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 Post subject: Re: AR-15 "Off the books"
PostPosted: Thu Apr 26, 2012 6:27 am 
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Or print one with a 3D printer!

Not that the info about owning it by boing boing is actually that accurate....



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 Post subject: Re: AR-15 "Off the books"
PostPosted: Thu Apr 26, 2012 7:23 am 
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bunkerguy wrote:
i am thinking about doing this,but there is no machine shop that i know of in vegas that offer this, what should i do?


Welcome, bunkerguy.

Are you sure you don't work for the BATFE? If so, get yourself a mill, or go back and ask around the machine shops. A block of aluminium in the shape of an 80%-finished AR receiver will cost you about 200 US Dollars, from any number of online sources.


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 Post subject: Re: AR-15 "Off the books"
PostPosted: Thu Apr 26, 2012 6:00 pm 
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Denis wrote:
bunkerguy wrote:
i am thinking about doing this,but there is no machine shop that i know of in vegas that offer this, what should i do?


Welcome, bunkerguy.

Are you sure you don't work for the BATFE? If so, get yourself a mill, or go back and ask around the machine shops. A block of aluminium in the shape of an 80%-finished AR receiver will cost you about 200 US Dollars, from any number of online sources.

Actually about $80 to $90 from the source linked above.



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 Post subject: Re: AR-15 "Off the books"
PostPosted: Thu Apr 26, 2012 7:32 pm 
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Flintlock Tom wrote:
Actually about $80 to $90 from the source linked above.


My mistake - I was thinking of milled, rather than forged, 80% receivers, which a bit more expensive.


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 Post subject: Re: AR-15 "Off the books"
PostPosted: Fri Apr 27, 2012 11:35 pm 
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Denis wrote:
bunkerguy wrote:
i am thinking about doing this,but there is no machine shop that i know of in vegas that offer this, what should i do?


Welcome, bunkerguy.

Are you sure you don't work for the BATFE? If so, get yourself a mill, or go back and ask around the machine shops. A block of aluminium in the shape of an 80%-finished AR receiver will cost you about 200 US Dollars, from any number of online sources.


if i did i would be making far more money that i am making now. lol :jacked:


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 Post subject: Re: AR-15 "Off the books"
PostPosted: Fri Apr 27, 2012 11:36 pm 
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Denis wrote:
Flintlock Tom wrote:
Actually about $80 to $90 from the source linked above.


My mistake - I was thinking of milled, rather than forged, 80% receivers, which a bit more expensive.


how do they differ?


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 Post subject: Re: AR-15 "Off the books"
PostPosted: Sat Apr 28, 2012 2:45 am 
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CombatController wrote:
Or print one with a 3D printer!

Not that the info about owning it by boing boing is actually that accurate....

Ever notice the ones most enamored with "3d printing" are those that have the least experience(if any) with manufacturing?

Denis wrote:
or go back and ask around the machine shops.

I don't know any shop that would do it. Don't want the hassle, don't want the liability, and it certainly isn't profitable to them.



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 Post subject: Re: AR-15 "Off the books"
PostPosted: Tue May 08, 2012 1:16 am 
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Somebody won't need to go to a machine shop to make off the book lowers.
http://coolstuffwelike.blogspot.com/201 ... upply.html
Now, will the information about how to make such lowers become the "thing" prohibited from unregistered interstate movement?



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 Post subject: Re: AR-15 "Off the books"
PostPosted: Tue May 08, 2012 2:38 am 
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Too small. I'd consider something in the Seig X2 size to be a minimum if you're going to self build lowers.



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 Post subject: Re: AR-15 "Off the books"
PostPosted: Tue May 08, 2012 3:17 am 
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HTRN wrote:
Too small. I'd consider something in the Seig X2 size to be a minimum if you're going to self build lowers.


I have a superX2 (the grizzly version as linked above in fact). I wouldn't want to machine more than one lower on it even if it was CNC retrofit. There's not enough room for precision fixtures for you to be able to do all coaxial/coreference operations without repositioning.

It's doable, but you're going to have to rehome the head, table, and fixture every repositioning.

Also, how are you going to line bore the rear ring? You don't have the clearance for that with a mill as small as the X2/SX2.

Again, it's doable, but you don't want to do it often... Personally I'd build a transfererable fixture to move from my mill table to my lathe carriage; and line bore it on the lathe right in the fixture. Only have to worry about centering the fixture once, not moving the piece in it.



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 Post subject: Re: AR-15 "Off the books"
PostPosted: Tue May 08, 2012 8:13 pm 
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CByrneIV wrote:
Also, how are you going to line bore the rear ring? You don't have the clearance for that with a mill as small as the X2/SX2.


Hell if I know, "I'm a DoctorLawyer, not a machinist!"
I'm always fascinated by the efforts to regulate things that don't need to be grown in a specific place with specific climatic requirements, things that schools turn out thousands of graduates every year who are trained in all the techniques and steps necessary to make things, and which the "precursor" machines are all for sale everywhere at (now) reasonable prices. This one I linked to might not be the best suited for this purpose, but I take it that it could be done.



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 Post subject: Re: AR-15 "Off the books"
PostPosted: Wed Jul 04, 2012 10:16 am 
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The lower receiver is no different than a standard AR-15 receiver I have also been looking for a AR-15 upper receiver.
ar15 lower receiver


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 Post subject: Re: AR-15 "Off the books"
PostPosted: Wed Jul 04, 2012 10:35 am 
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So the X2 is technically feasable, but just barely, making it a hassle to use. I thought it would work, but then I rarely use mills that small.



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 Post subject: Re: AR-15 "Off the books"
PostPosted: Thu Jul 05, 2012 7:11 pm 
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So, the X2 is not big enough. What would the next-size-up, the just-big-enough machine be?



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 Post subject: Re: AR-15 "Off the books"
PostPosted: Fri Jul 06, 2012 12:04 am 
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Windy Wilson wrote:
So, the X2 is not big enough. What would the next-size-up, the just-big-enough machine be?


Forget the "next size up" - when buying machine tools, always buy the biggest work envelope you can afford/have room for, because invariably you'll have a job that's too big for the machine soon enough. I suggest an IH mill. As a bonus, the column mill design is better for CNC conversion that Bridgeport style machines, as the Head setup is stiffer.



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 Post subject: Re: AR-15 "Off the books"
PostPosted: Fri Jul 06, 2012 8:29 am 
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Windy Wilson wrote:
So, the X2 is not big enough. What would the next-size-up, the just-big-enough machine be?


For AR lower receivers, the X2/SuperX2 (the Grizzly G6019 is a SuperX2, and is my mill. I've got a power feed and DRO setup for it, and I have a CNC kit I can put on it but haven't yet) is doable (CNC or otherwise), if you make the right fixtures.

http://www.biggerhammer.net/ar15/cad/

An AR lower is just under 8"x4"x1.5" at its greatest extents. In theory, this means you could perform the primary milling operations on a mill with about a +5/-5X;+3/-3Y;3"Z table/toolhead travel, without repositioning the workpiece more than on a larger mill (or half that with twice as many repositions, for mirror operations).

...And you could... but it would be a stone ass bitch, and you'd still have a problem broaching the magwell, and boring the buffer tube boss. You'd have to do them on other machines in fact.

In order to have room for workpiece clamping, billet clearance, tool clearance, and fixtures; in an ideal world you want to take your workpiece dimensions, add at least 2" to each (for billet, fixture, and tool diameter), and thats your minimum table travel; then double those dimensions and add another 2" to each for tool clearance; and that would be your minimum table size.

Padding and doubling the dimensions, allows you to home (set X,Y,Z, to zero point) any operation at any corner (the intersection of three known reference planes is a perfectly referenced home point) of a fixture, rather than the center of the workpiece (with any reasonable fixture anyway); and to address the edges of the workpiece, from any side of the fixture, without repositioning either workpiece or fixture (this is particularly important for non reversing toolheads, when using directional tools, to avoid binding and chatter). It also allows for mirrored operations by reversing the fixture on the other side of the table.

Essentially, doubling and padding each dimension, allows you to treat each quadrant of the table, as its own table; homed from either the center point, or any known reference point... like the intersection of three known reference planes (precision machine your table so that its corners ARE the intersection of three known reference planes. If you can't, because of the design or materials of the table then make a new table, or table overlay, that you can), or the center of the line segment formed by two known reference planes

This is far faster and easier to repeat (and remember, precision is repeatability, nothing more nothing less) than centerhoming; though if you maintain a proper set of reference datums (say the x and y axis edges of a true and square fixture the workpiece is precision fixed in reference to), centerhoming one axis while edgehoming the other two is nearly as good (it just takes longer).

So, for an AR lower, your ideal 3 axis mill would have a minimum of 10"x6" table travel (and I'd really prefer to see 12"x8"), with 4" single operation boring depth; and a 22"x14" table with at least 12" of vertical workpiece clearance (see below why you need that vertical clearance).

However, in the spirit of your question, if you wanted to be able to make AR receivers on demand, but not necessarily in series production, you don't need quite that.

The SuperX2 actually has most of that. It's got a 6-1/4"x21-5/8" table, with 14-3/4" workpiece clearance, 5-3/4"x14" table travel and 2-3/4" boring depth in the quill (on a 1" bore, which is more than enough to broach the magwell, with the right fixture). With the right fixture design, and a little extra effort you could do repeatable CNC work on AR lowers with it... It's just BARELY big enough.

The first real constraint for machining AR's (at least on a 3 axis mill. 5 axis machines/machining centers are an entirely different beast) is vertical workpiece clearance, because you're going to want to do at least one long axis vertical operation.

For an AR, if you intend to broach and bore your magwell and buffer tube boss on the mill, you either need to have sufficient side bore capacity (and toolhead clearance) to do so; or you need to make two vertical repositions and have sufficient vertical boring capacity, and vertical workpiece clearance to do so.

If you have a big enough mill, with a swivel head (or a combo machine with side boring capability), you can create a fixture (or mount the fixture on a rotary table, 2 axis table, 2 axis vise etc...) that will allow you to bore and broach horizontally, without refixing the workpiece; however, you still have to swivel the head, retram it to the table, and rehome, so the advantage isn't all that large.

Honestly, from a precision standpoint, and int erms of workflow; you're better off repositioning the work piece for vertical bore, and vertical broach, than to attempt to make a fixture that will allow bore and broach without the vertical repositions, even on a machine with a swivel head (at least on a 3 axis machine. Again, 5 axis machines are totally different). It's a lot easier to reposition and refix a workpiece, and rehome a fixture; than it is to retram a head and table THEN rehome a fixture.

Even on a machining center, they usually do this in multiple programs (primary milling, magwell and trigger trench, and buffer tube boss) using three different fixtures, batched up (face and end milling 6 or 8 blanks at a time using half plates rather than small billets, then using a gang fixture for broaching 6 or 8 magwells and trigger trenches at a time, then another gang fixture for boring 6 or 8 buffer tube bosses at once).

So, for the buffer tube boss operations, you need to have 8" vertical clearance for the work piece, 2" for the tool, and 2" for the fixture... call it 12". For the magwell broach operation and trigger trench operation, you need about 2.5" bore depth capacity if you have toolhead clearance to the buffer tube boss, or 4" boring depth capacity if you don't (or back to 2.5" if you don't mind splitting trenching and broaching into two operations, repositioning, and broaching from the bottom).

As far as table travel, I really think your absolute minimum for not wanting to shoot yourself, is still about 6"x10".

That's the real pain with the SuperX2; the cross travel is a little bit shorter than ideal (though just a little bit)... that and the table is a bit shallow at just 6" (which you can work around with the right fixtures, but then you need more clearance for the fixtures).

So, no matter how big your mill is, with a 3 axis mill, your operational breakdown is going to look something like this:

All of this presumes you start with a rectangular, or profile cut billet (with clamping bosses), not a rough forging or casting. You need completely different fixtures, and operations for a rough forging or casting. Also, there are several possible orders of operations for this depending on options you choose).

First, prepare your workpiece:

1. Fix and home the workpiece and fixture for A faceoff operation
2. Rough A face off operation (Z home = center of billet, face the entire billet off to the highest Z offset from center plus a few thousandths, creating a flat and true reference plane)
3. Fix and home the workpiece and fixture for B faceoff operation, clamping flat off the reference datum face
4. Rough B face off operation (Z home = Reference datum face A, face the work area of the billet off to greatest thickness plus a few thousandths)
5. Find and rehome to the exact center of the billet face, to set the reference throughbore center position
6. Facebore throughbore operation on the forward receiver pin throughbore (which becomes the reference center)
7. Rehome (and possibly refix) the workpiece and fixture, referencing the forward pin bore center
8. Bore the remaining throughbores (and possibly refix)
9. End cut at least one reference edge datum each (preferably two, verified at each endpoint against all other reference points to set a precision reference frame in space) on the X and Y axes, from the reference bore center (two parallel and two perpendicular reference edges are preferred, opposite parallel edges of the billet are best, if practical; but on an AR receiver it generally isn't, except on clamping bosses). This whole process gives you a reference datum for each edge, and each plane, as well as at least two reference datums within each plane, all mastered off the reference plane, and the reference bore center.

This by the way is how you set up ANY precision milling operation on a manual machine, or a 3 axis machine of any kind.

If you're concerned about precision in any way, don't trust that your billet is true, flat, and square. You want to create a reference plane datum by clamping the billet to a level midline, and facing off to a maximum Z offset from midline plus a few thou (you don't have to be all that precise about the midline here since you're going to face both sides referenced off each other, not the midline; which will reset the midline in relation to the reference face anyway). Then flip the piece and clamp it flat from the reference face, to face the other side off at maximum Z plus a few thou. This will give you a true and flat workpiece (just like planing a piece of lumber on both sides for furniture).

Do this, whether you're using a full rectangle, or a profile cut billet; but make sure that even with a profile cut billet, you leave sufficient reference flat, square, and true area outside the final machined dimensions (for clamping bosses and reference edges), and to support the workpiece enough to keep it from warping or deflecting under clamping pressure (more on this below).

You always make it plus a few thou, for the rough and finish cuts, and buffing out. Also, that gives you a second bite at the apple if you're very slightly off in setting your initial total thickness, or there's some surface chatter etc...

In this case "A few thou" should be AT LEAST whatever the maximum precision of your mill is, per face operation, rounded up to the nearest even decimal, per side. So, if your mill is accurate to .001, and you have three facing operations (face off, rough facing, fine facing), make it .003, round up to .004 so you can split it evenly if you need to, then double it to .008 total for both sides, MINIMUM.

My personal preference, is to to leave .016 (appx. 1/64th) each side in the faceoff operation. That leaves more work for the rough face cuts, but that IS the point of doing your face cuts in three operations.

Once the billet is faced, you can choose to leave the workpiece rectangular, you can saw cut a rough profile, you can part off a rough profile, or you can can hog out a rough profile; but whatever you do, you need to leave flat, square, and true clamping bosses of sufficient area, in the proper locations to provide reference points and edges, and prevent warping or deflection.

Depending on what you choose to do, you may want to change your fixture, from an edge fix, to a throughbore fix; either using existing internal workpiece throughbores, or by boring additional throughbores in the clamping bosses (or both).

You can edge fix or through fix (by making two additional through bores) the workpiece at clamping bosses at the top corner, where the buffer tube boss squares off, and on one end where the forward receiver pin boss is (leaving fully square , flat, and true surfaces, to the reference datum of the billet, for ease of clamping and rehoming, and to simplify the final parting off operations).

Either of the suggested alternate fixing methods will allow you greater workpiece access for easier cuts with the end mill, and will allow you to saw cut, part cut, or hog out the profile easier.

The other option, is to keep the billet rectangular, make all your billet cuts internal part/slot/hog cuts, and have a final partoff operation; leaving a perimeter of full reference thickness metal around the workpiece, which you can edge clamp, or through clamp.

That method will take more time (slower cut speed, more metal removed) requires extra operations (you have to part or hog off the areas around the generate more heat, and cause more tool wear; but it's also easier to reposition, refix, and rehome; and maintains a consistent reference datum for all axes, edges, and faces, all the way around the workpiece. Finally, it keeps the workpiece more stable in general, particularly keeping it from warping or deflecting with clamping.

You can also do a bit of each; leaving fairly large rims around the corners, but also leaving plenty of clearance for the boring and broaching operations.

My preferred choice is to create large enough clamping bosses that I can bolt through them into the fixture, and using hardened, precision machined (lathe turned and surface polished) reference pins in the internal workpiece throughbores, extending into the fixture, for precision location. The pins in this case actually act both as positioning, and as another set of reference datums, ensuring precise indexing of an irregular shape to a known reference datum outside the workpiece (the fixture itself).

Then you can always rehome off the fixture without needing to worry about the changes to the workpiece; and you can always set your CNC programs off the fixture. This allows you to treat your workpiece as if it was regular.

On a machining center, you wouldn't be doing all this (because machining centers always reference off their own internal frame of reference. You just home the billet at 0,0,0 and the machining center verifies its own precision in, and after, each operation)... and strictly speaking, it isn't absolutely necessary even in 3 axis CNC... or even in a manual million operation for that matter; but it makes your life a LOT easier, in providing a consistent set of reference datums for each axis.

With this kind of workpiece preparation (even without doing the pins), every possible operation or workpiece position, has at least two reference datums for each axis; so you can reposition and rehome to consistent points after each operation.

At this point, you hit the ACTUAL machining operations:

1. Rough A face cut operation
2. Rough A end cut operation
3. Fine A face cut operation
4. Fine A end cut operation
5. Refix and rehome B for B face operations (reposition to mirrored reference datum)
6. Rough B face cut operation
7. Rough B end cut operation
8. Fine B face cut operation
9. Fine B end cut operation
10. Short Y to Z vertical workpiece reposition for magwell broach and trigger trench operation
11. Magwell broach operation (this may be done as one, or two operations, depending on tools; and may include the trigger trench operation)
12. Trigger trench operation (may be included in 11 depending on tools)
13. Trigger slot broach operation (may be included in 11 or 12 depending on tools)
14. Long X to Z vertical workpiece reposition for buffer tube operations
15. Buffer tube through bore operation (can be a single bore operation, or a bore and broach, depending on tools)
16. Buffer tube thread operation (may be performed separately, using a manual tap, or on a lathe fixture)
17. Final parting off operation (use internal through hole fixing for this)
18. Final boring, tapping, chasing, deburring, and cleanup operations on partlines, broaches, througbores, and threads (best done by hand, or in a boring fixture on a drill press, not on the mill)

Even with CNC, that's 19 operation sets (some of which have multiple tool changes, so can't be a single program unless you have an auto tool change head), 9 repositions or refixes, and at least 3 fixture changes; and then you have to bore the various spring and pin passages.

So... still want to try it?



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 Post subject: Re: AR-15 "Off the books"
PostPosted: Fri Jul 06, 2012 10:53 am 
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308Mike wrote:
Darrell wrote:
A tech question--the receiver appears to be anodized, and the milling operations have exposed bare aluminum. Is that a concern?


I was wondering the same thing. Are you going to have to re-anodize the receiver after the milling, or is it not a concern?


Ehhh... yes and no.

The bare aluminum will not have the surface hardening, or surface protection, of an anodized piece.

Frankly, if it were my own receiver, I would heat treat it after final machining, then have it anodized with proper type three anodizing (I got a local guy who will do it for $20).

HOWEVER... it's really not absolutely necessary.

Eventually, your pinholes might egg out the tiniest bit, and there might be some galling... but really, I wouldn't expect anything else from it.



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 Post subject: Re: AR-15 "Off the books"
PostPosted: Fri Jul 06, 2012 10:55 am 
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bunkerguy wrote:
Denis wrote:
Flintlock Tom wrote:
Actually about $80 to $90 from the source linked above.


My mistake - I was thinking of milled, rather than forged, 80% receivers, which a bit more expensive.


how do they differ?


All those 27 things I mentioned above? A billet milled receiver goes through all of them first. It allows for extremely precise quality control and machining, vs. the use of a rough forging. It is howeever a LOT more machining time, and tool wear etc... And thus is more expensive.

Oh and of course, if you're going to fully machine your own from billet, it's a HELL of a lot more work than an unfinished lower.

In particular, the "80%" receivers out there almost all have the magwell broached and the buffer tube boss bored and threaded; as well as the majority of the small non-through bores, off axis bores etc... already done. That alone is HOURS of work, as well as at least two repositions, and at least two additional fixtures, you don't have to deal with. Also, all the final radius cuts are done, and ready for surface buffing. That's damn near impossible to do quickly and efficiently by hand, and needs a very good CNC rig to come out right.

Just so everyone is clear though, there is no such thing legally as an "80% receiver". That's just a convenient way for sellers of these things to describe them. In reality, there is no standard for what constitutes "gun" vs. "not a gun". The ATF technical branch makes a case by case determination (which is why some say "we have the atf letter" etc...). Unfortunately they have been known... frequently... to change their minds.



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 Post subject: Re: AR-15 "Off the books"
PostPosted: Mon Jul 09, 2012 11:15 pm 
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Just machining out the trigger trench looks non-trivial to me if you want precision parallel interior surfaces.
properly space apart. I would guess you have to have a pretty rigid spindle that can handle a large enough diameter end mill that won't chatter or push off at the bottom of the cut. If you were just doing the trigger trench what would be the recommended size of end mill??

I remember a number of guys that started projects that got ruined on the price of the cutting tools they needed. I remember one guy with his own shop with a really large lathe that he used to bid on projects from other shops that didn't have a big enough lathe to do. He said he bid on one off and per contract he had to mill one slot in the piece and found he had to go out a buy an end mill. It ate up about half his net profit on the job.


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 Post subject: Re: AR-15 "Off the books"
PostPosted: Mon Jul 09, 2012 11:43 pm 
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toad wrote:
Just machining out the trigger trench looks non-trivial to me if you want precision parallel interior surfaces.
properly space apart. I would guess you have to have a pretty rigid spindle that can handle a large enough diameter end mill that won't chatter or push off at the bottom of the cut. If you were just doing the trigger trench what would be the recommended size of end mill??

I remember a number of guys that started projects that got ruined on the price of the cutting tools they needed. I remember one guy with his own shop with a really large lathe that he used to bid on projects from other shops that didn't have a big enough lathe to do. He said he bid on one off and per contract he had to mill one slot in the piece and found he had to go out a buy an end mill. It ate up about half his net profit on the job.


I'd probably go with a 3/8" to get a reasonably tight radius in the corners, if I wanted to do the cut with one tool. You could also trench it out with a 5/8" and then swap down.

I bought my mill for around $1500... and then I immediately spent around $3,000 in JUST cutting tools for it, and another $3,000 in vices, clamps, fixtures, accessories etc...



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 Post subject: Re: AR-15 "Off the books"
PostPosted: Tue Jul 10, 2012 4:17 am 
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I remember many moons ago trying to find a GSA surplus tool and cutter grinder. Even a pretty worn was just too expensive.


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 Post subject: Re: AR-15 "Off the books"
PostPosted: Tue Jul 10, 2012 4:22 am 
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toad wrote:
I remember many moons ago trying to find a GSA surplus tool and cutter grinder. Even a pretty worn was just too expensive.


Yeah, the cheapest I've seen are around $2k, and they go up well over $10k



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 Post subject: Re: AR-15 "Off the books"
PostPosted: Wed Jul 11, 2012 12:48 pm 
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2K is what you'll get for a smallish bare bones machine. A KO Lee with a decent number of accessories? You're looking at 5 grand and up. Frankly, any machinetool you can buy used for less than 2 grand tend to be either too small, too thrashed, or so obscure/obsolete nobody wants it(case in point: Large shapers and frequently screw machines often go for scrap these days).



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 Post subject: Re: AR-15 "Off the books"
PostPosted: Wed Jul 11, 2012 9:09 pm 
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Well, thank you all for the very thorough answers. It got really esoteric really fast, but you all laid it out pretty clear for someone who has never done any machining at all (I've built some crude things out of wood). I was able to follow along (to my mind) pretty well, even though my only exposure to non-woodworking machinery was a glimpse of an auto-insertion machine and a solder tank(?) in the Automation Lab at *** aerospace company.



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 Post subject: Re: AR-15 "Off the books"
PostPosted: Wed Jul 11, 2012 10:55 pm 
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HTRN:
The last time I laid hands on a shaper was in 1983, and that was after 1965 in a training school. They were tricky to set up, and didn't have the versatility, IMHO, of a milling machine but the had the advantage of just using a single tool bit. You could shape the tool bit for rough out work or finish work. In the training school I used one to machine out a large V-block and finished it on an old hand powered surface grinder. My last job using one was to cut an internal key slot on the inside diameter of a large pipe. They'd made an extension bit holder so it could get inside the pipe. Eurk! I just flashed on a shaper with digital read outs.
http://en.wikipedia.org/wiki/Shaper
If you want a new shaper you can get one from India IIRC. errrh.....


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 Post subject: Re: AR-15 "Off the books"
PostPosted: Wed Jul 11, 2012 11:49 pm 
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Location: North Idaho
Actually, shapers can be extremely useful for the tasks they are good at. In fact, they make for a FAR smoother and cleaner operation in a lot of situations.

Shapers make truly excellent increasing or decreasing radius curves for example (particularly inside curves); and until EDM, there was no better way of machining inside bore features... and in many ways for many metals, there still isn't. Shapers STILL make smoother radius cuts than all but the best CNC mills can make; and they are still far better gear cutters than mills, even for helical gears (using a sine bar cutting head for example).

What they are, is slow, and inflexible. They have a very limited series of operations and positions they work in, and they take a LONG time to make their cuts vs high speed rotary cutting operations, and they require many more tools and tool changes, to do so.



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 Post subject: Re: AR-15 "Off the books"
PostPosted: Thu Jul 12, 2012 11:13 am 
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Shapers do certain, VERY limited jobs well, mostly involving cutting recesses/keyways that have to be square, rather than radiused. Stuff that would otherwise have to be done with a sinker EDM or a broach setup(may not be possible in blind holes). Other than that? They're boat anchors. I will say the smaller ones are usually more valuable, as they're popular with hobbiests - up to maybe 12 inch, mostly stuff in the 8-10" range. The big 20" shapers? scrap for the most part when they come up for auction. Planers are in a similar situation(Interestingly, planers are popular for cutting pressbrake dies, because they induce less stress in the work, causing less distortion).



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 Post subject: Re: AR-15 "Off the books"
PostPosted: Thu Jul 12, 2012 10:11 pm 
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:jacked:

You had to go and mention planers. We were using planed large flats of hot roll for jig and fixture tables. We started getting plates that not only were rough as cobs but that we couldn't get level. They were warped. We sent some spies down to the tooling machine shop and the problem was the "operator" would just clamp the plate down then start hogging material off of it. He wouldn't put shim under the parts where he clamped and the plate wasn't touching. Then he'd turn the plate over and hog it again. So to use the plate we had to shim or get parts ground down for locators, drill jig plates, and stuff. It made putting tooling reference point on fun also. It was a union shop and we couldn't get him to do it right, moved or fired. :evil:


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