Aluminum AR180B lower. *Update DONE!*

I think I've sent you this pic before...
alu_plate.jpg

But yes, for commercial purposes it's advertised as 7075 or something like that.
That is because not all customers heard of 7475 and when they do,
they usualy start with all kind of weird questions about that material.
In my understanding, 7475 does everything 7075 can do and then some.
It's machined best on automatics and CNC.
It's pretty hard to do anything by hand like hand-drilling, filing, grinding, etc. (when I try, I usualy get frustrated and I have to drink beer:D )
 
Jesus guys, give my time! If you only knew the ideas banging around in this head of mine!

One you might enjoy is a sheet metal lower kit. Rivet together with trunions, almost like an AK. A true do it yourself at home build. :D

As for the billet lower, turns out they do a Saturday class so I'll be going in then and using the shop. I should be able to accomplish a lot with a full 8 hour day!
 
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Teapot said:
Steyr made the GB by welding two halves of the frame together. It would be possible to split the plastic frame in two and have them investment cast in any material you wanted including stainless steel.
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Or I could CNC mill it from a solid billet. :rolleyes:

Heh, I'm a poet and I didn't know it.


Please, keep you comments on how I could have done it to yourselves, people. It's quit obvious I've already decided to do it this way. :rolleyes:
 
Screw castings, they can be porous, have inclusions, are more difficult to reference off of and you still have to machine them anyway! Stick with billet !
 
Deckard said:
What did I do?
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You did OK, I was kidding, don't worry about it.

Teapot said:
Steyr made the GB by welding two halves of the frame together.
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Finnaly somebody mentioning Steyer GB on this website.
Another excellent HG which didn't go anywhere.
Partly because it was kind of over-engineered, very hard and expensive to make, partly because of some austrian idiot's decision, the government contracts were given to the new kid in town (Glock with its stupid Browning action).
However, GB's gas op system, fixed barrel (polygonal) remains one of the best IMO in calibers which cannot be handled by streight blow-back.
Anyway, don't buy the "made in US" P-18, the so-called GB copy (it's a POS).

Armedsask said:
I have no plans to make and sell these billet lowers in the near future, stop asking.
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What do you mean? Not even for me?
Please, please, pretty please (with sugar on top). Pleeeeeeeeease;)
 
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Precision casting is not as simple as taking an original, and making a mould from it for the production of the wax masters. All sorts of shrinkage issues, dimensional problems emerge, in the transition from original to the die, to the wax, to the invested wax, to the actual casting. If a precision part is going to be produced by casting, it must be engineered for that style of production from the beginning. For limited production, casting is simply not a good choice. You are also at the mercy of the foundry.
Armedsask wisely is using modern machining techniques.
 
While your posts (including the above) make a lot of sense,
I think the discussion about the cast receiver is a little useless.
Precision cast has its advantages (in places like automotive).
However, the receiver IMO is another story.

Armedsask has his little obsessions with CNC and other odd ones I wouldn't mention here (understandable if you think he's from the Saskachewan country side).
Perhaps they didn't buy him toys when he was a kid.
Or maybe he doesn't have TV and tries to compensate by looking through the CNC window.
I'm not a psychiatrist, but who knows, maybe deep inside he misses torching mice with the flame thrower.
Sorry, I couldn't resist.

However, I think a better way to go is forging.
Compared to CNC, forging is several hundreds times faster, at least ten times cheaper (if you think of the outside of the AR15 receiver)
and has another related great advantages that CNC will never have:
-superior grain structure,
-the "fiber" will "flow" following the outside contour,
-superior strenght on preferential directions.

Another way is sheet metal stampings. Welded or riveted together.
To each, its own.

Anyway, people, no more making fun of Armedsask.
 
The problem with forging and casting is they are expensive when you are only making one. :D

The reason I like CNC is it is the cheapest way to go for a small production run. Yes, the AR15 reciever has some complicated geometry but that is why I have mine designed for ease of machining.

Still, I'd say the majority of mine will be manual cut. Probably even some use of files and die grinders. :D
 
I had a whole day in the shop today all by myself, it was great! I got so much done. I'm basically done the function essential portions of the lower. Fire control well, mag catch, front pivot, etc. Good lord did I make a whole mess of chips. :D

I can not mount the upper though as I ran out of time before I got the rear tower shaved down so the ears on the upper would fit around it. I did test fit it one on top of each other and it looks perfect. Also, the little hole at the back for the recoil spring guide rod assembly to lock into is too small. I did this on purpose as I want a tight fit. I'll drill it out later.

Now for pictures!

milling_1.jpg

Action shot! Shaving the rear tower down to the proper height. The 6 tooth carbide cutter is turning at around 1200 rpm and shooting chips all over the place.

milling_2.jpg

Cutting the fire control group well. This was a slow process as I would have to stop every so often and clean all the chips out of the hole. 1/2" highspeed steel endmill turning at 1500 rpm. I got absolutely soak in coolant during this.

How it looks so far:
lower_jan20_1.jpg

I'm either lucky or I know what I'm doing, mag catch works perfect. Before any one comments, more material will be cut off so the button sticks out. :rolleyes:

lower_jan20_2.jpg

Fire control group pocket. The two holes at the botton are either end of the slot for the trigger to stick through. I didn't have an endmill the right diameter that was long enough so I just drilled them. I'll finish it later with a hand saw and files when the trigger guard area is cut out.

And that's what I've got done so far. You can get a lot done when you have 8 hours to play.
 
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