I'm close to milling my AR lower receiver, this "95%" machined receiver
needs a pocket for the fire control group and 3 holes cross drilled for 2
pins and a selector/safety.

I found some instructions for machining the pocket using a DRO, they
recommend drilling the selector switch hole, machining the pocket then
drilling the trigger & hammer pin holes. Why not drill all 3 cross holes in
that 1 setup and then machining the pocket? I would think the drill bits
might be more likely to walk as they start through the 2nd side. I don't
see a benefit to set up for drilling, turn turn the part for milling, then
turn back to the first setup to drill 2 more holes, any idea why they would
do, or recommend this?

https://colfaxtactical.com/docs/Fire...%20a%20DRO.pdf

RogerN

RogerN wrote:

I'm close to milling my AR lower receiver, this "95%" machined receiver
needs a pocket for the fire control group and 3 holes cross drilled for 2
pins and a selector/safety.

I found some instructions for machining the pocket using a DRO, they
recommend drilling the selector switch hole, machining the pocket then
drilling the trigger & hammer pin holes. Why not drill all 3 cross holes in
that 1 setup and then machining the pocket? I would think the drill bits
might be more likely to walk as they start through the 2nd side. I don't
see a benefit to set up for drilling, turn turn the part for milling, then
turn back to the first setup to drill 2 more holes, any idea why they would
do, or recommend this?

https://colfaxtactical.com/docs/Fire...%20a%20DRO.pdf

RogerN

I drill all the holes in one setup long before milling the FCG cavity. I
suppose one theory for drilling after the FCG cavity would be to reduce
the chances of the drill getting off course, but that doesn't seem to be
an issue in my experience. The Ray-Vin guide is the best reference IMO.

"Pete C." wrote in message ...

RogerN wrote:

I'm close to milling my AR lower receiver, this "95%" machined receiver
needs a pocket for the fire control group and 3 holes cross drilled for 2
pins and a selector/safety.

I found some instructions for machining the pocket using a DRO, they
recommend drilling the selector switch hole, machining the pocket then
drilling the trigger & hammer pin holes. Why not drill all 3 cross holes
in
that 1 setup and then machining the pocket? I would think the drill bits
might be more likely to walk as they start through the 2nd side. I don't
see a benefit to set up for drilling, turn turn the part for milling,
then
turn back to the first setup to drill 2 more holes, any idea why they
would
do, or recommend this?

https://colfaxtactical.com/docs/Fire...%20a%20DRO.pdf

RogerN

I drill all the holes in one setup long before milling the FCG cavity. I
suppose one theory for drilling after the FCG cavity would be to reduce
the chances of the drill getting off course, but that doesn't seem to be
an issue in my experience. The Ray-Vin guide is the best reference IMO.

That's more what I was thinking, drill the cross holes first in one setup
and then mill the fire control group. I have the Ray-Vin guide and a blank
lower also, the "95%" machined lower should get me shooting right away and
the 0% won't be rushed. Do you know how long it takes to completely machine
a lower using the Ray-Vin guide?

RogerN

RogerN wrote:

"Pete C." wrote in message ...

RogerN wrote:

I'm close to milling my AR lower receiver, this "95%" machined receiver
needs a pocket for the fire control group and 3 holes cross drilled for 2
pins and a selector/safety.

I found some instructions for machining the pocket using a DRO, they
recommend drilling the selector switch hole, machining the pocket then
drilling the trigger & hammer pin holes. Why not drill all 3 cross holes
in
that 1 setup and then machining the pocket? I would think the drill bits
might be more likely to walk as they start through the 2nd side. I don't
see a benefit to set up for drilling, turn turn the part for milling,
then
turn back to the first setup to drill 2 more holes, any idea why they
would
do, or recommend this?

https://colfaxtactical.com/docs/Fire...%20a%20DRO.pdf

RogerN

I drill all the holes in one setup long before milling the FCG cavity. I
suppose one theory for drilling after the FCG cavity would be to reduce
the chances of the drill getting off course, but that doesn't seem to be
an issue in my experience. The Ray-Vin guide is the best reference IMO.

That's more what I was thinking, drill the cross holes first in one setup
and then mill the fire control group. I have the Ray-Vin guide and a blank
lower also, the "95%" machined lower should get me shooting right away and
the 0% won't be rushed.


Do you know how long it takes to completely machine
a lower using the Ray-Vin guide?

Nope, but close. I use the 30% lowers from TM, so that saves the magwell
and decking steps. The 30s take most of a day to machine on a manual
mill working at a careful pace with lunch and dinner breaks. A good
chunk of the time is the 8 or so setups and getting each one indicated
and edge located.

"Pete C." wrote in message ...


RogerN wrote:

snip

Do you know how long it takes to completely machine
a lower using the Ray-Vin guide?

Nope, but close. I use the 30% lowers from TM, so that saves the magwell
and decking steps. The 30s take most of a day to machine on a manual
mill working at a careful pace with lunch and dinner breaks. A good
chunk of the time is the 8 or so setups and getting each one indicated
and edge located.

I have one lower raw forging now and 4 more that have been on order since
early February. I'm hoping the other 4 come in and I can machine them as a
batch of 5. I would like to machine them all to the 80% stage so I could
legally sell some if I wanted to. I could complete however many I think I
wanted to keep. I now have one rifle and one carbine less lowers, would
like to also get a 300 blackout, I hear barrel and ammo is the only
difference from the .223/5.56. An area gun shop had a Bushmaster 450 upper,
I'm not sure what cartridge they shoot.

RogerN

On Sun, 7 Apr 2013 19:12:24 -0500, "RogerN" wrote:


I'm close to milling my AR lower receiver, this "95%" machined receiver
needs a pocket for the fire control group and 3 holes cross drilled for 2
pins and a selector/safety.

I found some instructions for machining the pocket using a DRO, they
recommend drilling the selector switch hole, machining the pocket then
drilling the trigger & hammer pin holes. Why not drill all 3 cross holes in
that 1 setup and then machining the pocket? I would think the drill bits
might be more likely to walk as they start through the 2nd side. I don't
see a benefit to set up for drilling, turn turn the part for milling, then
turn back to the first setup to drill 2 more holes, any idea why they would
do, or recommend this?

https://colfaxtactical.com/docs/Fire...%20a%20DRO.pdf

RogerN


Know where a complete drawing is? Would 6016-t6 bar be a suitable
peice to start with?

Remove 333 to reply.
Randy

Randy333 wrote:

On Sun, 7 Apr 2013 19:12:24 -0500, "RogerN" wrote:


I'm close to milling my AR lower receiver, this "95%" machined receiver
needs a pocket for the fire control group and 3 holes cross drilled for 2
pins and a selector/safety.

I found some instructions for machining the pocket using a DRO, they
recommend drilling the selector switch hole, machining the pocket then
drilling the trigger & hammer pin holes. Why not drill all 3 cross holes in
that 1 setup and then machining the pocket? I would think the drill bits
might be more likely to walk as they start through the 2nd side. I don't
see a benefit to set up for drilling, turn turn the part for milling, then
turn back to the first setup to drill 2 more holes, any idea why they would
do, or recommend this?

https://colfaxtactical.com/docs/Fire...%20a%20DRO.pdf

RogerN


Know where a complete drawing is? Would 6016-t6 bar be a suitable
peice to start with?

There are a bunch of AR prints on the 'net, just search around a bit.
7075-T6 is what you want.

RogerN wrote:

I'm close to milling my AR lower receiver, this "95%" machined receiver
needs a pocket for the fire control group and 3 holes cross drilled for 2
pins and a selector/safety.

I found some instructions for machining the pocket using a DRO, they
recommend drilling the selector switch hole, machining the pocket then
drilling the trigger & hammer pin holes. Why not drill all 3 cross holes in
that 1 setup and then machining the pocket? I would think the drill bits
might be more likely to walk as they start through the 2nd side. I don't
see a benefit to set up for drilling, turn turn the part for milling, then
turn back to the first setup to drill 2 more holes, any idea why they would
do, or recommend this?

https://colfaxtactical.com/docs/Fire...%20a%20DRO.pdf

RogerN

does anybody make plastic unfinished lowers, just for machining practice?

It would seem like a shame, and expensive to be using trashed lowers for
the next aluminum casting project.

On Mon, 8 Apr 2013 17:14:22 +0000 (UTC), Cydrome Leader
wrote:

RogerN wrote:

I'm close to milling my AR lower receiver, this "95%" machined receiver
needs a pocket for the fire control group and 3 holes cross drilled for 2
pins and a selector/safety.

I found some instructions for machining the pocket using a DRO, they
recommend drilling the selector switch hole, machining the pocket then
drilling the trigger & hammer pin holes. Why not drill all 3 cross holes in
that 1 setup and then machining the pocket? I would think the drill bits
might be more likely to walk as they start through the 2nd side. I don't
see a benefit to set up for drilling, turn turn the part for milling, then
turn back to the first setup to drill 2 more holes, any idea why they would
do, or recommend this?

https://colfaxtactical.com/docs/Fire...%20a%20DRO.pdf

RogerN

does anybody make plastic unfinished lowers, just for machining practice?

It would seem like a shame, and expensive to be using trashed lowers for
the next aluminum casting project.

Real AR-15s and M-16s have 7075-grade uppers and lowers. You can't
cast that with home hobby equipment.

I've read that some of the aftermarket is using 6061 for lowers. But
the people making those comments probably don't really know. Yield
strength of 6061 is roughly half that of 7075.

6061 is a wrought grade, but it can be cast without doing anything
special.

--
Ed Huntress

Ed Huntress wrote:
On Mon, 8 Apr 2013 17:14:22 +0000 (UTC), Cydrome Leader
wrote:

RogerN wrote:

I'm close to milling my AR lower receiver, this "95%" machined receiver
needs a pocket for the fire control group and 3 holes cross drilled for 2
pins and a selector/safety.

I found some instructions for machining the pocket using a DRO, they
recommend drilling the selector switch hole, machining the pocket then
drilling the trigger & hammer pin holes. Why not drill all 3 cross holes in
that 1 setup and then machining the pocket? I would think the drill bits
might be more likely to walk as they start through the 2nd side. I don't
see a benefit to set up for drilling, turn turn the part for milling, then
turn back to the first setup to drill 2 more holes, any idea why they would
do, or recommend this?

https://colfaxtactical.com/docs/Fire...%20a%20DRO.pdf

RogerN

does anybody make plastic unfinished lowers, just for machining practice?

It would seem like a shame, and expensive to be using trashed lowers for
the next aluminum casting project.

Real AR-15s and M-16s have 7075-grade uppers and lowers. You can't
cast that with home hobby equipment.

I've read that some of the aftermarket is using 6061 for lowers. But
the people making those comments probably don't really know. Yield
strength of 6061 is roughly half that of 7075.

6061 is a wrought grade, but it can be cast without doing anything
special.

I meant once you bungle a partially made lower, you're finished, and it's
just expensive scrap metal, of a useless shape probably only good for
tossing into the aluminum scrap pile for some backyard casting. It seems
like a shame.

On Mon, 8 Apr 2013 19:24:51 +0000 (UTC), Cydrome Leader
wrote:

Ed Huntress wrote:
On Mon, 8 Apr 2013 17:14:22 +0000 (UTC), Cydrome Leader
wrote:

RogerN wrote:

I'm close to milling my AR lower receiver, this "95%" machined receiver
needs a pocket for the fire control group and 3 holes cross drilled for 2
pins and a selector/safety.

I found some instructions for machining the pocket using a DRO, they
recommend drilling the selector switch hole, machining the pocket then
drilling the trigger & hammer pin holes. Why not drill all 3 cross holes in
that 1 setup and then machining the pocket? I would think the drill bits
might be more likely to walk as they start through the 2nd side. I don't
see a benefit to set up for drilling, turn turn the part for milling, then
turn back to the first setup to drill 2 more holes, any idea why they would
do, or recommend this?

https://colfaxtactical.com/docs/Fire...%20a%20DRO.pdf

RogerN

does anybody make plastic unfinished lowers, just for machining practice?

It would seem like a shame, and expensive to be using trashed lowers for
the next aluminum casting project.

Real AR-15s and M-16s have 7075-grade uppers and lowers. You can't
cast that with home hobby equipment.

I've read that some of the aftermarket is using 6061 for lowers. But
the people making those comments probably don't really know. Yield
strength of 6061 is roughly half that of 7075.

6061 is a wrought grade, but it can be cast without doing anything
special.

I meant once you bungle a partially made lower, you're finished, and it's
just expensive scrap metal, of a useless shape probably only good for
tossing into the aluminum scrap pile for some backyard casting. It seems
like a shame.

Well, it is a shame, but I wouldn't toss a high-zinc alloy, which also
has around 1.5% copper, into a pile I was going to use for backyard
aluminum casting. Zinc and copper will hake it hard to make a casting
without internal shrinkage voids.


--
Ed Huntress

Ed Huntress wrote:
On Mon, 8 Apr 2013 19:24:51 +0000 (UTC), Cydrome Leader
wrote:

Ed Huntress wrote:
On Mon, 8 Apr 2013 17:14:22 +0000 (UTC), Cydrome Leader
wrote:

RogerN wrote:

I'm close to milling my AR lower receiver, this "95%" machined receiver
needs a pocket for the fire control group and 3 holes cross drilled for 2
pins and a selector/safety.

I found some instructions for machining the pocket using a DRO, they
recommend drilling the selector switch hole, machining the pocket then
drilling the trigger & hammer pin holes. Why not drill all 3 cross holes in
that 1 setup and then machining the pocket? I would think the drill bits
might be more likely to walk as they start through the 2nd side. I don't
see a benefit to set up for drilling, turn turn the part for milling, then
turn back to the first setup to drill 2 more holes, any idea why they would
do, or recommend this?

https://colfaxtactical.com/docs/Fire...%20a%20DRO.pdf

RogerN

does anybody make plastic unfinished lowers, just for machining practice?

It would seem like a shame, and expensive to be using trashed lowers for
the next aluminum casting project.

Real AR-15s and M-16s have 7075-grade uppers and lowers. You can't
cast that with home hobby equipment.

I've read that some of the aftermarket is using 6061 for lowers. But
the people making those comments probably don't really know. Yield
strength of 6061 is roughly half that of 7075.

6061 is a wrought grade, but it can be cast without doing anything
special.

I meant once you bungle a partially made lower, you're finished, and it's
just expensive scrap metal, of a useless shape probably only good for
tossing into the aluminum scrap pile for some backyard casting. It seems
like a shame.

Well, it is a shame, but I wouldn't toss a high-zinc alloy, which also
has around 1.5% copper, into a pile I was going to use for backyard
aluminum casting. Zinc and copper will hake it hard to make a casting
without internal shrinkage voids.

So it's a total loss then.

How much might it cost to make some really crappy molds (we're talking
1970s Hong Kong grade stuff) to make these out of plastic?

"Ed Huntress" wrote in message
news
On Mon, 8 Apr 2013 19:24:51 +0000 (UTC), Cydrome Leader
wrote:

Ed Huntress wrote:
On Mon, 8 Apr 2013 17:14:22 +0000 (UTC), Cydrome Leader
wrote:

RogerN wrote:

I'm close to milling my AR lower receiver, this "95%" machined
receiver
needs a pocket for the fire control group and 3 holes cross drilled
for 2
pins and a selector/safety.

I found some instructions for machining the pocket using a DRO, they
recommend drilling the selector switch hole, machining the pocket
then
drilling the trigger & hammer pin holes. Why not drill all 3 cross
holes in
that 1 setup and then machining the pocket? I would think the drill
bits
might be more likely to walk as they start through the 2nd side. I
don't
see a benefit to set up for drilling, turn turn the part for milling,
then
turn back to the first setup to drill 2 more holes, any idea why they
would
do, or recommend this?

https://colfaxtactical.com/docs/Fire...%20a%20DRO.pdf

RogerN

does anybody make plastic unfinished lowers, just for machining
practice?

It would seem like a shame, and expensive to be using trashed lowers for
the next aluminum casting project.

Real AR-15s and M-16s have 7075-grade uppers and lowers. You can't
cast that with home hobby equipment.

I've read that some of the aftermarket is using 6061 for lowers. But
the people making those comments probably don't really know. Yield
strength of 6061 is roughly half that of 7075.

6061 is a wrought grade, but it can be cast without doing anything
special.

I meant once you bungle a partially made lower, you're finished, and it's
just expensive scrap metal, of a useless shape probably only good for
tossing into the aluminum scrap pile for some backyard casting. It seems
like a shame.

Well, it is a shame, but I wouldn't toss a high-zinc alloy, which also
has around 1.5% copper, into a pile I was going to use for backyard
aluminum casting. Zinc and copper will hake it hard to make a casting
without internal shrinkage voids.


--
Ed Huntress

Neither would I . I'd toss it into the pile for ZA alloy casting . Ed ,
where did you acquire your knowledge about casting and alloys ? Some of the
stuff you've posted is directly opposite what experience and hobbycasting
yahoogroup has taught me .
--
Snag
Cast 5 ingots and
a pulley this am ...

Cydrome Leader wrote:

Ed Huntress wrote:
On Mon, 8 Apr 2013 17:14:22 +0000 (UTC), Cydrome Leader
wrote:

RogerN wrote:

I'm close to milling my AR lower receiver, this "95%" machined receiver
needs a pocket for the fire control group and 3 holes cross drilled for 2
pins and a selector/safety.

I found some instructions for machining the pocket using a DRO, they
recommend drilling the selector switch hole, machining the pocket then
drilling the trigger & hammer pin holes. Why not drill all 3 cross holes in
that 1 setup and then machining the pocket? I would think the drill bits
might be more likely to walk as they start through the 2nd side. I don't
see a benefit to set up for drilling, turn turn the part for milling, then
turn back to the first setup to drill 2 more holes, any idea why they would
do, or recommend this?

https://colfaxtactical.com/docs/Fire...%20a%20DRO.pdf

RogerN

does anybody make plastic unfinished lowers, just for machining practice?

It would seem like a shame, and expensive to be using trashed lowers for
the next aluminum casting project.

Real AR-15s and M-16s have 7075-grade uppers and lowers. You can't
cast that with home hobby equipment.

I've read that some of the aftermarket is using 6061 for lowers. But
the people making those comments probably don't really know. Yield
strength of 6061 is roughly half that of 7075.

6061 is a wrought grade, but it can be cast without doing anything
special.

I meant once you bungle a partially made lower, you're finished, and it's
just expensive scrap metal, of a useless shape probably only good for
tossing into the aluminum scrap pile for some backyard casting. It seems
like a shame.

It depends on exactly what you bungle, but most mistakes in the
machining can be remedied/worked around to make a perfectly serviceable
lower.

On the 7075 vs. 6061 thing, operationally it won't make much difference
since the AR receiver basically guides parts and have very very little
stress placed on it due to the fact that the bolt locks into the barrel
extension and no into any portion of the receiver. I believe the first
M16s were 6061 and they only changed to 7075 due to corrosion issues in
the 'Nam jungles.

With the lower forgings running in the $25-$80 range depending on
completion state, the financial risk isn't really much more than the
financial risk of breaking an end mill or reamer in the machining.

Pete C. wrote:

Cydrome Leader wrote:

Ed Huntress wrote:
On Mon, 8 Apr 2013 17:14:22 +0000 (UTC), Cydrome Leader
wrote:

RogerN wrote:

I'm close to milling my AR lower receiver, this "95%" machined receiver
needs a pocket for the fire control group and 3 holes cross drilled for 2
pins and a selector/safety.

I found some instructions for machining the pocket using a DRO, they
recommend drilling the selector switch hole, machining the pocket then
drilling the trigger & hammer pin holes. Why not drill all 3 cross holes in
that 1 setup and then machining the pocket? I would think the drill bits
might be more likely to walk as they start through the 2nd side. I don't
see a benefit to set up for drilling, turn turn the part for milling, then
turn back to the first setup to drill 2 more holes, any idea why they would
do, or recommend this?

https://colfaxtactical.com/docs/Fire...%20a%20DRO.pdf

RogerN

does anybody make plastic unfinished lowers, just for machining practice?

It would seem like a shame, and expensive to be using trashed lowers for
the next aluminum casting project.

Real AR-15s and M-16s have 7075-grade uppers and lowers. You can't
cast that with home hobby equipment.

I've read that some of the aftermarket is using 6061 for lowers. But
the people making those comments probably don't really know. Yield
strength of 6061 is roughly half that of 7075.

6061 is a wrought grade, but it can be cast without doing anything
special.

I meant once you bungle a partially made lower, you're finished, and it's
just expensive scrap metal, of a useless shape probably only good for
tossing into the aluminum scrap pile for some backyard casting. It seems
like a shame.

It depends on exactly what you bungle, but most mistakes in the
machining can be remedied/worked around to make a perfectly serviceable
lower.

On the 7075 vs. 6061 thing, operationally it won't make much difference
since the AR receiver basically guides parts and have very very little
stress placed on it due to the fact that the bolt locks into the barrel
extension and no into any portion of the receiver. I believe the first
M16s were 6061 and they only changed to 7075 due to corrosion issues in
the 'Nam jungles.

With the lower forgings running in the $25-$80 range depending on
completion state, the financial risk isn't really much more than the
financial risk of breaking an end mill or reamer in the machining.

hmm, I've not stumbled across the $25 ones, but that would be worth it
just for the practice.

On Apr 8, 11:26*am, Ed Huntress wrote:
On Mon, 8 Apr 2013 17:14:22 +0000 (UTC), Cydrome Leader





wrote:
RogerN wrote:

I'm close to milling my AR lower receiver, this "95%" machined receiver
needs a pocket for the fire control group and 3 holes cross drilled for 2
pins and a selector/safety.

I found some instructions for machining the pocket using a DRO, they
recommend drilling the selector switch hole, machining the pocket *then
drilling the trigger & hammer pin holes. *Why not drill all 3 cross holes in
that 1 setup and then machining the pocket? *I would think the drill bits
might be more likely to walk as they start through the 2nd side. *I don't
see a benefit to set up for drilling, turn turn the part for milling, then
turn back to the first setup to drill 2 more holes, any idea why they would
do, or recommend this?

https://colfaxtactical.com/docs/Fire...%20with%20a%20....

RogerN

does anybody make plastic unfinished lowers, just for machining practice?

It would seem like a shame, and expensive to be using trashed lowers for
the next aluminum casting project.

Real AR-15s and M-16s have 7075-grade uppers and lowers. You can't
cast that with home hobby equipment.

I've read that some of the aftermarket is using 6061 for lowers. But
the people making those comments probably don't really know. Yield
strength of 6061 is roughly half that of 7075.

6061 is a wrought grade, but it can be cast without doing anything
special.

--
Ed Huntress- Hide quoted text -

- Show quoted text -

The original ARs back in the Vietnam timeframe had 6061 forgings.
They had some trouble with corrosion from guys' sweat, so 7075 was the
next step. Some of the early clone lowers were castings, some so bad
that they broke when the rifle fell over onto the floor. Stoner's
genius was you could probably make a lower out of recycled bubblegum
and have it work as long as it stood up to the fire control springs'
pressure. So 6061 or 7075, doesn't make much difference except when
anodizing. .223 recoil is about nil, the forgings/castings don't
directly take chamber pressure so yield strength is irrelevant for
most civilian uses. If you intend on beating up bunnies or whacking
coyotes with the buttstock, it might make a difference.

Stan

On Mon, 8 Apr 2013 13:43:26 -0700 (PDT), Stanley Schaefer
wrote:

On Apr 8, 11:26*am, Ed Huntress wrote:
On Mon, 8 Apr 2013 17:14:22 +0000 (UTC), Cydrome Leader





wrote:
RogerN wrote:

I'm close to milling my AR lower receiver, this "95%" machined receiver
needs a pocket for the fire control group and 3 holes cross drilled for 2
pins and a selector/safety.

I found some instructions for machining the pocket using a DRO, they
recommend drilling the selector switch hole, machining the pocket *then
drilling the trigger & hammer pin holes. *Why not drill all 3 cross holes in
that 1 setup and then machining the pocket? *I would think the drill bits
might be more likely to walk as they start through the 2nd side. *I don't
see a benefit to set up for drilling, turn turn the part for milling, then
turn back to the first setup to drill 2 more holes, any idea why they would
do, or recommend this?

https://colfaxtactical.com/docs/Fire...%20with%20a%20...

RogerN

does anybody make plastic unfinished lowers, just for machining practice?

It would seem like a shame, and expensive to be using trashed lowers for
the next aluminum casting project.

Real AR-15s and M-16s have 7075-grade uppers and lowers. You can't
cast that with home hobby equipment.

I've read that some of the aftermarket is using 6061 for lowers. But
the people making those comments probably don't really know. Yield
strength of 6061 is roughly half that of 7075.

6061 is a wrought grade, but it can be cast without doing anything
special.

--
Ed Huntress- Hide quoted text -

- Show quoted text -

The original ARs back in the Vietnam timeframe had 6061 forgings.
They had some trouble with corrosion from guys' sweat, so 7075 was the
next step.

Something is strange there. I'd have to dig out my ASM book to check,
but 7075 has low corrosion resistance overall and is not recommended
at all for marine environments (or salty sweat, one would assume).
6061 is somewhere in the middle.

Some of the early clone lowers were castings, some so bad
that they broke when the rifle fell over onto the floor. Stoner's
genius was you could probably make a lower out of recycled bubblegum
and have it work as long as it stood up to the fire control springs'
pressure. So 6061 or 7075, doesn't make much difference except when
anodizing. .223 recoil is about nil, the forgings/castings don't
directly take chamber pressure so yield strength is irrelevant for
most civilian uses. If you intend on beating up bunnies or whacking
coyotes with the buttstock, it might make a difference.

Stan

On 4/8/2013 4:06 PM, Ed Huntress wrote:

Snipped - just to show it's technically possible...

Something is strange there. I'd have to dig out my ASM book to check,
but 7075 has low corrosion resistance overall and is not recommended
at all for marine environments (or salty sweat, one would assume).
6061 is somewhere in the middle.


I wondered about that too.

What's the story here?

"Ed Huntress" wrote
Real AR-15s and M-16s have 7075-grade uppers and lowers. You can't
cast that with home hobby equipment.


--
Ed Huntress


You're wrong Ed , I've melted and cast 7075 in my home foundry . Now what
I can't do is heat-treat and forge it at home . I'm not sure what's
involved with forging , though I'm pretty sure Al is worked cold . Might
have to carry a billet up the road and see what my neighbor can do with his
trip hammer ... Heat-treat requires some expensive precision equipment
though .
--
Snag

On Mon, 8 Apr 2013 21:55:22 -0500, "Terry Coombs"
wrote:

"Ed Huntress" wrote
Real AR-15s and M-16s have 7075-grade uppers and lowers. You can't
cast that with home hobby equipment.


--
Ed Huntress


You're wrong Ed , I've melted and cast 7075 in my home foundry . Now what
I can't do is heat-treat and forge it at home . I'm not sure what's
involved with forging , though I'm pretty sure Al is worked cold . Might
have to carry a billet up the road and see what my neighbor can do with his
trip hammer ... Heat-treat requires some expensive precision equipment
though .

Well, you may have gotten lucky, or you may have a casting with
sub-surface porosity and segregation. The closest casting alloy to
7075 is 713.0, and it has less than half as much copper as 7075.

And a fraction of the strength. If they could cast 7075 versus using
713.0, they surely would.

But I hope you got lucky.

--
Ed Huntress

Cydrome Leader wrote:
RogerN wrote:
I'm close to milling my AR lower receiver, this "95%" machined receiver
needs a pocket for the fire control group and 3 holes cross drilled for 2
pins and a selector/safety.

I found some instructions for machining the pocket using a DRO, they
recommend drilling the selector switch hole, machining the pocket then
drilling the trigger & hammer pin holes. Why not drill all 3 cross holes in
that 1 setup and then machining the pocket? I would think the drill bits
might be more likely to walk as they start through the 2nd side. I don't
see a benefit to set up for drilling, turn turn the part for milling, then
turn back to the first setup to drill 2 more holes, any idea why they would
do, or recommend this?

https://colfaxtactical.com/docs/Fire...%20a%20DRO.pdf

RogerN

does anybody make plastic unfinished lowers, just for machining practice?

It would seem like a shame, and expensive to be using trashed lowers for
the next aluminum casting project.






As long as you follow the directions and have some ability they are not
real hard to machine. The biggest thing involved is to KNOW the machine
you will be using. If you know that your machine has .020 backlash on
the X axis repeatably then you can correct for it. If you think it does
but in reality it isn't repeatable then OOPS you get a scrap upper.


--
Steve W.

Steve W. wrote:
Cydrome Leader wrote:
RogerN wrote:
I'm close to milling my AR lower receiver, this "95%" machined receiver
needs a pocket for the fire control group and 3 holes cross drilled for 2
pins and a selector/safety.

I found some instructions for machining the pocket using a DRO, they
recommend drilling the selector switch hole, machining the pocket then
drilling the trigger & hammer pin holes. Why not drill all 3 cross holes in
that 1 setup and then machining the pocket? I would think the drill bits
might be more likely to walk as they start through the 2nd side. I don't
see a benefit to set up for drilling, turn turn the part for milling, then
turn back to the first setup to drill 2 more holes, any idea why they would
do, or recommend this?

https://colfaxtactical.com/docs/Fire...%20a%20DRO.pdf

RogerN

does anybody make plastic unfinished lowers, just for machining practice?

It would seem like a shame, and expensive to be using trashed lowers for
the next aluminum casting project.






As long as you follow the directions and have some ability they are not
real hard to machine. The biggest thing involved is to KNOW the machine
you will be using. If you know that your machine has .020 backlash on
the X axis repeatably then you can correct for it. If you think it does
but in reality it isn't repeatable then OOPS you get a scrap upper.

It's a chicken and egg sort of deal to anybody (like me) that's new to
machining, but familiar with what the finished product should be.

Do I right now have the ability to finish a lower receiver? No, I do not.

Could I learn? sure, but it will take lots of practice, which at this
point would be futile and expensive if I bought a box of forgings and
jumped right in. I'm sure I'd learn quite a bit trying though, while
making a huge pile of scraps, but again, it costs to much to try.

On Apr 8, 2:48*pm, Cydrome Leader wrote:
Steve W. wrote:
Cydrome Leader wrote:
RogerN wrote:
I'm close to milling my AR lower receiver, this "95%" machined receiver
needs a pocket for the fire control group and 3 holes cross drilled for 2
pins and a selector/safety.

I found some instructions for machining the pocket using a DRO, they
recommend drilling the selector switch hole, machining the pocket *then
drilling the trigger & hammer pin holes. *Why not drill all 3 cross holes in
that 1 setup and then machining the pocket? *I would think the drill bits
might be more likely to walk as they start through the 2nd side. *I don't
see a benefit to set up for drilling, turn turn the part for milling, then
turn back to the first setup to drill 2 more holes, any idea why they would
do, or recommend this?

https://colfaxtactical.com/docs/Fire...%20with%20a%20....

RogerN

does anybody make plastic unfinished lowers, just for machining practice?

It would seem like a shame, and expensive to be using trashed lowers for
the next aluminum casting project.

As long as you follow the directions and have some ability they are not
real hard to machine. The biggest thing involved is to KNOW the machine
you will be using. If you know that your machine has .020 backlash on
the X axis repeatably then you can correct for it. If you think it does
but in reality it isn't repeatable then OOPS you get a scrap upper.

It's a chicken and egg sort of deal to anybody (like me) that's new to
machining, but familiar with what the finished product should be.

Do I right now have the ability to finish *a lower receiver? No, I do not.

Could I learn? sure, but it will take lots of practice, which at this
point would be futile and expensive if I bought a box of forgings and
jumped right in. I'm sure I'd learn quite a bit trying though, while
making a huge pile of scraps, but again, it costs to much to try.

You are not as far off as you think if you invest the time and you
continue to think and ask questions about why you are having problems
You have tremendous resources in this group: Lloyd Sponenburgh,
Precision Machinist, Bottlebob, and lots of others. Use them. The more
parts you make out of different materials, the better you will get.

On Mon, 8 Apr 2013 17:14:22 +0000 (UTC), Cydrome Leader
wrote:

RogerN wrote:

I'm close to milling my AR lower receiver, this "95%" machined receiver
needs a pocket for the fire control group and 3 holes cross drilled for 2
pins and a selector/safety.

I found some instructions for machining the pocket using a DRO, they
recommend drilling the selector switch hole, machining the pocket then
drilling the trigger & hammer pin holes. Why not drill all 3 cross holes in
that 1 setup and then machining the pocket? I would think the drill bits
might be more likely to walk as they start through the 2nd side. I don't
see a benefit to set up for drilling, turn turn the part for milling, then
turn back to the first setup to drill 2 more holes, any idea why they would
do, or recommend this?

https://colfaxtactical.com/docs/Fire...%20a%20DRO.pdf

RogerN

does anybody make plastic unfinished lowers, just for machining practice?

It would seem like a shame, and expensive to be using trashed lowers for
the next aluminum casting project.



Buy a 0% forging, make a mold from it using bondo (autobody filler)
then make some machinable wax castings from that. Screw it up, just
remelt the wax!

Remove 333 to reply.
Randy

Randy333 wrote:
On Mon, 8 Apr 2013 17:14:22 +0000 (UTC), Cydrome Leader
wrote:

RogerN wrote:

I'm close to milling my AR lower receiver, this "95%" machined receiver
needs a pocket for the fire control group and 3 holes cross drilled for 2
pins and a selector/safety.

I found some instructions for machining the pocket using a DRO, they
recommend drilling the selector switch hole, machining the pocket then
drilling the trigger & hammer pin holes. Why not drill all 3 cross holes in
that 1 setup and then machining the pocket? I would think the drill bits
might be more likely to walk as they start through the 2nd side. I don't
see a benefit to set up for drilling, turn turn the part for milling, then
turn back to the first setup to drill 2 more holes, any idea why they would
do, or recommend this?

https://colfaxtactical.com/docs/Fire...%20a%20DRO.pdf

RogerN

does anybody make plastic unfinished lowers, just for machining practice?

It would seem like a shame, and expensive to be using trashed lowers for
the next aluminum casting project.



Buy a 0% forging, make a mold from it using bondo (autobody filler)
then make some machinable wax castings from that. Screw it up, just
remelt the wax!

Remove 333 to reply.
Randy

good idea.

I make some hillarious measurement mistakes. For whatever reason, the
various number of decimal places on measuring tools is what throws me off.