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

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.

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

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?

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 Mon, 8 Apr 2013 20:54:33 +0000 (UTC), Cydrome Leader
wrote:

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.

Well, if you have enough aluminum to sell your scrap from time to
time, you could toss it in there.


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?

First off I'd look at the redesign of the plastic lower that those 3D
printing guys have designed. Just duplicating the aluminum one in
plastic led to a very short life, so they've redesigned it.

As for the molds, it depends on what plastic and how many. It also
will depend somewhat on the configuration and drafts. For machined
molds, aluminum (2024 or 6061) is used for injection-mold prototyping
and very short runs but some plastics require a chrome plating. After
that, it's mold steel, and big bucks unless you're machining it
yourself.

If you're using a pourable resin, like epoxy or rigid polyurethane,
you can make molds out of plaster of Paris. They'd be stronger than
most injection-moldable plastics but they're much more expensive, too.

--
Ed Huntress

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.

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.

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?

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 Mon, 08 Apr 2013 18:29:54 -0500, Richard
wrote:

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?

Ok, from ASM's "Metals Handbook," 9th Edition:

7075 is more corrosion-resistant thant 2024 but worse than any other
wrought alloy.

The zinc is no help, but it's the copper that's the big problem, as it
is with 2024. However, the copper improves resistance to
stress-corrosion cracking.

So in terms of general corrosion, 7075 kind of stinks. 6061 is good
even in marine environments -- although some 5xxxx and 1100 are
better.

--
Ed Huntress

Richard wrote:
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?

Current Mil spec is 7075 - T6

The original design called for either a 6 or 7 series alloy. The 6 was
cheaper and easier to work with so that was what ended up being used.
The problem is that between corrosion and thread deformation the spec
was re-written to 7075 - T6 being the "correct" alloy to use.

I have shot both and other than knowing the alloy due to the makers you
couldn't tell any real difference. 6061 is still used by a few companies
and with the design of the AR the strength in Civilian use isn't an issue.

However if you plan on needing to depend on the rifle in real combat
where you may be using it as a club, hammer or whatever, the 7075 has
the edge with regard to wear and tear.

I have used both forgings and solid billet as a starting point.
With forgings you are limited as to what you can add/subtract.
With billet you can have fun. I machined in a solid trigger guard,
milled my logo in 3D on the side, and a few other tricks.


--
Steve W.

On Mon, 08 Apr 2013 20:00:59 -0400, Ed Huntress wrote:
On Mon, 08 Apr 2013 18:29:54 -0500, Richard cavelamb wrote:
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?

Ok, from ASM's "Metals Handbook," 9th Edition:

7075 is more corrosion-resistant thant 2024 but worse than any other
wrought alloy.

The zinc is no help, but it's the copper that's the big problem, as it
is with 2024. However, the copper improves resistance to
stress-corrosion cracking.

So in terms of general corrosion, 7075 kind of stinks. 6061 is good
even in marine environments -- although some 5xxxx and 1100 are
better.

Which of 7075 and 6061 has better corrosion resistance when they
are anodized?

--
jiw

"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

"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 ...

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

On Mon, 8 Apr 2013 22:04:03 -0500, "Terry Coombs"
wrote:

"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 .

Mostly as Materials Editor at _American Machinist_. I had to study
basic metallurgy for a couple of years to be able to handle the tech
papers coming in from Alcoa, U.S. Steel, and so on.

I'm hardly an expert but I know the sources. I'm very curious about
what the hobbycasting group is saying that's directly opposite. Does
it concern 7075? It's notorious for having lousy corrosion resistance.
There are some 7xxxx alloys that are much better, but not 7075.

As for copper in aluminum, it makes it extremely hot-short and prone
to porosity. That's why welding 2024 is not recommended except by some
specialized techniques. It cracks like crazy, and if it happens not to
crack today, it may in a couple of weeks, as the HAZ age-hardens.

Anyway, what is opposite?

--
Ed Humtress

Gunner Asch wrote:
On Mon, 08 Apr 2013 20:02:47 -0400, "Steve W."
wrote:

Richard wrote:
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?
Current Mil spec is 7075 - T6

The original design called for either a 6 or 7 series alloy. The 6 was
cheaper and easier to work with so that was what ended up being used.
The problem is that between corrosion and thread deformation the spec
was re-written to 7075 - T6 being the "correct" alloy to use.

I have shot both and other than knowing the alloy due to the makers you
couldn't tell any real difference. 6061 is still used by a few companies
and with the design of the AR the strength in Civilian use isn't an issue.

However if you plan on needing to depend on the rifle in real combat
where you may be using it as a club, hammer or whatever, the 7075 has
the edge with regard to wear and tear.

I have used both forgings and solid billet as a starting point.
With forgings you are limited as to what you can add/subtract.
With billet you can have fun. I machined in a solid trigger guard,
milled my logo in 3D on the side, and a few other tricks.


Could you machine one out of a stainless steel block?



Already been done. There are a few companies that already sell stainless
lowers.

I did one out of 416 just to see what it took. It will be the only one I
ever do as well. It machined very well but even when I thinned areas
down to reduce weight it's still pretty hefty. Does make the .308 a lot
nicer to shoot though. I have been tossing around the idea of making one
out of steel though. Thinking of areas like the sides of the mag well
for skeletonizing...

Anyone with a mid sized mill can handle the job. If you buy some guides
you can even use a good drill press!


--
Steve W.

On Tue, 09 Apr 2013 00:19:34 -0400, "Steve W."
wrote:

Gunner Asch wrote:
On Mon, 08 Apr 2013 20:02:47 -0400, "Steve W."
wrote:

Richard wrote:
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?
Current Mil spec is 7075 - T6

The original design called for either a 6 or 7 series alloy. The 6 was
cheaper and easier to work with so that was what ended up being used.
The problem is that between corrosion and thread deformation the spec
was re-written to 7075 - T6 being the "correct" alloy to use.

I have shot both and other than knowing the alloy due to the makers you
couldn't tell any real difference. 6061 is still used by a few companies
and with the design of the AR the strength in Civilian use isn't an issue.

However if you plan on needing to depend on the rifle in real combat
where you may be using it as a club, hammer or whatever, the 7075 has
the edge with regard to wear and tear.

I have used both forgings and solid billet as a starting point.
With forgings you are limited as to what you can add/subtract.
With billet you can have fun. I machined in a solid trigger guard,
milled my logo in 3D on the side, and a few other tricks.


Could you machine one out of a stainless steel block?



Already been done. There are a few companies that already sell stainless
lowers.

I did one out of 416 just to see what it took. It will be the only one I
ever do as well. It machined very well but even when I thinned areas
down to reduce weight it's still pretty hefty. Does make the .308 a lot
nicer to shoot though. I have been tossing around the idea of making one
out of steel though. Thinking of areas like the sides of the mag well
for skeletonizing...

Anyone with a mid sized mill can handle the job. If you buy some guides
you can even use a good drill press!

Id not mind having a lower someday. Though given the prices of the
upper Stuff..it would likely remain a door stop.

ARs are quasi legal here in California..but they have to be neutered
with a 10 rd mag and a bullet button etc etc

Gunner

On 4/8/2013 11:19 PM, Steve W. wrote:

Could you machine one out of a stainless steel block?



Already been done. There are a few companies that already sell stainless
lowers.

I did one out of 416 just to see what it took. It will be the only one I
ever do as well. It machined very well but even when I thinned areas
down to reduce weight it's still pretty hefty. Does make the .308 a lot
nicer to shoot though. I have been tossing around the idea of making one
out of steel though. Thinking of areas like the sides of the mag well
for skeletonizing...

Anyone with a mid sized mill can handle the job. If you buy some guides
you can even use a good drill press!



What does that do to the weight???

On Tue, 09 Apr 2013 00:04:40 -0500, Richard
wrote:

On 4/8/2013 11:19 PM, Steve W. wrote:

Could you machine one out of a stainless steel block?



Already been done. There are a few companies that already sell stainless
lowers.

I did one out of 416 just to see what it took. It will be the only one I
ever do as well. It machined very well but even when I thinned areas
down to reduce weight it's still pretty hefty. Does make the .308 a lot
nicer to shoot though. I have been tossing around the idea of making one
out of steel though. Thinking of areas like the sides of the mag well
for skeletonizing...

Anyone with a mid sized mill can handle the job. If you buy some guides
you can even use a good drill press!



What does that do to the weight???


It would center it nicely..and by the time folks get done putting all
the lasers, launchers and other sundry bull**** on them...shrug...a
steel lower really wouldnt be noticed too much.

Gunner

On Mon, 08 Apr 2013 21:56:51 -0700, Gunner Asch
wrote:

On Tue, 09 Apr 2013 00:19:34 -0400, "Steve W."
wrote:

Gunner Asch wrote:
On Mon, 08 Apr 2013 20:02:47 -0400, "Steve W."
wrote:

Richard wrote:
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?
Current Mil spec is 7075 - T6

The original design called for either a 6 or 7 series alloy. The 6 was
cheaper and easier to work with so that was what ended up being used.
The problem is that between corrosion and thread deformation the spec
was re-written to 7075 - T6 being the "correct" alloy to use.

I have shot both and other than knowing the alloy due to the makers you
couldn't tell any real difference. 6061 is still used by a few companies
and with the design of the AR the strength in Civilian use isn't an issue.

However if you plan on needing to depend on the rifle in real combat
where you may be using it as a club, hammer or whatever, the 7075 has
the edge with regard to wear and tear.

I have used both forgings and solid billet as a starting point.
With forgings you are limited as to what you can add/subtract.
With billet you can have fun. I machined in a solid trigger guard,
milled my logo in 3D on the side, and a few other tricks.


Could you machine one out of a stainless steel block?



Already been done. There are a few companies that already sell stainless
lowers.

I did one out of 416 just to see what it took. It will be the only one I
ever do as well. It machined very well but even when I thinned areas
down to reduce weight it's still pretty hefty. Does make the .308 a lot
nicer to shoot though. I have been tossing around the idea of making one
out of steel though. Thinking of areas like the sides of the mag well
for skeletonizing...

Anyone with a mid sized mill can handle the job. If you buy some guides
you can even use a good drill press!

Id not mind having a lower someday. Though given the prices of the
upper Stuff..it would likely remain a door stop.

ARs are quasi legal here in California..but they have to be neutered
with a 10 rd mag and a bullet button etc etc

Gunner


Bullet button?

Remove 333 to reply.
Randy

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, 08 Apr 2013 21:56:51 -0700, Gunner Asch
wrote:

On Tue, 09 Apr 2013 00:19:34 -0400, "Steve W."
wrote:

Gunner Asch wrote:
On Mon, 08 Apr 2013 20:02:47 -0400, "Steve W."
wrote:

Richard wrote:
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?
Current Mil spec is 7075 - T6

The original design called for either a 6 or 7 series alloy. The 6 was
cheaper and easier to work with so that was what ended up being used.
The problem is that between corrosion and thread deformation the spec
was re-written to 7075 - T6 being the "correct" alloy to use.

I have shot both and other than knowing the alloy due to the makers you
couldn't tell any real difference. 6061 is still used by a few companies
and with the design of the AR the strength in Civilian use isn't an issue.

However if you plan on needing to depend on the rifle in real combat
where you may be using it as a club, hammer or whatever, the 7075 has
the edge with regard to wear and tear.

I have used both forgings and solid billet as a starting point.
With forgings you are limited as to what you can add/subtract.
With billet you can have fun. I machined in a solid trigger guard,
milled my logo in 3D on the side, and a few other tricks.

Could you machine one out of a stainless steel block?


Already been done. There are a few companies that already sell stainless
lowers.

I did one out of 416 just to see what it took. It will be the only one I
ever do as well. It machined very well but even when I thinned areas
down to reduce weight it's still pretty hefty. Does make the .308 a lot
nicer to shoot though. I have been tossing around the idea of making one
out of steel though. Thinking of areas like the sides of the mag well
for skeletonizing...

Anyone with a mid sized mill can handle the job. If you buy some guides
you can even use a good drill press!
Id not mind having a lower someday. Though given the prices of the
upper Stuff..it would likely remain a door stop.

ARs are quasi legal here in California..but they have to be neutered
with a 10 rd mag and a bullet button etc etc

Gunner


Bullet button?

Remove 333 to reply.
Randy

Kali semi-auto guns are supposed to have "fixed or not readily removable
magazines" So the bullet button was born.
Instead of the normal magazine release there is a small release button
that requires the tip of a bullet or similar to depress.

http://bulletbutton.com/


--
Steve W.

Richard wrote:
On 4/8/2013 11:19 PM, Steve W. wrote:
Could you machine one out of a stainless steel block?


Already been done. There are a few companies that already sell stainless
lowers.

I did one out of 416 just to see what it took. It will be the only one I
ever do as well. It machined very well but even when I thinned areas
down to reduce weight it's still pretty hefty. Does make the .308 a lot
nicer to shoot though. I have been tossing around the idea of making one
out of steel though. Thinking of areas like the sides of the mag well
for skeletonizing...

Anyone with a mid sized mill can handle the job. If you buy some guides
you can even use a good drill press!



What does that do to the weight???

Adds about 8 oz. to the bare lower compared to a "normal" lower.

--
Steve W.

Pete C. wrote:

Cydrome Leader wrote:

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.

I haven't looked recently, but that's what 0% forgings were going for
last I looked. The 30% TM ones I got for $45 in qty 5+, I think the
broached magwell is worth the $20.

One key thing is to have a lower parts kit when you start the machining
so you can test fit many of the parts as you go before you tear down
each setup. It's also helpful to have a regular factory AR for visual
sanity check reference, but you can use good pictures as well.

On the first one I did I grabbed the wrong drill and drilled the hammer
and trigger pin holes oversized. After staring at it and scratching my
head for a few minutes I re-drilled the holes a bit larger to give a
reasonable size for a bushing, grabbed a piece of brass rod, threw it in
the lathe and made a set of four bushings to bring the holes down to the
correct size. I assembled the lower with a set of anti-rotation links to
act as bushing retainers and all works perfectly, you can hardly even
see the bushings under the AR links.

nice save.

Now it has "bearings".

I was examing some sort of German rifle and pretty much any sliding parts
had actual bearings, including the ends of torsion springs- they had
little metal sleeves acting as rollers. They must have had lots of spare
time to come up with all of that.

Gunner Asch wrote:
On Tue, 09 Apr 2013 00:04:40 -0500, Richard
wrote:

On 4/8/2013 11:19 PM, Steve W. wrote:

Could you machine one out of a stainless steel block?



Already been done. There are a few companies that already sell stainless
lowers.

I did one out of 416 just to see what it took. It will be the only one I
ever do as well. It machined very well but even when I thinned areas
down to reduce weight it's still pretty hefty. Does make the .308 a lot
nicer to shoot though. I have been tossing around the idea of making one
out of steel though. Thinking of areas like the sides of the mag well
for skeletonizing...

Anyone with a mid sized mill can handle the job. If you buy some guides
you can even use a good drill press!



What does that do to the weight???


It would center it nicely..and by the time folks get done putting all
the lasers, launchers and other sundry bull**** on them...shrug...a
steel lower really wouldnt be noticed too much.

I enjoy watching clowns with laser sights at the range. They are good if
you have a spotter and are trying to tame flinch.

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.

"Ed Huntress" wrote in message
...
On Mon, 8 Apr 2013 22:04:03 -0500, "Terry Coombs"
wrote:

"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 .

Mostly as Materials Editor at _American Machinist_. I had to study
basic metallurgy for a couple of years to be able to handle the tech
papers coming in from Alcoa, U.S. Steel, and so on.

I'm hardly an expert but I know the sources. I'm very curious about
what the hobbycasting group is saying that's directly opposite. Does
it concern 7075? It's notorious for having lousy corrosion resistance.
There are some 7xxxx alloys that are much better, but not 7075.

As for copper in aluminum, it makes it extremely hot-short and prone
to porosity. That's why welding 2024 is not recommended except by some
specialized techniques. It cracks like crazy, and if it happens not to
crack today, it may in a couple of weeks, as the HAZ age-hardens.

Anyway, what is opposite?

--
Ed Humtress

Not that 7075 is corrosion-resistant , just that it can indeed be cast by
a home shop foundry . I've cast a couple of pieces with no problem - in fact
it casts nicely and machines well if you chill it in water straight out of
the mold then let it age for a couple of weeks . 6061 is very gummy
especially when freshly cast , and 356 is sweet to work with .
As far as copper in aluminum , we try to avoid it . It does indeed cause
problems , mostly in the machinibility of the items . A trace is no problem
, but get too much in the melt and you'll find that it's nearly impossible
to machine , even with carbide tooling . Some of the best bronzes are mostly
copper with small amounts of al , ampco 45 for example my bike rides on
swingarm bushings made of it ... and they too are difficult to machine .
I'm not set up to weld aluminum , and cannot speak to the weldability of any
of the alloys . When I need that knowledge I'll be looking for info !
--
Snag