Jigging up for an 80% lower with benchtop tools

pastera

pastera

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Picked up an 80% in the last group buy just to see how hard it would be to finish.

Will be machining on a micro mill, as in 3/8 max endmill and 1/3 hp, so setup will be tight with a max Z of 8.5"
Step 1: make some vice plates to hold the lower
One down with the second blanked out.

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This will be great to see. I've been thinking of doing an 80% lower. Pictures of the mill?
 
Nice job.
I see that you have one of the newer 80% blanks with the take down pocket already done. I really like them, they are much quicker/easier to complete since they can be done in one set up.
 
Will put up pictures of the mill with the lower for scale.

Rear shelf doesn't seem to be complete as an upper won't mount. As far as legality, no clue. Don't see a problem because if you can machine the fire control pocket you can cut the rear shelf.
 
Yeah. Legally that 80% blank you have is a firearm.

http://www.ammoland.com/2014/11/atf-answers-questions-on-80-receiver-blanks/#ixzz3IijwdmXZ

3. Are “80%” or “unfinished” receivers illegal?
Receiver blanks that do not meet the definition of a “firearm” are not subject to regulation under the GCA. The ATF has long held that items such as receiver blanks, “castings” or “machined bodies” in which the fire-control cavity area is completely solid and un-machined have not reached the “stage of manufacture” which would result in the classification of a firearm per the GCA.
Click to expand...
 
well, technically the fire control pocket is not milled, and the rear of the receiver which he has that's milled--that's not part of the fire control group. the picture in the ammoland link which identifies the lower as a firearm has a cut which extends from the rear takedown pin area into the fire control group.

he does not, his fire control pocket needs to be milled 100%.

OP, i wouldn't worry about it.

mill that shit. post pics.
 
Gillham said:
Weird - that 80 has the rear shelf completely or partially milled out already? Is that legal?

All my 80's have the rear takedown drilled, but the pocket isn't started. I forget what the ATF deems at "80%"
Click to expand...

Most of the newer 80%ers now have the take down pocket done.

As far as the ATF is concerned there is no such thing as an 80% receiver or any other percentage for that matter, it's either a receiver or it isn't. The 80% term was coined by home builders several years ago.
The mfg sends a sample to the ATF and they determine whether or not it is complete enough to be classified as a receiver.
 
The only thing the machined area does is give an easy point of reference. Nothing I can't pick up from the takedown hole and buffer surface.
If the ATF has an issue, I'll return it for one without the pocket.
 
That extra bit being machined out helps a lot for guys using drills and routers to finishes these. Getting in close to the buffer tube area can be a pain. If you have a full size mill then no f's are given.
 
Gator9329 said:
That extra bit being machined out helps a lot for guys using drills and routers to finishes these. Getting in close to the buffer tube area can be a pain. If you have a full size mill then no f's are given.
Click to expand...
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Not a full size - more like Irish on a cold day.
 
By the looks of it you have already looked into what order to machine lowers on that machines. maybe you would think about drilling the side holes before milling out the pockets.
member 7.62x39 has a great website that offers all kinds of info on doing these on your machine.
gunco.net
 
Will be drilling for the fire controls before milling the pocket.

Finishing up the 10° angle on the vice plate needed to clear the flare on the mag well. Forgot to take a picture of the crazy setup on the bandsaw to rough out this cut.
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Clamped and indicated - ready to cut the second vice block.

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I have a feeling that the blocks will take more work than the lower.
 
Looking good!

p.s. I wasn't shitting on the OP because his 80 had part of the lower pre-milled. I just wanted to start a conversation to see what everyone else thought. I'd much rather have an 80 with a pocket started for me. Onus is on the seller, not me - unless they start going around trying to collect them.
 
I've got thicker skin than that.
Not worried about the feds at all - even if they show up to collect.
If I get off my back side and cnc my mill, I should be able to start at 0% between the micro-mill and mini-lathe.
Some guys here could probably do a zero percent by just turning knobs - Boris could probably do it with empty beer cans, a file, hand drill, and a case of cheap vodka.
 
pastera said:
... If I get off my back side and cnc my mill, I should be able to start at 0% between the micro-mill and mini-lathe.
Some guys here could probably do a zero percent by just turning knobs...
Click to expand...

I did a few "0%" ones back in the days when "80%" lowers were still rather expensive (yeah, just turned them dials - and could have used the vodka too [wink] ).

Now that "80%" lowers can be had for ~ $50, doing a "0%" is just plain torture.

If you decide you need that sort of torment in your life, I do have the tooling to complete a "0%" available.
 
For me, it would be a educational experience. My only machining instruction was making a pen holder in junior high, so I am learning as I go. Last project was a muzzle thread protector to learn blind, internal single point threading - felt great to pull it out of the chuck and spin like silk onto a barrel.
 
atilla said:
well, technically the fire control pocket is not milled, and the rear of the receiver which he has that's milled--that's not part of the fire control group. the picture in the ammoland link which identifies the lower as a firearm has a cut which extends from the rear takedown pin area into the fire control group.

he does not, his fire control pocket needs to be milled 100%.

OP, i wouldn't worry about it.

mill that shit. post pics.
Click to expand...

What he said. I see those slung by 10 different folks at gun shows all the time. See them sold online too.
 
pastera said:
For me, it would be a educational experience. My only machining instruction was making a pen holder in junior high, so I am learning as I go. Last project was a muzzle thread protector to learn blind, internal single point threading - felt great to pull it out of the chuck and spin like silk onto a barrel.
Click to expand...


That's what I need to look into. Single point threading. I've got a '47 South Bend lathe with the quick change gearbox for threading. I need to grind some 60° cutting tools for external threads.

Do you run 1/4" tooling on the mini lathe?

BTW, nice job so far.
 
5/16 normally but I can use 1/4 by adjusting a tool holder

I've ground both internal and external threading tools - easier to just buy a triangular insert tool to start with.
 
pastera said:
5/16 normally but I can use 1/4 by adjusting a tool holder

I've ground both internal and external threading tools - easier to just buy a triangular insert tool to start with.
Click to expand...


I hear ya. I've been grinding all my tooling at work (carbide). I do need to invest in a quick change tool post. Once I do that I'll pick up some threading inserts. I'm running a lantern tool post currently. Holds 1/4" tooling, but I can run 3/8" if I only use the lantern and shim it to just below center.
 
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Setting up to drill - located from both buffer face and front takedown and I have a 0.020 discrepancy on the drawing it was using (generic 80%).
I need to sit down with a full drawing and figure out what to use as a datum point.

Getting from the buffer face to front pin takes a lot of turns at only 0.050/turn.
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