My first polymer 80 AR

[Mobuck]

I've been watching the market and decided to give the polymer lowers a try. I have a couple of "PlumCrazy" (sometimes referred to as 'carbon fiber' which I doubt)lowers that I bought way back in 2010 and have used them enough to see that they are adequate for most uses.
Anyhoo, I cleaned up my drill press and remounted the X/Y vise and had at it today. I'd watched the utoobers and company videos so not any big surprises. It took longer than I thought it should but I was being real careful to not hurry and color outside the lines.
I ended up with a decent finished lower with one little oops. Apparently, it's very easy to nibble through the paper thin area between the fire control cut and the mag catch cutout. This must be a common error since it has an almost universal 'fix'. Shove a bit of backing into the mag catch cutout and mix up some JB Weld then smear a thin layer where the cut is a bit deep. A few hours later file or Dremel out the extra JB and get on with installing the parts. Next time, I'll just shy away from the line in that spot so I don't have a repeat.
Hammer and trigger pin holes lined up well and the depth of cut in the FCG pocket came out good. As a bit of advice, I only took 1/4-3/8" per cut with the end mill. Any deeper and I was getting chatter and run out. I think it took 5 full passes with the end mill plus the final 'shave' pass to even out the FCG pocket bottom.
Had a few issues with the el-cheapo X/Y vise that may smooth out with use. Kind of wishing I'd spent $80 instead of $40.

 

[RSIno1]

My first one was from what they refer to as a 10% lower - only the mag well was finished. Took me a lot of time on the Bridgeport. Bought an 80% Arms genII Jig and have done 5 AR15s an AR9mm and 2 AR10s so far. I found a pack of 10 80% lowers for cheap a few years ago. I figure if .gov (CA makes you register them) comes for the finished ones I'll give them the empty lowers and just make some more.

 

[Mobuck]

Sounds like a solid plan. When I started down this path, I was looking for something to occupy my time. Then all sorts of 'stuff' happened and my 'extra' time went away for several months. Now that it's hot as an oven in the pole barn where my drill press is set up, I have some time before harvest prep begins.
I was able to turn out a decent looking product on the first attempt and learned a couple of important details so I call it a win. I have no idea just how these things will hold up but also don't intend to use them as the main component of a spear, club, or prybar which the military considers aluminum suitable for.

 

[Dave P.]

Mobuck
You probably already know this but some drill press chucks if held on with
a taper shank do not like side loads when being used as a mill.
They have and will come off at the wrong time.
Dave

 

[krw]

I have expected for the last several years that Glock would jump in on the polymer lowers. All the stress and work goes on in the upper. If Glock would make a lower I would sure give it a try!!

 

[wheelgun1958]

I have expected for the last several years that Glock would jump in on the polymer lowers. All the stress and work goes on in the upper. If Glock would make a lower I would sure give it a try!!

https://www.glockstore.com/SS80-M-Model

 

[Mobuck]

"If Glock would make a lower I would sure give it a try!!"
Several internet sellers offering GLOCK 80% 'lowers'. I think the completion is even easier than an AR lower but I'm fully stocked on handguns and for a while, I could buy Ruger or Taurus complete 9mm for the price of a GLOCK slide and guts kit.
I fixed the slight OOPS and ran it back through the end mill stage taking a bit less off that area. Lower is assembled and fully functional although I may stock up on the anti-rotation/anti-walk trigger/hammer pin sets. That may be the weak link area on these. If there's any shift/flex/wear on those pinholes, it could lead to sear contact issues. Anti-walk pins with the external solid bars on either side will support the pins better. I've used those as a safety factor on a couple of aluminum lowers in which I had low pull weight triggers and sort like the 'look' in addition to the support.