Folks, Polymer80 is making some solid 80% frames that you can easily machine into a lower receiver that accepts Glock parts. The design of the frame and jig are elegantly simple and the quality of the end product is really up to you. The great news is that you don’t need to be a machinist to do the work. You just need to be patient, follow instructions and pay attention to details.
If you haven’t done so yet, be sure to check out Polymer80’s own How To page. I definitely recommend watching the videos and reading the relevant PDF before you begin.
In my last post, I linked to a number of resources you can use to guide you through your build. My aim is to give you a bunch of tips that can help you turn out a quality receiver. Let’s hit the four categories of things you will need to do.
Drill Six Short Holes As Labeled On The Jig
If you are concerned that this will take a ton of work, Polymer80 has designed a frame (what will ultimately become your pistol’s lower receiver). Folks, you drill six holes – the jig is marked with the exact spot and which size drill bit they supply that you should use.
- Stand the clamp on its side and secure it in a vise. It was not designed to be drilled laying on its side.
- You want the jig to be held firmly at its bottom by the vise but do not crush/deform the plastic.
- Using a drill with level indicators can greatly aid you in making a hole at right angles to the receiver.
- Do not drill the holes straight through. Because the frame is relatively thin, it is forgiving if you drill a short hole slight off square, meaning not perpendicular. If you go straight through then you are way more likely to be way off, ruin the geometry and have just ruined the receiver, So, drill three holes on each side, six holes in total, being careful to line them up as best you can.
- Take the time to read the jig markings – the M3 holes are for the pins that hold the blocks in place. The larger M4 bit is for the trigger pin.
- After drilling, blow out your frame to get all the little pieces of plastic debris out. A common problem guys run into is having a small piece of plastic down in the slide stop spring channel that the recoil spring can hang up on. So, blow it out. I use compressed air in my shop but do what you can even if it means blowing with your mouth and visually inspecting the frame to make sure all the plastic scraps from drilling are gone.
- Use a deburring tool or razor to carefully remove any waste plastic sticking out from either side of the plastic surface that you drill.
Remove the Tabs From The Top Of The Frame
This seems to freak people out because they think they are going to need a milling machine. You definitely do not need a milling machine – you can use a Dremel or file to remove the tabs. The trick here is to remove the tabs and have the end result look decent and not like a hack with a file went crazy and turned out something fugly.
- The first step is to get rid of as much of the tabs as you can with nail nippers. The idea is simple, snip off a bunch of the material so when you either Dremel or file the remainder down, you have less to deal with. On my Glock 34 build,I used an old pair of nail nippers (in the photo above) that belonged to my dad – my way of remembering him. On the second one, I took a cheap set of nippers and ground the head down so they would cut the tabs off even closer to flush. Either way works.
- Leave the jig on if you want to play it safe. When you see red filings or dust from sanding, you know you are going to deep and need to stop,
- You can either Dremel or file the balance down but when you get down near the surface start using a sanding block. Just take a piece of wood, wrap a strip of sand paper on it and then sand the receiver using even pressure. Start with 100-120 grit sandpaper and then go to 220, 440, and then 800. If you want to go higher, go right ahead but at some point your plastic is as smooth as it needs to be.
- I use the little rubberized abrasive Dremel bits to smooth things out. You then apply a drop of oil and you will never know the tabs were there.
Clear Out the Barrel Channel
Again, the dreaded need for a milling machine seems to exist and again, you don’t need one. It is really important you do a nice clean job with a smooth finish or you will have seemingly random jams as the operating spring catches on some part of the frame that is still in the way.
- You want to only remove the designated slot they show in the instructions plus what needs to be removed is marked in the casting. Like I said, they put some thought into this.
- DO NOT TRY TO REMOVE IT ALL AT ONCE!! You remove the material in sections.
- If you decide to use their supplied end mill and put the frame in your drill press, do not treat the end mill but like a drill bit. An end mill bit requires a very rigid machine and that the operator has carefully and firmly secured the work piece. In short, you can’t plunge the end mill into the plastic with your hobby drill press without considerable vibration. The trick come down with the drill press (if you have one) and cut off a little crescent at a time. If you have mill, just ignore me – you know what to do I bet.
- Some guys will use regular drill bits and drill a series of holes in the area that needs to be removed.
- Unless you are a machinist and know what you are doing, don’t try to mill or drill material right up to the line where they say to stop at. Instead, remove material just shy of the line and then use a sandpaper to do the rest. I wrapped 100 grit sand paper around a dowel to rough in the shape and then went to 240 grit to finish up. You really do not need to go beyond that unless you want, The goal is to have a smooth surface that the barrel and spring will not catch on during operation.
- We have a toolkit now that makes cleaning the barrel channel out way, way easier. Click here to read more.
Polish Metal Surfaces
When people make parts they usually get them close enough and call it even. This means there are small tooling marks, grooves, bumps and rough areas left in general. When you look at a firearm made by a high-end shop, you will notice that the surfaces are incredibly smooth – sometimes polished to a mirror-like surface.
Have you ever bought a firearm and at first it was really rough and over time in “wore in” or maybe somebody said “broke in”? What is happening is that the rough spots are smoothing out with wear. We identify the surfaces and do the same thing very easily.
- With polishing the goal is always to remove as little material as possible using polishing bits, stones or really fine 1000+ grit sandpaper.
- Polish the hardened locking block rail system bearing in mind how it contacts the slide. You just need to polish the parts that engage the rail and not everything.
- Same goes with the rear rail module that is just stamped stainless steel
- Look at the trigger and polish all surfaces that rub against each other – the connector, trigger bar, etc.
- When you are done, lightly grease these surfaces (I like SuperLube) and then cycle the action by hand a few hundred times and the same goes for squeezing the trigger. You will find that the action will smooth out even further … unless you do an awesome job polishing and everything is already mirror smooth.
I hope this helps you out. My two Polymer80 built pistols are the smoothest cycling pistols I own now.
6/20/2019 Update: The Glock 34-style pistol is now my favorite. It is a tack driver and I plan to replace the trigger at some point this summer or at least go with some reduced power springs to lighten the pull.
Note, I have to buy all of my parts – nothing here was paid for by sponsors, etc. I do make a small amount if you click on an ad and buy something but that is it. You’re getting my real opinion on stuff.
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