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Finishing an 80 Lower Receiver with a Router

So, you’ve decided to pull the trigger on building an 80% lower receiver! There are some ways to go about it – some good, some not so good. Folks try to get around using the right tools, but this usually results in a poor-quality receiver that’s unreliable, even dangerous. If you want a proper AR-15, you gotta do it right. We’re going to provide some tips and tricks for finishing an 80% lower receiver with a router.


Picking the Right Router for Your 80% Lower

The 80% lower jig allows you to finish an 80% lower receiver by using an end mill bit and a handheld router. Your 80% jig helps to guide the router along with guide pins and side plates, allowing you to machine the fire control area. This, in turn, allows you to install a lower parts kit and – voila! You’ve got a functional firearm by the ATF’s definition.


But to the job done, you need a good handheld router. Obviously, we’re recommending our personal favorite and our customers’ favorite: The Porter Cable Handheld Laminate Router, otherwise called the Porter Cable 6430 router. This tough, precise little guy is perfect for machining 80% lowers.


The Porter Cable router was practically designed for machining aluminum: It operates at 31,000 RPM using a 4.5-amp motor – just enough cutting speed to power through, but slow enough to remain stable and predictable.


The cast aluminum base ensures your router will never scratch or mar up the finish on your lower, too. Locking clips allow for quick motor release and depth adjustment – exactly what you need to swap bits and depths while you machine that fire control group.


Tips for Finishing an 80% Lower with a Router

#1: Secure your 80% jig to your tabletop or workspace. Most jigs are heavy enough to remain stable, but you will be manipulating a high-torque power tool while attempting a precise machine job. You do not want your 80% jig to move at all while machining. Even a slight mishap can result in your lower parts kit not fitting.


#2: Measure twice, machine once. Most 80% jigs have drill depth and machining depth guides, and you should double-check you’re at the right depth before making any holes or passes with your end mill bit.


#3: Do not attempt to “jump” milling depths. Most 80% jigs will provide depth guides so you can make multiple passes with your end mill bit, before you reach the final, correct depth. Never attempt to mill more than what is recommended. Those layered passes reduce tool wear and they ensure your router can spin at the appropriate speed.


Jumping milling depths will wear down your end mill bit quickly and it could create rough cuts and improper machining depths.

#4: Buy a lot of spray lubricant. While you’re milling and drilling, your power tools are generating a ton of friction and heat. This can stress tools and cause poor drilling and milling results. You should keep your 80% lower’s surfaces lubricated while you’re working.


#5: Clean as you go. Most 80% jigs have shop vac attachments, and even if they don’t, you should never skip on cleaning up your aluminum waste. Those fragments can get spun up or captured by your drill or router, causing damage or ruining your machining surfaces.



DISCLAIMER: If you are new to the world of DIY AR-15 building, you likely have a lot of questions and rightfully so. It’s an area that has a lot of questions that, without the correct answers, could have some serious implications. We are by no means providing this content on our website to serve as legal advice or legal counsel. We encourage each and every builder to perform their own research around their respective State laws as well as educating themselves on the Federal laws. When performing your own research, please be sure that you are getting your information from a reliable source.

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