The ultimate guide to finishing an 80 lower the best way

The Ultimate Guide to Finishing an 80% Lower the Best Way

How To Finish An 80 Lower

Finishing an 80 lower to turn it into a functioning AR-15 lower receiver can be a challenging yet enjoyable project. If you find yourself wanting to take on this project like many others do, you’ll quickly find there are a number of methods to finish an 80 lower. How you finish your 80 lower receiver depends a lot on the tools you have at your disposal and the type of jig you use. Questions you need to think about – do I use a drill press? What 80 lower jig will work? Can I use a router? Can I use a hand drill? Do I need or can I use a 2-axis vice? If you’ve never milled and finished your own 80% lower, you’ll likely have these and many other questions. The important thing is to follow the process and take your time.

This guide will cover finishing of an 80% lower receiver with different jigs from a couple of the biggest manufacturers. For the most part, the process is very similar but differences exist in the construction of the 80% lower jigs themselves. This means that the placement of certain jig plates will need to be added or taken away as you are drilling.

Juggernaut Tactical 80% Lower Jig

Tools Needed

  • 5/32 drill bit
  • 3/8 drill bit
  • 1/4 drill bit
  • 80% lower jig
  • Hand drill

Juggernaut Tactical 80% Lower Jig Instructions

  1. Start by placing the 80% lower into the jig.
  2. Initially you’ll want to install the four side plate screws hand tight as indicated on the jig plate.
  3. Next install the upper plate #1 and tighten until approximately 60 inch lbs.
  4. Double check that there is no movement between the 80% lower receiver and the 80% lower receiver jig.
  5. The first hole to drill is for the safety selector.
  6. Start with the 3/8″ bit and set the depth stop so it goes approximately half way through the receiver. Depth isn’t critical here as you’ll be drilling from both sides eventually.
  7. Set the spindle speed of your drill to around 400 rpm and apply lubricant before beginning the drilling process.
  8. As you drill the hole for the safety selector, periodically back the drill bit out to clear any turnings you may have produced.
  9. If at any time you detect excessive heat, slow down the entire process and apply additional lubricant.
  10. Once you’ve completed drilling the hole from one side, turn the jig over and complete the hole from the second side.
  11. You can now drill the holes for the trigger pins using the same processes outlined for the safety selector.
  12. Make sure you set the depth correctly. Since a smaller drill bit is being used, the spindle speed can be set up to 700 rpm, if applicable.
  13. Once the trigger pins are drilled, you can now turn your attention towards marking the holes which will be drilled out at a later point.
  14. With the top of the jig turned upright, lightly apply cutting lubricate over the top plate holes.
  15. Drill down through each hole approximately an 1/8″. Depth is not important here as you are only trying to make slight marks so you can remove the top plate and finish the process.
  16. Once you have marked all the holes, remove the four screws holding down the top plate. You should have clear indentations drilled for all the holes.
  17. Before proceeding to the next step, you need to set the depth stop guide on your drill. The final depth of the lower shelf is 1.25 inches. Because of this you want to start a little shallow at a depth of 1.2 inches.
  18. Double check the depth stop before you start drilling.
  19. As before, you will want to keep a light coating of oil on the drill bit. Keeping the drill bit cool not only aides in service life but also helps to increase cutting speed.
  20. Throughout the process do not forget to reapply cutting lube and raise the drill bit back out to clear any turnings you have produced.
  21. With all the holes for the lower shelf drilled, it’s time to start working on the six holes for the upper shelf.
  22. Reset the drill depth stop guide to .61 inches for this process.
  23. Remove the rear screw from the jig so you do not drill through it in the next process.
  24. As with before, drill the holes for the upper shelf while keeping the drill bit cover in a light coat of oil.
  25. With all the holes drilled out for both the lower and the upper shelves, switch back to the 3/8″ drill bit.
  26. Reinstall the screw in the rear of the jig to keep things steady while drilling.
  27. At this point, you are going to drill out all the inside holes that you previously drilled. You will likely notice chatter or shaking while you are drilling. This is the last step you can complete without a milling vice or jig. The key thing to remember here is to take your time and reapply cutting lube often. It’s also a good idea to periodically check the depth stop to make sure you are not over drilling your receiver.
  28. Secure your lower receiver and the jig into a two-axis vice.
  29. Install a 3/8″ end mill bit into your drill press. You’ll want to make sure that the cutting depth is deep enough that the end mill bit runs along the guide and doesn’t cut into the guide itself.
  30. Take your time as you’ll be making shallow passes of up to 1/8″ each pass.
  31. As you drill, periodically apply lubricant.
  32. If you start to notice chips collecting inside the guide, stop drilling and blow them out with compressed air.
  33. At this point you should focus on just doing a rough cut in inside the jig. Removing most of the material, you can go back and finish cleaning up later on. Make sure that you only cut to 1.2 to 1.23 inches in depth to insure you don’t cut out the bottom of the receiver. You can use the smaller holes you drilled earlier as a rough idea of how much more material needs to be removed.
  34. Once you’ve finished the first pass, you’ll need to lower the end mill bit approximately 1/16″ to begin the process over again.
  35. For the final pass, set the stop guide for the final 1.24 inches.
  36. Make a shallow pass and try to avoid vibration of the bit as much as possible.
  37. Before beginning any cuts for the top shelf, you’ll want to remove the screw that holds the jig together.
  38. Like in previous steps, you’ll want to use oil to keep the bit lubricated.
  39. Due to clearance issues, you may need to use a long reach end mill bit.
  40. In this step, you’ll cut to a final depth of .61 inches.
  41. Once the upper shelf is milled, with a 3/8″ end mill bit turn your attention to drilling the trigger hole.
  42. With the holes drilled, you can now go back with a full finish end mill bit and clean up any machining on the receiver. While this is not necessary, it will make the receiver look a little more finished.

Easy Jig 80% Lower Jig

Before beginning, you want to make sure you have all the Easy Jig parts including the right jig wall, left jig wall, pocket drilling template, template spacer, trigger pocket template, rear shelf pocket template, router base support plate, four 2.5″ long screws, and 1.75″ screws.¬†After you verify that you have all the components ready for your Easy Jig, you’ll need to make sure you have all the appropriate tools. If you have the optional Easy Jig tool kit includes a 1/4″ by 4″ long, three flute carbine end mill bit. It also includes a 3/8″ drill stop, 3/8″ drill bit, 5/32″ drill bit, and a 19/64″ drill bit.

Tools Needed

  • 80% Arms Easy Jig
  • Router
  • Hand drill or drill press
  • Lubricating oil
  • Allen wrenches
  • Drill press vice

80% Arms Easy Jig Instructions

  1. The first step when starting the build process is to assemble the Easy Jig. Take the left and right wall plates and place your 80% lower between them. Take the four 2.5″ jig wall screws and thread them into the holes for the takedown and pivot pins as well as into the bottom of the jig. Tighten down all four screws but do not over-tighten them. Once you’ve assembled the side plates to the lower, attach the drilling template to the top of the side plates by threading the four screws through the top of it. If you have trouble tightening the top screws, make sure you haven’t over-tightened the side plate screws. It may be necessary to loosen the side plate screws until you thread the top plate screws.
  2. Secure the Easy Jig into a vice.
  3. The next step is to start finishing your lower. On the drilling template, it’s divided into two sections – one part labeled rear and one part is labeled main. The two depths you are going to be drilling to are 1.249″ for the main pocket and .63″ for the rear shelf.
  4. Tape off the rear holes until we are ready to drill the rear shelf. This will help remind you to not drill that part of the lower until you are ready.
  5. Set your 3/8″ drill bit to 1.249″ depth by taking the trigger pocket template and insert the 3/8″ drill bit into the depth gauge labeled main.
  6. Once the drill bit has been inserted into the bottom of the pocket, take your drill stop collar and attach it firmly to the drill bit. The drill stop collar will prevent you from drilling too far into your lower.
  7. Start drilling the holes in the section that is labeled main. Before you drill out the holes in the template labeled rear, remove the screw immediately below that area so you don’t accidentally drill through the screw.
  8. Occasionally check the drill bit stop collar to make sure it hasn’t slipped during drilling. This can be done by checking the depth gauge against your drill bit.
  9. You will likely need to use force if drilling using a hand drill. Make sure to lift up on your drill to clear out all the shavings.
  10. Apply WD-40 or other lubricant as you are drilling to help keep the bit cool.
  11. If the built in clearing channel on the Easy Jig gets full or backed up, use a vacuum cleaner or air compressor to remove the chips.
  12. Once all holes have been drilled out on the main template, move on to drill the holes in the section labeled rear.
  13. These holes are drilled to a shorter depth of .63″.
  14. Set the depth by placing the bit into the depth gauge labeled rear.
  15. Readjust the stop collar to prevent over drilling.
  16. Begin drilling the rear holes being mindful of keeping the stop collar at the right depth.
  17. Once the rear holes are drilled, we are ready to move to the next step.
  18. Remove the top drilling template and reinsert the rear jig wall screw that was removed in an earlier step.
  19. Install the template spacer, trigger pocket template, and router base plate.
  20. Place the router base plate on top with the recessed screw holes facing up.
  21. Thread the screws through the router base plate into the side plates.
  22. Place the assembled jig back into the vice.
  23. Install the 1/4″ drill bit into your router.
  24. Adjust the depth using the trigger pocket plate and set the depth to the 1st hash mark.
  25. With the router off, set the bit on the router into the first 3/8″ hole.
  26. With the end mill bit in the center of the hole, turn the router on while securely holding it with both hands.
  27. In a clockwise motion, make arc like passes with a light cut. The goal is to join the adjacent holes.
  28. Repeat this process until all the holes are completely joined together. It’s essential to not touch the sides of the jig with the router otherwise you may damage the jig. Make sure to move the router slow and steady. It’s important to maintain steadiness so that your end mill bit doesn’t engage to much material. If the router is starting to jump up, you are taking too deep of a cut or you are going too fast.
  29. Once your first pass is complete you will need to adjust your end mill bit by 1/3 to 1/2 of a hash mark for each pass. It’s best to take it slow so don’t exceed more than 1/2 of a hash mark for each pass.
  30. To make the finishing pass, start in the center and make multiple clockwise passes that follow the contour of the jig until the end mill touches the template in a spiral fashion. Only the shank of the end mill should be touching the jig during this process.
  31. Once you’ve cleaned up the sides of the lower, move the router to the center of the lower and turn the router off. You are now 75% done with the milling process.
  32. We will now mill out the rear shelf of the lower. To do this you are going to need to use the rear shelf pocket template. The rear shelf pocket template can be identified by the depth gauge named main.
  33. Like previously when drilling the holes in the rear shelf, remove the screw from the jig side plate so you don’t mill through it.
  34. Take the router base plate off the jig and then take the trigger pocket template off of the spacer.
  35. Replace the trigger pocket template with the rear shelf pocket template.
  36. Reinstall the router base plate on top of the rear shelf pocket template. The rear pocket template should be oriented with the larger slot being closer to the buffer tube area of the lower.
  37. Reassemble the screws the same way you did in the previous step.
  38. Using the depth gauge labeled rear, set your end mill bit to the first hash mark.
  39. With the end mill fastened to the router and the depth set to the first hash mark, place the bit in the center of one of the rear shelf holes you previously drilled.
  40. Make clockwise passes until you connect the two drilled holes.
  41. Once the cutting portion of the end mill is lower than the top jig plate, you can begin cleaning the sides up by running the bit along the sides of the jig.
  42. Continue making shallow passes with a depth ranging from 1/3 to 1/2 of a hash mark per pass.
  43. Once you have completed the rear shelf, remove the router base plate, spacer, and the template.
  44. We are now ready to drill the trigger hole. Install the trigger template with the two 3/4″ screws to hold it in place.
  45. Put the 19/64″ drill bit into your drill press or hand drill.
  46. Drill through the bottom of your lower using the template.
  47. You can now install the rear shelf template and router base plate over the middle of the lower.
  48. Insert the end mill through the hole you just drilled and very carefully move the router around to mill out the trigger hole in the shape of the trigger hole template.
  49. The next part you will need the 5/16″ drill bit.
  50. Turn the jig and lower over to expose the 5/16″ holes in the side of the jig.
  51. Drill through both holes.
  52. Once both of the holes are drilled, switch to your 3/8″ drill bit to drill the safety selector hole.
  53. Drill through the hole indicated.
  54. Once you have drilled the safety selector hole, your lower is now 100% complete.
  55. Remove the lower from the jig and clean up any of the chips and burs that may be left.

One thought on “The Ultimate Guide to Finishing an 80% Lower the Best Way

  1. Great step by step. Like having someone in the room with you guiding you Thank you for this great information. 5 stars for sure.

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