Plunge cutting an 80% lower?

Collector98 · Mar 30, 2018

Hey everyone! I have been looking into completing an 80% AR lower for some time now, but have kept away from it due to only having a drill press and some other basic tools. Recently I found a video online of a guy using a "plunge milling" method and I thought that it might be a good way to complete an 80% using my limited resources. would this be a viable method? I know they have drill press jigs out there, but I am trying to have a cleaner looking cut-out due to the fact that I may turn it into a repro lower with all of the expensive engraving. I've done some research and it seems like I would need a center-cutting end mill for this task, but I am inexperienced when it comes to milling. I look forward to hearing from everyone. Thanks in advance!

Plunge milling video
https://www.youtube.com/watch?v=SSY-0hrWlho

RwWilly · Mar 30, 2018

Its all about removing material. Alot of ways to do it. Drill it out is quick and efficient. Then clean it up with an end mill bit. Double check your parallel travel, ensure the work doesn't walk when traversed left to right or fore and aft.
Experiment with the first one then do the second one "perfectly"! Good luck

Collector98 · Mar 30, 2018

Since a drill bit is rounded and I have to go to a final depth of 1.25", what depth would you recommend I drill to before making the bottom flat with an end mill? Also, if there any specific type of end mill you would recommend? I'm thinking about going with a 1/4" 4 flute. Thoughts?

K-43 · Apr 1, 2018

I used a drill bit to get close and the bulk out. Then I switched to and end mill and worked in small layers. Works fine in a drill press.

Ranchero50 · Apr 1, 2018

Ditto. A center cutting 4 flute carbide end mill with 1.25" fluke length is a little tricky to find and not very rigid. I run 3/4" long fluke ones but the shank rubs at full depth. I also use a CNC mill. On a drill press I'd drill a series of 1/4" deep 1/4" diameter pilot holes as guides for the end mill. Bunch of different ways to do it. A block clamped to the table base could act as a guide for the clean up cuts. Not purdy but...

For reference when I mill mine out on the mill I do the profile in small increments of depth because the 1/4" mill is a little skinny to be doing full flute depth wall cuts without a really good work holding and control system.

kalister1 · Apr 1, 2018

I use 2 flute end mills on AL.

RwWilly · Apr 1, 2018

I drilled to the proper depth then used end mill until the point marks were gone. Don't overthink it. The FC pins are critical. Not much else is .001 critical.

K-43 · Apr 2, 2018

Here's what I actually used in my drill press.
https://www.amazon.com/gp/product/B014PES6FW/ref=oh_aui_search_detailpage?ie=UTF8&psc=1
They're stiff enough and just long enough. Like Willy said, it's not that critical, just deep enough for the trigger to fully rock.
A cross slide vise is nice so the end mill will cut a nice clean bottom and clean up the sides.
I got my depth measurement from a commercial lower.

Collector98 · Apr 3, 2018

Thanks for all the feedback guys! I really appreciate it!

K-43 · Apr 5, 2018

Post some build pics when you take the plunge!
Yeah, that's lame, but this is MDS and no one can slap me.

Collector98 · Apr 5, 2018

K-43 said:
Post some build pics when you take the plunge!
Yeah, that's lame, but this is MDS and no one can slap me.

That's a terrible pun... I like it... :lol:

Plunge cutting an 80% lower?

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