No Plunge Cut?

[mineralman55]

I've been watching a number of AR machining videos and when it comes to machining the fire control pocket, it is always drill a matrix of holes first, then sort of "connect the dots", then mill out and clean up. Why doesn't anyone recommend using center-cut mill with a ramping plunge cut? It would seem to me that technique would save a lot of time.

[Toolndie7]

I think most of those videos are geared towards the drill press guys using a jig and a sketchy mill setup,   but I havent watched any videos?

[shibiwan]

I think most of those videos are geared towards the drill press guys using a jig and a sketchy mill setup,   but I havent watched any videos?

 

+1 on this. 

 

I believe most homebrew builders finishing up an 80% upper are using a regular knee mill (like a Bridgeport, at best, or a cheap Harbor Freight one, at the worst). It's hard to control these during a ramped plunge, and especially with aluminum, the flutes of the endmill will clog up.

 

The other thought is that most of these guys end up doing a full depth cut and doing it one pass, hence the need to drill-rough in order to  (again) prevent the endmill from clogging up.

 

In a CNC environment with proper coolant/cutting fluid, the pocket can be easily machined with a z-ramp contour cut, or multiple profile passes with proper controlled ramping. The coolant and the multiple pass cutting will prevent the endmill from loading up with aluminum.

Edited June 10, 2014 by shibiwan

[mineralman55]

I watched a youtube video by usmcdoc14 where he used a Sieg X2 minimill and plunge-cut the fire control pocket with a 4-flute center cut endmill. The key is small cuts and feeds which didn't seem to strain that machine, so, it can be done. Patience is the watchword. I'm beginning to think the drill multiple hole approach is as Toolndie7 said, mostly for the guys with the drill presses. The whole 80% process looks like fun.