Chapter 5

FCG Well and Magazine Well

AKA: Hoggin' It!

Now comes the moment you all have been waiting for, the dreaded Magazine well and (to a lesser extent) the FCG well. What makes the magazine well so dreaded? To start off with, its a milled 2-1/2" deep pocket less than an inch wide so you can't use large diameter tooling. Next it has some tiny (1/16") radii in the corners of the pocket to try and make. Lastly, you can only get to it from 2 ends, top or bottom, which isn't so bad because it cuts the depth in half. Now, doing all of this on a mini-mill? I've gone off the deep end!

In Chapter 2 I did the magwell corners and shallow pocketing operations. Now I will get down to some serious material removal and complete the FCG well and the top half of the Magazine well. So getting right down to business, I used a 3/4" long 3/8" cutter (max diameter cutter you can use in an ER-16 and about the bigest I would use on a Taig anyways) to do half of the pocketing operations. Using an end mill as stubby as possible helps keep the deflection low, the cut true, the surface finish clean, and the chatter down. With this operation I was able to run it fairly fast with plenty of flood coolant to blast the chips out of the pocket.

For programming, I first made a full width pass on the centerline of both pockets. This would allow me to use a contour operation in my CAM program, which saves time, and puts less deflection on the cutter by removing the "heart" of the pocket. I wrote those simple programs by hand and left the contouring to the CAM program.

Cutting the first centerline pocket to 0.75" deep:

(This is going to get messy)

And during the next operation - pocketing to 0.75":

(told you so!)

Thank goodness for the enclosure I built!

And all cleaned off:

Now I'm basically doing the same operation again, just deeper, and naturally, slower. It took some playing around with RPM's, feeds and speeds to get everything nice and happy, but once I figured everything out I tested out the numbers in the deep centerline cut. For the 1.5" long 3/8" end mill I used I could only go 3 IPM longitudinally and 1.5 IPM when plunging at 3400 RPM. I suppose I could drop the RPM a bit more, but the next slowest setting is 1900 and I didn't want to drop it too much. Slow and steady wins the race though, right? Once again, flood coolant helps evacuate the chips nicely.

(Notice the stream coming out of the 5/16" hole drilled through the magazine well)

With this end mill I will be able to finish out the FCG well completely, less the trigger pocket which I'll be using a 5/16" end mill for, and I can get 1.5" deep into the magwell. In another chapter, or maybe later in this one, I will flip the receiver over and get at it from the other side. I'm still up in the air about about how I want to finish out the magwell. I could a) just finish the walls with the same 3/8" end mill, then hand file the corners later on. b) use a 1/4" long end mill and really clean up the corners for a minimal amount of hand filing or c) make a vertical shaper and shape where the walls meet the 1/8" thru holes. I imagine I'll settle for a happy medium of option a and b

Centerline pocket cut to full 1.5" deep. The rest will come tomorrow (or whenever I get around to it!)

Ran another short little program to rough out the deep part of the FCG pocket. This clears out a lot of the central material to put less force on the cutter when it does the contour passes.

Had the rest of this finished last week, but didn't have a chance to post up the pictures. With the deep slotting completed, I just had to finish out the rest of the pockets. Just a simple program and some time on the mill and it was finished out. After I ran the program I just had to test fit a magazine. It didn't fit down in it so I took a 1/4" long end mill and plunged each of the corners to get a smaller radius and smaller scallops. Now the magazine just barely slides down about a 1/2" into the magazine well. This is ideal because I will be hand finishing out the magwell with a file to get the ideal no-slop fit.

There's nothing like freshly machined aluminum!

2 down, 2 to go. Finished out the trigger hole with a 5/16" end mill piloted with a 1/4" drill.

Will get the other 2 finished out soon enough, but I had to order some more end mills. Seems that the learning curve took its toll on learning how to use longer tooling and resulted in a little bit of chipping at the edges of the teeth. Will get the new mills in next week and maybe have some more progress done. After this I believe I counted 5 more operational setups in the mill and the lower will be done! Almost there!