- Joined
- Jan 17, 2013
- Messages
- 18
I made 2.5 hours of progress Thursday night not including the 45 minutes to get everything set up and 20 minutes to clean up my mess.
While not enough to finish the magwell it was sufficient to complete all but one corner, put in the rivet clearance hole, and start waste removal with drills.
I used an N drill (.302") on the rivet cut and reamed to 5/16 (.3125) so run-out (chucking reamers are long which makes them flexible and lets them follow drill holes without cutting over-size) didn't eat into the little metal I had left from the deep front lug cut. Although I intended to have that hole .010" aft of the middle of the tolerance range that didn't happen. I was tired when I calculated where to put the rivet cut, and upon review accidentally put it at the .005" forward end of its clearance (apex .052" forward of mag well front, center .104 aft not .042 and .114") thus undoing the extra .010" clearance I was trying to make for myself and putting the apex exactly where it would be with everything in the center of its tolerance range. Next time I'll review anything I draw after midnight when I'm better rested. It seems to have worked out OK - the front wall of my magazine well is intact.
Astute observers will count all eight corners which implies one 1/8 hole doesn't go all the way through.
The magazine catch slot inner surface essentially bisects the rear 1/8" hole intersecting it making almost perfect geometry to grab the drill bit. You can see the tip of my screw-machine length drill stuck in the slot from when it broke 1/4" below the top-deck surface even though I was pecking.
I raised the remnants to just shy of the surface using a hammer and 1/16" pin punch working through the magazine catch slot at an angle. Then I rotated the top 45 degrees counter clockwise with hammer and awl which sent it back down the hole. Another tap from the bottom dislodged a small piece of drill and some aluminum swarf leaving the left over loose enough to push out from the bottom with a bent paper clip.
I suspect the best approach to drilling that corner is setting the depth stop to drill with a screw machine bit to just above the magazine catch slot top edge. Then I'd switch to a 1/8" D x 1" flute length end-mill which would do a nice job cutting the inner slot face down to just below the bottom edge of the slot. Finally I'd finish drilling with my 1/8" parabolic drill. Stroking out the corners would avoid the problem, slow going on the 1/8" holes due to the flexible parabolic drill, and is probably the best idea. Cutting the magazine catch slot separate from the rest of the passenger side may also help but would mean an additional setup.
The other issue I had was with my parabolic drill. You can see that the outer rear passenger side hole is a bit over-sized at the deck surface. That's because I naively assumed it'd run like an aircraft drill (just with better swarf extraction from deep holes) and work nice at the squeal free 1500 RPM I was using for the short bit and found I was wrong. The substantial flutes mean parabolic drills are very flexible. At 1500 RPM it spun like a jump rope on entering the hole, still did that at 1000 RPM, and I had to switch to low gear and 400 RPM to make it behave.
I also don't like Ray's setups drilling the lower clamped to an angle-plate with drilling forces trying to push it through the clamps with nothing solid below the receiver. I was particularly concerned in this case because removing material from the magazine well will make it more flexible and reduce the front clamp's grip.
To avoid that I positively located the front with a piece of 1/4" drill rod through the pivot pin hole with one end atop an angle plate and put a machinist's jack under the aft end to get solid and adjustable. The 8" tall angle plate dictated using the extensions and putting it under the rear trigger guard boss which is still uncut. I started off with the front clamp tight, rear clamp loose, and receiver a hair (.015") below level based on where a drill rod in the take-down hole was. A little pressure from the jack rotates the receiver about the front clamp until the front drill rod contact with receiver and angle plate is as solid as it can get and time to zero a test indicator at the front. Then I traversed back to the rear just before the 3/4" radius transitioning to the buffer tower and lifted with the jack until the indicator was zero. Since that point (6" aft) was moving approximately 24X as far as the front of the magazine well (.25" aft) I was within .001" of level over 6". Heading left, adjusting the zero by less than .001", heading back to the buffer, and lifting back to zero got me flat within .00025" at which point I finished clamping.
That was satisfying.
While not enough to finish the magwell it was sufficient to complete all but one corner, put in the rivet clearance hole, and start waste removal with drills.
I used an N drill (.302") on the rivet cut and reamed to 5/16 (.3125) so run-out (chucking reamers are long which makes them flexible and lets them follow drill holes without cutting over-size) didn't eat into the little metal I had left from the deep front lug cut. Although I intended to have that hole .010" aft of the middle of the tolerance range that didn't happen. I was tired when I calculated where to put the rivet cut, and upon review accidentally put it at the .005" forward end of its clearance (apex .052" forward of mag well front, center .104 aft not .042 and .114") thus undoing the extra .010" clearance I was trying to make for myself and putting the apex exactly where it would be with everything in the center of its tolerance range. Next time I'll review anything I draw after midnight when I'm better rested. It seems to have worked out OK - the front wall of my magazine well is intact.
Astute observers will count all eight corners which implies one 1/8 hole doesn't go all the way through.
The magazine catch slot inner surface essentially bisects the rear 1/8" hole intersecting it making almost perfect geometry to grab the drill bit. You can see the tip of my screw-machine length drill stuck in the slot from when it broke 1/4" below the top-deck surface even though I was pecking.
I raised the remnants to just shy of the surface using a hammer and 1/16" pin punch working through the magazine catch slot at an angle. Then I rotated the top 45 degrees counter clockwise with hammer and awl which sent it back down the hole. Another tap from the bottom dislodged a small piece of drill and some aluminum swarf leaving the left over loose enough to push out from the bottom with a bent paper clip.
I suspect the best approach to drilling that corner is setting the depth stop to drill with a screw machine bit to just above the magazine catch slot top edge. Then I'd switch to a 1/8" D x 1" flute length end-mill which would do a nice job cutting the inner slot face down to just below the bottom edge of the slot. Finally I'd finish drilling with my 1/8" parabolic drill. Stroking out the corners would avoid the problem, slow going on the 1/8" holes due to the flexible parabolic drill, and is probably the best idea. Cutting the magazine catch slot separate from the rest of the passenger side may also help but would mean an additional setup.
The other issue I had was with my parabolic drill. You can see that the outer rear passenger side hole is a bit over-sized at the deck surface. That's because I naively assumed it'd run like an aircraft drill (just with better swarf extraction from deep holes) and work nice at the squeal free 1500 RPM I was using for the short bit and found I was wrong. The substantial flutes mean parabolic drills are very flexible. At 1500 RPM it spun like a jump rope on entering the hole, still did that at 1000 RPM, and I had to switch to low gear and 400 RPM to make it behave.
I also don't like Ray's setups drilling the lower clamped to an angle-plate with drilling forces trying to push it through the clamps with nothing solid below the receiver. I was particularly concerned in this case because removing material from the magazine well will make it more flexible and reduce the front clamp's grip.
To avoid that I positively located the front with a piece of 1/4" drill rod through the pivot pin hole with one end atop an angle plate and put a machinist's jack under the aft end to get solid and adjustable. The 8" tall angle plate dictated using the extensions and putting it under the rear trigger guard boss which is still uncut. I started off with the front clamp tight, rear clamp loose, and receiver a hair (.015") below level based on where a drill rod in the take-down hole was. A little pressure from the jack rotates the receiver about the front clamp until the front drill rod contact with receiver and angle plate is as solid as it can get and time to zero a test indicator at the front. Then I traversed back to the rear just before the 3/4" radius transitioning to the buffer tower and lifted with the jack until the indicator was zero. Since that point (6" aft) was moving approximately 24X as far as the front of the magazine well (.25" aft) I was within .001" of level over 6". Heading left, adjusting the zero by less than .001", heading back to the buffer, and lifting back to zero got me flat within .00025" at which point I finished clamping.
That was satisfying.