Drilling and tapping hard receivers

Tyskjohn · February 20, 2011, 09:02 PM

Worked on a 1917 Enfield receiver, that thing is HARD--tore up a HSS endmill on the first pass to cut off the "ears." Managed to tear up a carbide endmill cutting the receiver bridge to a square contour. Then heated the bridge to about 600 F; this softened it enough that it would cut with an M42 end mill and I could complete the contour work. Next the drilling-- I burned up a HSS # 3 center drill on the third hole, then a cobalt drill while opening up the fourth hole, finished the fourth hole with a solid carbide drill.
How to tap this monster? "Spot annealing" might be fine for case hardened receivers, but I did not want to chance it on "hard clear through." I dipped into my tiny supply of original "Tap-Magic", from 20-30 years ago. Tapped all four holes with the same carbon steel tap, easily, keeping the tap just barely wet. Of course, I had indexed all hole locations on my milling machine when drilling, and held the tap in a drill chuck which I turned with my fingers. Keep it wet until you get it out or it might get stuck. Not much luck with new Tap Magic.

February 20, 2011, 09:02 PM	#1
Tyskjohn Junior Member Join Date: February 20, 2011 Posts: 1	Drilling and tapping hard receivers Worked on a 1917 Enfield receiver, that thing is HARD--tore up a HSS endmill on the first pass to cut off the "ears." Managed to tear up a carbide endmill cutting the receiver bridge to a square contour. Then heated the bridge to about 600 F; this softened it enough that it would cut with an M42 end mill and I could complete the contour work. Next the drilling-- I burned up a HSS # 3 center drill on the third hole, then a cobalt drill while opening up the fourth hole, finished the fourth hole with a solid carbide drill. How to tap this monster? "Spot annealing" might be fine for case hardened receivers, but I did not want to chance it on "hard clear through." I dipped into my tiny supply of original "Tap-Magic", from 20-30 years ago. Tapped all four holes with the same carbon steel tap, easily, keeping the tap just barely wet. Of course, I had indexed all hole locations on my milling machine when drilling, and held the tap in a drill chuck which I turned with my fingers. Keep it wet until you get it out or it might get stuck. Not much luck with new Tap Magic.