1911 sear and hammer holes

Natrona · Sep 21, 2022

Gentleman: I have searched a lot of threads on the site but have not found an answer to my specific problem. I would appreciate your expert input.

Building a 80% 1911 (416 SS Frame) and have some questions on drilling the sear and hammer pin holes. I will be using a mill with a DRO and indexing off the cross pin hole and using dimensions to the sear and hammer pins per Kuhnhausen 3rd addition.

Questions:
1. I will use a center drill to locate pin centers but should I drill through with small pilot (1/16") and then follow with full size. Or just one shot full size and final ream.
2. Cobalt or Carbide drills (4 mm for hammer and #35 drill for sear)?
3. Final ream size for holes?
Thank you in advance for your help.
Nathan

a2x4bbl · Sep 22, 2022

Center drill , drill undersize and ream to size .

a2x4bbl · Sep 23, 2022

Natrona said:
Gentleman: I have searched a lot of threads on the site but have not found an answer to my specific problem. I would appreciate your expert input.

Building a 80% 1911 (416 SS Frame) and have some questions on drilling the sear and hammer pin holes. I will be using a mill with a DRO and indexing off the cross pin hole and using dimensions to the sear and hammer pins per Kuhnhausen 3rd addition.

Questions:
1. I will use a center drill to locate pin centers but should I drill through with small pilot (1/16") and then follow with full size. Or just one shot full size and final ream.
2. Cobalt or Carbide drills (4 mm for hammer and #35 drill for sear)?
3. Final ream size for holes?
Thank you in advance for your help.
Nathan

Please post pictures as you progress .

Telekinesis · Sep 23, 2022

I haven’t built an 80% 1911, but in machining it’s usually best to take small bites and work slowly. If you’re working at a shop and concerned about throughput and how many you can produce in a certain amount of time, that’s a different story. But for hobby stuff, I’ve found I have more issues when I try to work fast than when I take extra time.

For pins, I agree with doing a center drill, drill undersize, and then ream to final dimension. Drills usually result in slightly oblong holes, so if you’re fitting something like a pin you’ll want to ream and make sure the hole is perfectly round.

And thank you for using a mill for this. I cringe every time I see someone try to do something like this with a hand drill.

1911 sear and hammer holes

Natrona

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a2x4bbl

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a2x4bbl

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Telekinesis

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