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Author Topic: Drill Depth needed  (Read 2354 times)

Offline Long Ears

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Drill Depth needed
« on: March 11, 2017, 03:56:46 AM »
I need to install a peep sight on a Colrain 15/16 straight barrel in 50cal. How deep can I drill the 6-48 mounting screws. The holes will be 5" forward of the face of the breech. Thanks, Bob
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Offline L. Akers

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Re: Drill Depth needed
« Reply #1 on: March 11, 2017, 06:39:15 AM »
Even with rifling .018" deep you will still have a .200" wall thickness.  If you drill .093" deep you will have almost 4 threads of engagement which is more than adequate.  I would not go past .100" deep.
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Offline flehto

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Re: Drill Depth needed
« Reply #2 on: March 11, 2017, 08:00:10 AM »
.100 deep should do it. ....this leaves .100 wall thickness. I use the lockable depth gage on the drill press to prevent going too deep. After the pointed drill is used, I then use a flat bottom drill to get  maximum amount of threads.

The drilling is easy, but the tapping can be more difficult.  A slight ctsk helps, but it can't be too deep  The tap has to have most of the lead in ground off which makes it hard to start followed w/ a flat bottom tap. A light touch is necessary when bottoming out the tap so the threads aren't stripped.

Also ensure that the screw doesn't bottom out in the hole and strip the threads....some bbl steels are fairly soft.....Fred
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ron w

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Re: Drill Depth needed
« Reply #3 on: March 11, 2017, 04:16:30 PM »
set up your drilling operation and drill a hole then change out to the tap without moving the barrel. you can use the down pressure the drill press will give to reliably start the tap. turn the chuck by hand while putting pressure on the tap with the quill.  then move on the next hole repeating the process.
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Offline Tim Crosby

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Re: Drill Depth needed
« Reply #4 on: March 11, 2017, 05:24:30 PM »
 How about Dovetailing a pre tapped piece in then mounting the sight? Just a thought.

  Tim C.
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Offline flehto

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Re: Drill Depth needed
« Reply #5 on: March 11, 2017, 06:41:43 PM »
The dovetailing is the way to go...eliminates a nasty tapping job.....Fred
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Offline T*O*F

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Re: Drill Depth needed
« Reply #6 on: March 11, 2017, 06:52:05 PM »
I'm assuming the sight comes with mounting screws.  Put one of the screws in the mounting hole and hang it over the front of the barrel.  Scribe a line at the bottom of the screw.  Measure that distance which should be around 1/2 the barrel thickness or less.  That is the depth to drill your holes.  You will need to ensure that your drilled hole is flat bottomed and that you have a bottoming tap to cut the final threads.  Others have already suggested how to do that.
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Offline Bob Roller

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Re: Drill Depth needed
« Reply #7 on: March 11, 2017, 08:40:19 PM »
Quote from: flehto on March 11, 2017, 06:41:43 PM
The dovetailing is the way to go...eliminates a nasty tapping job.....Fred

Special thread taps&dies are in every industrial supply catalog and are not expensive.
I would probably use a 6x56 or 60 for the dove tailed method.

Bob Roller
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