Bore bottom radius tool - Graybeard Outdoors
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post #1 of 6 (permalink) Old 03-19-2017, 09:38 AM Thread Starter
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Default Bore bottom radius tool

I am building a small BP Parrott style cannon.
I would like some feed back on finishing the bottom of the bore from the drilling process to a finished radius to relieve potential stress. I have considered regrinding a spade drill and using a ball nose end mill attached to an extended arbor. I would like to be able to use a cordless hand drill to do this since only a little metal has to be removed.
Bore: .75 dia.
Length: 14 in.
Material: Steel-Ford Tractor axle with reinforcing sleeve.
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post #2 of 6 (permalink) Old 03-19-2017, 12:05 PM
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Location: Oakridge Oregon
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If you are handy at the grinder shaping your drill bit for a radius would be the most direct approach, then just sharpen to a drill shape again.
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post #3 of 6 (permalink) Old 03-19-2017, 06:37 PM
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A full radius bottom is not necessary. Only the corners need a radius.

Here is an excerpt from the N-SSA regulations on breech plugs showing how it is supposed to be.

You are asking for trouble trying do this with a hand drill. You will do nothing but wallow your hole out.

Last edited by Double D; 03-19-2017 at 06:44 PM.
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post #4 of 6 (permalink) Old 03-20-2017, 12:21 AM
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What is the shape of the bottom now? You can find end mills with radiused corners but the problem will be holding it. Unless you have the shank relieved, a conventional extension will not fit. Ideally you could find a 3 flute drill and regrind the point to the desired shape. That would more likely be long enough and the 3 flutes would help to center the cut better than a 2 flute drill. I would not try a spade drill, as without the point, it will not center well.

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post #5 of 6 (permalink) Old 03-20-2017, 08:10 PM
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Why do you need a radius without a powder chamber?
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post #6 of 6 (permalink) Old 03-20-2017, 09:19 PM
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The purpose of a radius is eliminate the square corner which is a stress riser and a place that can holds sparks and is difficult to clean.
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