Drill stop for drilling screw holes for underrib

[bioprof]

I rummaged around a hardware store for about a half an hour last week trying to find a drill stop for controlling the depth when drilling screw holes for an underrib on a halfstock rifle. I finally ran across some clevis pins that aleady had holes drilled through the sides. I just cut off the end of the pin, drilled a hole through the middle, and tapped a hole in the side for a set screw. Took me about 5 minutes to make. I now see that I need to get a shorter set screw though so it doesn't stick out so much. I do have a depth stop on my drill press, but I don't have much confidence in it yet. Now I can set a backup depth control. This might also work well if you're trying to drill by hand.

 

[Zonie]

Sounds like a good idea!

You are wise not to trust the depth stop on your drill press.
Relying on that thing is the reason I drilled the underlug staple hole thru my $200 Colerain barrel. :cry: :cry:

 

[bioprof]

Zonie,

How deep should I go when I drill the holes for the underrib screws? I am drilling a 1" barrel in 54 cal.

 

[Zonie]

That depends on what size screw your installing.

If I was going to calculate the depth, I would do it like this:

(1 inch barrel minus .54 diameter minus .020 groove depth) divided by 2 =.220 wall (this is the depth that will gurantee a break thru).

The tip of the drill stands proud of the drills shoulder. To calculate this, you need to know the drill diameter.
For a standard drill tip of 118 degree included angle, the drill diameter multiplied by .300 will give you this height.

Tap drill for a #6-32 screw =#36 (.1065 diameter).

.1065 X .300 =.0319 so the maximum depth from the barrel flat to the shoulder of the drill is .220 minus .032 or .188 This is the maximum depth of the cylindrical hole.

This is all theoretical and it disreguards the barrel tolerances and the precision that one can set the drill depth
so I would say measuring from the drill stop face you've mounted on the drill bit to the very end , or tip of the drill should be set at .140-.160. This should assure a wall of .060-.080.
The thread depth will be about .110 if you "bottom tap" the hole.