DIY Drilling & Tapping 870 Receiver

[gewehr3]

Greetings,

I would like to install XS ghost ring sights on an 870 shotgun. The rear sight requires two 8-40 holes drilled and tapped into the receiver. One problem I see is the rear sight requires the rearmost 8-40 hole to be drilled on the slope of the receiver. The XS sight instructions call this a compound surface radius. This is located 1" from junction of the receiver and stock.

What type of vise or jig would you recommend for securing the receiver under the drill press?


Thank you for the help.

 

[dfariswheel]

That one's going to be tough.

The slope is going to make the drill bit tend to flex and wander "down hill".

You can get it done with a good drill press vise.
I'd make up a block of wood to insert into the bottom of the receiver where the trigger group rests.
This will prevent crushing the receiver, and allow you to clamp it tightly.

Pad the vise VERY well.

Buy a NEW, unused drill, and if necessary break part of the shank off so you can "choke up" on the bit. You want the absolute minimal amount of drill sticking out of the press's chuck to reduce bit flexing.
If necessary, after getting the hole started straight, you can loosen the chuck, and allow more bit to protrude.

Center punch the drill spot on the receiver with a good, DEEP punch mark to help hold the bit.

After drilling, leave the receiver in place, unplug the press and disconnect the drive belt from the spindle. Remove the drill bit and put the tap in it's place.
Tap the hole while the receiver is still in the set-up.

When drilling holes on sloped surfaces, you're better off doing it on a milling machine, and using a mill bit to at least start the hole.

Again, watch it, because the drill bit is going to try to wander down the slope.

 

[redneck]

This type of drilling is very difficult. I would do like dfariswheel suggested to clamp it but I would not just break a bit off and give it a go.
Center punch it, then get a center drill to start the hole these are stubby drill bits with the tip ground specifically for starting holes it will not walk as much as a normal bit will.
To be honest I'm not sure I would try it. Having a gunsmith do it would be expensive but then if they mess it up THEY pay to fix it

 

[Jim K]

If you are going to try to center the holes by eyeball, you won't. If you try to drill with a standard drill, the result will not be good.

If you don't want to buy a good quality drill jig, and the proper drill, take the gun to a gunsmith.

Jim

 

[gewehr3]

Thank you for the replies. Sounds like this is best suited for a gunsmith.