Jig to drill and tap my 870 receiver?

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G.Mitchell

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So I’m looking to install Mesa receiver rails on two of my 870 shotguns.

I got a price from a local gunsmith and it’s more than I can afford to spend. I’m confident I can do the work myself with a good jig to ensure centering and good alignment of the hole and threading.

Can anyone recommend a good jig? Alternatively is anyone here in the Grande Prairie AB area?

Thanks

Geoffrey
 
Do you really need a jig? The one 870 I have that’s drilled and tapped is drilled straight through the receiver, so no need for a blind hole and bottoming tap.

If it were me I’d carefully mark a center line down the receiver from the front sight, extending past the rear of the rail. Mark the center of the rail and line both up, once you have it dry fit and lined up center punch your mounting holes and get it in a sturdy drill press vice. Drill it and tap it, use lots of cutting oil and back the tap out to clear chips frequently.

Take your time and double check all your marks and make sure your lined up well, start your holes with a center drill. It shouldn’t be hard to get things all tickity bo, make sure your screws are flush with the inside surface of the receiver. Trim to fit if they sit proud.
 
G.Mitchell said:
Fair enough, Brownells has one I was considering.

May ship the receivers to one of our sponsors instead of trying the DIY method.
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I would think you can get 4 holes located correctly, drilled and tapped for $100... what have your previous quotes been?
 
Thank you all.

I am fairly confident I can do it myself but don’t want to ruin a receiver.

I need to get clarification on the last local estimate I got... If I understood correctly it’s $150-$200, I asked about having two receivers done so I’m not sure if that’s per gun or total for both guns...
 
If you already have the mount, use a bit of hot melt glue to attach it to your receiver where you need it to be. Use a center punch to mark the holes and remove the mount from the receiver. The hot melt glue will clean off easily.

I don't know what kind of tools you have. A hand drill, will likely end up causing your holes to be off center.

The best way to do this is with your stripped receiver clamped in a vice on the table of a good drill press. USE A CENTERING DRILL BIT TO START THE HOLES. Center bits are very rigid and won't bend when pressure is applied. This will ensure your holes will be where the punch marks indicate. Finish the holes with a regular HSS drill bit.

Leave the receiver in the vice. Chuck up your tap into the drill press. DON'T TURN IT ON.

Put a bit of lube on the hole and on the tap. Lower the spindle until the tap is just inside the hole. YOU DON'T NEED much pressure. With one hand holding the tap against the hole, use the other to turn the spindle by hand. This will start your tap in a perfectly aligned position. Try to get a few threads started on the first hole. WITH THE TAP STILL IN THE HOLE, USE THE CHUCK KEY TO OPEN THE CHUCK AND RELEASE THE TAP.

The tap will still be in the hole. Add a bit more tapping fluid, attach your tap handles and finish tapping the holes by hand.

Repeat the process until all the holes are finished.

There may be better ways to do this, or quicker ways, this works for me.

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I used to think hot melt glue was for "Martha Stewart" projects, but that was years ago...... :)

Good tips Bearhunter!
 
Bearhunter has provided some excellent instruction. Love the hot glue tip!
The only advice I could add would be to use a transfer punch rather than a centre punch. A set of transfer punches is not expensive and the punch mark can wander when centre punching through a hole.
 
Butcherbill said:
Do you really need a jig? The one 870 I have that’s drilled and tapped is drilled straight through the receiver, so no need for a blind hole and bottoming tap.

If it were me I’d carefully mark a center line down the receiver from the front sight, extending past the rear of the rail. Mark the center of the rail and line both up, once you have it dry fit and lined up center punch your mounting holes and get it in a sturdy drill press vice. Drill it and tap it, use lots of cutting oil and back the tap out to clear chips frequently.

Take your time and double check all your marks and make sure your lined up well, start your holes with a center drill. It shouldn’t be hard to get things all tickity bo, make sure your screws are flush with the inside surface of the receiver. Trim to fit if they sit proud.
Click to expand...

Butcherbill has it right . I would do the same as he suggests . Not really that hard if you have basic machine shop / mechanical skills .
I have done many of these type of jobs. with success .
 
unstableryan said:
I used a manual mill for mine. A drill press is for kids :)
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Now your bragging.

Many more people have access to a drill press than those that have access to milling machines. A good drill press can do some very good work but it takes more care and time.

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B_noser said:
Bearhunter has provided some excellent instruction. Love the hot glue tip!
The only advice I could add would be to use a transfer punch rather than a centre punch. A set of transfer punches is not expensive and the punch mark can wander when centre punching through a hole.
Click to expand...

You're absolutely right. I just assumed the OP understood. MY BAD, never assume something is obvious just because you're familiar with the subject.

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G.Mitchell said:
Thank you all.

I own and have used center punches and have seen them wander in use.

I’ll look into transfer punches and see if they’re something I can get locally.
Click to expand...

Let us know how it goes, I’m sure you’ll be fine if you don’t rush any of the steps. I was talking to one of the gunsmiths at Reliable a few years ago about it and he said if you don’t feel comfortable marking and drilling all the holes at once, to drill and tap the rearward hole first and screw it down semi snug. Once you have it lined up transfer the other marks and drill and tap the rest.

Is the rail just attached to the receiver or is it the full length rail that bolts to the muzzle end of the barrel as well?
 
bearhunter said:
If you already have the mount, use a bit of hot melt glue to attach it to your receiver where you need it to be. Use a center punch to mark the holes and remove the mount from the receiver. The hot melt glue will clean off easily.

I don't know what kind of tools you have. A hand drill, will likely end up causing your holes to be off center.

The best way to do this is with your stripped receiver clamped in a vice on the table of a good drill press. USE A CENTERING DRILL BIT TO START THE HOLES. Center bits are very rigid and won't bend when pressure is applied. This will ensure your holes will be where the punch marks indicate. Finish the holes with a regular HSS drill bit.

Leave the receiver in the vice. Chuck up your tap into the drill press. DON'T TURN IT ON.

Put a bit of lube on the hole and on the tap. Lower the spindle until the tap is just inside the hole. YOU DON'T NEED much pressure. With one hand holding the tap against the hole, use the other to turn the spindle by hand. This will start your tap in a perfectly aligned position. Try to get a few threads started on the first hole. WITH THE TAP STILL IN THE HOLE, USE THE CHUCK KEY TO OPEN THE CHUCK AND RELEASE THE TAP.

The tap will still be in the hole. Add a bit more tapping fluid, attach your tap handles and finish tapping the holes by hand.

Repeat the process until all the holes are finished.

There may be better ways to do this, or quicker ways, this works for me.
Click to expand...

THIS is the RIGHT way to do it!! Bearhunter, it's always nice to see a post from someone who has done this kind of work before, and knows what he's talking about! It took me a lot of experimentation to arrive at that same practice (ruined a LOT of pieces along the way!) - wish I'd had your advice way back when!!

Well said, sir, well said!
 
G.Mitchell said:
Thank you all.

I own and have used center punches and have seen them wander in use.

I’ll look into transfer punches and see if they’re something I can get locally.
Click to expand...

Princess Auto has them at very reasonable prices. You can also pick up an appropriate size Center Drill bit there. They don't bend or wander because of their rigidity. I always use the when tapping receiver holes.

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