Gunsmithing A little help drilling a bolt carrier??

[2aBaC̶a̶]

I need to drill and tap a small hole in a bolt carrier. this thing is hard as fuck and even after grinding the black coating off ive smoked a couple drill bits giving it a go. do I need a specific bit? ive tried slow to fast with oil. barely puts a scratch in it. wtf?

 

[msgriff]

Solid carbide bit, but they're very brittle. A tungsten carbide pointed or ball burr works well to break through hardened surface finishes, like nitride, and works on curved surfaces.

 

[The King]

A milling machine is your buddy

 

[Wannashootit]

^^^
This. You need rigidity.
My son asked me to do this for him a couple of years ago. I told him no way was I going to try to D&T that hardened shit- buy the correct side-charging BCG.

 

[The King]

Wait till you get it drilled. Then you get to break a carbide tap off in there lol.

 

[2aBaC̶a̶]

A milling machine is your buddy

I wish, unfortunately im stuck with a medium sized drill press.

Wait till you get it drilled. Then you get to break a carbide tap off in there lol.

yeah, Im already dreading that part. its an 8-32. could I drill it a little oversized to reduce the amount of cutting the tap needs to do? this is a test and proof of concept so I dont need perfect threads.

 

[2aBaC̶a̶]

^^^
This. You need rigidity.
My son asked me to do this for him a couple of years ago. I told him no way was I going to try to D&T that hardened shit- buy the correct side-charging BCG.

I'm prototyping an Idea I had so I need to make it work. not a side charger.

 

[buffalowinter]

Google "carbide bit for hardened steel". Start with a two-flute bit. It helps to buy two or three bits and start with a small hole and then enlarging it with increasingly larger bits. Also, it helps enormously to continuously irrigate the hole with a cutting fluid. These bits are not cheap.

 

[Slick66]

Did you spot it? Are you drilling on a flat? .136 is not tiny, but if your drilling on a round surface the drills gonna walk. Also feed slow as hell and peck lightly.

 

[2aBaC̶a̶]

So Im thinking plan B. opening up up the firing pin retaing pin holes from 3/32" to 1/8" and then whatever the hole is next to it on the right side that is already 1/8" and then tap the two for 6-32.

 

[2aBaC̶a̶]

Did you spot it? Are you drilling on a flat? .136 is not tiny, but if your drilling on a round surface the drills gonna walk. Also feed slow as hell and peck lightly.

I filed a flat and spot it. Im using old bits which doesnt help but I couldnt get any to bite, not even sma sliver.

 

[DeathBeforeDismount]

You shouldn't need Carbide, a new colbat bit should be fine. Just make sure you have feeds and speeds correct. The harder the material the slower you want to go RPM wise. Otherwise you are just work hardening the piece you are trying to drill. Lots of lube will be your friend as well.

 

[502Chevelle]

“Lots of lube will be your friend.” I swear I have heard that somewhere before.

 

[2aBaC̶a̶]

You shouldn't need Carbide, a new colbat bit should be fine. Just make sure you have feeds and speeds correct. The harder the material the slower you want to go RPM wise. Otherwise you are just work hardening the piece you are trying to drill. Lots of lube will be your friend as well.

I tried new bits to no avail could not get them to cut. so reluctantly I ended up taking my torch set and a #0 tip, setting the BCG upright in a pan of water and annealing the area around the holes. only then would the bits cut into it. got them drilled and tapped which was a struggle in and of itself. even being annealed to some degree was a pita.

 

[S197]

I need to drill and tap a small hole in a bolt carrier. this thing is hard as fuck and even after grinding the black coating off ive smoked a couple drill bits giving it a go. do I need a specific bit? ive tried slow to fast with oil. barely puts a scratch in it. wtf

if It’s just for a prototype, put most of the carrier under water and heat the area that you need to tap. This should take the hardening out of that area.

 

[DeathBeforeDismount]

I tried new bits to no avail could not get them to cut. so reluctantly I ended up taking my torch set and a #0 tip, setting the BCG upright in a pan of water and annealing the area around the holes. only then would the bits cut into it. got them drilled and tapped which was a struggle in and of itself. even being annealed to some degree was a pita.

Did you use a drill starter?

 

[2aBaC̶a̶]

Did you use a drill starter?

no, not even sure what that is.

 

[DeathBeforeDismount]

no, not even sure what that is.

Called a centre drill. Used to make a small dimple so the drill bites in exactly where you want.

 

[strikeeagle1]

After creating the flat as mentioned, it may be wise to use the smallest center drill as an initial pilot hole to follow-on with yet a larger center drill slightly over-sized in preparation for using the final tap drill bit size for the 8-32 screw. I fabricate roll pin starter punches from hardened drill rod stock. This is a 1/4" rod for a 5/32" roll pin I made last week. Sharp carbide bits, a rigid setup of the work, low speed & pressure, small depth pecks with the drill bits, lubrication are your friends; IF you see smoke stop, cool off parts and begin again.

 

[2aBaC̶a̶]

Called a centre drill. Used to make a small dimple so the drill bites in exactly where you want.

View attachment 7969022

oh shit, I actually have a couple of those kicking around in my misc drawer.

 

[DeathBeforeDismount]

After creating the flat as mentioned, it may be wise to use the smallest center drill as an initial pilot hole to follow-on with yet a larger center drill slightly over-sized in preparation for using the final tap drill bit size for the 8-32 screw. I fabricate roll pin starter punches from hardened drill rod stock. This is a 1/4" rod for a 5/32" roll pin I made last week. Sharp carbide bits, a rigid setup of the work, low speed & pressure, small depth pecks with the drill bits, lubrication are your friends; IF you see smoke stop, cool off parts and begin again.

View attachment 7969318View attachment 7969319View attachment 7969320View attachment 7969321

Those starter pins look great. Do you sell them?

 

[strikeeagle1]

I like the short tools to be close to the work with small pins. The standard roll pin starter punches are too long for my liking. Also made some from brass stock. I just make them for the hobby.

 

[2aBaC̶a̶]

I have the wheeler set and to be honest I find them to be a pain. the pins get stuck in the end of the punch. I kinda wish they were a little oversized and magnetic.

 

[2aBaC̶a̶]

I like the short tools to be close to the work with small pins. The standard roll pin starter punches are too long for my liking. Also made some from brass stock. I just make them for the hobby.

View attachment 7969414View attachment 7969415View attachment 7969416

ok how about this? make individual bits that fit in a magnetic bit holder?

 

[Yondering]

LOL.
AR15 bolt carriers are case hardened, usually fairly deep; you're not going to tap threads in that without either removing or softening the case hardened layer. I do it by using a carbide end mill to cut through the case hardening on the outside, then reach inside with a diamond burr to clean up the other end of the hole.

Even then, the softer inner material is still tool steel and not the easiest thing to tap, so be careful. And don't use 6-32, that size is the most likely to break out of all your possible choices. Besides for a charge handle, a #10-32 grade 8 is more appropriate for the size and strength demands.

If you use a mill to give yourself a flat for the handle to register against, the whole assembly can be a lot stronger.

 

[strikeeagle1]

I like the Widia "super taps" for small gunsmith sized fasteners: tool steel, stainless, cast iron tapping.