Drilling/tapping 416SS question

[AlNyhus]

Looking for some guidance and advice for a project.

I've got a new Mack Bros. EVO 416SS, single shot, 700 foot print action for a build of my own. I'd like to add an additional action screw 2.500" back from the forward one. Since this action uses a trigger hanger, there ends up not being that much contact area on the tang. The additional action screw would allow the rear tang area behind the bolt notch cut to be 'floated'....no contact with the stock.

I'd like the new hole to be a blind hole. The solid area in the bottom of the receiver where this would go is .325" thick. Allowing for the leading edge of a good bottoming tap, I was thinking that .225 would be a good hole dept. Final tapping would get about .200 of thread length...which is the same as the front thread engagment that goes through the threaded tenon portion. I've got a new Cobalt material spiral fluted 50% 1/4-28 bottoming tap on hand which seems to be the material of choice for tapping 416SS.

For a hole, a #3 (.213) or a #7 (.201) seem to be recommended, depending on the material. I also have a new 1/4" shank 7/32" (.2188) solid carbide end mill on hand. My though was to split the difference and use the 7/32" carbide end mill to mill the hole.

For tapping, I was thinking of putting the tap in the R8 1/4" collet and tapping the threads by hand rather than under power.

I'm completely open to thoughts and suggestions on this. I've done a bunch of this on aluminum bodied actions (Pandas/Kodiaks) and 700/XP steel receivers but want to be cautious before wading into a 416SS action. Here's some pics for reference.

Looking forward to your thoughts and ideas. -Al

 

[CNC-Dude]

Since a bottoming tap is relatively blunt, and difficult to start in the hole straight, I would at least put it in a collet in a mill and at least let one or two threads cut so you know its straight. You can go the rest of the way by hand from there.

 

[338 Mollett]

I like the hand tapping idea.

 

[LVLAaron]

+1 start it in the mill for a couple threads and then go by hand.

If you really want the threads to bottom out, thread with your tap, and then grind the tap flat so you can get the extra thread all the way in the bottom.

 

[Walt Krafft]

Get the threads started with a non bottoming tap. Also check your drill sizes. They dont sound right.

 

[AlNyhus]

Since a bottoming tap is relatively blunt, and difficult to start in the hole straight, I would at least put it in a collet in a mill and at least let one or two threads cut so you know its straight. You can go the rest of the way by hand from there.

I should have been more clear. The tap would be in a collet in the mill.

Thanks! -Al

 

[GenePoole]

+1 start it in the mill for a couple threads and then go by hand.

If you really want the threads to bottom out, thread with your tap, and then grind the tap flat so you can get the extra thread all the way in the bottom.

I have to disagree with you on this. Bottoming taps are designed to do this. Grinding a tap to a sharp edge will only add stress risers and multiply the odds of breaking pieces off the tap in the blind hole and nobody want to deal with that.

 

[LVLAaron]

Agreed it's a delicate process. But I've taken the very bottom of the taps off with no problems. That very bottom part is just there to get the tap started. A good cobalt cutter will go through 416 like butter.

 

[brcman]

I notice the trigger hanger slot only has one hole at the rear to hold the trigger hanger- never seen this before?

 

[AlNyhus]

I notice the trigger hanger slot only has one hole at the rear to hold the trigger hanger- never seen this before?

It's a bit different. The front of the hanger has a lip that goes into a notch machined into the hanger mortise. It's kind of delicate to get in there...have to hold my tongue just right. -Al

 

[ridgeway]

The leade on a bottom tap is a bit more than .025. Measure it. I'd hand tap it with the tap being supported with a spring loaded center. If your tap does not have a center, most 1/4 taps don't, put on in with a carbide center drill.

 

[gunsandgunsmithing]

Looking for some guidance and advice for a project.

I've got a new Mack Bros. EVO 416SS, single shot, 700 foot print action for a build of my own. I'd like to add an additional action screw 2.500" back from the forward one. Since this action uses a trigger hanger, there ends up not being that much contact area on the tang. The additional action screw would allow the rear tang area behind the bolt notch cut to be 'floated'....no contact with the stock.

I'd like the new hole to be a blind hole. The solid area in the bottom of the receiver where this would go is .325" thick. Allowing for the leading edge of a good bottoming tap, I was thinking that .225 would be a good hole dept. Final tapping would get about .200 of thread length...which is the same as the front thread engagment that goes through the threaded tenon portion. I've got a new Cobalt material spiral fluted 50% 1/4-28 bottoming tap on hand which seems to be the material of choice for tapping 416SS.

For a hole, a #3 (.213) or a #7 (.228) seem to be recommended, depending on the material. I also have a new 1/4" shank 7/32" (.2188) solid carbide end mill on hand. My though was to split the difference and use the 7/32" carbide end mill to mill the hole.

For tapping, I was thinking of putting the tap in the R8 1/4" collet and tapping the threads by hand rather than under power.

I'm completely open to thoughts and suggestions on this. I've done a bunch of this on aluminum bodied actions (Pandas/Kodiaks) and 700/XP steel receivers but want to be cautious before wading into a 416SS action. Here's some pics for reference.

Looking forward to your thoughts and ideas. -Al

I think your plan is sound. How far back can you move the new hole? I'd rather see the new screw moved further back, which would also make me consider a different approach. If you can't see a through hole, is it really there? Lol!

 

[Tucker65]

These taps work great for what you're trying to do.

https://www.grainger.com/product/OSG-Spiral-Flute-Tap-1-4-28-Thread-2PJK9

 

[gunsandgunsmithing]

On taps and drill size...more tap sizes

Tapping Tip - How H-Limits Relate to Class of Fit (Part 2)

Welcome to another post on our Tapping Tips! This is the second part of a two-part series on the relationship of inch tap size and class of thread. In this second part, we will explain the relationship of tap sizes and class of threads. We should mention that H and L limits are also expressed […]

www.gwstoolgroup.com

 

[Edd]

I think your plan is sound. How far back can you move the new hole? I'd rather see the new screw moved further back, which would also make me consider a different approach. If you can't see a through hole, is it really there? Lol!

Holes that are functional don’t offend me. I would drill it through regardless of where I put it.

 

[gunsandgunsmithing]

Holes that are functional don’t offend me. I would drill it through regardless of where I put it.

The only real reason for a blind hole is astetics. If it can be under the rear receiver bridge, I think it serves two purposes. One being astetics.

 

[Alex Wheeler]

Al, 416 is easy stuff to work with and actions are not very hard. Personally I would use the endmill and go as deep as I could without going through into the action bore. A spiral fluted bottoming tap would be the correct tap to use. Then without moving anything swap out collets and grab onto one of these, https://www.mscdirect.com/product/details/95267472
It will guide your tap in straight.
If you choose to do a through hole, a spiral point tap under power would be no problem. This is easy so most any tap fluid works. When I was still messing with Remingtons and doing the 8-40 scope mount thing, I broke a lot of taps. I found the best way was to use a spiral point 2 flute tap, under power with moly-d. And only use the tap for 2 actions and toss it. Moly-d is the best I found.

 

[WayneShaw]

As Alex has said, I have a guided tap handle from McMasterCarr https://www.mcmaster.com/2550A64/. Once the hole is located, I lock the mill table down then drill and tap. Perfect alignment. You got this Al.

 

[tobnpr]

For tapping, I was thinking of putting the tap in the R8 1/4" collet and tapping the threads by hand rather than under power.

I've never tapped any holes in a rifle receiver under power. Drill the hole, and then I use a spring loaded tap guide in the chuck and spin the tap in by hand. Granted, action screws are substantially beefier than scope mount screws (which you'd have to be crazy to tap under power) but depth is so short it seems ridiculous to me to do that under power.

Very shallow blind holes like this- even a bottoming tap isn't going to get you maximum engagement.
I start with a plug tap (a taper tap isn't going to work because the hole isn't deep enough to get to the full threads), and then -flame suit on- I use a "bottoming" tap made by grinding any other tap down to full engagement. Then set it up in the tap guide with light downward pressure and by carefully feel to make sure it isn't going in cross-threaded, run it home. Eliminating the partial threads on the tap gets it all the way to the bottom of the hole rather than losing 2 or 3 threads from even a bottoming tap.

Just how I do them....YMMV.

 

[Dusty Stevens]

Use a hss tap either 2 or 3 flute so you can get it out if it breaks. No spiral flutes