8-40 Tap

[gunsandgunsmithing]

Blind holes, I like a spiral tap, or any decent tap that pulls the chip up and out of the hole. Through holes, I like taps that push them out the bottom.

Yes, just a few holes from cheap but sharp taps IMHO, is better than a tap that holds an edge but is harder to break up or drill out WHEN you break one. That's why sharp, carbon steel is best in many of our applications that are gun related. One instance where cheap might really be better. But, it's not cheap if you toss them after a few holes for a reason, too. As long as they get the job done, that's the objective. All ya have to do to see why I prefer the carbon taps is break one off and have to get it out of a small blind hole, once with both types.

 

[LVLAaron]

Rapid Tap

This stuff smells like static electricity. I feel like I'm getting cancer any time I have used it.

 

[AlNyhus]

On the last two I've done for myself, I made them 8-32's instead of 8-40's.

 

[WSnyder]

When doing a 700 with no barrel in the action fixture in the mill where I can mill and tap a through hole I use Titan brand gun taps. They cut like butter and last a long time. I use a lot of the Titan brand, they’ve been good and pretty cost effective. Other taps that have been really good are the USA from Shars. I’ve been using some of the steam oxide coated on stainless 1/2” and up. Cut easy and long wear.

 

[whatsupdoc]

Four holes and toss?! Wow.
Anything a little odd like UNS taps is a pain to source up here. I've lost count of the jobs done with some of my taps.

I worked for a Govt contractor and did a lot of tapping in stainless and aluminum
we used the taps for more than 4 holes, way more.

 

[gunsandgunsmithing]

I worked for a Govt contractor and did a lot of tapping in stainless and aluminum
we used the taps for more than 4 holes, way more.

No doubt, but that's only a part of it and without more info, means little. The reason is in part, the material and the size, as well as many gun holes being blind holes. Simply put, a sharp tap cuts better and less likely to break. My reason is about after it breaks. It's much easier to break up a carbon tap broken off in a blind hole than hss. Larger taps, softer material and production work are a different animal vs breaking off a tap in a $1500 action. Just apples to oranges, really. No problem using whatever until it breaks. Carbide will cut lots of holes but is very brittle and you're likely gonna have a hard time getting a small one out without an edm or tap burner is all.

 

[std7mag]

Carbide sucks if you break the tap off in a blind hole!!!
The smaller the hole, the more it sucks!!

We do use a lot of carbide taps in our vertical and horizontal CNC mills, and our CNC lathes.
Material runs the gammot between 7075 aluminum, 1018 & 4140 steel.

The real issues arise when we have plate that has been flame cut, or cut on our Kinetic table.
It case hardens the outside.

I've heard of some old Mausers being case hardened and being a real hassle to drill and tap.

 

[Sniperhandle]

I think the ones I had said regal on them.

Yes I have used the Regal Carbide taps for super hard Rec. Good quality.

 

[Ledd Slinger]

Yeah not fun to remove when they break. Have to use carbide bits to break the taps apart for removal.

Irwin makes good custom drill bits in sizes that graduate by a few thousandths of an inch so you can get the hole size just right. I don’t recommend using the taps on a lot of holes either, but I use Irwin drill bit #27 which measures .1440” and it seems to give the 8-40 taps a little better life and far less chance of breakage without really sacrificing much thread strength. Normal size drill bit people use for 8-40 taps is .1405”, so the #27 Irwin bit I use is only .0035” larger in total diameter. It will save you so much frustration by not getting nearly as many broken taps

I also only HAND tap the holes using the head of my milling machine with a tap guide mounted so everything is perfectly straight. Use good cutting oil and back it out often to keep the tap clean. If you plan on tapping by hand in a vice, you probably won’t like the results.

If you also need to modify a scope base rail, an 11/64” drill bit and 1/4” chamfer seats the 8-40 oval head torx screws almost perfectly. I wouldn’t recommend using Fillister head screws because they can allow movement of the base under recoil if it’s not pinned. Could also pin the bases, but that’s another story a little off subject here.

 

[gunsandgunsmithing]

Yeah not fun to remove when they break. Have to use carbide bits to break the taps apart for removal.

Irwin makes good custom drill bits in sizes that graduate by a few thousandths of an inch so you can get the hole size just right. I don’t recommend using the taps on a lot of holes either, but I use Irwin drill bit #27 which measures .1440” and it seems to give the 8-40 taps a little better life and far less chance of breakage without really sacrificing much thread strength. Normal size drill bit people use for 8-40 taps is .1405” so the #27 Irwin bit is only .0035” larger in total diameter. It will save you so much frustration by not getting nearly as many broken taps

I also only tap the holes using the head of my milling machine so everything is perfectly straight. Back out often to keep the tap clean. If you plan on tapping by hand in a vice, you probably won’t like the results.

If you also need to modify a scope base rail, an 11/64” drill bit and 1/4” chamfer seats the 8-40 oval head torx screws almost perfectly. I wouldn’t recommend using Fillister head screws because they can allow movement of the base under recoil if it’s not pinned. Could also pin the bases, but that’s another story a little off subject here.

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Yes, that's the beauty of carbon steel taps, that you can drill most or all of it out pretty easily with carbide. Most small holes on gun stuff can be done with a pretty inexpensive carbide center drill. At the least, it makes it easier to bust up what's left of the old tap. Removing a broken tap is not often a pretty job. One I prefer no one to be watching me beating on. The finished product is what matters though.