holes and threads

So, I have a hole that I drilled and tapped with 4-40 threads. The problem is it was supposed to be 5-40 threads. So here's my question:

Is 5-40 larger enough that I can drill out the existing 4-40 hole and retap it for 5-40?

or

Just ram a 5-40 tap in the existing 4-40 hole?

or

Just use a 4-40 screw and not be OCD that it doesn't match the 5-40 fastener next to it that was already there?

jg

Edit: Looked it up. It's only .010" difference. The diameter is close enough to just run the 5-40 through, and the pitch being the same is a bonus.

If i remember correctly...

the inside of 5-40 is smaller than the outside of a 4-40... so you are screwed either way, and need to sleeve it. it is a difference of .013 in "size" ... what is this holding?

Machine screw sizes go bigger as the number increases, a 5-40 screw is bigger than a 4-40 but the thread pitch is the same so you should be OK to tap it out. Just be careful; the last thing you need is a tap broken off in the hole.

I'd be inclined to run the 5-40 tap through it and call it done. But it might be good to know if it's a "mission critical" application first...

JG,
If the part is thick enough, drill a little way in to it with the correct drill for a #5-40 (outside diameter). That will give you a good index on keeping the 5-40 tap aligned with the hole/threads already there.
The threads having the same pitch will help get the tap started, but the 0.013" undersize will probably snap the 5-40 tap in a 5-40 hole (unless you drilled it oversize a bit).
Try the correct 5-40 tap drill in the hole and see if it runs through cleanly. If so jump right in with the tap. If not run the drill through carefully, then tap it. Use cutting oil to help reduce sticking/breaking.

I'd plug the tap in and see if it look/felt like it was going to work.

If not, I'd grab my trusty box of a zillion sized bits and drill the hole slightly larger and then run the 5-40 tap.

This is a 5-40 screw. It isn't like it is gonna be holding anything critical or heavy.

The tap drill for 4-40 is 0.0890" and the tap drill for 5-40 is 0.1015"

You will be just fine tapping it up to #5.

Worked fine on one hole, broke the tap off in the second hole. Luckily I could get to both sides of the tap and just grind it flush, and we shall never speak of that hole again (against my better judgment I started with the important hole—turns out that was a good move).

I blame a combination of a cheap tap and the fact that the first one went so well I was probably going a little hard in the less important hole.

Speaking of going a little hard in the less important hole... oh, never mind.

jg

10-32 thread for example: 32 threads per inch. 10 diameter means 10 X .013 + .060 or .190 major diameter.

The drill used to tap this is the major diameter minus the Single Depth. "S" = 1 divided by the # of threads per inch. .190 - .031 or .159

4-40 = 4 X .013 + .060; .112

5-40 + 5 X .013 + .06; .125

Difference is .012 diameter or .006 per side.

Yeah, chance it.

No kidding, just take your time, it's fine.

Dan

JG, just read your post, good for you! Do you need more taps? Perhaps a tap extractor?

Dan

914Driver wrote: JG, just read your post, good for you! Do you need more taps? Perhaps a tap extractor? Dan

He said were never speaking of that hole again, so drop it.

Pass on free stuff?

OK.

When I was racing RC boats I ran a lot of small taps. #4, #6, and #8, we drilled and tapped all the hardware and motor mounts for SS cap screws. Most of it was aluminum, but occasionally steel and stainless.

Rule #1: Don't buy cheap taps.

Rule #2: Don't buy cheap taps.

Rule #3: Don't buy cheap taps.

Rule #4 Use a tap fluid made for whatever material you are cutting.

Rule #5: Replace the tap after every 20-30 holes in soft metals, every 15-25 holes in steel and every 5-10 holes in SS. They fatigue and the tiny ones are easy to break and a bitch to extract. There is nothing worse than spending hours machining a part only to snap a tap off on the last hole. BTDT

Glad you got the important hole tapped.

Toyman01 wrote: Glad you got the important hole tapped.

That's what she said.

jg

JG Pasterjak wrote:

Toyman01 wrote: Glad you got the important hole tapped.

That's what she said. jg

Really cause all she tells me is no.

This was my project.

Swapping the optic mount from this dual-sided dealie:

To a single-sided type that holds the optic at a 90º angle:

The two-sided mount has three mounting holes in each side, while the single sided mount has five (three in the same pattern as the two-sided one, plus two additional in between the holes). Three was plenty, five was overkill, so I'm fine with four. And, yes,the scratch on the bottom of the slide is from a chunk of the tap that broke off. It's dead now.

jg

Cool. What's the advantage to the single side mount. Pretend I know nothing about pistol optics. (Because I don't.)

It looks like it's mounted a lot closer to the center line of the barrel.

Ahhhh....a tack driver...

Toyman01 wrote: Cool. What's the advantage to the single side mount. Pretend I know nothing about pistol optics. (Because I don't.) It looks like it's mounted a lot closer to the center line of the barrel.

You answered your own question. It's almost 3/4 of an inch closer, actually.

That said, I'm not sure I'm going to like it. It seemed like it was a lot easier to pick up the dot with the regular vertical mount, but maybe that'll take some getting used to. One of the issues I have is that I'm right handed, but I'm left-eye dominant, plus my near vision is turning to crap when I have my prescription glasses on. That's part of the reason I switched to an open-class gun—I was having too tough a time focusing on the sights of an iron-sighted gun. With the dot, i can just keep both eyes open and focus on targets.

So it's a little weird drawing and trying to find the dot, since my left eye just wants to find the big black housing. If I can train myself to get the dot with my right eye, I think I'll be in good shape. If not, we slap the old sight back on and I just remember to aim a little higher on the close stuff.

jg

JG Pasterjak wrote: So, I have a hole that I drilled and tapped with 4-40 threads. The problem is it was supposed to be 5-40 threads. So here's my question: Is 5-40 larger enough that I can drill out the existing 4-40 hole and retap it for 5-40? or Just ram a 5-40 tap in the existing 4-40 hole? or Just use a 4-40 screw and not be OCD that it doesn't match the 5-40 fastener next to it that was already there? jg

4-40--43 drill=.089

5-40--38 drill=.102

JG,

How about some more details on that piece?

JG Pasterjak wrote: Just ram a 5-40 tap in the existing 4-40 hole?

Yep.

I repaired a stripped 12x1.5 thread (wheel bolt hole) by tapping it to 1/2-20, then tapping to 14x1.5 and using a bolt from a late model Volkswagen.

Woody wrote: JG, How about some more details on that piece?

My buddy David Pruitt, who is also my coach Dave Pruitt, Gand Master class shooter Dave Pruitt, and gun builder dave Pruitt. Basically every year Dave builds a new gun. Then the previous one get redone for backup use, Pretty much the only thing that survives the rebuild is the slide, lower frame and barrel. The slide and frame are filled and recut, anyway, just to make sure the actions are similar to his main gun. So then the gun spends the year traveling around and either coming out if the primary fails, or staying in the bag and getting cleaned. After that year It gets sold to a guy like me.

STI 2011 modular frame and grip. Caspian slide (most race gun builders use Caspian or Springfield slides since the metal is thicker and they can be more aggressive with the lightening cuts. Schuemann tribrid barrel with six-port step-down compensator, EGW trigger group and hammer. STI short trigger. Mitchell custom engineering right side mag release. Dawson Ice magwell, C-More optics, Aftec extractor, and lots of labor to make sure everything ran well.

Set up for .38 Super, but also runs .38 Supercomp just fine, which is cool.

jg

In reply to JG Pasterjak:

The joys of getting older. Without my glasses the sights are two fuzzy bumps on top of a big fuzzy blob, with my glasses I might be able to see the broad side of a barn. If only my arms were about 3 feet longer.

I might have to look into something like that. A fuzzy red dot has to be easier to see than a iron sight.