How do I drill small holes straight? (I made a suppressor adapter)

[strantor]

A friend brought me this cheap little .22lr pistol, wanted me to come up with a way to adapt a suppressor to it. This is what I came up with. Turned down the end of the barrel and threaded it 7/16-20, then made this adapter with a 7/16-20 internal thread and a 1/2-28 outer thread. Worked well, after going through 4 failed blanks where the bore was crooked. Drill bit wander. How do I get better than a 20% success rate? I have somehow avoided learning this lesson; everything I've drilled/bored thus far has been larger diameter. The bigger bits don't wander as bad, and I'm usually going in with a boring bar afterwards anyway so it doesn't matter. I plan to do this again and I want to do it better, more predictable outcome. Is there a different tool I should be using other than a drill bit? I know a better ground drill drills a straighter hole but what drills a straight hole?

 

[GL]

1. I like stub length drill bits, less deflection. 2. Bore the hole - less wonder, but you have to start with a hole so .22+a little is a small boring bar (assuming that is the wonky hole) 3. As you suggested, good grind helps a lot. This also assume your lathe is all squared up and wants to drill straight holes, sometimes they don't, which is a PITA but fixable usually.

 

[graham-xrf]

I once came across one of these among a flea market batch of stuff. It was about 5" long, and at first I did not know what it was. Turns out it is called a "gun drill", for the obvious reason.



It still lurks somewhere lost in the garage. There is something about the cut in the end that makes it able to drill deep holes without wandering off, provided you keep blowing air or pumping liquid up it up it to clear the swarf.

The wiki explains it. These are not so common as regular spiral flute drills, so I would guess they might be expensive. If I can find it again, and it happens to be 0.22", you are welcome to it gratis. From memory, it might be about that size.

https://en.wikipedia.org/wiki/Gun_drill

 

[GunsOfNavarone]

I'm all about this subject...don't get me wrong...but can you even do more than hypothetically discuss this subject? If nothing else, I've had far larger drill bits wander even after a spot drill... interested in the problem.

 

[graham-xrf]

The wiki mentions drill-to-diameter ratios of 90:1 and 300:1
If there is any run-out at all, it will tend to flex the end. The article does mention that on lathes, it is practical for hole depths less than 50mm, but does not say why. I just followed some of the references - and got distracted!

Looking at it, it would seem that it has a single cutting edge, and then quite a large fraction of the remaining circumference is devoted to being a perfectly round guide, and that "round guide" extends back a little before it gets to the rod relief. This I get from looking at the close-ups of the business end.

--> LINK

 

[strantor]

I once came across one of these among a flea market batch of stuff. It was about 5" long, and at first I did not know what it was. Turns out it is called a "gun drill", for the obvious reason.

View attachment 313276

It still lurks somewhere lost in the garage. There is something about the cut in the end that makes it able to drill deep holes without wandering off, provided you keep blowing air or pumping liquid up it up it to clear the swarf.

The wiki explains it. These are not so common as regular spiral flute drills, so I would guess they might be expensive. If I can find it again, and it happens to be 0.22", you are welcome to it gratis. From memory, it might be about that size.

https://en.wikipedia.org/wiki/Gun_drill

There you go, gun drill! This has the faint odor of something I once knew, long since triaged in favor of other information. Yeah, I don't have any gun drills. Looking at them online now. You're correct, they're not cheap or easy to find. I haven't found exactly what I'm looking for and when I do, I estimate it will be around $75 (+/- $25) so if you've got one you don't need or want, I would gladly lighten you load. I appreciate the offer.

P.s. it doesn't need to be exactly .22 for what I'm doing. Anything between .22 and roughly .30 would work to make this adapter. Just as long as it makes a straight hole, I can work with it.

 

[strantor]

I'm all about this subject...don't get me wrong...but can you even do more than hypothetically discuss this subject? If nothing else, I've had far larger drill bits wander even after a spot drill... interested in the problem.

Are you saying it's against the laws of physics to drill a straight hole, or that it's against the rules of the forum (and possibly local governments) to discuss gunsmithing?

In the case of the former, there's always the "there's no such thing as a perfect circle" argument which holds water if we're talking about sub-micron tolerances (which I'm not).

In the case of the latter, I seem to remember there used to be a gunsmithing sub forum here. Am I wrong? Was that another forum? Pretty sure it was here. Did it get taken down? Am I in breach of some new TOS? I'll have to look into that. As far as local gun laws, I only know the ones for my locale, and AFAIK I'm not in breach of those. Note that I did not machine that suppressor; it's a commercial unit. All I did was thread the end of a barrel and machine a thread adapter.

 

[MontanaLon]

For a piece that short, I'd drill it and then bore it with a solid carbide boring bar.

There is nothing illegal about making an adapter unless it has oil filter threads on one end and then ATF has ruled that is a suppressor itself.

 

[graham-xrf]

There you go, gun drill! This has the faint odor of something I once knew, long since triaged in favor of other information. Yeah, I don't have any gun drills. Looking at them online now. You're correct, they're not cheap or easy to find. I haven't found exactly what I'm looking for and when I do, I estimate it will be around $75 (+/- $25) so if you've got one you don't need or want, I would gladly lighten you load. I appreciate the offer.

P.s. it doesn't need to be exactly .22 for what I'm doing. Anything between .22 and roughly .30 would work to make this adapter. Just as long as it makes a straight hole, I can work with it.

This is something I know I have, and it is in there somewhere. For a while at least, the whole garage, (and everything I play with involving machines), is at present being messed up by a building operation that will create a washing/utility room and hopefully leave me with a nice man-space for my lathe activities. I will have serious look for it, but I don't promise it is not stashed a bit far to get at easily.

Like a gun-drill, a boring bar also cuts at only one place relative to the rest of the machine, and the forces and support are constant direction.

As to ethics, notice that it is not the makers nor users honestly out in the open that are the problem, regardless those who apply laws as if they were the guilty. The bad guys will acquire them anyway, and they won't be on a public forum. Here (UK) one is in serious trouble if anything to do with a handgun, which is seen as having only one possible illegitimate purpose. Strangely, it is however, legal to be a licensed gunmaker, the various goods often for export also. I am not sure the position on handguns specifically.

 

[SLK001]

It could be your drilling technique. I start a hole with a center drill that I continue to drill with until I'm as deep with it as I can go. If the hole is larger than 1/8", I start there. It's a PITA, because you have to clear it FREQUENTLY. But this creates a straight hole that I can now put a drill WITH THE SAME DIAMETER as the center and continue drilling. The hole created by your center will perfectly guide your twist drill and minimize wondering. Peck drill a hole with no thru pilot. Clear the bit frequently. Use adequate oil. If you need a larger hole, step drill in small increments up to close to your finished size. Bore to final size, if straight is your goal (and it usually is).

That's the technique I use for drilling (mostly steel).