Drilling/Boring a deep hole

[The_Apprentice]

So, for a project my girlfriend is working on, she has a 4.5" long roundbar. She needs about a 1/8" hole down the length of it.

I thought, no problem, I'll just add it into collet-chuck and use the tailstock to drill a hole. And maybe even bore it out smoothly in the end.

Here's the problem, even the longest drills I have in 1/8" size, have flutes just under 2". So even if drill down the length of the roundbar from BOTH ENDS, I still can't meet in the center. And even if I could meet in the center, I wouldn't be able to even bore that out, unless I magically have perfect concentricity, which I'm really not expecting with chinese machinery here.

Also, I tried looking for long boring tools in that size/length on Amazon, etc, but they seem to be extremely rare, and I'm sure for a good reason.

Checking here to see if I missed any possible unorthodox work-around, or if there are a special type of drill/boring bars that long for a 1/8" size shank?

 

[JimDawson]

Most good hardware stores carry long drill bits, this is not normally the case with the big box stores but you might get lucky. I have several long 1/8'' bits, in different lengths, that I purchased from my local Ace Hardware.

You can drill well past where the flutes end on the drill bit, but you have to pull the bit all the way out about every half drill diameter of cut depth and clear the flutes. Use plenty of cutting oil and don't turn too slow.

 

[David S]

Aircraft drill bits are 6" long overall, but still have a flute length that is only around 2" or less. So with lots of patience and "pecking" you could get it done. Now does this hole have to be really nice inside?

Not sure of a boring bar that long that would be strong enough to not deflect considerably.

David

 

[RJSakowski]

Aircraft drills are normally 6" or 12". Taper length drills are around 5" long in 1/8" diameter. If I werwe drilling this, I would drill with a smaller drill and finish bore with the 1/8".

 

[The_Apprentice]

Hey Jim, I did try experimenting with going past the flutes. But there is a problem with this. Even though the shank doesn't look thicker than the flute edges, I get a lot of restriction and a hell of a lot of rubling and chatter, etc. the second I reach the end of the flutes. Not to mention, everything gets VERY hot quick.

Maybe my Titanium Coated MasterCraft drill-bits just are designed a bit unorthodox from the norm. I'll see about picking up another brand. Now that I think of it, I should have done so while at Harbor Freight this morning. Doh!

 

[T Bredehoft]

For a product for your girl friend (quality) you might want to buy your tooling from a more 'reliable' source.

 

[Nogoingback]

Now does this hole have to be really nice inside?

Not sure of a boring bar that long that would be strong enough to not deflect considerably.

David

If the hole needs to be accurate, you might consider drilling first and reaming to size. A long skinny drill may deflect quite a
bit, and as David said, boring will be sketchy as well.

 

[Chuck K]

Unfortunately, the reamer will follow the drill. Boring it would staighten it out, but like you said, thats a tall order for such a small deep hole.

 

[EmilioG]

Straight flute or single flute gun drill should work, but I think they're fairly expensive. Good ones, like Guhring, have pilot tips.
Also, the RT100 T Guhring. These are all $200 plus drills! Msc has them and some USA made, that are less expensive.

http://www.guhring.com/Documents/Catalog/Drills/DeepHoleFlyer.pdf

 

[Chipper5783]

That's a pretty "deep" hole. The L/D is not in your favor. The length of the flutes probably won't help you. For most metals, once you get past L/D of about 5 the chips will start to pack up any way - you still need to "peck" away.

You need to provide more information. What is the material? What tolerance are you looking for in size, straightness and surface finish? If you just want to pop a hole - get at it.

You can't bore more than about 10 L/D - especially such a small hole. As holes get bigger there is some fancy tech that will get you further but no way are you going to bore a 1/8 hole 2.3" deep.

Single flute gun drills can make incredibly deep & straight holes. The actual drill is the cheapest component of the system. One of the main features of a gun drilling system is that the chips must be cleared as you are drilling. The systems I have seen employ high pressure / high volume coolant - either pumped or air driven. The material must also chip properly so that the chips can fit down the flute.

The technology is amazing, and certainly if this were a revenue task and you had very many holes to make - then it would be worth it to acquire a gun drill set up.

Don't sweat it - just get some decent drills, start with a shorter one, then work up to a longer (i.e. "aircraft"), load up the hole with your favorite potion and peck away. Make sure you give the hole a nice on center start (i.e. drill it 0.1" and then bore it to 0.125" for a depth of about 1/4"). For boring such small holes, I use a small end mill held in a toolpost mounted drill chuck. The end mill is clocked so one edge is acting as a small boring bar - just take out a little skim to center up the starting hole.

Let us know how you make out. David