Drilling deep with a dinky drill?

[Doc Nickel]

Keep your mind out of the gutter.

I have to drill some aluminum blocks (6061 extruded bar, off-the-shelf stuff) almost 10" deep with some tiny holes, either 3/32" or 7/64".

The holes don't have to be prefect dimensionally, but they can NOT wander more than a fine frog hair off of true. In one spot, I have a bit under 0.050" to an air passage, and that's near the center of the block where any wandering of the bit would be most pronounced.

I have a couple of 3/32" 6" drills, brand-new never used, never resharpened, and I'll be drilling in the mill using the quill as normal. Center drilling to start, lots of lube, rigid setup, the works.

Is there anything I can do to minimize any wandering?

Doc.

[Norman Atkinson]

Doc,
Gawd knows what you want to do it for.

I've done it on things like African Blackwood and with thinner and longer drills.Most of the time it has proved hair raising.

The first thing is to remember is that you need to start the drill. Ideally, a conventional twist drill is unsuitable.
What you really need is to start the job with a spade drill. Then it should have the burr removed and a D Bit will carefully be inserted- until the side is almost full of swarf. then it is removed and cleaned and re-oiled with neat cutting fluid. The process is repeated until the hole is made.

There may be other readers with ideas about things called gun barrel reamers or spills but I have no direct experience.

What must be said is that there is the constant risk of the drill overheating and jamming in the hole.

With precious little clair voyance, I think that you have made this discovery already!

Good Luck

Norman

[Timleech]

<font face="Verdana, Arial" size="2">Originally posted by Doc Nickel:

Is there anything I can do to minimize any wandering?

Doc.</font>

I can't offer the benefit of any direct experience except to remember that your quill extension or table height will be different between centre drilling and starting your long drill, & you need to be sure that the alignment doesn't change, so there's no sideways force on the drill. You might be lucky enough to have a perfect mill, but it's something you ought to check.

Tim

[precisionworks]

Parabolic drills are made to drill as deep as twenty diameters. MSC, J&L, etc. have them.

------------------
Barry Milton

[J Tiers]

Use an aircraft bit, one with about 3/8" max of fluting, and the rest solid.

use the lathe, and have the part turning, not the drill. You'll have to peck drill.

I have drilled 9" with a 3/16 bit, but your length to diameter ratio is more than that. I came out about 0.005 off center, which was perfectly acceptable.

[SGW]

Withdraw to clear chips about every drill diameter of depth (i.e., extremely frequently!)

[pete913]

Start with a center drill, then a short drill of the same diameter as yourlonger drill, then start the long drill. Feed carefully,and if after plunging back down the hole,you meet with more than normal resistance,you may have a chip caught under the tip. Time to back out and clean the hole out before proceeding, as this can cause the drill to wander off center.

[darryl]

I would be inclined to do that in a lathe, and start by getting the start of the hole exactly centered. If you snug up the tailstock so you can still slide it by hand, you can save time and handcranking as long as you can push the tailstock and make the bit cut. It would be great if you could spin the drill bit from the tailstock end as well as have the work revolve in the spindle.
You said you'll do it in the mill, if there's any way you can arrange to rotate the workpiece say 90 degrees after every quarter inch or so of drilling, that should help keep the hole going straight. After you're in about an inch, rotating the workpiece won't be able to make any difference. That's going to be a lot of mucking about drilling that small of a hole that deep.

[elbryant]

I met a guy in the St. Paul who did research on injectors - lots of small holes. He used a laser.


Ed

[Paul Alciatore]

I've never done anything like that but it would scare the heck out of me. Even if you do 10 perfectly, you could hit a hard spot or void in #11 and go way off. It wouldn't take much to deflect a 3/32" drill 1/8" over 10 inches.

I would be tempted to try laser like was suggested above or perhaps making a pilot hole with EDM and then bringing it to size with a drill. And definitely a lot of pecking to clear chips from the drill.

Sounds like some real expensive holes to me. I would do it as early in the process of machinning the part as possible to avoid too much expense in the rejects.

Paul A.

[Paul Alciatore]

20 X 7/32" = 4 3/8". He wants 10.

Paul A.

<font face="Verdana, Arial" size="2">Originally posted by precisionworks:
Parabolic drills are made to drill as deep as twenty diameters. MSC, J&L, etc. have them.

</font>

[Norman Atkinson]

Paul A-

Agreed, Agreed, Agreed!

This is why I suggested using D Bits

I was drilling- or trying to go to -13" with .125 silver steel-( your drill rod.)

Doc,
I had the use of all the facilities of an Engineering College. I finally went home and did it as suggested.

It is a matter of- constantly clearing chips.
This is what other contributors have affirmed. In your costing, you should add a loading for grey or disappearing hair!

Norman