Very Deep Hole Drilling

[No1_sonuk]

I have a project that requires a 0.43 inch (roughly) hole drilled 11 inches long in aluminium.

I've tried contacting a couple of local gun drill manufacturers, but got no reply.
Any ideas how to make one?  A normal D-bit might be too slow to use - peck-drilling that far.

[sbwhart]

Blimey what do you want a hole that deep for ?.

Any way this is what you can do you need a couple of drills of the required size, with parallel shanks. You'll find the the shank ends are soft, set them up in the lathe and turn a spigot on the end of the shank then silver solder or braze fasten in some way an extension to this to get the length you want, you may have to do this on two or three drills making each one progresivley.

When you come to drill the hole first use an unmodified drill as deep as you can can get, then an extended drill as deep as that one will go and finally the longest modified one you've got to get the depth you want.

You'll need to keep withdrawing the drill to clear the swarf and give it a squirt of WD40.

You didn't say what machine you will do it on lathe drill or mill, you may find that feed travel is a problem you may have to keep moving your set up:- the tail stop forward to get feed thats why you'll need more than one extended drill.

I'd have a good look and a think at what your trying to do, a design change may get you around the problem,
allowing you to use a length of tube.


Hope this makes sense

good luck

Stew

[bogstandard]

What Stew has said hits the mark.

Even with a 1/2" drill at that depth, it acts just like a 1/16" one at say 4" depth, if you don't take it very gently, with continual withdrawing and swarf clearance, plus as much flood coolant as you can get down the hole, it will wander way off course.

If you could drill from both ends accurately enough with a shorter, say 6" drill, then maybe you could get away with a long D-bit for final finishing.

You can buy special deep hole drills that tend to keep the wander under control, but you will most probably have to save your pocket money for a few weeks.

http://www.tapdie.com/html/drills_long__long_metric_hss_d.html

http://www.tapdie.com/html/oilfeed_coolbor_long_mts_drill.html

I have an 8.6mm one that would help you get to 9" deep, and a 3/8" reamer that will get you to about 7.5" if they would help. My 12" long 1/8" ones were cut down ages ago to make 6" ones.

Bogs

[No1_sonuk]

It's a lathe that I'll be using.

It's needed to cover a smaller tube running down the centre.  As such, the finish on the inside of the hole isn't all that important, and can be a bit smaller than 0.43".

The extended drill bit idea just reminded me of something similar I've seen elsewhere.  Someone extended the shank.

[Jonny]

I'll just add that i would extend standard straight shank drills its far cheaper. First one well under size something like 5/16" or 3/8" and drill through. More than likely it will have cut a taper or veered off, thats where the coolant and dragging the drill out often counts. Doubt you will have 11" tailstock travel so will have to push drill in with tailstock, lock up, drill 3 to 6mm deep increments, keep pulling tailstock out with drill. What you dont want is the drill or job to get warm plus clog up with aluminium swarf, loads of coolant.
Next get near the finished size hole with another extended drill. May find it will straighten up the previous hole!
Finally dependant upon required finish slap another extended reamer down as slow as you can go even better back gear loads of torque.

Did this well over 6 years ago so a bit hazy. In this block of HE30TF top is 1/2" dia thru hole 9 1/2" long, middle is 5/8", silver steel rods inserted in holes total runout a few thou, surprised me considering i slid it down in a four jaw chuck. Tailstock travel i have is 4".
http://pic20.picturetrail.com/VOL15/728921/1723145/20513282.jpg

[Jonny]

Missed this bit but for me to get any concentricity and runout after extending i do it my way.
Turn down the shank, often softish even morse tapers can be. I turn a stub of substantial length and fit to go in a drilled hole in a bit of steel round. Chamfer both pieces and either braze or silver solder, it will be man enough but no good for draw bars. If welding tack in 3 or 4 places round circumference to eliminate some of the warp/veering off.

[No1_sonuk]

Thanks.

WRT feed length, mine is 2" (Chester DB7) I had thought about holding the bit in a boring bar holder on the carriage to get a longer travel.
I know it'd be a pain to centre, but any thoughts on how practical that might, or might not be otherwise.  I will be able to get at least 1/3 the blank into the spindle bore.

From my point of view, it's looking more and more like making a D-bit is the lesser of several evils.

[Jonny]

Unless i am missing something, you are not going to be able to do it.
11" long, say 4" in chuck leaves approx 7" protruding.
Lathe centres only 12" minus chuck etc, probably only have 3 to 4" before tailstock and an 11" cutters got to go through!
May be able to nick some length by dismantling carriage etc but its not going to gain you 7" at best.
Will need at least on your set up about 19" centres.

Any way of mounting the part on carriage and drilling with the lathe chuck?
You could then drill in with normal standard drills then replace with the made up long ones which would be in the hole already done!

[Stilldrillin]

Hasn`t an 11" long hole got 2 ends?  

I make that 2 x 5.5" holes.....  

David D

[No1_sonuk]

Good points.

Mounting it on the carriage is a possibility if I make a fixture for it.

Drilling one end, then the other would be problematic because of the short between-centres issues Jonny mentioned.  It can go in 1/3 of the way one way round, but not the other - probably about an inch or so.

Hmm.  It might be feasible to make it in 2 parts, though...