View Full Version : Deep hole in steel

04-12-2004, 04:52 PM
Folks -
I need to drill a 3" hole in a "sandwich" of steel plate that is 11" thick. The sandwich is made up of a piece of 1" plate, a piece of 9" plate, and then another piece of 1" plate. The sandwich is horizontal, but I have access from both sides. I was thinking of a pilot hole thru the sandwich, so I have a common work axis, then using a mag base drill to go from both sides to minimize the depth of drilling from each side. All the plate is SA516, Grade 70. Trouble is, I'm having a hard time finding a hole hawg or cutter that'll cut a minimum of 5 1/2" deep (kind of like a concrete hole saw). Any sources or other ideas?
Thanks, Zim

Bruce Griffing
04-12-2004, 05:02 PM
Does this have anything to do with a bank?

04-12-2004, 07:05 PM
http://bbs.homeshopmachinist.net//biggrin.gif http://bbs.homeshopmachinist.net//biggrin.gif
"....a bank". http://bbs.homeshopmachinist.net//biggrin.gif http://bbs.homeshopmachinist.net//biggrin.gif

That, I think, is the best laugh I've had yet on this board!

Tho I wonder how many questions are posed on the internet each day to solicit info for illegal purposes, if the truth were known.

....can anybody here suggest a good method for cutting thru 1" steel bars when your only cutter is a shoelace and some toothpaste? http://bbs.homeshopmachinist.net//biggrin.gif

[This message has been edited by lynnl (edited 04-12-2004).]

04-12-2004, 07:19 PM
Have you thought of waterjet? If you need a tight tolerance on the hole you could water jet then drill or ream it out to the final size to get rid of the taper left by the water jet expansion.

04-12-2004, 07:23 PM
Lynnl, time... lots of time.

04-12-2004, 07:28 PM
Will what your dirilling fit in a lathe or
on a mill? If on a mill there are an abundance of cutters for deep holes and of course boaring bars for lathes.

04-12-2004, 07:33 PM
Well if you have one of those mag drill with a long stroke then you could use a pilot spade drill such as the ones made by APT.But you will need to pour on the coolant.

John Stevenson
04-12-2004, 07:35 PM
<font face="Verdana, Arial" size="2">Originally posted by glenj:
Have you thought of waterjet? If you need a tight tolerance on the hole you could water jet then drill or ream it out to the final size to get rid of the taper left by the water jet expansion.</font>

3"diameter, thru 10" of steel??
Only if your name is Mad Mountain Dean http://bbs.homeshopmachinist.net//biggrin.gif http://bbs.homeshopmachinist.net//biggrin.gif

John S.

04-13-2004, 12:03 AM
Take it to a military firing range. They'll take care of it in no time.

Mike W
04-13-2004, 12:18 AM
"the bank" almost made me spit my coffee on my monitor. http://bbs.homeshopmachinist.net//biggrin.gif

G.A. Ewen
04-13-2004, 12:24 AM
Quite a challenge. I think that I would step drill a pilot hole as large as possible using twist drills and then fashion a pilot bushing for the back side of the pilot hole so as to support a boring bar. It's going to be a big job no mater how you do it.

Forrest Addy
04-13-2004, 01:52 AM
You have one hole? Take it to a mahine shop and have them put it up on a HBM or a radial drill. There's a boring kit that works with smalled drill where you drill 1" and increase the bore incrementally with a piloted boring bar.

This is not a casual job. If not gone about rationally you could get in big trouble. I wouldn't reccommend drilling except to remove the bulk of the stock. Leave 1/8" stock. Boring for size, tolerence, and location is the way for go if you have to do this job with portable tooling.

04-13-2004, 08:38 AM


I see cutters listed up to 4" diameter by 6" depth of cut.

Of course you'll need something larger than a common mag base drill to power it.

We use the Rotabroach cutters in the CNC mill all the time with a coolant adaptor for through the shank application which is essential for deep work.

The cutters hold diameter very well. I'd say most of our work holds to within plus .005" on diameter using the 2" size.

04-13-2004, 11:37 AM
Spade Drill, to size, 1 pass. Radial Drill Press, or HBM, VTL, or Engine Lathe. If you can lash this mess down to a machine, there are many ways to do it. If you are stuck with portable tools it's going to be a bitch any way you do it, and take a long time.

04-13-2004, 12:02 PM
DR -
Perfect. I knew somebody made that type of "hole cutter", but couldn't find anything surfing. Kind of hard to move the 9 ton piece of gear I need the hole in to the big radial drill in the machine shop - so I was thinking mag. base drill or something like it.
As to the bank, I had a good laugh over that too. But come to think of it, a bundle of US bills will nicely pass thru a 3" hole. Why didn't I think of that before? Screw working, let's broach a hole in a bank! If some 90 year old guy in Texas can do banks, can't we?

04-13-2004, 12:17 PM
I would first ask the enginear,what the hell
where you thinking?,then since your working
with 10" worth of steel,get out yuor BIG
blaster and blow about a 4" hole and weld in
a sleve.
I still think this is a joke.Give us some
more details. Are there any noise restrictions,or time requirements,and if
portable tools are needed do they have to fit
in a 3' hole in the ground?

Bob Indiana

04-13-2004, 12:23 PM
Fast hole EDM can handle it easily.

J Tiers
04-13-2004, 12:48 PM
He DID say he had access from both sides, I think that kinda lets out the bank aspect of things.

I am assuming there isn't about a 4" hollow in the middle of this stackup...........that might change my mind.

04-13-2004, 02:54 PM
Not a joke. Kind of wish it was. Threads are torn up pretty bad in a 6" deep 1 1/2"- 6 blind threaded hole. The threads are in the 9" piece of plate, trapped between the pieces of 1". All the plates are about 7' in diameter and welded to beat hell. Threads take a bolt that is installed, torqued, then removed a number of times during the space of a job. Thought it would be easier to roto-broach (thanks DR) a plug of material concentric to the blind hole than to overdrill and bush back to 1 1/2" (no room for a larger dia. bolt anyway). Considering hundreds of boltup cycles, a helicoil didn't sound like a long term fix. Also no room at the bottom side for a nut - as in just drill the hole out and use a nut and bolt. Once the plug is out, our very capable machinist could turn a plug, with a new 1 1/2-6 hole in it, for a nice fit, then weld in the plug. Seemed easier to drill at the jobsite than other machining processes. But I'm open to anything.

metal mite
04-13-2004, 03:27 PM
Helicoil sounds easier.

They do sell coil removing tools for when it gets screwed up.

We used to install helicoils on drive shaft couplings for atomac submarines

To do it the other way,
You'll have to rent one of those mag drills about four feet high with low rpm.
My little Black and Decker will burn a 1" drill.