Expand hole in steel?

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I have a grating which is held down by two padlocks which go through a hole in the part that is cemented-in and the other side through the grating itself. Unfortunately the holes are about 3/8 inch diameter (poor design by the contractor) so this makes it hard to get the shackle properly lined up and the padlock closed. I want to expand the hole to around 3/4 inch. Oh, BTW the steel (mild) is about 3/8 inch thick.
What tool can I use? I don't have the luxury of removing it all to a machine shop and using a boring machine or an arbor press and a punch. I have to do it in place using hand tools but from prior experience I know that if I try to feed the 3/4 inch bit through the 3/8 inch hole it'll immediately seize and likely break the bit. A step drill will be far too small--only good for sheet metal really. Do they make some sort of tapered drill bit like the old-fashioned type for wood screws? Where would I look and what would I search for?
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On 7/22/2011 9:57 PM, snipped-for-privacy@nowhere.gov wrote:

Cutting torch. AKA blue tipped chisel. AKA acetylene sixteenths
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Steve Barker
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Hmmm. Don't I need oxygen to do cutting using acetylene?
In any event sounds like overkill. If I wanted to do some welding I'd use a stick welder which I have and weld on two rings (eye bolts cut to length) a couple of inches away. This is what I anticipated the contractor doing BTW but unfortunately my attention lapsed.
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wrote:

The type of steel would determine that. If it is cast iron, you'd be wasting time, and possibly magnifying the problem.
Steve
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On Fri, 22 Jul 2011 22:57:46 -0400, snipped-for-privacy@nowhere.gov wrote:

Do the job in small increments. Start with a 7/16, then a 1/2" etc.
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It's called a reamer. Google "reamer".
Steve
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snipped-for-privacy@nowhere.gov wrote:

Hi, Reamer?
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Rat-tailed file. Been kickin' ass and takin' names since the 16th century. You'd be amazed what the right file is capable of, specially on soft steel.
nb
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vi ...the root of evil

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On Jul 22, 10:57pm, snipped-for-privacy@nowhere.gov wrote:

Use a padlock with a smaller diameter shackle with a longer length...
Rather than expanding the holes make the thing you are threading through them smaller and longer and therefore easier to line up...
~~ Evan
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No can do. The hole in the part that is cemented in is about 1/2 inch from the wall, thus the shackle has to swing to the down position in this distance. Hard to explain but I've tried what you're suggesting.
Further I'm limited by the availability of rust-proof padlocks. I already have two padlocks that fill the bill by means other than coating it. Coatings would make the size of the hole even larger.

Already I'm at what I consider to be the bottom limit thickness-wise for reasonable burglar proofing.
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On Sun, 24 Jul 2011 00:02:15 -0400, snipped-for-privacy@nowhere.gov wrote:

If you are worried about burglar "proofing" a hardened shank padlock in a mild steel "ear" is a waste. The ear pert can be hack-sawed off quite easily - while even a 3/8" hardened padlock will require either a grinder or a torch. No such thing as "burglar proof".
The setup on a shipping container is as close as you'l get - hardended padlock up inside a 1/4" thick steel box for the main lock, and 1/4" hardened padlocks on each of the four "draw-in" larches.
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Google "how to pick a padlock". Someone experienced can be in there in fifteen seconds or less. OR, I have a pair of bolt cutters that are 54" tall. Ironically, I bought them at a police evidence auction.
Steve
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On Sun, 24 Jul 2011 13:52:44 -0700, "Steve B"

You will NOT pick either of the padlocks I have occaision to open on a weekly bsis 0 not in 15 seconds, or 15 DAYS. I'll guarantee it. And a bolt cutter won'r cut the shank either. a cutoff wheel will get you through in a few minutes - per side. And you need to cut both if you are going to get in.
On the one application you will need to cut off the 1/4" thick box to get to the shackle before you start grinding on it.
C4 would be a lot easier, and likely less expensive.
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wrote

There are applications that would be difficult. There are very few that are impossible. Today's padlocks can be picked, bumpkeyed or opened in many ways. They are just devices, and a key is an easy thing to get. Look at the lock. Is there a number by the keyhole? Anyone in the locksmith world can buy a duplicate.
I'm not saying yours is one that can be compromised. I saw a lot of fine lock arrangements that were on pool tables, dispensing machines, etc. But none were foolproof or burglarproof. And with a pro, all bets are off.
A cutting torch even in the hands of an amateur can cut 1/4" steel very quickly.
Every device I have ever created was merely to delay entry, or to make the bad buy move on to the next location. I knew how easy it would be to defeat them if someone chose to do so. And would tell that to the purchaser. Many can be defeated as easily as a chain with a hook and a truck with a receiver hitch and a ball.
And C4 is NOT hard to get, either. Thermite is easier, cheap, is silent, and that will melt rocks.
Steve
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On Sun, 24 Jul 2011 21:01:33 -0700, "Steve B"

I'd LOVE to see someone pick either a Medeco or a Multi-Lock Interactive padlock, and unless the locksmith is also a crook, good luck getting a key!!!!!

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snipped-for-privacy@snyder.on.ca wrote:

You are of course absolutely correct about burglar-proofing however even the shipping container isn't burglar-proof. Forget padlocks! Can't they (whoever "they" are) just go in through the sides? A plasma cutter will go through just about anything, I'm told.
But that's not the sort of burglar-proofing I'm talking about. Like they say, if you encounter a bear in the woods you don't have to outrun him, you just have to outrun your companion (something like that).
This is part of a thing referred to as a coal-hole cover and is just below an air conditioner cage which is just to the right of the mail box which is a couple of feet from the front gate (think prison cell door, not the thing in most people's front fence). The coal hole cover is a frame set in concrete with a steel plate (about 3' by 3') held on by two side facing strap hinges on the house side and a liftable rosette on the front side (to lift the plate for access and originally to dump coal down (the reason for the name)). At the bottom of the hole (concrete lined) there's a double thick (2 sheets of 3/4 glued and screwed together) plywood door bolted on the inside with 2 vertical bolts and one cross (or normal) one. The bottom of the hole is about 15 feet from the cover. To increase the security, 20 years ago I welded two pieces of angle iron on the sides of the frame (underneath the cover) and constructed a guard of 1/2 inch bars in a cross formation (think prison again). These were secured by welded-on bolts going under the angle iron and held in position (closed) by padlocks going through the hole in the slide portion. The prison bars are needed because sometimes the plywood door and the cover are open for ventilation leading to the fear that not only could some mope (ask Hey Bub) enter with malicious intent but the mailman or UPS guy could stumble and kill himself by falling down the shaft.
Well, about 2 years ago, due to my poor maintenance (and the fact that it's about 110 years old) the cover finally rusted beyond saving so I had it rebuilt but instead of the prison type bars (the mailman could still break a leg) I had the contractor use the grating steel that's seen on subway ventilation covers. Now (change of locking hole size) I want to make it easier to open and close the grating (I also use it to get out ladders from the cellar). Phew! Now you know everything. Let me emphasize that everything is mild steel; no cast iron.
Thanks to all of you for your help.
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On Jul 24, 10:42pm, snipped-for-privacy@nowhere.gov wrote:

Given your better description of the problem, seems to me the ideal solution then is to borrow or rent a torch set if you don't have one, and simply bring the hasps up to dull red heat and mold into position with a nice long piece of stiff steel sized to the holes. Allow to cool and done. Fabricators do this all the time.
Joe
Joe
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On 07/22/2011 08:57 PM, snipped-for-privacy@nowhere.gov wrote:

The material to be removed is steel, not concrete?
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e

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wrote:

Yep, both of these will work. Buy lots of dremel bits. But for the cost of those bits, you might be able to rent a cutting torch for an hour and do the job in minutes rather than spend many hours.
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On 07/23/2011 03:23 AM, snipped-for-privacy@myplace.com wrote:

Or just borrow a big hand drill with a 1/2" chuck and a 3/4 drill bit (I say borrow as these are Not Cheap) and drill it out. Make sure the drill has a handle for your other hand, and have a friend handy to drizzle cooling oil on the bit as you go. Use a slow speed to keep from burning up your friend's $20 drill bit.
good luck
nate
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