How to extract set screw?

Deep in a large machine (offset printing press) an allen set screw holds a shaft in a casting. The set screw is also locked in place with a lock nut
(the screw protrudes from the casting enough to fit the nut).
The allen wrench is 2.5mm and the lock nut is 10mm so the diameter of the screw is probably 6mm (1/4 inch)...
I removed the nut but the allen wrench (a new one) is slipping in the screw. How do I go about removing this? Access is only head-on (no side room for vice-grips or such). The environment is one where lubricating oil is literally raining on these parts so the "blue flame wrench" solution is out.
I tried a bit of banging on the side of the screw (yes, funged up the threads so the nut won't go back on) but this didn't budge it.
Are these allen screws hardened? Is it OK to try drilling for a screw extractor?
Thanks,
--
Al, the usual


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could the hex drive be metric instead of inch?
i ** Sent from my Google phone ** I apologize for any typos **

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If it slips, check the alternate system (metric/SAE)for the similar sized wrench. I see many pieces of machinery that have both systems in use. Makes for very frustrated mechanics!!
If that does not work, drill it out with LEFT HANDED drill that is slightly smaller than the minor diameter of the threads (the drill should be a sloppy fit for the nut you took off). Use very low speed (200rpm is great) and lots of pressure. The set screw is likely somewhat hard but not carbide hard.
Usual Suspect wrote:

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wrote:

Alloy set screws are quite a bit harder than regular socket heads, around Rc 50, and drillable with HSS in a pinch, but just barely. The corners of the socket are almost guaranteed to chip the cutting edges of the bit, so expect to resharpen it a few times, or have some spares handy.
In this case, where the set screw is bottomed on a shaft and an Allen wrench didn't loosen it, I don't think LH bits will make much difference.
The other thing to watch for is, since the screw is much harder than the casting, if you allow the drill to wander it's going to want to walk into the casting in preference to cutting the screw.

--
Ned Simmons

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If there is enough room, use a 7/64" bit on a hammer driven impact driver. A 12oz hammer will be about right. The bit should be a very tight fit in the slightly waled out hole and the impact driver should shake the screw loose. If the bit won't go into the hole at all, either a 2.5mm bit on the impact driver might work, or grind a slight 45 deg lead on the end of the 7/64" bit with an oilstone or diamond file etc.
Forget the screw extractor except as a last resort if you've sheared the top off the screw.
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6mm grub screws require a 3mm wrench.
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Usual Suspect wrote:

Use a punch that will just fit into the hex hole and drive down on the set screw. This will dent the shaft or the end of the screw and take pressure off the screw so it will turn much easier.
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Ralph Henrichs wrote:

Ralph
I have never heard that one before but I think I will add that to my bag of tricks, sounds like a winner Thanks
CarlBoyd
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A really hard axial blow with a hammer (and punch if needed) will do wonders for freeing many types of stuck fasteners. Where possible, radial blows can help but are more likely to cause unwanted damage. Heavy blows around a nut or external pipe fitting will nearly always stretch the metal enough to free any frozen connection.
An oversize hex key can be tapered on a grinder to get a good bite in stripped holes, especially if driven in.
Don Young
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I just had to remove 4 well rusted set screws just like you describe today. I had to use every trick in my book, but I got them all out. The two best tricks: 1. This is similar to what one othe poster said: Get a brand new hex key and cut off the short leg with an abrasive wheel. Clean up the cut off end. Stick the non-cut off end into the set screw and beat on the newly cut off end with a couple pound hammer. Several sharp taps are better than huge blows, I think. 2. If the hex key is slipping, even after you do all the size checking that others are offering, try this. Get some valve grinding compound. If it is in dry form, add a little oil to make a slurry. Dip the hex key into the valve grinding compound and then stick the key into hole, allowing as much of the valve grinding compound as you can to go down into the hole. Now turn the key. This is a remarkably effective!!!
I assume that you do have enough room to turn the long leg of the hex key.
Pete Stanaitis ----------------
Usual Suspect wrote:

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"spaco" wrote: (clip) Get some valve grinding compound.

^^^^^^^^^^^^^^^^ There is a product on the market in a little tube, that is meant to keep your screwdriver from slipping in the slot. It is overpriced, but I bought some, thinking that if it saves me from one bad situation, it is worth it. I have never needed it, and, of course, by now I don't remember where I put it. Your idea sounds cheaper and better. I never thought of using it on Allen heads, and many of you probably never thought of using it on ordinary screws. I'll bet it would work well on Phillips heads where the driver wants to cam its way out.
Aside: Do you suppose the astronaughts took WD-40 or Liquid Wrench with them when they went to change the camera?
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Not likely. Volitals are a bad idea in a vacuum.
JC

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I don't know what kind but I did hear them referring to using a lubricant of some sort.
Don Young
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Dichronite was originally developed in the sixties for aerospace applications as a dry lubricant where it would be exposed to deep vacuum or liquid oxygen. It is referred to as a modified tungsten disulfide coating and exhibits several desirable dry lubricant properties.
The Coating: Dichronite coating is a thin, uniform, chemically inert , non-toxic, coating with high lubricity. It is non-magnetic, contains no organic binders, solvents, or adhesives and has high load capacity.
It is intimately attached to the substrate using molecular bonds and acts like a permanent mold release. It will not rub off or transfer.
These guys make other stuff as well. http://www.chemical-supermarket.com/product.php?productid90
Interesting site if you want to poke around.
JC
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    [ ... ]

    I somehow doubt that either would work well in a vacuum.
    Enjoy,         DoN.
--
Email: < snipped-for-privacy@d-and-d.com> | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
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You've gotten quite a few very useful suggestions, but I would recommend that the nut be put back on if at all possible, before trying to drive something into the socket that fits tighter, to try to keep the sides from splitting away.
Another method that's commonly mentioned is to weld a nut on if there is room to fit a socket or nut driver. This wouldn't be so easy to do inside an oily gearcase, but possible with a MIG welder if some foil or other material can be used to catch any splatter from the arc. If attempted, check the current path to see that the welding current isn't passing thru precision bearings.
--
WB
.........
metalworking projects
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Many many thanks for all the great suggestions. When Monday morning arrives I'll try them all.
Thanks!
--
Al, the usual


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wrote:

Try driving in a Torx bit. Works fairly well and pulls out the bolt
Gunner
"Somewhere a True Believer is training to kill you. He is training with minimum food or water,in austere conditions, day and night. The only thing clean on him is his weapon. He doesn't worry about what workout to do--- his rucksack weighs what it weighs, and he runs until the enemy stops chasing him. The True Believer doesn't care 'how hard it is'; he knows he either wins or he dies. He doesn't go home at 1700; he is home. He knows only the 'Cause.' Now, who wants to quit?"
NCOIC of the Special Forces Assessment and Selection Course in a welcome speech to new SF candidates
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Drive in a torx bit is the best, if possible. I think you are telling that the Allen is as the top of the hole in the casting. Can you use a hacksaw or dremel to cut a straight blade screw driver slot in the top of Allen? I've had good luck using a really heavy screwdriver that is a good fit, lots of pressure, and a crescent type wrench to turn the screwdriver.
--
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Keep the whole world singing . . . .
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