Removing Socket Cap Screws With Lok-Tite

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Discussion Overview

The discussion centers around the challenges of removing socket cap screws that have been secured with Loctite. Participants explore the effects of heating on the screws and the surrounding material, as well as the implications of different methods for removal.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant describes their experience trying to remove screws secured with Loctite, noting the use of heat and penetrating oil.
  • Another participant suggests that heating the hole part of the screw may help loosen it, questioning the effectiveness of the Loctite used.
  • A participant expresses surprise at the concept that the hole expands as the surrounding material heats up, prompting a discussion about the mechanics of expansion.
  • One participant uses an analogy involving a chain to illustrate how material expands outward rather than inward, relating it to the expansion of holes in materials.
  • Another participant concludes that if all parts are heated equally, the screws should remain equally tight regardless of temperature, but notes practical limitations in their specific situation.
  • A suggestion is made that an impact tool might have been a more effective method for removal.

Areas of Agreement / Disagreement

Participants express differing views on the effectiveness of heating in loosening screws and the mechanics of material expansion. There is no consensus on the best method for removing the screws, and practical limitations are acknowledged.

Contextual Notes

Participants discuss assumptions regarding the uniformity of heating and the coefficients of expansion, as well as the specific context of the screws being used in a wood chipper, which limits access for removal.

gnome
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OK, not the usual kind of question posed here, but not entirely off-topic either.

Last weekend I was trying to remove a couple of socket cap screws (recessed hexagonal drive) that were installed with lok-tite (thanks to the lawyers). After multiple applications of heat from a propane torch, liberal amounts of penetrating oil, and using a hex socket drive on a torque wrench, I managed to remove 1 and strip 2 others, so I'm looking forward to an adventure of drilling, screw extractors, etc.

During the struggle, at first I was trying to turn the screws immediately after heating. Later, after heating again, I waited until everything had cooled to try again. Now I'm wondering, ignoring the effects of the loktite, is heating more likely to make a screw looser or tighter, or neither? Clearly, the screw must expand. What happens to the hole? Does it get bigger as the drilled part expands, or does the material expand into the hole, making it smaller?
 
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gnome said:
OK, not the usual kind of question posed here, but not entirely off-topic either.

Last weekend I was trying to remove a couple of socket cap screws (recessed hexagonal drive) that were installed with lok-tite (thanks to the lawyers). After multiple applications of heat from a propane torch, liberal amounts of penetrating oil, and using a hex socket drive on a torque wrench, I managed to remove 1 and strip 2 others, so I'm looking forward to an adventure of drilling, screw extractors, etc.

During the struggle, at first I was trying to turn the screws immediately after heating. Later, after heating again, I waited until everything had cooled to try again. Now I'm wondering, ignoring the effects of the loktite, is heating more likely to make a screw looser or tighter, or neither? Clearly, the screw must expand. What happens to the hole? Does it get bigger as the drilled part expands, or does the material expand into the hole, making it smaller?

If you heat quickly, heat the hole part and the screw will loosen. Be ready - you'll have a fairly short time before the screw comes up to temperature. I'm surprised lok-tite, even the permanent stuff, worked that well. Were these stainless screws? Or, small diameters?
 
No, they don't seem to be stainless. They're 5/16, 18tpi, 3/4 in. flathead screws, marked with letters 'Y' 'D' on the head. And the loctite was supposed to be the non-permanent type, but who knows what they used in the factory.

So, ignoring the screws for the moment, you're saying that the hole gets bigger as the material expands? That's a bit surprising. Clearly, if I draw a circle on a solid piece of material, the circle will grow as the material is heated. That makes sense because the material inside the circle must expand. But it's not so obvious when the circle is actually a hole. Why doesn't the surrounding material expand inward towards the axis of the hole?
 
gnome said:
But it's not so obvious when the circle is actually a hole. Why doesn't the surrounding material expand inward towards the axis of the hole?
Take a 6 foot length of chain, lie it on the ground in a circle, joining the ends.
Now try to add one link to the loop. Will the loop increase or decrease in radius? Obviously, it will increase.

Next, instead of adding one link, replace each individual link with links that are 10% larger. Once you've replaced them all, will the loop have a larger or smaller radius?

The links, obviously, are your atoms of metal around the hole.


Finally, add another chain around the first (which will be slightly larger in radius than the first and use a couple more links). Add as many as you want in concentric circles. Now do your swapping-in of larger links again.

See what happens? Every chain, in order to take up more room, will have to expand outward, not inward.
 
OK, thanks, that's a helpful analogy. Applying simple geometry to it convinces me that even though the individual links expand in all directions, the distances between their centers increases sufficiently so that the inside diameter of the circle expands by the same ratio.

Then apparently, except for any effects relating to the speed of transmission of heat through the parts, assuming all parts are heated approximately equally and that the coefficients of expansion are approximately equal, the screws will be equally tight whether hot or cold, correct?

Unfortunately, TVP45's suggestion doesn't help me. These screws are fastening a blade onto a rotor (it's a wood chipper), passing through the blade into threaded holes on the rotor, and I have access only to one side. I can't get to the back of the rotor without taking the whole machine apart, and heat applied to the blade is likely to be transmitted to the screws faster than to the rotor.
 
You may have done better with an impact tool.