# Hypothetical Question



## KenB259 (Mar 16, 2021)

Here's the scenario.
Blank is glued with epoxy or CA, for that matter.  In addition to the glue, you have the blank held together by a mechanical means, eg external clamp.
While drilling, the heat becomes hot enough to soften the adhesive. Even though the glue is soft, it doesnt come apart because of the clamp. Here's my question. If you leave it clamped long enough for it to thoroughly cool, will the glue reharden ?


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## skiprat (Mar 16, 2021)

Well, as the question is only hypothetical, I won’t bother answering.......


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## KenB259 (Mar 16, 2021)

I wish I could say I won't bother reading your answer then. 


skiprat said:


> Well, as the question is only hypothetical, I won’t bother answering.......


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## Displaced Canadian (Mar 16, 2021)

That is a definite maybe. I'm not sure but I think so because people have wrapped blanks in cloth or paper, stacked in glue to hold them together for drilling and it has worked. However I can't say it works from personal experience. When I've built a delicate blank I put thin CA on it until it no longer soaks in and when the blank gets warm I stop and take a break.


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## KenB259 (Mar 16, 2021)

Well, I found this. Now I want to find out about the high temperature epoxies.


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## jttheclockman (Mar 16, 2021)

I bet there never was a study on this. First is never get the blank hot enough to get to that point. Next question is what is hot enough??  Every glue has a different heat ratio. I would never trust CA. If you reached the melting point of CA I would not trust it. I believe glues like epoxy have more tolerances because they remain flexible to a degree. Never tested the theory and never will. Good luck.


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## KenB259 (Mar 16, 2021)

jttheclockman said:


> I bet there never was a study on this. First is never get the blank hot enough to get to that point. Next question is what is hot enough??  Every glue has a different heat ratio. I would never trust CA. If you reached the melting point of CA I would not trust it. I believe glues like epoxy have more tolerances because they remain flexible to a degree. Never tested the theory and never will. Good luck.


I agree, never get it that hot, but I bet we've all been there anyways.


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## jttheclockman (Mar 16, 2021)

KenB259 said:


> I agree, never get it that hot, but I bet we've all been there anyways.


How would you know?? I know this is a hypethetical question but what circumstance would this happen. We brace segmented blanks from shear force when drilling and not heat. There are glues you can heat and cool such as hide glues. Segmented blanks are made from thin material with very little glue surface to begin with so that joint is weak right from the start.


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## KenB259 (Mar 16, 2021)

jttheclockman said:


> How would you know?? I know this is a hypethetical question but what circumstance would this happen. We brace segmented blanks from shear force when drilling and not heat. There are glues you can heat and cool such as hide glues.


I'm sorry, I forgot, you are perfect and all your blanks turn out awesome and you never have failures. You are a pen making GOD. Forgive me if I don't bow down to your greatness.


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## jttheclockman (Mar 16, 2021)

KenB259 said:


> I'm sorry, I forgot, you are perfect and all your blanks turn out awesome and you never have failures. You are a pen making GOD. Forgive me if I don't bow down to your greatness.


Now what the heck kind of answer is that Ken?? I am trying to add some discussion to your question and asking questions to maybe get some inner thoughts. Must be having a bad day. Have a good one I am out of this.


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## wolf creek knives (Mar 16, 2021)

To your question...Yes, Epoxy will re-harden after it cools down.  When I file off knife scale pins sometimes the pins get hot and the Epoxy does loosen.  Let it sit overnight and the next day the Epoxy is hard again and the pins no longer move.  Can't speak to CA as I don't use it.  I use the System Three T-88 two part Epoxy.  After almost 300 knives I've never had an Epoxy failure except on two and that was due to abuse.


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## sorcerertd (Mar 16, 2021)

I think that, as long as the heat does not cause a change to the molecular structure of the glue, it would return to its previous state as it cools.  So it depends on the glue and how it was designed to form the bond.  As an example, polymer clay changes structure when heated, even more so with metal clay, and it does not return to the previous pliability when it cools.  I know that's an apples to oranges comparison, but I think it demonstrates my theory pretty well.


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## wood128 (Mar 16, 2021)

I would also agree , the glue will reharden.


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## monophoto (Mar 16, 2021)

KenB259 said:


> Here's the scenario.
> Blank is glued with epoxy or CA, for that matter.  In addition to the glue, you have the blank held together by a mechanical means, eg external clamp.
> While drilling, the heat becomes hot enough to soften the adhesive. Even though the glue is soft, it doesnt come apart because of the clamp. Here's my question. If you leave it clamped long enough for it to thoroughly cool, will the glue reharden ?


Ken

You've stimulated my curiosity.  But I think you may not be asking the right question.  Bear with me as I try to think through the issue.

First, your simple question is 'will the glue reharden' and I'm pretty sure that the simple answer is 'yes'.  My understanding is that these are essentially thermoplastics which means that the pass from the solid state to the liquid state as temperature increases, but then return to the solid state when the temperature falls.   But the real question that I think you wanted to ask is whether the glue bond will be as strong after the thermal excursion as it was before.   I don't know the answer to that question.  I suspect that it all depends on specifically which kind of glue are you dealing with, and that there are at least  four  issues that affect the answer.

1.  The obvious issue is that if the glued components are allowed to move with respect to each other, the bond could be very different after the glue has cooled down.  You mentioned that the components were held together mechanically (clamped) which may neutralize this concern except as discussed below.

2.  Plastics have a 'coefficient of thermal expansion' which means that as they get hotter, they expand.  So if the glue expands as it is heated, this expansion could cause glue to migrate out of the joint where it will remain after it cools.  In addition, the clamping force would essentially force the joint to 'extrude', or squeeze glue out of the joint.  So when the glue rehardens after the temperature excursion, it is possible that there will be less glue in the joint, which means that the strength of the joint could be compromised.

3.  In addition, there is the issue of whether the molecular structure of the rehardened plastic will be the same as it was prior to being heated.  I really don't know much about plastics, but, it would not surprise me to learn that there is a hysteresis effect involved that results in a change in the physical properties of the plastic (glue) as it goes through this thermal cycle.  That effect could cause the internal molecular bonds within the  rehardened glue to be weaker - or perhaps stronger - compared with the initial state.

4.  Finally, there is the matter of how hot did it get?  Again, my ignorance around this subject is pretty comprehensive, but it would not surprise me to learn that there is one temperature at which the glue starts to soften, and a higher temperature at which some other molecular changes take place within the plastic, and the strength of the rehardened glue will depend on where on that spectrum the temperature excursion ended, and also how long the temperature was elevated.

Any polymer chemists out there who can educate us?  Inquiring minds want to know - - -


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## Dehn0045 (Mar 16, 2021)

I think @sorcerertd is sort of on the right track.  My minimal research says that both epoxy and CA are "thermoset" plastic, which by definition will change molecular structure when melted.  "Thermoplastics" don't change structure (as much anyway).  I'm sure that this is measured on a curve, so some plastics/adhesives are very "thermoplastic" and some are very "thermoset" and some are in between.  It also probably depends on the specific temperature and environment that the heating is done.  My gut feel is that epoxy will respond better than CA to heat cycles, but both probably weaken to some extent.  I personally wouldn't trust the blank without a tube flued in (preferably epoxy or polyurethane), a CA finish would add some rigidity also.  I didn't find any specific data for either and I don't have much personal experience with this specific topic, so my comment is probably worth about what you paid for it


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## MRDucks2 (Mar 16, 2021)

For epoxy I would tend to agree but are we certain CA is considered thermoset? Yes, it does get hot but I thought it was different...

Here we go, epoxy is a thermoset adhesive and more durable. CA is a thermoplastic and I believe more likely to break down. I have had epoxy get sticky after the fact and appear to be fine afterward but believe heated CA, to the point of becoming tacky, did not set back up well. 









						What is the difference between thermoplastic and thermoset adhesives?
					

Adhesives can be classified in several ways, including their material origin (e.g., natural or synthetic) and their type of cure (e.g., physical curing such as drying or chemical curing).




					www.adhesivesmag.com


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## PatrickR (Mar 16, 2021)

I can’t answer the original question.
If one wanted the highest temp adhesive look at ceramic adhesives. Some are rated to 2300. When I was looking into high temp epoxy JB Weld was the choice, but I can’t remember the rating. I used it on an exhaust manifold and it has held for 5 years. So it can take some heat.


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## Dehn0045 (Mar 16, 2021)

@MRDucks2 it seems there is some disagreement on the interwebs about whether CA is a thermoset or thermoplastic.  Maybe there is a difference in terminology -- "thermoset adhesive" versus just "thermoset", I'm not really sure.  It might also depends on different additives that determine where CA falls on the spectrum.  My guess is that it isn't strongly in either group and therefore can be classified either way depending 9n what it is being compared to.









						Do adhesives melt at high temperature?
					

Will adhesives melt when exposed to high temperatures (such as high service temperature exposure, autoclaving, wave soldering).




					www.permabond.com


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## mark james (Mar 16, 2021)

*Yes, it happened on this blank.*  It separated like a flower as I was drilling.  I used blue painters tape to pull the 'flower' tight again.  I had use 2 part epoxy, set overnight, but even with pulling the drill bit out every 1/4" and using a water/wet paper towel to wick the heat off, it still softened the segments.

I did get it drilled and turned.  Not the most perfect pen in the end, but it was an experiment to simply see if I could do it.

I'll check with my wife and get back tomorrow on the chemistry.  (I'll brag, she is a PhD Polymer chemist.  Retired, 30 yrs with Lubrizol on Carbopol).


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## TonyL (Mar 16, 2021)

I defer to those that know much more about this stuff, but I would ask the manufacturer who is likely to same "no" because that is not what their product was designed to do and how it is to be used.

From my experience, I have never had CA, epoxy, etc. re-cure. I don't know if the curing reactions can be turned-back, then resumed. 

Good question!


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## MRDucks2 (Mar 16, 2021)

At the end of the day, I believe Patrick has the right answer. If anyone is experiencing or concerned about thermal breakdown of adhesive, the answer is to find a higher thermal rated adhesive that meets your bonding needs. The available selections are mind boggling.


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## skiprat (Mar 17, 2021)

Wow......sometimes the threads on this site really show the cliques amongst members.  C’mon guys. Jeesh ...

Perhaps instead of wondering if the glue will return to its hard and strong state, why not simply prevent the heat build up in the first place? 
There are many way to do this...
Sharpened drills.
Lube
Peck drilling
Use several smaller drills until finished diameter is achieved 

Another thing that is very often overlooked is he age of the drill bit. You can freshly sharpen it, but if the bit it old and had a hard life, the lands ( cutting edges on the sides) wear down towards the tip and the bit becomes tapered and dull. I’m 60 next month and I still have drills and taps from when I was an apprentice.  Some of the drills probably should have been put out to stud by now. (Like me...)


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## PatrickR (Mar 17, 2021)

I’m not sure about “clique”. Just two ways of looking at a problem. Either reduce the heat generated or increase the temp rating of the adhesive. I would pick the later.


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