Adhesion: Making Handle Scales Stick, and Stay Stuck, on Blade Tangs

Discussion in 'Shop Talk - BladeSmith Questions and Answers' started by Cushing H., Jul 10, 2019.

  1. David Mary

    David Mary KnifeMaker / Craftsman / Service Provider Knifemaker / Craftsman / Service Provider

    Jul 23, 2015
    The jury is not out. :) This forum has existed for over two decades, and the owner already decided.

    https://www.bladeforums.com/help/site-rules/

    Nothing against "necro" posting. It is more a question of etiquette and good sense. "Is my post going to potentially add value to a discussion?" Yes? Then post. Or "would my post be merely an empty comment for my own gratification?" Yes? Then don't waste everyone's time.
     
  2. Cushing H.

    Cushing H. Gold Member Gold Member

    Jun 3, 2019
    Fair enough .... I mis spoke.

    Hopefully then the comments added just now add to the value of the thread ....
     
    David Mary likes this.
  3. David Mary

    David Mary KnifeMaker / Craftsman / Service Provider Knifemaker / Craftsman / Service Provider

    Jul 23, 2015
    You have added a ton of value to this thread with your posts in general. And this last post, in my opinion, adds the additional value of mutual understanding. We discussed the "taboo" of necro posting and found an agreement on its legal status in the forum, as well making distinctions between good and bad forms of posting in an old thread. That value can translate to anyone reading the thread in the form of reduced conflict and stress in future cases where old threads are reopened by posts bearing new and relevant matter for valid discussion, such as new questions or perspectives on, or closely related to the thread topic.

    People who read this discussion and who may want to - or do inadvertently - post in old threads for such valid reasons in the future can do with confidence knowing they are not breaking a rule or performing a legit social no-no.

    Those who read this discussion, and see old threads reopened in the future can feel free to participate in the discussion anew, or if the thread is reopened by a violation of site rule number 2 (which is what I believe to be part of the reason that so-called necro-posting became a taboo in the first place), can feel free to say "Really? You reopened a XXX year old thread for that?"

    But posting for valid reasons in old threads is a great way to bring new members up to speed on old discussion without having to make them search far and wide for the background of the discussion, and a great way to help threads become more comprehensive resources for their given topic, as Oliver's posts, and the replies they prompted from you have done for this thread.
     
  4. olivier coen

    olivier coen

    33
    Sep 18, 2020
    Right now I feel both impolite and stupid. Don't seem to be able to find the introduce yourself thread. My apologies for both but I would be quite gratefull for a link.
     
  5. David Mary

    David Mary KnifeMaker / Craftsman / Service Provider Knifemaker / Craftsman / Service Provider

    Jul 23, 2015
    @olivier coen my new friend, I'm sorry, and I truly regret that my post has prompted such a feeling, and I'll take ownership of the "stupid" part of the equation, because I didn't give you the correct thread title or a link. It seems I had forgotten the title and just tossed "introduce yourself" out there because it sounded right. Here is a link sir: https://www.bladeforums.com/threads/we-were-all-new-here-once.1010696/
     
  6. olivier coen

    olivier coen

    33
    Sep 18, 2020
    Dear sir,
    My area of expertise is not making knives so far, if I have any at all. I worked with metals a lot and occasionally had to glue them together. With brass on brass it failed. Don't know why, it might be a reaction of brass Vs epoxy...
    Glue manufacturers almost always give a minimum thickness. Except for CA glues they tend to be above 0,1mm (0,05" I think) and I don't think you get there with 60 grit scratches.

    I think, but can not prove it, that this is both because of thermohardening where mass is a factor and maybe contaminations with air and dust.
    You might be right that defects are uniformly pushed out but without disrespecting your knowledge I still am not sure about it. If they are, I fully agree with you. If they aren't, my concrete analogy still stands (even with the nerdy part I think)

    That being said I feel like this is becoming an academic discussion. Your original guidelines are the ones I follow too, except that I am still scared of clamping stuff to the max.

    I too would have no objections to continue this discussion in private and maybe find a conclusion before we post it as this was a perfectly condensed bit of usefull information that I feel I contaminated with raising doubt without being able to give a definitive answer.
     
  7. olivier coen

    olivier coen

    33
    Sep 18, 2020
    I thank you very much for helping me with being respectful to the community. It should have been a reflex to introduce myself instead of being hungry for more knowledge. I tend to be clumsy in those matters so I will keep the stupid part with me. I will happily accept the friendship though
     
  8. Cushing H.

    Cushing H. Gold Member Gold Member

    Jun 3, 2019
    Oliver - please, no worries. Agreed - the problem with anything "academic" is that eventually reality hits, and something that was not taken into account in the original thinking is present and throws everything awry - which is why it is important to have input like you are giving. I cant say I know a lot about CA adhesive, except that much of is it quite thin, and not gap filling likely? And maybe that is why those joints must be thin - but that is just a guess?

    Re. "bulk defects" - I am really thinking mostly about bubbles - which cause internal "voids" and "corners", which act as stress risers and can cause a crack to initiate. In a relatively viscous material like epoxy, they do not really move around on their own, instead move along with the material around them. If that material is squeezed out, then so will the bubble - does that make sense? Particles I can see would be a different story - if they were big enough to span the distance between the parts being joined, they would clearly get hung up and not be squeezed out (which is a problem). On the other hand, if an adhesive as supplied had so many particles of such a size - I would strongly consider a different adhesive!

    I have mostly dealt with pretty stiff (non elastic) adhesives. What might shed light on my thinking is the following quote from "Advances in Structural Adhesive Bonding, 2010, chapter 14":

    "With thick bondlines there is higher the risk of incorporating voids and stresses at the corners of the joint tend to be larger as it is difficult to maintain axial loading with a very thick bondline. Thick adhesive layers can change the cure properties producing internal stresses, thereby reducing short and long-term performance. Conversely very thin bondlines can result in adhesive starvation and debonding. Optimum bond thickness will depend on the type of adhesive used. The method used to control bondline thickness must not introduce voids in the adhesive or the joint performance will be compromised."

    and

    "more ductile adhesives often provide more fracture resistance in moderately thicker bondlines than do brittle adhesives"


    Here you see the concern about thin layers incorporating more voids/defects, along with thicker layers producing problems with uneven curing (another stress riser). You also see the concern about starving the joint of adhesive .... but I gotta point out that I have always said that the surface has to be thoroughly and uniformly rough enough to create spaces for the adhesive to be present in - if those spaces are not present, then of course you are going to push all the adhesive out when you squeeze enough. But, on the other hand, if your surface is not rough enough to hold sufficient adhesive, then you have different issues (lack of the mechanical "interlocking" mechanism. Also, as I mentioned, my own personal experience has been with pretty non-ductile/brittle adhesives - and in the above you see the comment that brittle adhesives dont do well in a thicker joint.....

    As with all things, it is a "balance" I guess. If you have faith in your ability to roughen the surface, then you can squeeze harder. If you do not, then dont squeeze as hard. The final balance of where to be would come from your own particular experience.

    QUESTION - your experience with brass - could you please elaborate?????? Was this a one time thing, or did you always have problems??? did the problems occur during later machining (where heat might have been generated), or under some other condition?????

     
    GABaus likes this.
  9. Natlek

    Natlek

    Jun 9, 2015
    Starving the joint of adhesive................ :Dtake two piece of glass , mix some epoxy and apply it on both pieces of glass .Then join them and put as much as you can/want pressure , and WATCH how ALL epoxy is going out :D leave what is left from epoxy to cure and let me know when you manage to separate them .......
     
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  10. olivier coen

    olivier coen

    33
    Sep 18, 2020
    I'll tell you in a few days, curious about the result. Worth the experiment
     
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  11. olivier coen

    olivier coen

    33
    Sep 18, 2020
    The brass issue was an experiment for a job where I particularly didn't want to apply heath to the object. I had to make a desk with a quite specific patine on the brass which I couldn't apply to the assembled piece of furniture. So I experimented with glues adviced by different manufacturers.
    None of them worked satisfactory. The best results where CA based and one PU based, probably quite similar to gorilla glue (don't Google that in my area) The 2 epoxie glues failed first.
    I did some work for modern art conservation and restoration and they don't want to work with anything PU related because of its rapid decay (in conservation perspective off course)
    My guess, but its only a guess is that humidity and oxidation did the biggest harm, and maybe direct sunlight on one of both parts. I don't know. I used hidden bolts in the end since I couldn't trust the glue.

    Wasn't direct knife related experience but it might have value.
    As I said, I use epoxy for my knives too but I wouldn't make a knife without pins to give mechanical security.
    But I will be happy to investigate the subject more.
     
    Natlek likes this.
  12. Cushing H.

    Cushing H. Gold Member Gold Member

    Jun 3, 2019
    Wear safety glasses!!!

    actually, natlek is leading you down the primrose path. Take two pieces of good flat glass. Get them nice and clean. Press them together HARD. if you really want to make it interesting, put it in a vacuum chamber while pressing together hard. No adhesive ... you will likely also never get those things apart (unless you put them back under vacuum and try to pry them apart there)

    you have expelled all the air between the plates, and the outside atmospheric pressure is holding them together. One side of the glass also has the ability to form weak chemical bonds with the other side...
     
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  13. Cushing H.

    Cushing H. Gold Member Gold Member

    Jun 3, 2019
    On the brass - first thought is oxidation on the brass? Solvents won’t take it off ... you would need to sand it ... and even then it will quite quickly form a thin oxidation layer. Could it have been Something like that? They were roughened I assume?
     
  14. Natlek

    Natlek

    Jun 9, 2015
    I have chosen glass because it will show that it is impossible to squeeze out ALL epoxy no matter how hard you press.....:)
    The most common mistake are insufficient mixing of most often a greater amount of epoxy than is required , pouring epoxy full with trapped air/have white color / inadequate room temperature , not clean surface , not true flat parts , shallow scratches on steel .............
     
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  15. olivier coen

    olivier coen

    33
    Sep 18, 2020
    They were roughened up with an angle grinder 60 grit cubitron disc.

    On your and Natleks point about the glass; That might be true for testing it directly after curing of the glue but the question is also how it behaves with elements and time.
    My vacuum chamber is not big enough for my press so I'll need to improvise...
    I learned that sometimes you get surprised by results of experiments.
     
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  16. olivier coen

    olivier coen

    33
    Sep 18, 2020
    I agree
     
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  17. Cushing H.

    Cushing H. Gold Member Gold Member

    Jun 3, 2019
    Hmmm. Stacy - if you are reading, can you think of a reason his brass joints failed with epoxy? Freshly sanded and roughened . I got nothing right now....

    Oliver, I was tongue in cheek on the vacuum chamber. Could be you are pulling my leg, but if you have one, go for it!
     
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  18. Randydb

    Randydb Basic Member Basic Member

    Sep 27, 2014
    I was helping a student make a knife with brass bolsters that we glued on with 30 minute epoxy (it was early in my knife making learning...didn't know about gflex then). Roughed with 60 grit, cleaned with methyl hydrate, clamped gently. Th joins failed a couple times in a few months. I finally used jbweld and peened pins in them and it all stayed together.
    Basically it is the only thing that failed glue wise for me and it was brass. Lots of glue in the joints each time. I wonder if that was something to do with brass.

    I find this discussion regarding "glue starvation/thin as possible" very interesting. With woodwork and carpenter's glue I clamp things very tight and want there to be very little glue left in the joint and the joint winds up being stronger than the wood around it.
    It I have glued other things with epoxy and clamped pretty hard...and when I have broken them apart or caused them to fail I have always been surprised by how much glue had actually remained in the joint. From my small sample size and experience it seems highly unlikely to me that you could starve a joint of epoxy. Which is what I think Natlek is talking about when he says glue glass. I think it is to prove that you can't force all the glue out.
    I definitely could see critical mass or heat or something else requiring epoxy joints to be thicker than carpenter's glue. I just don't know if that is true or not.
    Very interesting thread. I missed seeing it a year ago and am very glad that it showed up now
     
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  19. Natlek

    Natlek

    Jun 9, 2015
    This thing which still look like knife I make more then 20 years ago. I used Araldite glue back then .It was used in my daily work most time to scrap old gasket from some engine parts or to cut some hose and other things .Exposed to sun ,temperatures in deep minus or plus , oil , gasoline ,diesel and many other liquids ...............Well ,i can t see that scale have some failure .........that small tube pins are slightly extended by a cone...sorry i can t recall in the moment the right expression ....
    [​IMG]
    [​IMG]
     
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  20. Cushing H.

    Cushing H. Gold Member Gold Member

    Jun 3, 2019
    I did a little poking around, and found some references (mostly in boatbuilding forums) that after bonding, the brass surface against the epoxy will oxidize (presumably becoming brittle) and cause the joint to fail. Not definitive, but at least a heads up against not putting pins in there...
     
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