Glueing topmast - epoxy or sikaflex?

  • 27 May 2018 14:02
    Reply # 6266451 on 6266045
    David Tyler wrote:
    - Epoxy + screws or rivets, plus clever extrusion design to maintain the bonding gap at 0.2mm.

    I've read that these bonded vehicle chassis generally use toughened epoxy adhesives, though these days, there are so many different adhesives, it's difficult for the layman to make an informed decision. Jami has done the job now, but WEST G Flex epoxy would be one to consider. 

    I have read that the screws and or rivets were really only there to support the structure while the epoxy set up, allowing the chassis to be moved to another production station sooner, but have also read that they were there for "crash loadings" rather than normal service. Apparently though there are "dimples" of some sort in the extrusions which assist in maintaining a uniform glue thickness. Not something your average mast gluer-together might achieve easily though. The west epoxy looks eminently suitable, although I stopped using West when I became allergic to it. Quite likely I may not be allergic to the exotics, and frankly a small exposure for sticking a mast together would be no big deal. 

    I am minded that we can of course easily debate the ultimate solution but there are plenty of "lesser" solutions that will be fine. I am sure Jami's mast will stick together.

    Cheers




  • 27 May 2018 12:27
    Reply # 6266221 on 6260678
    Anonymous member (Administrator)

    Jamie we can not always achieve the ideal and we have to make do with the materials which are readily to hand, and with what skills we have. Sounds to me you have done that, and done a very good job, including your mast collar and masthead fitting which are a credit to you. And I will bet if you ever have a mast failure, it won’t be any of these items, or the join that fails.

    Jami, it has indeed become an interesting thread, and since you have now glued your mast, I hope you will not mind if I weigh in here with a few more ideas, because I am sure there will be many more composite masts made in the future. I don’t want to pretend to be an expert, I just want to bounce a few more ideas with anyone who has made or will be making a composite mast by joining two unequal aluminium tubes.

    This afternoon, after applying three layers of glass tape to the two places where the bandage packers will go – I began to worry a little. First, I could see it was going to use up a lot of tape and epoxy to fill the gap – and second because I was afraid that by the time I had built up enough thickness it might not be perfectly circular any more – I even dreaded that it might sag or become out of alignment. In order to be able to do lots of “trial and error” while building up that annular gap, to make sure it would fit nicely and also maintain alignment, I wondered how I could manage, as my topmast is 5.5m in length and weighs about 20kg – quite unwieldy, especially inside the shed. I would be interested to know how you did yours.

    Anyway, so I hit on the idea of reversing the topmast and sliding it almost full length inside the main tube, supported at each end by a sliding collar which allows the top mast to slide in and out at will, in situ, maintaining concentricity, while I build up and trial-fit that annular gap.

    The sliding collar would best be a grommet made from that cheap slippery kind of rope, if a rope with just the right diameter could be found. But I was too impatient so I just took the nearest bit of old synthetic rope which was lying around, about the right diameter, and just wound it around the topmast one turn and a bit of overlap, then taped over it with duct tape and kept applying duct tape until it was a nice tight sliding fit inside the main tube. I did that at each end and the result looks rough but works perfectly. It slides in and out and maintains concentric alignment to within a mm or two which is as close as I can measure. I can now focus on building up the gap, and some more possibilities have now opened up.

    If anyone is interested here are a couple of photographs of my “trombone.” I can now work on the base of the topmast, protruding from its cradle (the main tube), and slide it in and out at will, filling, sanding etc until a sliding fit is achieved. I’ll do the inner one first, then remove the rope grommet there, slide the topmast further in, supported at this end now by the newly made epoxy collar - and then do the outer one.

    This seems to be a workable procedure – and I am now wondering what would be the best way to fill that gap. (The clearance is just about 1cm all round.) It doesn’t seem necessary now, to fill all that gap with epoxy, and if it gets out of shape, I hate sanding that stuff.  One way would be to cut up about 40 little strips of wood (say 8mm x 8mm) and lay them all parallel across a strip of duct tape, then wrap the bundle around the tube (layered up with glue) and lash the bundle in place there until the glue cures. The result at this stage will look like a “spline”. It can slide in for a test fit. The interstices can then be filled with epoxy and microballoons, sanded – and the final clearance and fit achieved with an outer coat of just a layer or two of glass tape and epoxy. It won’t matter if its not perfectly circular, it could be multi-hedral, as long as it can be bounded by a perfect tube, ie as long as “it fits where it touches” - and the two tubes remain concentric.

    I’m doing an experiment tonight – gluing two aluminium surfaces together with a thick layer of thickened glue, but separated by four layers of “grease-proof” or “baking paper” which has been sprayed with that spray-on parting agent. If it falls apart tomorrow morning, I might consider doing the final fit “wet”, wrapped with four layers of sprayed baking paper, and use the outer tube as a mould. 4 layers of paper will give just a nice sliding clearance, and if all went according to plan, would allow a perfect “casting”, the topmast to be pressed out from the other end after it has cured. I am just not sure if I have the guts to try it. So much for Jami worrying his tubes might not stick.  At this stage my top mast is in backwards, and I’m more worried they just might! As stated, I probably won’t have the guts to try it.

    A real “quick and dirty” way to do the whole job in one go, and have it stick, might be to wind on a lining of the right diameter rope like this. The rope would be saturated with epoxy resin, and might as well be wound on for the full length of the join, lather it all up with lashings of epoxy and that white power which makes it thixotropic, slip the two parts together and job done. Alignment, fit and adhesion all taken care of in one go. But I am not sure if I want a hard rigid bond between the tubes.

    (Winding with rubber round bar instead of rope, and gooping it with simsons or polyurethane from a tube would be an interesting variation!)

    I think I prefer to go more slowly and just aim for a nice dry sliding fit. If I can do that (haven’t done it yet) then I am only going to use minimal glue or maybe even just a dab of cheap silicone rubber mainly just to help it slip together. I am banking the cone fairing will take care of telescoping, and relative rotation of the two tubes, and if I am wrong then it will come apart won’t it? and it can easily be remedied. I can appreciate that ocean-going sailors might perhaps rightly worry about possible slow deterioration or fatigue of the bond between the epoxy fairing cone and the two tubes.

    Any actual mast failure is going to occur outside of the overlapping part, I am confident about that. And top mast failure is a possibility in my case, maybe just above the fairing cone which I think will be the weakest part, as I think my top tube may be just a little on the light side. If it ever happens I want something I can hopefully salvage and repair.

    I may be way out of line here, but apart from Arne I think there has been too much worry given to bonding the two tubes together on the inside, and rivets etc. I am sure the two Davids are each correct in terms of what would be the ideal glue to use, but I can not see why the inner tube needs to be glued to the outer tube at all - any more than a mast has to be glued into a tabernacle – it’s the same thing isn’t it? Provided its tight, can’t slide down and can’t rotate. I suppose rivets could be put in later if it were ever proved necessary, but I really can’t imagine the need, and it would seem a shame to drill holes there unless really necessary.

    Didn’t Annie just stick her topmast in with what glue she had at hand, probably correctly (see pps below) choosing the simsons in preference to the epoxy - and hoist Fantail’'s sail a couple of days later? We’re not building a Lotus here. I do admit that too much of a nonchalant attitude would not do if preparing for an ocean crossing.

    I hope at least this will bounce a few more ideas, and would be more than happy to receive negative criticism – sooner rather than later please!

    PS sorry to wade in over the top of Arne, who is an expert - I posted this before I saw Arne's previous post.

    PPS after going back and reading the posts of Arne and Annie, I think we can now fairly conclude that both epoxy and simsons have proved to be effective enough in this application, and Jami's original question (the topic of this thread) has been answered.

    Last modified: 27 May 2018 23:50 | Anonymous member (Administrator)
  • 27 May 2018 10:02
    Reply # 6266082 on 6260678
    Anonymous member (Administrator)

    I have made two aluminium-wood hybrid masts and they work just fine, the oldest being five years old now. I used West-epoxy. The epoxy-only fairing shoulder was glassed over and then painted with 2-pot paint.

    I know that epoxy is not very flexible, but I reasoned like this:

    ·         The epoxy layer between the outer tube and inner topmast (of wood in this case), will be very thin, with a reasonably good fit. This minimises any chances that the epoxy joint will break because of the micro-bend the mast will take over those 50-60cm.

    ·         All the glue surfaces, several hundred square cm, will work in unison and only deal with shear forces. The joint cannot rip itself apart, little by little.

    ·         The fairing shoulder will provide another few hundred square cm glue surface working together with those inside the mast.  Even with a compression force of 200kp (I doubt it will ever reach that on that Gallion),  the glue joint will hardly see more load than 0.2-0.4kp/cm2. Now, glue two bits of aluminium together with a contact surface of about 1-2 cm2. and pull them apart. You will find that it takes several kilos force.

    Frankly, Jami, I think you are inventing a problem, which is not there in the real life. Your mast will not go telescopic. So go ahead  -  the summer doesn’t last forever!

    Arne.

    PS: To maximise the epoxy’s holding power on aluminium, I read somewhere that one should sand the surface to remove the oxide, and then prime it with resin at once. I confess to have skipped that step except when I made the epoxy joint between the two tubes of the yard. However, it will be easy to add that step when fitting the fairing shoulder.

    Good luck!

    Last modified: 27 May 2018 10:41 | Anonymous member (Administrator)
  • 27 May 2018 09:20
    Reply # 6266045 on 6265830
    Gary Pearce wrote:

    As far as I am aware the Lotus Elise has been stuck together with epoxy since 1996, the Audi A8 and numerous others. All without incident to date as far as I am aware. 

    Airbus also use epoxy extensively, as do the manufacturers of the French TGV trains.



    http://www.sandsmuseum.com/cars/elise/
    information/technical/autodesign.html

    - Epoxy + screws or rivets, plus clever extrusion design to maintain the bonding gap at 0.2mm.

    I've read that these bonded vehicle chassis generally use toughened epoxy adhesives, though these days, there are so many different adhesives, it's difficult for the layman to make an informed decision. Jami has done the job now, but WEST G Flex epoxy would be one to consider. 

  • 27 May 2018 05:51
    Reply # 6265983 on 6260678

    Whoa, this turned into a very interesting topic - especially for me now that I just glued my mast yesterday! I finally went with the original plan of using only epoxy. Let’s hope this works ok.

  • 27 May 2018 01:09
    Reply # 6265830 on 6265728
    David Thatcher wrote:


    Based on my experience of joining wood and aluminium I think that a semi flexible adhesive sealant such as the Simson Marine Adhesive is by far the best way to go. I don't know if they recommend a primer for use with aluminium but if so that would provide added security of the bond. It is very difficult to get a good long term glue joint to aluminum with epoxy, and when one considers that alloy car chassis, and planes are bonded together with these types of adhesives, and not epoxy, then the Simson type adhesive seems the simplest way to go.

    As far as I am aware the Lotus Elise has been stuck together with epoxy since 1996, the Audi A8 and numerous others. All without incident to date as far as I am aware. 

    Airbus also use epoxy extensively, as do the manufacturers of the French TGV trains.

    Marstroms of Sweden who are arguably the leading manufacturer of high performance masts also use epoxy for secondary bonding of mast fittings such as goosenecks.

    In the absence of nasty ablative preparations the "trick" to getting a good bond between epoxy and aluminium is to wet sand the aluminium first. I.e. coat the aluminium with your chosen epoxy and then sand. Recoat as most of the epoxy will have been dispersed and then place the parts together. 

    In the event that it is difficult to apply pressure to the joint (such as the case where you are bonding one tube inside another) I would consider a thixotropic epoxy such as Araldite 2015. There is a higher spec Araldite for carbon/carbon bonds but I have none left and do not recall the number. Sorry.

    No epoxies like exposure to UV so paint is the order of the day where there is any exposure.

    Not to say you could not glue the two with sikaflex or the like and have it work. You only really need to determine that the area of the join provides sufficient shear for the expected compression. If insufficient you merely need to increase the length of the join.

    Sikaflex does seem to break down in a marine environment after about 10 years, at least 2019 which is the one specified for windows does. Hidden away from UV and differential expansion inside a mast it _should_ last much longer but I have no empirical results on that.

    I am not a fan of sleeved joints in aluminium epoxied and backed up by rivets, to me it just seems "wrong" although the mast industry has used this technique for many years without too much trouble. Often without any epoxy. 

    My 10 cents



  • 26 May 2018 23:31
    Reply # 6265728 on 6265570
    Deleted user
    Graeme Kenyon wrote:


    I don’t know what is best, epoxy or Simsons adhesive, but since the bandages and fairing cone will be made from glass/epoxy in my case, and same as Jami I am making a close sliding fit, I think Arnie is right and just a further lick of epoxy to lubricate the two tubes into position will be sufficient. 

    I think it would be a shame if Jami drilled holes and used rivets unless it really is necessary and I certainly will not be doing that.


    Based on my experience of joining wood and aluminium I think that a semi flexible adhesive sealant such as the Simson Marine Adhesive is by far the best way to go. I don't know if they recommend a primer for use with aluminium but if so that would provide added security of the bond. It is very difficult to get a good long term glue joint to aluminum with epoxy, and when one considers that alloy car chassis, and planes are bonded together with these types of adhesives, and not epoxy, then the Simson type adhesive seems the simplest way to go.
    Last modified: 26 May 2018 23:32 | Deleted user
  • 26 May 2018 22:56
    Reply # 6265570 on 6260678
    Anonymous member (Administrator)

    I am doing exactly the same as Jami at the present time, joining two tubes of unequal diameter using a sliding fit of the smaller tube, packed with two glass/epoxy bandages. 

    I am going to challenge both David and Reed here because there seems to be slight misunderstanding.

    First to Reed: this is not two equal diameter tubes being joined with an inner sleeve.

    And David: surely the epoxy/glass conical fairing above the join (which you have referred to on 15 May of this thread) will provide the necessary shoulder?

    I note that on Fantail Annie used adhesive only, this and the (timber) fairing piece took care of all the forces concerned, no metal fastenings necessary.

    I don’t know what is best, epoxy or Simsons adhesive, but since the bandages and fairing cone will be made from glass/epoxy in my case, and same as Jami I am making a close sliding fit, I think Arnie is right and just a further lick of epoxy to lubricate the two tubes into position will be sufficient. 

    I think it would be a shame if Jami drilled holes and used rivets unless it really is necessary and I certainly will not be doing that.

    Here is another question though: I think (but don’t know) it would be a good idea in practice (mabe not in theory) to let the fairing cone incorporate a couple of extra layers of cloth taken over the top of the join and down onto the outer tube. This would make a very slight swelling at that point, but would cover any possible crevice, also make a handy contribution to holding everything together including rotational forces. At any rate, I can’t see that it would create any new problem but please correct me if I am wrong.


    Last modified: 26 May 2018 23:23 | Anonymous member (Administrator)
  • 26 May 2018 18:03
    Reply # 6264942 on 6260678

    Certainly, with no shoulder on the topmast to bear against the top of the tube, some mechanical fasteners to back up the adhesive makes sense to me.

  • 26 May 2018 06:28
    Reply # 6263803 on 6260678

    Hmm,

    What about using epoxy as Arne suggests, but with some riveting?

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