JB weld for FG assembly?

Discussion in 'Techniques' started by bclark989, May 2, 2018.

Help Support The Rocketry Forum by donating:

  1. May 2, 2018 #1

    bclark989

    bclark989

    bclark989

    Well-Known Member

    Joined:
    Dec 27, 2014
    Messages:
    191
    Likes Received:
    5
    Is JB Weld an acceptable construction epoxy for FG to FG joints? I have G5000 for fillets, but I am trying to decide what the best epoxy is for the assembly.

    Thanks!
     
  2. May 2, 2018 #2

    Keisling

    Keisling

    Keisling

    Licensed Practical Rocket Surgeon

    Joined:
    Jan 22, 2017
    Messages:
    194
    Likes Received:
    79
    Location:
    Florida
    JB works fine for FG. There are other epoxies that are easier to work with but I still use JB for anything that touches the motor tube.
     
  3. May 2, 2018 #3

    Bat-mite

    Bat-mite

    Bat-mite

    Rocketeer in MD

    Joined:
    Dec 5, 2013
    Messages:
    10,534
    Likes Received:
    1,349
    Gender:
    Male
    Location:
    Maryland
    If you don't mind paying the exorbitant price, then it's fine. JB Weld is $5.67 per ounce, whereas RocketPoxy is $1.09 per ounce (before shipping). Why not just use the RocketPoxy? I only use JB Weld for the retainer.

    Make sure you wash the surfaces with soap and water, rinse thoroughly, rough up the surface with 60-grit sandpaper, then use acetone or isopropyl alcohol to clean away the dust.
     
    Wallace likes this.
  4. May 2, 2018 #4

    bclark989

    bclark989

    bclark989

    Well-Known Member

    Joined:
    Dec 27, 2014
    Messages:
    191
    Likes Received:
    5
    Keisling, thanks. That's what i was thinking.

    Bat-mite, I suppose the main reason would be that I'm going to use so little of it. One package of JB Weld will probably build the whole rocket. I'll need an ounce or two to do fillets, but I'll be doing those with the G5000. To me its not worth the hassle to go through an online vendor, pay for shipping, etc, just to save $5.
     
  5. May 2, 2018 #5

    G_T

    G_T

    G_T

    Well-Known Member

    Joined:
    Dec 29, 2011
    Messages:
    2,196
    Likes Received:
    261
    FWIW, JB Weld is a good grade of epoxy with calcium carbonate and powdered iron (or steel; I forget which) added.

    Gerald
     
  6. May 2, 2018 #6

    Bat-mite

    Bat-mite

    Bat-mite

    Rocketeer in MD

    Joined:
    Dec 5, 2013
    Messages:
    10,534
    Likes Received:
    1,349
    Gender:
    Male
    Location:
    Maryland
    G5000 is RocketPoxy. You already have some, apparently. I'm confused....
     
  7. May 2, 2018 #7

    AfterBurners

    AfterBurners

    AfterBurners

    Well-Known Member

    Joined:
    May 8, 2012
    Messages:
    7,124
    Likes Received:
    202
    Gender:
    Male
    Location:
    Dallas Texas
    You can always buy some hobby epoxy in the small bottles. 4.5 or 9 oz. Pretty reasonable price. Probaby get several builds out of the bottled. I use JB Weld mainly on the motor retainer.
     
  8. May 2, 2018 #8

    cavecentral

    cavecentral

    cavecentral

    Well-Known Member

    Joined:
    Jul 1, 2011
    Messages:
    3,094
    Likes Received:
    22
    You can find larger tubes of jb weld on ebay. Cheaper per ounce than the little ones.
     
  9. May 3, 2018 #9

    solid_fuel

    solid_fuel

    solid_fuel

    Lifetime Supporter TRF Lifetime Supporter

    Joined:
    Aug 13, 2017
    Messages:
    1,750
    Likes Received:
    233
    Location:
    SEPA
    isn't JB weld much heavier then BSI epoxy per the same volume? I am just guessing but it seems heavier
     
  10. May 3, 2018 #10

    amarillo_rocket

    amarillo_rocket

    amarillo_rocket

    Well-Known Member

    Joined:
    Jan 20, 2009
    Messages:
    289
    Likes Received:
    0
    I buy JB 10oz tubes on Ebay for around $1.30/oz including shipping. I use JB for fillets and motor mounts on all of my larger rockets (N motor being the largest). It works well and if I need it to flow a little better I use a heat gun for about 10 seconds. I use Aeropoxy light for fillets on smaller rockets. It's very easy to sand and slightly thicker consistency than JB but not as strong.
     
  11. May 3, 2018 #11

    G_T

    G_T

    G_T

    Well-Known Member

    Joined:
    Dec 29, 2011
    Messages:
    2,196
    Likes Received:
    261
    Actually JBWeld isn't really that strong. IIRC, it is about 40% the strength of the strongest stuff. But it is reasonably resistant to cracking and seems to adhere fairly well. Those are two common failure modes for bulk epoxy. It also has reasonable tolerance for a bit of mild heating. So being weaker is not usually a big deal.

    Gerald
     
  12. Jan 12, 2020 #12

    tollyman

    tollyman

    tollyman

    Well-Known Member

    Joined:
    Oct 9, 2016
    Messages:
    65
    Likes Received:
    14
    Gender:
    Male
    Location:
    Wisconsin
    40% strength of what stuff? Rocketpoxy or the best epoxy there is? Any suggestions to smoothing out fillets with jb weld?
     
  13. Jan 12, 2020 #13

    David Schwantz

    David Schwantz

    David Schwantz

    Well-Known Member

    Joined:
    Jul 23, 2018
    Messages:
    960
    Likes Received:
    257
    Gender:
    Male
    Location:
    MN
    Spit. Spit on your finger as you pull the fillet.
     
    Zertyme and Titan II like this.
  14. Jan 13, 2020 #14

    G_T

    G_T

    G_T

    Well-Known Member

    Joined:
    Dec 29, 2011
    Messages:
    2,196
    Likes Received:
    261
    Water in epoxy is a negative. Epoxy, uncured, on your hands is a negative also as it is toxic. You should not be making any physical contact with it.

    Epoxy is an allergin. You do not want to become allergic to it! Exposure to uncured epoxy triggers the allergy. The more exposure, the more likely you are to get the allergy. Some epoxy systems are also much more likely to give you the allergy quickly, than others. But in general, eliminate physical contact with uncured epoxy. Treat it like a poison. It IS poisonous, but it is also an allergin.

    You can research epoxy strength if you want. You don't need me to do it for you! But, since you didn't research it, here is one quick link: https://www.rocketryforum.com/threads/epoxy-comparisons-and-technical-data-sheets.138953/

    An epoxy system I often recommend considering: http://www.cstsales.com/mgs_epoxy.html This has some of the best properties for a room temp cure epoxy system, and properties are improved by appropriate post-cure heat treatment cycle. But it is not a high temp system, such as those produced by Cotronics, or such as JBWeld. MGS is used for commercial plane manufacturing. Another similar product is System 2000.

    Note MGS, and System 2000, are unfilled epoxy systems. If you want it thicker (as in, more like JBWeld), you add your own fillers. That can include such materials as calcium carbonate and iron powder such as with JB Weld (IIRC), various fiber additives to make it an FRP, metallic additives, ceramic microfiber additives, and various other solids. You can tailor the properties a fair bit that way. But what you can't do is magically improve the Tg (glass transition temperature). If your temperature hits Tg, then your rigid epoxy turns into something more like a stiff taffy or a pitch. It will permanently deform under pressure. That is not usually a good thing...

    JBWeld is good if you need so-so mechanical properties, along with fairly good operational temperature tolerance, ready availability, low flow, and acceptible price.

    Gerald
     
    Steve Shannon likes this.
  15. Jan 13, 2020 #15

    Voyager1

    Voyager1

    Voyager1

    Forum Supporter TRF Supporter

    Joined:
    Oct 23, 2015
    Messages:
    407
    Likes Received:
    105
    Location:
    Oz
    Use disposable latex gloves. It makes smoothing out fillets easy.
     
  16. Jan 13, 2020 #16

    dmgrime

    dmgrime

    dmgrime

    Well-Known Member

    Joined:
    Jan 4, 2015
    Messages:
    244
    Likes Received:
    26
    Definitely gloves. I always wear gloves when working with any epoxies ... 5mil nitrile gloves are about $0.05 each and in my opinion well worth mitigating the risk of developing a sensitivity to epoxy.

    As for smoothing / shaping fillets ... I picked this up from a post here on TRF a couple years ago. Cake decorating tools! I mask my lines, fill, and pull the fillet with these. One pass to shape and then dip the ball in denatured alcohol and one more pass to smooth. Works like a charm! I use for wood glue also, but no alcohol dip there...

    https://smile.amazon.com/dp/B0771DY1LK/ref=cm_sw_r_cp_apa_i_opghEb4KESGXN
     
    Wallace, Greg Furtman and tollyman like this.
  17. Jan 13, 2020 #17

    Wallace

    Wallace

    Wallace

    Sponsor TRF Sponsor TRF Supporter

    Joined:
    Feb 16, 2017
    Messages:
    2,514
    Likes Received:
    449
    Personally I don't like JB Weld, but, If you insist on using alot of it, the big tubes'll save you about 40% of your dough...https://www.amazon.com/J-B-Weld-828...sr_1_4?keywords=jb+weld&qid=1578919848&sr=8-4
     
    o1d_dude likes this.
  18. Jan 13, 2020 #18

    dhbarr

    dhbarr

    dhbarr

    Amateur Professional

    Joined:
    Jan 30, 2016
    Messages:
    6,052
    Likes Received:
    776
    Use nitrile -- a person can become allergic to latex through repeat exposure -- no more Band-Aids.
     
  19. Jan 14, 2020 #19

    David Schwantz

    David Schwantz

    David Schwantz

    Well-Known Member

    Joined:
    Jul 23, 2018
    Messages:
    960
    Likes Received:
    257
    Gender:
    Male
    Location:
    MN
    Been doing it that way for 50 years. You also are suppose to use a non toxic willow tree for roasting marsh mellows in the state of CA.
     
    Titan II and Wallace like this.
  20. Jan 15, 2020 #20

    o1d_dude

    o1d_dude

    o1d_dude

    'I battle gravity'

    Joined:
    Jan 18, 2009
    Messages:
    7,082
    Likes Received:
    109
    Location:
    Urff
    For fillets, I remember Crazy Jim recommended pvc sprinkler pipe of appropriate diameter and wet in alcohol.

    His other trick was to wipe the sides of the pipe tool with felt tip marker and drag it along the fin where you want the fillet. The marker ink will transfer to the body tube and you lay down the edge of the tape along that line.

    Been using Jim's tips for years. He's a pretty clever country boy.
     
    blackjack2564 likes this.
  21. Jan 16, 2020 #21

    PatD

    PatD

    PatD

    Forum Supporter TRF Supporter

    Joined:
    Jul 25, 2015
    Messages:
    120
    Likes Received:
    45
    OMG! Obviously you don't know the dangers of salicylic acid which lurks in the willow tree. :D
     
  22. Jan 16, 2020 #22

    Wallace

    Wallace

    Wallace

    Sponsor TRF Sponsor TRF Supporter

    Joined:
    Feb 16, 2017
    Messages:
    2,514
    Likes Received:
    449
    Salicylic acid gives me a headache;)
     
  23. Jan 16, 2020 #23

    Greg Furtman

    Greg Furtman

    Greg Furtman

    Forum Supporter TRF Supporter

    Joined:
    Nov 10, 2018
    Messages:
    666
    Likes Received:
    263
    Gender:
    Male
    Location:
    Webster, Wisconsin
    Now that is a great idea! Thanks. :D
     
    Wallace likes this.
  24. Jan 16, 2020 #24

    Wallace

    Wallace

    Wallace

    Sponsor TRF Sponsor TRF Supporter

    Joined:
    Feb 16, 2017
    Messages:
    2,514
    Likes Received:
    449
    The real question then becomes...Can you turn out a decent looking Rose petal?
     
  25. Jan 16, 2020 #25

    David Schwantz

    David Schwantz

    David Schwantz

    Well-Known Member

    Joined:
    Jul 23, 2018
    Messages:
    960
    Likes Received:
    257
    Gender:
    Male
    Location:
    MN
    If that acid is good enough for the North American Spotted Ferret Bat, then it's good enough for me!
     

Share This Page

Group Builder